The medication pictured in Figure 9.3.1 with the brand name Progynon was a drug used to control the effects of menopause in women. The pills first appeared in 1928 and contained the human sex hormone estrogen. Estrogen secretion declines in women around the time of menopause and may cause symptoms like mood swings and hot flashes. The pills were supposed to ease the symptoms by supplementing estrogen in the body. The manufacturer of Progynon obtained estrogen for the pills from the urine of pregnant women, because it was a cheap source of the hormone. Progynon is still used today to treat menopausal symptoms. Although the drug has been improved over the years, it still contains estrogen, which is an example of an endocrine hormone.

Endocrine hormones like estrogen are messenger molecules secreted by endocrine glands into the bloodstream. They travel throughout the body in the circulation. Although they reach virtually every cell in the body in this way, each hormone affects only certain cells, called target cells. A target cell is the type of cell on which a hormone has an effect. A target cell is affected by a particular hormone because it has receptor proteins — either on the cell surface or within the cell — that are specific to that hormone. An endocrine hormone travels through the bloodstream until it finds a target cell with a matching receptor to which it can bind. When the hormone binds to the receptor, it causes changes within the cell. The manner in which it changes the cell depends on whether the hormone is a steroid hormone or a non-steroid hormone.

Steroid Hormones

A steroid hormone (such as estrogen) is made of lipids. It is fat soluble, so it can diffuse across a target cell’s plasma membrane, which is also made of lipids. Once inside the cell, a steroid hormone binds with receptor proteins in the cytoplasm. As you can see in Figure 9.3.2, the steroid hormone and its receptor form a complex — called a steroid complex — which moves into the nucleus, where it influences the expression of genes. Examples of steroid hormones include cortisol, which is secreted by the adrenal glands, and sex hormones, which are secreted by the gonads.

 

Non-Steroid Hormones

A non-steroid hormoneis made of amino acids. It is not fat soluble, so it cannot diffuse across the plasma membrane of a target cell. Instead, it binds to a receptor protein on the cell membrane. In the Figure 9.3.3 diagram, you can see that the binding of the hormone with the receptor activates an enzyme in the cell membrane. The enzyme then stimulates another molecule, called the second messenger, which influences processes inside the cell. Most endocrine hormones are non-steroid hormones. Examples include glucagon and insulin, both produced by the pancreas.

Endocrine hormones regulate many body processes, but what regulates the secretion of endocrine hormones? Most endocrine hormones are controlled by feedback mechanisms. A feedback mechanism is a loop in which a product feeds back to control its own production. Feedback loops may be either negative or positive.

• Most endocrine hormones are regulated by negative feedback loops. Negative feedback keeps the concentration of a hormone within a relatively narrow range, and maintains homeostasis.
• Very few endocrine hormones are regulated by positive feedback loops. Positive feedback causes the concentration of a hormone to become increasingly higher.

Regulation by Negative Feedback

A negative feedback loop controls the synthesis and secretion of hormones by the thyroid gland. This loop includes the hypothalamus and pituitary gland, in addition to the thyroid, as shown in the diagram (Figure 9.3.4). When the levels of thyroid hormones circulating in the blood fall too low, the hypothalamus secretes thyrotropin releasing hormone (TRH). This hormone travels directly to the pituitary gland through the thin stalk connecting the two structures. In the pituitary gland, TRH stimulates the pituitary to secrete thyroid stimulating hormone (TSH). TSH, in turn, travels through the bloodstream to the thyroid gland, and stimulates it to secrete thyroid hormones. This continues until the blood levels of thyroid hormones are high enough. At that point, the thyroid hormones feed back to stop the hypothalamus from secreting TRH and the pituitary from secreting TSH. Without the stimulation of TSH, the thyroid gland stops secreting its hormones. Eventually, the levels of thyroid hormones in the blood start to fall too low again. When that happens, the hypothalamus releases TRH, and the loop repeats.

 

Prolactin is a non-steroid endocrine hormone secreted by the pituitary gland. One of the functions of prolactin is to stimulate a nursing mother’s mammary glands to produce milk. The regulation of prolactin in the mother is controlled by a positive feedback loop that involves the nipples, hypothalamus, pituitary gland, and mammary glands. Positive feedback begins when a baby suckles on the mother’s nipple. Nerve impulses from the nipple reach the hypothalamus, which stimulates the pituitary gland to secrete prolactin. Prolactin travels in the blood to the mammary glands and stimulates them to produce milk. The release of milk causes the baby to continue suckling, which causes more prolactin to be secreted and more milk to be produced. The positive feedback loop continues until the baby stops suckling at the breast.

 

Anabolic steroids are synthetic versions of the naturally occurring male sex hormone testosterone. Male hormones have androgenic (or masculinizing) effects, but they also have anabolic (or muscle-building) effects. The anabolic effects are the reason that synthetic steroids are used by athletes. In addition to building muscles, they also accelerate the development of bones and red blood cells, increase endurance so athletes can train harder and longer, and speed up muscle recovery. Unfortunately, these benefits of steroid use come with costs. If you ever consider taking anabolic steroids to build muscles and improve athletic performance, consider the following myths and corresponding realities.

Myth	Reality
"Steroids are safe."	Steroid use may cause several serious side effects. Prolonged use may increase the risk of liver cancer, heart disease, and high blood pressure.
"Steroids will not stunt your growth."	Teens who take steroids before they have finished growing in height may have their growth stunted so they remain shorter throughout life than they would otherwise have been. Such stunting occurs because steroids increase the rate at which skeletal maturity is reached. Once skeletal maturity occurs, additional growth in height is impossible.
"Steroids do not cause drug dependency."	Steroid use may cause dependency, as evidenced by the negative effects of stopping steroid use. These negative effects may include insomnia, fatigue, and depressed mood, among others.
"There is no such thing as 'roid rage.'"	Steroid use has been shown to increase aggressiveness in some people. It has also been implicated in a number of violent acts committed by people who had not demonstrated violent tendencies until they started using steroids.
"Only males use steroids."	Although steroid use is more common in males than females, some females also use steroids. They use them to build muscle and improve physical performance, generally either for athletic competition or for self-defense.

 

Attributions

Figure 9.3.1

L0058274 Glass bottle for ‘Progynon’ pills, United Kingdom, 1928-1948 by Wellcome Collection gallery (2018-03-29)/ Science Museum, London on Wikimedia Commons is used under a  CC-BY-4.0 (https://creativecommons.org/licenses/by/4.0/) license.

Figure 9.3.2

Regulation_of_gene_expression_by_steroid_hormone_receptor.svg by Ali Zifan on Wikimedia Commons is used under a CC BY-SA 4.0  (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.

Figure 9.3.3

Non-steroid hormone pathway by CK-12 Foundation, Biology for High School is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.

Figure 9.3.4

Thyroid Negative Feedback Loop by CK-12 Foundation, College Human Biology is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.

©CK-12 Foundation Licensed under  • Terms of Use • Attribution

Figure 9.3.5

Lactation Positive Feedback Loop by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.

References

24 Physic. (2015,July 19). National Geographic | Benefits and side effects of steroids use 2015. YouTube. https://www.youtube.com/watch?v=qXaDDa3FB5Q&feature=youtu.be

Brainard, J/ CK-12 Foundation. (2016, August 15). Figure 4 Thyroid negative feedback loop [digital image]. In CK-12 College Human Biology (Section 11.3 Endocrine hormones). CK12.org. https://www.ck12.org/book/ck-12-human-biology/section/11.3/

CK-12 Foundation. (2019, March 5). Figure 3 A non-steroid hormone binds with a receptor on the plasma membrane of a target cell [digital image]. In Flexbook 2.0: CK-12 Biology For High School (Section 13.21 Hormone). CK12. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.21/primary/lesson/hormones-bio

CrashCourse. (2012, September 10). Great glands - Your endocrine system: CrashCourse Biology #33. YouTube. https://www.youtube.com/watch?v=WVrlHH14q3o&feature=youtu.be

TED-Ed. (2018, June 21). How do your hormones work? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=-SPRPkLoKp8&feature=youtu.be

As per caption.

Created by: CK-12/Adapted by Christine Miller

Like Pushing a Humvee Uphill

You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of energy trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a plasma membrane is a little like pushing a Humvee uphill — it can't be done without adding energy.

Some substances can pass into or out of a cell across the plasma membrane without any energy required because they are moving from an area of higher concentration to an area of lower concentration. This type of transport is called passive transport. Other substances require energy to cross a plasma membrane, often because they are moving from an area of lower concentration to an area of higher concentration, against the concentration gradient. This type of transport is called active transport. The energy for active transport comes from the energy-carrying molecule called ATP (adenosine triphosphate). Active transport may also require proteins called pumps, which are embedded in the plasma membrane. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.

The sodium-potassium pump is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cells — in all the trillions of cells in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this "uphill" process. The energy is provided by ATP. The sodium-potassium pump also requires carrier proteins. Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.

• Sodium is the principal ion in the fluid outside of cells. Normal sodium concentrations are about ten times higher outside of cells than inside of cells.  To move sodium out of the cell is moving it against the concentration gradient
• Potassium is the principal ion in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells than outside of cells. To move potassium into the cell is moving it against the concentration gradient.

These differences in concentration create an electrical and chemical gradient across the cell membrane, called the membrane potential. Tightly controlling the membrane potential is critical for vital body functions, including the transmission of nerve impulses and contraction of muscles. A large percentage of the body's energy goes to maintaining this potential across the membranes of its trillions of cells with the sodium-potassium pump.

Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called vesicle transport. Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.

Endocytosis

Endocytosis is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other solid particle is engulfed, the process is called phagocytosis. When fluid is engulfed, the process is called pinocytosis.

Exocytosis

Exocytosis is a type of vesicle transport that moves a substance out of the cell (exo-, like "exit"). A vesicle containing the substance moves through the cytoplasm to the cell membrane. Because the vesicle membrane is a phospholipid bilayer like the plasma membrane, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell.

Maintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it's no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high blood pressure, heart disease, diabetes, and other disorders.

If you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:

• Total sodium intake should be less than 2,300 mg/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg/serving (or 5 per cent daily value).
• Total potassium intake should be 4,700 mg/day. It's easy to add potassium to the diet by choosing the right foods — and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.

Figure 4.8.5 Potassium power! 

Attributions

Figure 4.8.1

Humvee challenge by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 4.8.2

Sodium Potassium Pump by Christine Miller is used under a CC BY 4.0  (https://creativecommons.org/licenses/by/4.0/) license.

Figure 4.8.3

Cytosis by Manu5 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 4.8.4 

Endocytosis and Exocytosis by Christine Miller is used under a CC BY 4.0  (https://creativecommons.org/licenses/by/4.0/) license.

Figure 4.8.5

• Canteloupes. Image Number K7355-11 by Scott Bauer/ USDA on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
• Spinach by chiara conti on Unsplash is used under the Unsplash license (https://unsplash.com/license).
• Eleven long purple eggplants by JVRKPRASAD on Wikimedia commons is used under a  CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
• Bananas by Marco Antonio Victorino on Pexels is used under the Pexels license (https://www.pexels.com/license/).
• Potato picking by Nic D on Unsplash is used under the Unsplash license (https://unsplash.com/license).
• Maldives by Sebastian Pena Lambarri on Unsplash is used under the Unsplash license (https://unsplash.com/license).

Figure 4.8.6

Active Transport by Christine Miller is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

References

Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https://www.youtube.com/watch?v=Ptmlvtei8hw&feature=youtu.be

ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis - White blood cell eats staphylococcus aureus bacteria. YouTube. https://www.youtube.com/watch?v=Z_mXDvZQ6dU

Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/diabetes/symptoms-causes/syc-20371444

Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/symptoms-causes/syc-20373410

Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org.  https://www.mayoclinic.org/diseases-conditions/heart-disease/symptoms-causes/syc-20353118

Wikipedia contributors. (2020, June 19). Ouabain. In Wikipedia.  https://en.wikipedia.org/w/index.php?title=Ouabain&oldid=963440756

A type of white blood cell and, specifically, a type of lymphocyte.

Many B cells mature into what are called plasma cells that produce antibodies (proteins) necessary to fight off infections while other B cells mature into memory B cells.

An antibody, also known as an immunoglobulin, is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses.

Image shows a photo of two children in a kayak. The older child is sitting behind the younger child and paddling.

 

Three weeks ago, 20-year-old Erica came down with symptoms typical of the common cold. She had a runny nose, fatigue, and a mild cough. Her symptoms were starting to improve, but recently, her cough has been getting worse. She is coughing up a lot of thick mucus, her throat is sore from frequent coughing, and her chest feels very congested. According to her grandmother, Erica has a “chest cold.” Erica is a smoker and wonders if her habit is making her cough worse. She decides that it's time to see a doctor.

Dr. Choo examines Erica and asks about her symptoms and health history. She checks the level of oxygen in Erica’s blood by attaching a device called a pulse oximeter to Erica’s finger.

Dr. Choo concludes that Erica has bronchitis, which is an infection that commonly occurs after a person has a cold or flu. Bronchitis is sometimes referred to as a “chest cold,” so Erica’s grandmother was right! Bronchitis causes inflammation and a build up of mucus in the bronchial tubes in the chest.

Because bronchitis is usually caused by viruses and not bacteria, Dr. Choo tells Erica that antibiotics are not likely to help. Instead, she recommends that Erica try to thin out and remove the mucus by drinking plenty of fluids and using a humidifier or spending time in a steamy shower. She recommends that Erica get plenty of rest as well.

Dr. Choo also tells Erica some things not to do — most importantly, to stop smoking while she is sick, and to try to quit smoking in the long-term. She explains that smoking can make people more susceptible to bronchitis and can hinder recovery. Finally, she advises Erica to avoid taking over-the-counter cough suppressant medication.

As you read this chapter about the respiratory system, you will be able to better understand what bronchitis is, and why Dr. Choo made the treatment recommendations that she did. At the end of the chapter, you will learn more about acute bronchitis, which is the type that Erica has. This information may come in handy to you personally, because chances are high that you will get this common infection at some point in your life — there are millions of cases of bronchitis every year!

Figure 13.1.1

Cold/ Look into my eyes forever [photo] by Spencer Backman on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 13.1.2

Wrist-oximeter by UusiAjaja on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.

Reference

Mayo Clinic Staff. (n.d.). Bronchitis [online article]. Mayoclinic.org. https://www.mayoclinic.org/diseases-conditions/bronchitis/symptoms-causes/syc-20355566

A microorganism which causes disease.

An organisms that is so small it is invisible to the human eye.

Created by CK-12 Foundation/Adapted by Christine Miller

Nineteen-year-old Malcolm is about to take his first plane flight. Shortly after he boards the plane and sits down, a man in his late sixties sits next to him in the aisle seat. About half an hour after the plane takes off, the pilot announces that she is turning the seat belt light off, and that it is safe to move around the cabin.

The man in the aisle seat — who has introduced himself to Malcolm as Willie — immediately unbuckles his seat belt and paces up and down the aisle a few times before returning to his seat. After about 45 minutes, Willie gets up again, walks some more, then sits back down and does some foot and leg exercises. After the third time Willie gets up and paces the aisles, Malcolm asks him whether he is walking so much to accumulate steps on a pedometer or fitness tracking device. Willie laughs and says no. He is actually trying to do something even more important for his health — prevent a blood clot from forming in his legs.

Willie explains that he has a chronic condition: heart failure. Although it sounds scary, his condition is currently well-managed, and he is able to lead a relatively normal lifestyle. However, it does put him at risk of developing other serious health conditions, such as deep vein thrombosis (DVT), which is when a blood clot occurs in the deep veins, usually in the legs. Air travel — and other situations where a person has to sit for a long period of time — increases the risk of DVT. Willie’s doctor said that he is healthy enough to fly, but that he should walk frequently and do leg exercises to help avoid a blood clot.

As you read this chapter, you will learn about the heart, blood vessels, and blood that make up the cardiovascular system, as well as disorders of the cardiovascular system, such as heart failure. At the end of the chapter you will learn more about why DVT occurs, why Willie has to take extra precautions when he flies, and what can be done to lower the risk of DVT and its potentially deadly consequences.

Attribution

Figure 14.1.1

aircraft-1583871_1920 [photo] by olivier89 from Pixabay is used under the Pixabay License (https://pixabay.com/de/service/license/).

A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.

Image shows a diagram of the negative feedback loop governing thyroid gland function. In the absence of sufficient levels of thyroid hormones, the hypothalamus will secrete TRH, which stimulates the pituitary gland to secrete TSH, which stimulates the thyroid gland to make thyroid hormones. Sufficient blood levels of thyroid hormone inhibit the hypothalamus from secreting TRH, halting the pathway, until thyroid hormone level sdrop again

Image shows a photograph of a cotton-top tamarin monkey, which displays the straight hair characteristic of non-human primates.

Image shows a diagram of the brain highlighting the region containing the hypothalamus and pituitary gland.

The process by which information from a gene is used in the synthesis of a functional protein.

 

Painting nails with coloured polish for aesthetic reasons is nothing new. In fact, there is evidence of this practice dating back to at least 3000 BCE. Today, painting and otherwise decorating the nails is big business, with annual revenues in the billions of dollars in North America alone! With all the attention (and money) given to nails as decorative objects, it’s easy to forget that they also have important biological functions.

Nails are accessory organs of the skin. They are made of sheets of dead keratinocytes and are found on the far (or distal) ends of the fingers and toes. The keratin in nails makes them hard, but flexible. Nails serve a number of purposes, including protecting the digits, enhancing sensations, and acting as tools.

A nail has three main parts: the root, plate, and free margin. Other structures around or under the nail include the nail bed, cuticle, and nail fold. These structures are shown in Figure 10.6.2.

• The nail root is the portion of the nail found under the surface of the skin at the near (or proximal) end of the nail. It is where the nail begins.
• The nail plate (or body) is the portion of the nail that is external to the skin. It is the visible part of the nail.
• The free margin is the portion of the nail that protrudes beyond the distal end of the finger or toe. This is the part that is cut or filed to keep the nail trimmed.
• The nail bed is the area of skin under the nail plate. It is pink in colour, due to the presence of capillaries in the dermis.
• The cuticle is a layer of dead epithelial cells that overlaps and covers the edge of the nail plate. It helps to seal the edges of the nail to prevent infection of the underlying tissues.
• The nail fold is a groove in the skin in which the side edges of the nail plate are embedded.

Nails grow from a deep layer of living epidermal tissue, known as the nail matrix, at the proximal end of the nail (see the bottom of the diagram in Figure 10.6.2). The nail matrix surrounds the nail root. It contains stem cells that divide to form keratinocytes, which are cells that produce keratin and make up the nail.

Formation of the Nail Root and Nail Plate

The keratinocytes produced by the nail matrix accumulate to form tough, hard, translucent sheets of dead cells filled with keratin. The sheets make up the nail root, which slowly grows out of the skin and becomes the nail plate when it reaches the skin surface. As the nail grows longer, the cells of the nail root and nail plate are pushed toward the distal end of the finger or toe by new cells being formed in the nail matrix. The upper epidermal cells of the nail bed also move along with the nail plate as it grows toward the tip of the digit.

The proximal end of the nail plate near the root has a whitish crescent shape called the lunula. This is where a small amount of the nail matrix is visible through the nail plate. The lunula is most pronounced in the nails of the thumbs, and may not be visible in the nails of the little fingers.

Rate of Nail Growth

Nails grow at an average rate of 3 mm a month. Fingernails, however, grow up to four times as fast as toenails. If a fingernail is lost, it takes between three and six months to regrow completely, whereas a toenail takes between 12 and 18 months to regrow. The actual rate of growth of an individual’s nails depends on many factors, including age, sex, season, diet, exercise level, and genes. If protected from breaking, nails can sometimes grow to be very long. The Chinese doctor in the photo below (Figure 10.6.3) has very long nails on two fingers of his left hand. This picture was taken in 1920 in China, where having long nails was a sign of aristocracy since it implied that one was wealthy enough to not have to do physical labour.

Both fingernails and toenails protect the soft tissues of the fingers and toes from injury. Fingernails also serve to enhance sensation and precise movements of the fingertips through the counter-pressure exerted on the pulp of the fingers by the nails. In addition, fingernails can function as several different types of tools. For example, they enable a fine precision grip like tweezers, and can also be used for cutting and scraping.

Healthcare providers, particularly EMTs, often examine the fingernail beds as a quick and easy indicator of oxygen saturation of the blood, or the amount of blood reaching the extremities. If the nail beds are bluish or purple, it is generally a sign of low oxygen saturation. To see if blood flow to the extremities is adequate, a blanch test may be done. In this test, a fingernail is briefly depressed to turn the nail bed white by forcing the blood out of its capillaries. When the pressure is released, the pink colour of the nail bed should return within a second or two if there is normal blood flow. If the return to a pink colour is delayed, then it can be an indicator of low blood volume, due to dehydration or shock.

How the visible portion of the nails appears can be used as an indicator of recent health status. In fact, nails have been used as diagnostic tools for hundreds — if not thousands — of years. Nail abnormalities, such as deep grooves, brittleness, discolouration, or unusually thin or thick nails, may indicate various illnesses, nutrient deficiencies, drug reactions, or other health problems.

Nails — especially toenails — are common sites of fungal infections (shown in Figure 10.6.4), causing nails to become thickened and yellowish in colour. Toenails are more often infected than fingernails because they are often confined in shoes, which creates a dark, warm, moist environment where fungi can thrive. Toes also tend to have less blood flow than fingers, making it harder for the immune system to detect and stop infections in toenails.

Although nails are harder and tougher than skin, they are also more permeable. Harmful substances may be absorbed through the nails and cause health problems. Some of the substances that can pass through the nails include the herbicide Paraquat, fungicidal agents such as miconazole (e.g., Monistat), and sodium hypochlorite, which is an ingredient in common household bleach. Care should be taken to protect the nails from such substances when handling or immersing the hands in them by wearing latex or rubber gloves.

Do you get regular manicures or pedicures from a nail technician? If so, there is a chance that you are putting your health at risk. Nail tools that are not properly disinfected between clients may transmit infections from one person to another. Cutting the cuticles with scissors may create breaks in the skin that let infective agents enter the body. Products such as acrylics, adhesives, and UV gels that are applied to the nails may be harmful, especially if they penetrate the nails and enter the skin.

Use the Internet to find several reliable sources that address the health risks of professional manicures or pedicures. Try to find answers to the following questions:

1. What training and certification are required for professional nail technicians?
2. What licenses and inspections are required for nail salons?
3. What hygienic practices should be followed in nail salons to reduce the risk of infections being transmitted to clients?
4. Which professional nail products are potentially harmful to the human body and which are safer?
5. How likely is it to have an adverse health consequence when you get a professional manicure or pedicure?
6. What steps can you take to ensure that a professional manicure or pedicure is safe?

Attributions

Figure 10.6.1

Nails by allison-christine-vPrqHSLdF28 [photo] by allison christine on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 10.6.2

Blausen_0406_FingerNailAnatomy by BruceBlaus  on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 10.6.3

Chinese_doctor_with_long_finger_nails_(an_aristocrat),_ca.1920_(CHS-249) by Pierce, C.C. (Charles C.), 1861-1946 from the USC Digital Library on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain).

Figure 10.6.4

Toenail fungus Nagelpilz-3 by Pepsyrock on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/public_domain).

Figure 10.6.5

OLYMPUS DIGITAL CAMERA by Stoive at the English language Wikipedia, on Wikimedia Commons is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license.

References

Blausen.com staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Guiness World Records. (2014, December 8). Longest fingernails - Guinness World Records 60th Anniversary. YouTube. https://www.youtube.com/watch?v=G35kPhbUZdg

SciShow. (2015, September 14). 5 things your nails can say about your health. YouTube. https://www.youtube.com/watch?v=aTSVHwzkYI4

TED-Ed. (2019, October 29). Claws vs. nails - Matthew Borths. YouTube. https://www.youtube.com/watch?v=7w2gCBL1MCg

Image shows an old photograph of a lady suffering from Grave's Disease, her eyes are protruding, giving her a permanent look of surprise.

One of two main divisions of the nervous system that includes the brain and spinal cord.

Image shows a diagram of the human body with labels pointing to all areas affected by hypothyroidism. Some examples include: General effects - fatigue, feeling cold, weight gain, poor appetite; Lungs - shortness of breath, pleural effusion; Skin - presthesia, myxedema; Muscular - delayed reflex action; Heart - slow pulse rate.

Image shows a diagram of how alzheimer's progresses. In preclinical AD, just a small portion of the brain is affected. More of the brain and more areas of the brain are affected in mild to moderate AD. In severe AD, most of the brain is affected.

Refers to the body system consisting of the heart, blood vessels and the blood. Blood contains oxygen and other nutrients which your body needs to survive. The body takes these essential nutrients from the blood.

Image shows a diagram of polymerase chain reaction, which occurs in three steps: 1) Denaturing, which separates the strands of DNA 2) Annealing, in which primers bind to the template DNA strands 3) Extension, in which Taq polymerase synthesizes new DNA strands from the original, now separated strands.

Image shows a diagram of the three stages of Translation. In Initiation, mRNA, a ribosome and tRNA carry methionine form a complex. In elongation, the ribosome moves along the mRNA, as tRNA with matching anticodons bring and then drop off the corresponding amino acids. In termination, a stop codon is reached, and the entire complex disassembles, and releases the newly synthesize polypeptide.

Image shows a Lego (TM) representation of Gregor Mendel with his plants.

A body system including a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system.

Image shows a photograph of a person getting a pedicure at a salon.

Created by CK-12 Foundation/Adapted by Christine Miller

Steady as She Goes

This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature — it's a thermostat. The device shows the current temperature in the room, and also allows the occupant to set the thermostat to the desired temperature. A thermostat is a commonly cited model of how living systems — including the human body— maintain a steady state called homeostasis.

Homeostasis is the condition in which a system (such as the human body) is maintained in a more or less steady state. It is the job of cells, tissues, organs, and organ systems throughout the body to maintain many different variables within narrow ranges compatible with life. Keeping a stable internal environment requires continually monitoring the internal environment and constantly making adjustments to keep things in balance.

Set Point and Normal Range

For any given variable, such as body temperature or blood glucose level, there is a particular set point that is the physiological optimum value. The set point for human body temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain homeostasis for temperature or any other internal variable, the value typically fluctuates around the set point. Such fluctuations are normal, as long as they do not become too extreme. The spread of values within which such fluctuations are considered insignificant is called the normal range. In the case of body temperature, for example, the normal range for an adult is about 36.5 to 37.5 degrees C (97.7 to 99.5 degrees F).

A good analogy for set point, normal range, and maintenance of homeostasis is driving.  When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane — this is analogous to the set point.  Sometimes, you are not driving in the exact centre of the lane, but you are still within your lines, so you are in the equivalent of the normal range.  However, if you were to get too close to the centre line or the shoulder of the road, you would take action to correct your position.  You'd move left if you were too close to the shoulder, or right if too close to the centre line — which is analogous to our next concept, negative feedback to maintain homeostasis.

Maintaining Homeostasis

Homeostasis is normally maintained in the human body by an extremely complex balancing act. Regardless of the variable being kept within its normal range, maintaining homeostasis requires at least four interacting components: stimulus, sensor, control centre, and effector.

1. The stimulus is provided by the variable being regulated. Generally, the stimulus indicates that the value of the variable has moved away from the set point or has left the normal range.
2. The sensor monitors the values of the variable and sends data on it to the control centre.
3. The control centre matches the data with normal values. If the value is not at the set point or is outside the normal range, the control centre sends a signal to the effector.
4. The effector is an organ, gland, muscle, or other structure that acts on the signal from the control centre to move the variable back toward the set point.

Each of these components is illustrated in Figure 7.8.2. The diagram on the left is a general model showing how the components interact to maintain homeostasis. The diagram on the right shows the example of body temperature. From the diagrams, you can see that maintaining homeostasis involves feedback, which is data that feeds back to control a response. Feedback may be negative (as in the example below) or positive. All the feedback mechanisms that maintain homeostasis use negative feedback. Biological examples of positive feedback are much less common.

 

 

In a negative feedback loop, feedback serves to reduce an excessive response and keep a variable within the normal range. Two processes controlled by negative feedback are body temperature regulation and control of blood glucose.

Body Temperature

Body temperature regulation involves negative feedback, whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.

The human body’s temperature regulatory centre is the hypothalamus in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point, it sets into motion the following responses:

• Blood vessels in the skin dilate (vasodilation) to allow more blood from the warm body core to flow close to the surface of the body, so heat can be radiated into the environment.
• As blood flow to the skin increases, sweat glands in the skin are activated to increase their output of sweat (diaphoresis). When the sweat evaporates from the skin surface into the surrounding air, it takes heat with it.
• Breathing becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases heat loss from the lungs.

Heating Up

When the brain’s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:

• Blood vessels in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.
• As temperature falls lower, random signals to skeletal muscles are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.
• The thyroid gland may be stimulated by the brain (via the pituitary gland) to secrete more thyroid hormone. This hormone increases metabolic activity and heat production in cells throughout the body.
• The adrenal glands may also be stimulated to secrete the hormone adrenaline. This hormone causes the breakdown of glycogen (the carbohydrate used for energy storage in animals) to glucose, which can be used as an energy source. This catabolic chemical process is exothermic, or heat producing.

Blood Glucose

In controlling the blood glucose level, certain endocrine cells in the pancreas (called alpha and beta cells) detect the level of glucose in the blood. They then respond appropriately to keep the level of blood glucose within the normal range.

• If the blood glucose level rises above the normal range, pancreatic beta cells release the hormone insulin into the bloodstream. Insulin signals cells to take up the excess glucose from the blood until the level of blood glucose decreases to the normal range.
• If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone glucagon into the bloodstream. Glucagon signals cells to break down stored glycogen to glucose and release the glucose into the blood until the level of blood glucose increases to the normal range.

In a positive feedback loop, feedback serves to intensify a response until an end point is reached. Examples of processes controlled by positive feedback in the human body include blood clotting and childbirth.

Blood Clotting

When a wound causes bleeding, the body responds with a positive feedback loop to clot the blood and stop blood loss. Substances released by the injured blood vessel wall begin the process of blood clotting. Platelets in the blood start to cling to the injured site and release chemicals that attract additional platelets. As the platelets continue to amass, more of the chemicals are released and more platelets are attracted to the site of the clot. The positive feedback accelerates the process of clotting until the clot is large enough to stop the bleeding.

Childbirth

Figure 7.8.6 shows the positive feedback loop that controls childbirth. The process normally begins when the head of the infant pushes against the cervix. This stimulates nerve impulses, which travel from the cervix to the hypothalamus in the brain. In response, the hypothalamus sends the hormone oxytocin to the pituitary gland, which secretes it into the bloodstream so it can be carried to the uterus. Oxytocin stimulates uterine contractions, which push the baby harder against the cervix. In response, the cervix starts to dilate in preparation for the passage of the baby. This cycle of positive feedback continues, with increasing levels of oxytocin, stronger uterine contractions, and wider dilation of the cervix until the baby is pushed through the birth canal and out of the body. At that point, the cervix is no longer stimulated to send nerve impulses to the brain, and the entire process stops.

Homeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do, homeostatic imbalance may result, in which cells may not get everything they need or toxic wastes may accumulate in the body. If homeostasis is not restored, the imbalance may lead to disease — or even death. Diabetes is an example of a disease caused by homeostatic imbalance. In the case of diabetes, blood glucose levels are no longer regulated and may be dangerously high. Medical intervention can help restore homeostasis and possibly prevent permanent damage to the organism.

Normal aging may bring about a reduction in the efficiency of the body’s control systems, which makes the body more susceptible to disease. Older people, for example, may have a harder time regulating their body temperature. This is one reason they are more likely than younger people to develop serious heat-induced illnesses, such as heat stroke.

Diabetes is diagnosed in people who have abnormally high levels of blood glucose after fasting for at least 12 hours. A fasting level of blood glucose below 100 is normal. A level between 100 and 125 places you in the pre-diabetes category, and a level higher than 125 results in a diagnosis of diabetes.

Of the two types of diabetes, type 2 diabetes is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes typically starts after the age of 40. However, because of the dramatic increase in recent decades in obesity in younger people, the age at which type 2 diabetes is diagnosed has fallen. Even children are now being diagnosed with type 2 diabetes. Today, about 3 million Canadians (8.1% of total population) are living with diabetes.

You may at some point have your blood glucose level tested during a routine medical exam. If your blood glucose level indicates that you have diabetes, it may come as a shock to you because you may not have any symptoms of the disease. You are not alone, because as many as one in four diabetics do not know they have the disease. Once the diagnosis of diabetes sinks in, you may be devastated by the news. Diabetes can lead to heart attacks, strokes, blindness, kidney failure, nerve damage, and loss of toes or feet. The risk of death in adults with diabetes is 50 per cent greater than it is in adults without diabetes, and diabetes is the seventh leading cause of death of adults. In addition, controlling diabetes usually requires frequent blood glucose testing, watching what and when you eat, and taking medications or even insulin injections. All of this may seem overwhelming.

The good news is that changing your lifestyle may stop the progression of type 2 diabetes or even reverse it. By adopting healthier habits, you may be able to keep your blood glucose level within the normal range without medications or insulin. Here’s how:

• Lose weight. Any weight loss is beneficial. Losing as little as seven per cent of your weight may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.
• Exercise regularly. You should try to exercise for at least 30 minutes, five days a week. This will not only lower your blood sugar and help your insulin work better, but it will also lower your blood pressure and improve your heart health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.
• Adopt a healthy diet. Decrease your consumption of refined carbohydrates, such as sweets and sugary drinks. Increase your intake of fibre-rich foods, such as fruits, vegetables, and whole grains. About one-quarter of each meal should consist of high-protein foods, such as fish, chicken, dairy products, legumes, or nuts.
• Control stress. Stress can increase your blood glucose and also raise your blood pressure and risk of heart disease. When you feel stressed out, do breathing exercises or take a brisk walk or jog. Try to replace stressful thoughts with more calming ones.
• Establish a support system. Enlist the help and support of loved ones, as well as medical professionals, such as a nutritionist and diabetes educator. Having a support system will help ensure that you are on the path to wellness, and that you can stick to your plan.

Attributions

Figure 7.8.1

Nest_Thermostat by Amanitamano on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.

Figure 7.8.2

Negative_Feedback_Loops by OpenStax  on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.

Figure 7.8.3

Body Temperature Homeostasis by OpenStax College, Biology is used under a CC BY 4.0 license.

Figure 7.8.4

Homeostasis_of_blood_sugar by Christinelmiller on Wikimedia Commons is used under a  CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.

Figure 7.8.5

Positive_Feedback_Diagram_Blood_Clotting by Elliottuttle on Wikimedia Commons is used under a CC BY-SA 4.0  (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 7.8.6

Pregnancy-Positive_Feedback by OpenStax  on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.

References

Amoeba Sisters. (2017, September 7). Homeostasis and negative/positive feedback. YouTube. https://www.youtube.com/watch?v=Iz0Q9nTZCw4&feature=youtu.be

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 1.10 Negative feedback loop [digital image/ diagram].  In Anatomy and Physiology (Section 1.5). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-5-homeostasis

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 1.11 Positive feedback loop normal childbirth is driven by a positive feedback loop [digital image/ diagram].  In Anatomy and Physiology (Section 1.5). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-5-homeostasis

Cognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https://www.youtube.com/watch?v=XMsJ-3qRVJM&feature=youtu.be

Mayo Clinic Staff. (n.d.). Type 2 diabetes [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/type-2-diabetes/symptoms-causes/syc-20351193

OpenStax CNX. (2016, March 23). Figure 4 The body is able to regulate temperature in response to signals from the nervous system [digital image]. In OpenStax, Biology (Section 33.3). https://cnx.org/contents/GFy_h8cu@10.8:BP24ZReh@7/Homeostasis

Whats Up Dude. (2017, September 20). Homeostasis - What is homeostasis - What is set point for homeostasis - Homeostasis in the human body. YouTube. https://www.youtube.com/watch?v=LSgEJSlk6W4&feature=youtu.be

Image shows a photograph of a women with a goiter. The centre bottom of her throat has a visible enlargement.

Created by CK-12 Foundation/Adapted by Christine Miller

Being bitten on the nose by an eel certainly qualifies as a frightening experience! The fear this man is experiencing produces the same physiological responses in most people — racing heart, rapid breathing, clammy hands. These and other fight-or-flight responses prepare the body to either defend itself or run away from danger. Why does fear elicit these changes in the body? The responses occur in large part because of hormones secreted by the adrenal glands.

The adrenal glands are endocrine glands that produce a variety of hormones. Adrenal hormones include the fight-or-flight hormone adrenaline and the steroid hormone cortisol. The two adrenal glands are located on both sides of the body, just above the kidneys, as shown in Figure 9.6.2. The right adrenal gland (on the left in the figure) is smaller and has a pyramidal shape. The left adrenal gland (on the right in the figure) is larger and has a half-moon shape.

Each adrenal gland has two distinct parts, and each part has a different function, although both parts produce hormones. There is an outer layer, called the adrenal cortex, which produces steroid hormones including cortisol. There is also an inner layer, called the adrenal medulla, which produces non-steroid hormones including adrenaline.

The adrenal cortex, or outer layer of the adrenal gland, is divided into three additional layers, called zones (see Figure 9.6.3). Each zone has distinct enzymes that produce different hormones from the common precursor molecule cholesterol, which is a lipid.

1. Zona glomerulosa is the outermost layer of the adrenal cortex. It lies immediately under the outer fibrous capsule that encloses the adrenal gland.
2. Zona fasciculata is the middle layer of the adrenal cortex. It is the largest of the three zones, accounting for nearly 80 per cent of the adrenal cortex.
3. Zona reticularis is the innermost layer of the adrenal cortex. It is directly adjacent to the medulla of the adrenal gland.

 

Hormones produced by the adrenal cortex are known by the general term corticosteroids. As steroid hormones, corticosteroids are endocrine hormones that are made of lipids and exert their effects on target cells by crossing the plasma membrane and binding with receptors within the cytoplasm. A steroid hormone and its receptor form a complex that enters the cell nucleus and affects gene expression. There are three types of corticosteroids synthesized and secreted by the adrenal cortex. Each type is produced by a different zone of the adrenal cortex, as shown in Figure 9.6.4.

Mineralocorticoids

Mineralocorticoids are produced in the zona glomerulosa and include the hormone aldosterone. These hormones help control the balance of mineral salts (electrolytes) in the body. In the kidneys, aldosterone increases the reabsorption of sodium ions and the excretion of potassium ions. Aldosterone also stimulates the retention of sodium ions by cells in the colon and by the sweat glands. The amount of sodium in the body affects the volume of extracellular fluids (including the blood) and thereby affects blood pressure. In this way, mineralocorticoids help control blood volume and blood pressure.

Glucocorticoids

Glucocorticoids are produced in the zona fasciculata and include the hormone cortisol, which is released in repsonse to stress and is considered the primary stress hormone. Glucocorticoids help control the rate of metabolism of proteins, fats, and sugars. In general, they increase the level of glucose and fatty acids circulating in the blood. Cells rely primarily on glucose for energy, but they can also use fatty acids for energy as an alternative to glucose. Glucocorticoids are also involved in suppression of the immune system, having a potent anti-inflammatory effect. In addition, cortisol reduces the production of new bone and decreases absorption of calcium from the gastrointestinal tract.

Androgens

Androgens are produced in the zona reticularis and include the hormone DHEA (dehydroepiandrosterone). Androgens are a general term for male sex hormones, although this is somewhat misleading, as adrenal cortex androgens are produced by both males and females. In adult males, they are converted to more potent androgens, such as testosterone in the male gonads (testes). In adult females, they are converted to female sex hormones called estrogens in the female gonads (ovaries).

Regulation of Adrenal Cortex Hormones

Steroid hormone production by the three zones of the adrenal cortex is regulated by hormones secreted by the anterior lobe of the pituitary gland, as well as by other physiological stimuli. For example, the production of glucocorticoids such as cortisol is stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary, which in turn is stimulated by corticotropin releasing hormone (CRH) from the hypothalamus. When levels of glucocorticoids start to rise too high, they provide negative feedback to the hypothalamus and pituitary gland to stop secreting CRH and ACTH, respectively. This negative feedback mechanism is illustrated in Figure 9.6.5. The opposite occurs when levels of glucocorticoids start to fall too low.

The adrenal medulla is at the center of each adrenal gland and is surrounded by the adrenal cortex. It contains a dense network of blood vessels into which it secretes its hormones. The hormones synthesized and secreted by the adrenal medulla are generally known as catecholamines, and they include adrenaline (also called epinephrine) and noradrenaline (also called norepinephrine). These water-soluble, non-steroid hormones are made of amino acids. As non-steroid hormones, they cannot cross the plasma membrane of target cells. Instead, they exert their effects by binding to receptors on the surface of target cells. The binding of hormone and receptor activates an enzyme in the plasma membrane that controls a second messenger. It is the second messenger that influences processes inside the cell.

Catecholamines function to produce a rapid response throughout the body in stressful situations. They bring about such changes as increased heart rate, more rapid breathing, constriction of blood vessels in certain parts of the body, and an increase in blood pressure. The release of catecholamines by the adrenal medulla is stimulated by activation of the sympathetic division of the autonomic nervous system.

Disorders of the adrenal glands generally include either hypersecretion or hyposecretion of adrenal hormones. The underlying cause of the abnormal secretion may be a problem with the adrenal glands or with the pituitary gland, which controls adrenal cortex hormone production. Both adrenal and pituitary glands are subject to the formation of tumors, which may cause adrenal disorders. The adrenal gland may also be affected by infections or autoimmune diseases.

Adrenal Hypersecretion: Cushing’s Syndrome

Hypersecretion of the glucocorticoid hormone cortisol leads to a disorder called Cushing’s syndrome. The most common cause of Cushing’s syndrome is a pituitary tumor, which causes excessive production of ACTH. The disease produces a wide variety of signs and symptoms, which may include obesity, diabetes, high blood pressure (hypertension), excessive body hair, osteoporosis, and depression. A distinctive sign of Cushing’s syndrome is the appearance of stretch marks in the skin, as the skin becomes progressively thinner. Another distinctive sign is a moon face, in which fat deposits give the face a rounded appearance. Treatment of Cushing’s syndrome depends on its cause and may include surgery to remove a tumor or medications to suppress activity of the adrenal glands.

Adrenal Hyposecretion: Addison’s Disease

Hyposecretion of the glucocorticoid hormone cortisol leads to a disorder called Addison’s disease. There may also be hyposecretion of mineralocorticoids with this disorder. Addison’s disease is generally an autoimmune disorder, in which the immune system produces abnormal antibodies that attack cells of the adrenal cortex. Untreated infections, especially of tuberculosis, may also damage the adrenal cortex and cause Addison’s disease. A third possible cause is decreased output of ACTH by the pituitary gland, generally due to a pituitary tumor. A distinctive sign of Addison’s disease is hyperpigmentation of the skin (see the photos in Figure 9.6.6). Other symptoms tend to be nonspecific and include excessive fatigue. Addison’s disease is generally treated with replacement hormones in pill form.

Does just looking at this photo (Figure 9.6.7) cause you to break out in a cold sweat and experience heart palpitations? Imagine how scary it would be to actually fling yourself backward off a tall building like the BASE jumper in the photo! There would be very little time to use a parachute to slow your fall before you hit the ground. BASE jumping is called the most dangerous sport on Earth. In fact, it is so dangerous that it is outlawed in some places.

People who participate in such dangerous activities as BASE jumping are likely to be adrenaline “junkies.” They are addicted to the adrenaline rush and euphoria — or “high” — it causes when their fight-or-flight response is triggered by danger. Why does adrenaline have this effect? Adrenaline is closely related to dopamine, a chemical messenger in the brain that plays a major role in pleasure and addiction.

Adrenaline addicts don’t have to participate in BASE jumping or other dangerous sports to get an adrenaline rush. They might choose a dangerous occupation like firefighting, participate in risky behaviors like reckless driving or bank robbing, or just pick fights with other people. They might even create their own stress by always taking on too much work or delaying projects until close to their deadline.

While some excitement in one’s life is generally a good thing, always putting oneself in danger or constantly being under stress are obviously not good things. If you think you might be an adrenaline addict, note that there are healthier ways to experience a hormonal “high.” Running, biking, or participating in some other form of vigorous aerobic exercise causes the pituitary gland and hypothalamus to produce opiate-like endorphins, leading to a so-called “runner’s high.” Like the euphoric feeling adrenaline causes, a runner’s high may last for hours.

Attributions

Figure 9.6.1

Attack from wikimedia commons by Jerry Kirkhart from Los Osos, Calif. on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.

Figure 9.6.2

Diagram_showing_where_the_adrenal_glands_are_in_the_body_CRUK_415.svg by Cancer Research UK uploader on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 9.6.3

Adrenal_cortex_labelled by Jpogi at English Wikipedia on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.

Figure 9.6.4

The_Adrenal_Glands by OpenStax College is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.

Figure 9.6.5

ACTH negative feedback loop by Christinelmiller is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.

Figure 9.6.6

A_69-Year-Old_Female_with_Tiredness_and_a_Persistent_Tan_01 by Petros Perros on Wikimedia Commons is used under a CC BY 2.5 (https://creativecommons.org/licenses/by/2.5/deed.en) license.

Figure 9.6.7

BASE_Jumping_from_Sapphire_Tower_in_Istanbul by Kontizas Dimitrios on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

References

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 17.17 Adrenal glands [digital image].  In Anatomy and Physiology (Section 17.6). OpenStax College. https://openstax.org/books/anatomy-and-physiology/pages/17-6-the-adrenal-glands

Henk van 't Klooster. (2013). Adrenaline: Fight or flight response. YouTube. https://www.youtube.com/watch?v=FBnBTkcr6No&feature=youtu.be

Perros, P. (2005). A 69-year-old female with tiredness and a persistent tan. PLoS Medicine, 2(8): e229. https://doi.org/10.1371/journal.pmed.0020229

TED-Ed. (2015, October 22). How stress affects your body - Sharon Horesh Bergquist. YouTube. https://www.youtube.com/watch?v=v-t1Z5-oPtU&feature=youtu.be

TED-Ed. (2015, November 6). How stress affects your brain - Madhumita Murgia. YouTube. https://www.youtube.com/watch?v=WuyPuH9ojCE&feature=youtu.be

 

 

Image shows a diagram of the situation of the pancreas in relation to the stomach (stomach sits in front), the gallbladder (gallbladder sits above and to the patient's right), and the duodenum, which curls around under the pancreas. The pancreas has major regions including the head, a widened portion at the lowest point, the body, and the tail (the highest point). The pancreas is made up of lobules and the central pancreatic duct.

Image shows an illustration of the thyroid gland. It is located in front of where an Adam's apple would be. It is roughly butterfly shaped. The "wings" are the right and left lobes, and the connecting part is the isthmus.

Created by CK-12 Foundation/Adapted by Christine Miller

Aiko, 22, and Larissa, 23, met through mutual friends and hit it off right away. They began dating and just four months later, they are now madly in love. They spend as much time as they can with each other, and have decided to move in together when Larissa’s roommate moves out. They are even discussing getting married one day.

Inspired by his passion for Larissa, Aiko is considering getting her name tattooed on his arm. As you probably know, tattoos are designs on the skin created by injecting pigments into the skin with a needle. Aiko looks up different tattoo styles online, and starts to envision what he would want in a tattoo.

One day at a street festival, Aiko sees a sign that says “Henna Tattoos.” Henna tattoos are not technically tattoos — they are temporary designs that artists can create on the skin using a paste made out of the leaves of the henna plant. The henna stains the skin a reddish-brown colour, and once the paste is scraped off, the design typically remains on the skin for a few weeks. The use of henna to create designs on the skin is called mehndi. It is traditionally used by people in and from regions such as India, Pakistan, the Middle East, and Africa to celebrate special occasions, particularly weddings. Mendhi is often done on the palms of the hands and soles of the feet, where the designs usually come out darker than on other areas of the skin. You can see some examples of henna art in the images below.

Aiko asks the mehndi artist to inscribe Larissa’s name on his arm, so that he can see whether he likes it without making the permanent commitment of a real tattoo. Two days later, Aiko visits his parents. They are not familiar with mehndi, and they have a moment of panic when they think he got a real tattoo. Aiko reassures them that it is temporary, but tells them that he is thinking about getting a real tattoo.

His parents are concerned. His father points out that he has not known Larissa long — what if they break up and he regrets the tattoo? His mother additionally worries about whether tattoos are safe. Aiko says that he doesn’t think he will regret the decision, but if he does, he can cover it up with another tattoo or get it removed with laser treatments. He also tells them that he would go to an artist and shop that are reputable, and take appropriate safety precautions. His parents warn him that getting a tattoo removed may not be as simple as he thinks, and that he should think very carefully before making such a permanent decision.

Humans have long decorated and adorned their skin with tattoos, makeup, and piercings. They also colour, cut, straighten, curl, and remove their hair; and paint, grow, and cut their nails. The skin, hair, and nails make up the integumentary system. As you read this chapter, you will learn about the important biological functions that these organs carry out, beyond being a convenient canvas for personal expression. At the end of the chapter you will find out if Aiko got his tattoo. You will also learn more about how tattoos, mehndi, and laser tattoo removal work, as well as the important considerations to protect your health if you are thinking about getting a tattoo.

 

Attributions

Figure 10.1.1

Arm tattoo by telly telly on Flickr is used under a CC BY 2.0  (https://creativecommons.org/licenses/by/2.0/) license.

Figure 10.1.2

• Henna for hair by Andrey "A.I." Sitnik ( www.sitnik.ru ) on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
• Henna on foot in Morocco by Bjørn Christian Tørrissen on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
• Mehndi (front) by AKS.9955 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
• Tags: Hand Jewelry Ornaments. . .Henna by BenBernardBags on Pixabay is used under the Pixabay License (https://pixabay.com/ja/service/license/).

visible part of a nail that is external to the skin

The space occurring between two or more membranes. In cell biology, it's most commonly described as the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast.

Groups of connected cells form tissues. The cells in a tissue may all be the same type, or they may be of multiple types. In either case, the cells in the tissue work together to carry out a specific function, and they are always specialized to be able to carry out that function better than any other type of tissue.  There are four main types of human tissues: connective, epithelial, muscle, and nervous tissues. We use tissues to build organs and organ systems.  The 200 types of cells that the body can produce based on our single set of DNA can create all the types of tissue in the body.

Epithelial Tissue

Epithelial tissue is made up of cells that line inner and outer body surfaces, such as the skin and the inner surface of the digestive tract. Epithelial tissue that lines inner body surfaces and body openings is called mucous membrane. This type of epithelial tissue produces mucus, a slimy substance that coats mucous membranes and traps pathogens, particles, and debris. Epithelial tissue protects the body and its internal organs, secretes substances (such as hormones) in addition to mucus, and absorbs substances (such as nutrients).

The key identifying feature of epithelial tissue is that it contains a free surface and a basement membrane.  The free surface is not attached to any other cells and is either open to the outside of the body, or is open to the inside of a hollow organ or body tube.  The basement membrane anchors the epithelial tissue to underlying cells.

Epithelial tissue is identified and named by shape and layering.  Epithelial cells exist in three main shapes: squamous, cuboidal, and columnar.  These specifically shaped cells can, depending on function, be layered several different ways: simple, stratified, pseudostratified, and transitional.

Epithelial tissue forms coverings and linings and is responsible for a range of functions including diffusion, absorption, secretion and protection.  The shape of an epithelial cell can maximize its ability to perform a certain function.  The thinner an epithelial cell is, the easier it is for substances to move through it to carry out diffusion and/or absorption.  The larger an epithelial cell is, the more room it has in its cytoplasm to be able to make products for secretion, and the more protection it can provide for underlying tissues. Their are three main shapes of epithelial cells: squamous (which is shaped like a pancake- flat and oval), cuboidal (cube shaped), and columnar (tall and rectangular).

Figure 7.4.2 The shape of epithelial tissues is important.  

Epithelial tissue will also organize into different layerings depending on their function.  For example, multiple layers of cells provide excellent protection, but would no longer be efficient for diffusion, whereas a single layer would work very well for diffusion, but no longer be as protective; a special type of layering called transitional is needed for organs that stretch, like your bladder.  Your tissues exhibit the layering that makes them most efficient for the function they are supposed to perform. There are four main layerings found in epithelial tissue: simple (one layer of cells), stratified (many layers of cells), pseudostratified (appears stratified, but upon closer inspection is actually simple), and transitional (can stretch, going from many layers to fewer layers).

Figure 7.4.3 The layerings found in epithelial tissues is important.  

See Table 7.4.1 for a summary of the different layering types and shapes epithelial cells can form and their related functions and locations.

Table 7.4.1

Summary of Epithelial Tissue Cells

So far, we have identified epithelial tissue based on shape and layering.  The representative diagrams we have seen so far are helpful for visualizing the tissue structures, but it is important to look at real examples of these cells.  Since cells are too tiny to see with the naked eye, we rely on microscopes to help us study them.  Histology is the study of the microscopic anatomy and cells and tissues.  See Table 7.4.2 to see some examples of slides of epithelial tissues prepared for the purpose of histology.

Table 7.4.2

Epithelial Tissues and Histological Samples

 

Epithelial Tissue Type	Tissue Diagram	Histological Sample
Stratified squamous (from skin)
Simple cuboidal (from kidney tubules)
Pseudostratified ciliated columnar (from trachea)

Connective Tissue

Bone and blood are examples of connective tissue. Connective tissue is very diverse. In general, it forms a framework and support structure for body tissues and organs. It's made up of living cells separated by non-living material, called extracellular matrix, which can be solid or liquid. The extracellular matrix of bone, for example, is a rigid mineral framework. The extracellular matrix of blood is liquid plasma.

The key identifying feature of connective tissue is that is is composed of a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, based on the nature of the matrix. They  look very different from one another, which is a reflection of their different functions:

1. Fibrous connective tissue: is characterized by a matrix which is flexible and is made of protein fibres including collagen, elastin and possibly reticular fibres.  These tissues are found making up tendons, ligaments, and body membranes.
2. Supportive connective tissue: is characterized by a solid matrix and is what is used to make bone and cartilage.  These tissues are used for support and protection.
3. Fluid connective tissue: is characterized by a fluid matrix and includes both blood and lymph.

Fibrous Connective Tissue

Fibrous connective tissue contains cells called fibroblasts.  These cells produce fibres of collagen, elastin, or reticular fibre which makes up the matrix of this type of connective tissue.  Based on how tightly packed these fibres are and how they are oriented changes the properties, and therefore the function of the fibrous connective tissue.

 

• Loose fibrous connective tissue:  composed of a loose and disorganized weave of collagen and elastin fibres, creating a tissue that is thin and flexible, yet still tough.  This tissue, which is also sometimes referred to as "areolar tissue", is found in membranes and surrounding blood vessels and most body organs.  As you can see from the diagram in Figure 7.4.4, loose fibrous connective tissue fulfills the definition of connectives tissue since it is a scattering of cells (fibroblasts) in a non-cellular matrix (a mesh of collagen and elastin fibres).  There are two types of specialized loose fibrous connective tissue: reticular and adipose.  Adipose tissue stores fat and reticular tissue forms the spleen and lymph nodes.
  
• Dense Fibrous Connective Tissue: composed of a dense mat of parallel collagen fibres and a scattering of fibroblasts, creating a tissue that is very strong.  Dense fibrous connective tissue forms tendons and ligaments, which connect bones to muscles and/or bones to neighbouring bones.
  

Supportive Connective Tissue

Supportive connective tissue exhibits the defining feature of connective tissue in that it is a scattering of cells in a non-cellular matrix; what sets it apart from other connective tissues is its solid matrix.  In this tissue group, the matrix is solid- either bone or cartilage.  While fibrous connective tissue contained cells called fibroblasts which produced fibres, supportive connective tissue contains cells that either create bone (osteocytes) or cells that create cartilage (chondrocytes).

Cartilage

Chondrocytes produce the cartilage matrix in which they reside.  Cartilage is made up of protein fibres and chondrocytes in lacunae.  This is tissue is strong yet flexible and is used many places in the body for protection and support.  Cartilage is one of the few tissues that is not vascular (doesn't have a direct blood supply) meaning it relies on diffusion to obtain nutrients and gases; this is the cause of slow healing rates in injuries involving cartilage.  There are three main types of cartilage:

• Hyaline cartilage: a smooth, strong and flexible tissue.  Found at the ends of ribs and long bones, in the nose, and comprising the entire fetal skeleton.
• Fibrocartilage: a very strong tissue containing thick bundles of collagen.  Found in joints that need cushioning from high impact (knees, jaw).
• Elastic cartilage: contains elastic fibres in addition to collagen,  giving support with the benefit of elasticity.  Found in earlobes and the epiglottis.
  

  

Bone

Osteocytes produce the bone matrix in which they reside.  Since bone is very solid, these cells reside in small spaces called lacunae.  This bone tissue is composed of collagen fibres embedded in calcium phosphate giving it strength without brittleness.  There are two types of bone: compact and spongy.

• Compact bone: has a dense matrix organized into cylindrical units called osteons.  Each osteon contains a central canal (sometimes called a Harversian Canal) which allows for space for blood vessels and nerves, as well as concentric rings of bone matrix and osteocytes in lacunae, as per the diagram here.  Compact bone is found in long bones and forms a shell around spongy bone.

• Spongy bone: a very porous type of bone which most often contains bone marrow.  It is found at the end of long bones, and makes up the majority of the ribs, shoulder blades and flat bones of the cranium.

Fluid Connective Tissue

Fluid connective tissue has a matrix that is fluid; unlike the other two categories of connective tissue, the cells that reside in the matrix do not actually produce the matrix. Fibroblasts make the fibrous matrix, chondrocytes make the cartilaginous matrix, osteocytes make the bony matrix, yet blood cells do not make the fluid matrix of either lymph or plasma.  This tissue still fits the definition of connective tissue in that it is still a scattering of cells in a non-cellular matrix.

There are two types of fluid connective tissue:

• Blood: blood contains three types of cells suspended in plasma, and is contained in the cardiovascular system.
  • Eryththrocytes, more commonly called red blood cells, are present in high numbers (roughly 5 million cells per mL) and are responsible for delivering oxygen from to the lungs to all the other areas of the body. These cells are relatively small in size with a diameter of around 7 micrometres and live no longer than 120 days.
  • Leukocytes, often referred to as white blood cells, are present in lower numbers (approximately 5 thousand cells per mL) are responsible for various immune functions.  They are typically larger than erythrocytes, but can live much longer, particularly white blood cells responsible for long term immunity.  The number of leukocytes in your blood can go up or down based on whether or not you are fighting an infection.
  • Thrombocytes, also known as platelets, are very small cells responsible for blood clotting.  Thrombocytes are not actually true cells, they are fragments of a much larger cell called a megakaryocyte.
• Lymph: contains a liquid matrix and white blood cells and is contained in the lymphatic system, which ultimately drains into the cardiovascular system.

Figure 7.4.11 A stained lymphocyte surrounded by red blood cells viewed using a light microscope. 

Muscular Tissue

Muscular tissue is made up of cells  that have the unique ability to contract- which is the defining feature of muscular tissue.  There are three major types of muscle tissue, as pictured in Figure 7.4.12 skeletal, smooth, and cardiac muscle tissues.

Skeletal Muscle

Skeletal muscles are voluntary muscles, meaning that you exercise conscious control over them.  Skeletal muscles are attached to bones by tendons, a type of connective tissue. When these muscles shorten to pull on the bones to which they are attached, they enable the body to move. When you are exercising, reading a book, or making dinner, you are using skeletal muscles to move your body to carry out these tasks.

Under the microscope, skeletal muscles are striated (or striped) in appearance, because of their internal structure which contains alternating protein fibres of actin and myosin.  Skeletal muscle is described as multinucleated, meaning one "cell" has many nuclei.  This is because in utero, individual cells destined to become skeletal muscle fused, forming muscle fibres in a process known as myogenesis.  You will learn more about skeletal muscle and how it contracts in the Muscular System.

Smooth Muscle

Smooth muscles are nonstriated muscles- they still contain the muscle fibres actin and myosin, but not in the same alternating arrangement seen in skeletal muscle.   Smooth muscle is found in the tubes of the body - in the walls of blood vessels and in the reproductive, gastrointestinal, and respiratory tracts. Smooth muscles are not under voluntary control meaning that they operate unconsciously, via the autonomic nervous system.  Smooth muscles move substances through a wave of contraction which cascades down the length of a tube, a process termed peristalsis. 

Watch the YouTube video "What is Peristalsis" by Mister Science to see peristalsis in action.

https://www.youtube.com/watch?v=kVjeNZA5pi4

What is Peristalsis, Mister Science, 2018.

 

 

Cardiac Muscle

Cardiac muscles work involuntarily, meaning they are regulated by the autonomic nervous system.  This is probably a good thing, since you wouldn't want to have to consciously concentrate on keeping your heart beating all the time! Cardiac muscle, which is found only in the heart, is mononucleated and striated (due to alternating bands of myosin and actin). Their contractions cause the heart to pump blood. In order to make sure entire sections of the heart contract in unison, cardiac muscle tissue contains special cell junctions called intercalated discs, which conduct the electrical signals used to "tell" the chambers of the heart when to contract.

Nervous Tissue

Nervous tissue is made up of neurons and a group of cells called neuroglia (also known as glial cells).  Nervous tissue makes up the central nervous system (mainly the brain and spinal cord) and peripheral nervous system (the network of nerves that runs throughout the rest of the body).  The defining feature of nervous tissue is that it is specialized to be able to generate and conduct nerve impulses.  This function is carried out by neurons, and the purpose of neuroglia is to support neurons.

A neuron has several parts to its structure:

• Dendrites which collect incoming nerve impulses
• A cell body, or soma, which contains the majority of the neuron's organelles, including the nucleus
• An axon, which carries nerve impulses away from the soma, to the next neuron in the chain
• A myelin sheath, which encases the axon and increases that rate at which nerve impulses can be conducted
• Axon terminals, which maintain physical contact with the dendrites of neighbouring neurons

 

Attributions

Figure 7.4.1

• Construction man kneeling in front of wall by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Beige wooden frame by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Tambour on green by Pierre Châtel-Innocention Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Tags: Construction Studs Plumbing Wiring by JWahl on Pixabay is used under the Pixabay License (https://pixabay.com/es/service/license/).

Figure 7.4.2 and Figure 7.4.3

• Simple columnar epithelium tissue by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. 
• Simple cuboidal epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
• Simple squamous epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. 

Figure 7.4.4

Loose fibrous connective tissue by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.

Figure 7.4.5

Connective Tissue: Loose Aerolar by Berkshire Community College Bioscience Image Library on Flickr is used under a CC0 1.0 Universal public domain dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.

Figure 7.4.6

Dense Fibrous Connective Tissue by by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.

Figure 7.4.7

Dense_connective_tissue-400x by J Jana on Wikimedia Commons is used under a  CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.

Figure 7.4.8

Types_of_Cartilage-new by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license. 

Figure 7.4.9

Compact_bone_histology_2014 by Athikhun.suw on Wikimedia Commons is used under a  CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.

Figure 7.4.10

Bone_normal_and_degraded_micro_structure by Gtirouflet on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.

Figure 7.4.11

Lymphocyte2 by NicolasGrandjean on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.  [No machine-readable author provided. NicolasGrandjean is assumed, based on copyright claims.]

Figure 7.4.12

Skeletal_muscle_横纹肌1 by 乌拉跨氪 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.

Figure 7.4.13

Smooth_Muscle_new by OpenStax on Wikimedia Commons is used under a CC BY 4.0  (https://creativecommons.org/licenses/by/4.0/deed.en) license.

Figure 7.4.14

Peristalsis by OpenStax on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.

Figure 7.4.15

400x Cardiac Muscle by Jessy731 on Flickr is used and adapted by Christine Miller under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.

Figure 7.4.16

Neuron.svg by User:Dhp1080 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.

Figure 7.4.17

400x Nervous Tissue  by Jessy731 on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.

Table 7.4.1

Summary of Epithelial Tissue Cells, by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license. 

Table 7.4.2

• Epithelial_Tissues_Stratified_Squamous_Epithelium_(40230842160) by
  Berkshire Community College Bioscience Image Library on Wikimedia Commons is used under a  CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
• Simple cuboidal epithelial tissue histology by Berkshire Community College on Flickr is used under a  CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
• Pseudostratified_Epithelium by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

References

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.8 Summary of epithelial tissue cells [digital image].  In Anatomy and Physiology (Section 4.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-2-epithelial-tissue

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.16 Types of cartilage [digital image].  In Anatomy and Physiology (Section 4.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-3-connective-tissue-supports-and-protects

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 10.23 Smooth muscle [digital micrograph].  In Anatomy and Physiology (Section 10.8). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-8-smooth-muscle (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 22.5 Pseudostratified ciliated columnar epithelium [digital micrograph].  In Anatomy and Physiology (Section 22.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-1-organs-and-structures-of-the-respiratory-system

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 23.5 Peristalsis [diagram]. In Anatomy and Physiology (Section 23.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/23-2-digestive-system-processes-and-regulation

Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/watch?v=kVjeNZA5pi4

MoomooMath and Science. (2017, May 18). Types of human body tissue. YouTube. https://www.youtube.com/watch?v=O0ZvbPak4ck&feature=youtu.be

Open Stax. (2016, May 27). Figure 6 Loose connective tissue [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues

Open Stax. (2016, May 27). Figure 7 Fibrous connective tissue from the tendon [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues

TED-Ed. (2019, October 17). How to 3D print human tissue - Taneka Jones. YouTube. https://www.youtube.com/watch?v=uHbn7wLN_3k&feature=youtu.be

TED-Ed. (2020, January 27). How bones make blood - Melody Smith. YouTube. https://www.youtube.com/watch?v=1Qfmkd6C8u8&feature=youtu.be

 

 

Image shows a microscopic view of the structure of spongy bone. It is an irregular lattice of bone and open space, which typically houses bone marrow and blood vessels.

Image shows the difference in morphology between a sickle cell and a normal red blood cell. The normal red blood cells are shaped like danishes, while the sickle cells are shaped like bananas

Image shows a photograph of an Amish man. His hairstyle and beard with no mustache is evidence that he is married.

Image shows a man jogging in the forest. His shirt is wet with sweat.

Image shows a diagram of the layers of the epidermis. The outermost layer is the stratum corneum, below that is the stratum lucidum, below that the stratum granulosum, below that the stratum spinosum, below that the stratum basale, and then a basement membrane which connects the dermis to the epidermis.

Image shows a pictomicrograph of staphylococcus.

The semipermeable membrane surrounding the cytoplasm of a cell.

A type of immune cell that is one of the first cell types to travel to the site of an infection. Neutrophils help fight infection by ingesting microorganisms and releasing enzymes that kill the microorganisms. A neutrophil is a type of white blood cell, a type of granulocyte, and a type of phagocyte.

Image shows a diagram of the types and locations of sensory receptors in the dermis.
There are free nerve endings towards the exterior of the dermis, Merkle cells and Meissners corpuscles are embedded just below the free nerve endings. Ruffini corpuscles and lamellated corpuscles are present deeper in the dermal tissue.

A type of immune cell that has granules (small particles) with enzymes that are released during allergic reactions and asthma. A basophil is a type of white blood cell and a type of granulocyte.

Image shows a picture of a child with very curly hair.

A type of immune cell that has granules (small particles) with enzymes that can kill tumor cells or cells infected with a virus. A natural killer cell is a type of white blood cell.

A type of immune cell that has granules (small particles) with enzymes that are released during infections, allergic reactions, and asthma. An eosinophil is a type of white blood cell and a type of granulocyte.

Image shows a diagram of the hormones secreted by the thyroid gland, and how it is both controlled by and acting upon in a negative feedback the hypothalamus and the anterior pituitary gland.

A type of immune cell that stimulates killer T cells, macrophages, and B cells to make immune responses. A helper T cell is a type of white blood cell and a type of lymphocyte.

Image shows a photograph of a person applying henna to a persons hand.

Created by CK-12 Foundation/Adapted by Christine Miller

Are you still wondering whether Ayko, who you read about in the beginning of this chapter, actually got a tattoo of his new girlfriend’s name on his arm? Figure 10.8.1 is your answer! Let’s hope his love for Larissa — and for the artwork — lasts as long as his tattoo. According to a poll conducted for Global TV by Ipsos Reid in 2012, 10% of Canadian and 11% of American adults regret getting a tattoo. Although laser tattoo removal is available, it does not always work fully, can cause pain and scarring, and is expensive and time-consuming. Some people who regret a tattoo opt instead (or additionally) to cover it with another tattoo, see Figure 10.8.2 below.

Why are tattoos essentially permanent? Tattoos are created by inserting a needle containing pigment through the epidermis and into the dermis of the skin. The pigment is injected into the dermal layer, creating the design. The pigment can remain in the dermal layer for a person’s lifetime for a few reasons. One, unlike the thinner outer epidermal layer, the dermis is not continually shed and replaced, so the pigment generally stays put. Two, the pigments used in tattooing mainly consist of large particles. When you get a tattoo, the penetration of the skin and insertion of foreign particles causes an immune response in which white blood cells attempt to engulf and remove the pigment. Because most of the pigment particles are so large, however, they cannot be removed from the dermis by the immune cells, and the design remains.

In laser tattoo removal, pulses from a high-intensity laser are applied to the tattoo and absorbed by the pigments. This breaks up the large pigment particles into particles that are small enough to be removed by the immune system. The pigments may then be excreted out of the body, or moved to other areas of the body, such as the lymph nodes. Different wavelengths of laser energy are often required to remove different colours of pigments, because they absorb different wavelengths of light. Generally, blue and black are the easiest colours to remove. Green, red, and yellow tend to be the hardest to remove. It may take as many as six to ten laser treatments — with a few weeks of recovery time in between — to remove a tattoo. Some tattoos can never be completely removed.

Why are mehndi designs (like Ayko’s trial “henna tattoo”) not permanent? Unlike real tattoos, henna paste is applied on the surface of the skin (shown below in Figure 10.8.3), and not injected into the skin with a needle. The dye molecules simply migrate from the paste into the top layer of the epidermis, the stratum corneum.

As you have learned, the stratum corneum consists of dead, keratin-filled keratinocytes, which are continually shed and replaced with new cells from the layers below. As a result, mehndi is not permanent. The design is lost as the cells that contain the dye are shed and replaced.

As you read in the beginning of this chapter, mehndi is often applied to the palms of the hands and soles of the feet, which generally results in a darker stain than other areas of the body. This is because the stratum corneum is thicker in these regions, so the dye penetrates through more layers of cells, making the design appear darker. What else is different about the epidermis of the palms and soles? You may recall that these regions are the only place where there is a fifth layer of epidermis — the stratum lucidum — making the skin in these areas even thicker and tougher.

Hopefully, Ayko thought carefully about the potential emotional and social implications of getting a tattoo — and learned how difficult they are to remove — before getting a real one. Health and safety should also be of utmost concern to anyone considering getting a tattoo. As you have learned in this chapter, the skin acts as a barrier against dangerous pathogens and substances. When you penetrate the skin using a needle, it can introduce harmful viruses and bacteria directly into the dermis, where the blood vessels are. Tattoo artists and shops need to take precautions to protect their clients against diseases that can be transmitted through blood (such as HIV and hepatitis), as well as bacterial infections. The tattoo artist should wear disposable gloves and a mask, use new and unopened needles and ink tubes, and properly sterilize other equipment. Even if the artist takes all the proper precautions, there is still a chance that the unopened ink could have been contaminated with pathogens during the production process. The shop should be aware of any ink recalls. Anyone getting a tattoo should make sure their artist and shop strictly adhere to all local health and safety regulations.

The risk of disease is not the only risk from tattoos. The pigments in tattoos may contain heavy metals and other potentially toxic substances.  Tattoo parlours are regulated by provincial guidelines in Canada, and these guidelines vary from province to province — but these guidelines are mainly concerned with sterilization of equipment and don't address anything about pigments.  A recent study published in the scientific journal Nature (Scientific Reports) showed that pigments from tattoos may migrate from a person's tattoos into their lymph nodes.  Among the substances that make up the tattoo ink that migrated were aluminum, chromium, iron, nickel and copper - all considered "toxic".

Additionally, people can sometimes have an allergic reaction to the pigments, or develop scarring or granulomas (small bumps of tissue due to an immune response) around the tattoo. Rarely, people can experience temporary swelling or burning of their tattoos when they get scanned in an MRI machine for a medical procedure. Clearly, people should think carefully about the potential health implications before getting a tattoo.

Fortunately, Ayko found a reputable and safe tattoo artist, and is not experiencing any ill effects from his tattoo. He is happy with his tattoo, at least for now. Tattoos — and other kinds of decoration of the integumentary system — are forms of artistic, personal, and cultural expression that have been used by many cultures over the course of human history. The system that protects us from the elements, helps us maintain homeostasis, and mediates our interactions with the outside world also happens to be easily modifiable! Whether it is a haircut, makeup, beard style, nail polish, piercing or a tattoo, humans have a variety of ways of altering our integumentary system, which changes our outward appearance and what we communicate to others.

References

Global News Staff. (2017, September 15). Health: ‘Toxic’ tattoo ink particles can travel to your lymph nodes: study. Globalnews.ca. https://globalnews.ca/news/3746925/tattoo-ink-safety-lymph-nodes/

Ipsos Reid. (2012). "Two in ten Canadians (22%), Americans (21%)
have a tattoo; One in ten tattooed Canadians (10%), Americans (11%) regret it" [News release]. Ipsos.com. https://www.ipsos.com/sites/default/files/publication/2012-01/5490.pdf

Rideout, K. (2010, July). Comparison of guidelines and regulatory frameworks for personal services establishments. National Collaborating Centre for Environmental Health. https://www.ncceh.ca/sites/default/files/PSE_Guidelines_Comparison_Table_July%202010.pdf

Schreiver, I., Hesse, B., Seim, C. et al. Synchrotron-based ν-XRF mapping and μ-FTIR microscopy enable to look into the fate and effects of tattoo pigments in human skin. Scientific Reports 7,11395. https://doi.org/10.1038/s41598-017-11721-z

 

 

Sophia loves wearing high heels when she goes out at night, like the stiletto heels shown in Figure 11.1.1. She knows they are not the most practical shoes, but she likes how they look.

Lately, she has been experiencing pain in the balls of her feet — the area just behind the toes. Even when she trades her heels for comfortable sneakers, it still hurts when she stands or walks.

What could be going on? She searches online to try to find some answers. She finds a reputable source for foot pain information — a website from a professional organization of physicians that peer reviews the content by experts in the field. There, she reads about a condition called metatarsalgia, which produces pain in the ball of the foot that sounds very similar to what she is experiencing.

She learns that a common cause of metatarsalgia is the wearing of high heels. Shoes like this push the foot into an abnormal position, resulting in excessive pressure being placed on the ball of the foot. Looking at the photograph above (Figure 11.1.1), you can imagine how much of the woman’s body weight is focused on the ball of her foot, because of the shape of her high heels. If she were not wearing high heels, her weight would be more evenly distributed across her foot.

As she reads more about the hazards of high heels, Sophia learns that they can also cause foot deformities, such as hammertoes, bunions, and small cracks in bone called stress fractures. High heels may even contribute to the development of osteoarthritis of the knees at an early age.

These conditions caused by high heels are all problems of the skeletal system, which includes bones and connective tissues that hold bones together and cushion them at joints (such as the knee). The skeletal system supports the body’s weight and protects internal organs, but as you will learn as you read this chapter, it also carries out a variety of other important physiological functions.

At the end of the chapter, you will find out why high heels can cause these skeletal system problems, as well as the steps Sophia takes to recover from her foot pain and prevent long-term injury.

 

Attribution

Figure 11.1.1

Heels by apostolos-vamvouras-_pdbqMcNWus [photo] by Apostolos Vamvouras on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Reference

Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/metatarsalgia/symptoms-causes/syc-20354790

 

Divide and Split

Can you guess what the colourful image in Figure 4.13.1 represents? It shows a eukaryotic cell during the process of cell division. In particular, the image shows the cell in a part of cell division called anaphase, where the DNA is being pulled to opposite ends of the cell. Normally, DNA is located in the nucleus of most human cells. The nucleus divides before the cell itself splits in two, and before the nucleus divides, the cell’s DNA is replicated (or copied). There must be two copies of the DNA so that each daughter cell will have a complete copy of the genetic material from the parent cell. How is the replicated DNA sorted and separated so that each daughter cell gets a complete set of the genetic material? To answer that question, you first need to know more about DNA and the forms it takes.

Except when a eukaryotic cell divides, its nuclear DNA exists as a grainy material called chromatin. Only once a cell is about to divide and its DNA has replicated does DNA condense and coil into the familiar X-shaped form of a chromosome, like the one shown below.

Most cells in the human body have two pairs of 23 different chromosomes, for a total of 46 chromosomes. Cells that have two pairs of chromosomes are called diploid. Because DNA has already replicated when it coils into a chromosome, each chromosome actually consists of two identical structures called sister chromatids. Sister chromatids are joined together at a region called a centromere.

 

The process in which the nucleus of a eukaryotic cell divides is called mitosis. During mitosis, the two sister chromatids that make up each chromosome separate from each other and move to opposite poles of the cell. This is shown in the figure below.

Mitosis actually occurs in four phases. The phases are called prophase, metaphase, anaphase, and telophase.

Prophase

The first and longest phase of mitosis is prophase. During prophase, chromatin condenses into chromosomes, and the nuclear envelope (the membrane surrounding the nucleus) breaks down. In animal cells, the centrioles near the nucleus begin to separate and move to opposite poles of the cell. Centrioles are small organelles found only in eukaryotic cells. They help ensure that the new cells that form after cell division each contain a complete set of chromosomes. As the centrioles move apart, a spindle starts to form between them. The spindle consists of fibres made of microtubules.

During metaphase, spindle fibres attach to the centromere of each pair of sister chromatids. As you can see in Figure 4.13.7, the sister chromatids line up at the equator (or center) of the cell. The spindle fibres ensure that sister chromatids will separate and go to different daughter cells when the cell divides.

Anaphase

During anaphase, sister chromatids separate and the centromeres divide. The sister chromatids are pulled apart by the shortening of the spindle fibres. This is a little like reeling in a fish by shortening the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes.

Telophase

During telophase, the chromosomes begin to uncoil and form chromatin. This prepares the genetic material for directing the metabolic activities of the new cells. The spindle also breaks down, and new nuclear envelopes form.

Cytokinesis is the final stage of cell division. During cytokinesis, the cytoplasm splits in two and the cell divides, as shown below. In animal cells, the plasma membrane of the parent cell pinches inward along the cell’s equator until two daughter cells form. Thus, the goal of mitosis and cytokinesis is now complete, because one parent cell has given rise to two daughter cells. The daughter cells have the same chromosomes as the parent cell.

 

No doubt you’ve experienced the tiny, hair-raising skin bumps called goose bumps, like those you see in Figure 10.4.1. They happen when you feel chilly. Do you know what causes goose bumps, or why they pop up when you are cold? The answers to these questions involve the layer of skin known as the dermis.

The dermis is the inner of the two major layers that make up the skin, the outer layer being the epidermis. The dermis consists mainly of connective tissues. It also contains most skin structures, such as glands and blood vessels. The dermis is anchored to the tissues below it by flexible collagen bundles that permit most areas of the skin to move freely over subcutaneous (“below the skin”) tissues. Functions of the dermis include cushioning subcutaneous tissues, regulating body temperature, sensing the environment, and excreting wastes.

The basic anatomy of the dermis is a matrix, or sort of scaffolding, composed of connective tissues. These tissues include collagen fibres — which provide toughness — and elastin fibres, which provide elasticity. Surrounding these fibres, the matrix also includes a gel-like substance made of proteins. The tissues of the matrix give the dermis both strength and flexibility.

The dermis is divided into two layers: the papillary layer and the reticular layer. Both layers are shown in Figure 10.4.2 below and described in the text that follows.

Papillary Layer

The papillary layer is the upper layer of the dermis, just below the basement membrane that connects the dermis to the epidermis above it. The papillary layer is the thinner of the two dermal layers. It is composed mainly of loosely arranged collagen fibres. The papillary layer is named for its fingerlike projections — or papillae — that extend upward into the epidermis. The papillae contain capillaries and sensory touch receptors.

The papillae give the dermis a bumpy surface that interlocks with the epidermis above it, strengthening the connection between the two layers of skin. On the palms and soles, the papillae create epidermal ridges. Epidermal ridges on the fingers are commonly called fingerprints (see Figure 10.4.3). Fingerprints are genetically determined, so no two people (other than identical twins) have exactly the same fingerprint pattern. Therefore, fingerprints can be used as a means of identification, for example, at crime scenes. Fingerprints were much more commonly used forensically before DNA analysis was introduced for this purpose.

Reticular Layer

The reticular layer is the lower layer of the dermis, located below the papillary layer. It is the thicker of the two dermal layers. It is composed of densely woven collagen and elastin fibres. These protein fibres give the dermis its properties of strength and elasticity. This layer of the dermis cushions subcutaneous tissues of the body from stress and strain. The reticular layer of the dermis also contains most of the structures in the dermis, such as glands and hair follicles.

Both papillary and reticular layers of the dermis contain numerous sensory receptors, which make the skin the body’s primary sensory organ for the sense of touch. Both dermal layers also contain blood vessels. They provide nutrients to remove wastes from dermal cells, as well as cells in the lowest layer of the epidermis, the stratum basale. The circulatory components of the dermis are shown in Figure 10.4.4 below.

Glands

Glands in the reticular layer of the dermis include sweat glands and sebaceous (oil) glands. Both are exocrine glands, which are glands that release their secretions through ducts to nearby body surfaces. The diagram in Figure 10.4.5 shows these glands, as well as several other structures in the dermis.

Sweat Glands

Sweat glands produce the fluid called sweat, which contains mainly water and salts. The glands have ducts that carry the sweat to hair follicles, or to the surface of the skin. There are two different types of sweat glands: eccrine glands and apocrine glands.

• Eccrine sweat glands occur in skin all over the body. Their ducts empty through tiny openings called pores onto the skin surface. These sweat glands are involved in temperature regulation.
• Apocrine sweat glands are larger than eccrine glands, and occur only in the skin of the armpits and groin. The ducts of apocrine glands empty into hair follicles, and then the sweat travels along hairs to reach the surface. Apocrine glands are inactive until puberty, at which point they start producing an oily sweat that is consumed by bacteria living on the skin. The digestion of apocrine sweat by bacteria causes body odor.

Sebaceous Glands

Sebaceous glands are exocrine glands that produce a thick, fatty substance called sebum. Sebum is secreted into hair follicles and makes its way to the skin surface along hairs. It waterproofs the hair and skin, and helps prevent them from drying out. Sebum also has antibacterial properties, so it inhibits the growth of microorganisms on the skin. Sebaceous glands are found in every part of the skin — except for the palms of the hands and soles of the feet, where hair does not grow.

Hair Follicles

Hair follicles are the structures where hairs originate (see the diagram above). Hairs grow out of follicles, pass through the epidermis, and exit at the surface of the skin. Associated with each hair follicle is a sebaceous gland, which secretes sebum that coats and waterproofs the hair. Each follicle also has a bed of capillaries, a nerve ending, and a tiny muscle called an arrector pili.

The main functions of the dermis are regulating body temperature, enabling the sense of touch, and eliminating wastes from the body.

Temperature Regulation

Several structures in the reticular layer of the dermis are involved in regulating body temperature. For example, when body temperature rises, the hypothalamus of the brain sends nerve signals to sweat glands, causing them to release sweat. An adult can sweat up to four litres an hour. As the sweat evaporates from the surface of the body, it uses energy in the form of body heat, thus cooling the body. The hypothalamus also causes dilation of blood vessels in the dermis when body temperature rises. This allows more blood to flow through the skin, bringing body heat to the surface, where it can radiate into the environment.

When the body is too cool, sweat glands stop producing sweat, and blood vessels in the skin constrict, thus conserving body heat. The arrector pili muscles also contract, moving hair follicles and lifting hair shafts. This results in more air being trapped under the hairs to insulate the surface of the skin. These contractions of arrector pili muscles are the cause of goose bumps.

Sensing the Environment

Sensory receptors in the dermis are mainly responsible for the body’s tactile senses. The receptors detect such tactile stimuli as warm or cold temperature, shape, texture, pressure, vibration, and pain. They send nerve impulses to the brain, which interprets and responds to the sensory information. Sensory receptors in the dermis can be classified on the basis of the type of touch stimulus they sense. Mechanoreceptors sense mechanical forces such as pressure, roughness, vibration, and stretching. Thermoreceptors sense variations in temperature that are above or below body temperature. Nociceptors sense painful stimuli. Figure 10.4.6 shows several specific kinds of tactile receptors in the dermis. Each kind of receptor senses one or more types of touch stimuli.

• Free nerve endings sense pain and temperature variations.
• Merkel cells sense light touch, shapes, and textures.
• Meissner’s corpuscles sense light touch.
• Pacinian corpuscles sense pressure and vibration.
• Ruffini corpuscles sense stretching and sustained pressure.

Excreting Wastes

The sweat released by eccrine sweat glands is one way the body excretes waste products. Sweat contains excess water, salts (electrolytes), and other waste products that the body must get rid of to maintain homeostasis. The most common electrolytes in sweat are sodium and chloride. Potassium, calcium, and magnesium electrolytes may be excreted in sweat, as well. When these electrolytes reach high levels in the blood, more are excreted in sweat. This helps to bring their blood levels back into balance. Besides electrolytes, sweat contains small amounts of waste products from metabolism, including ammonia and urea. Sweat may also contain alcohol in someone who has been drinking alcoholic beverages.

Acne is the most common skin disorder in the Canada. At least 20% of Canadians have acne at any given time and it affects approximately 90% of adolescents (as in Figure 10.4.7). Although acne occurs most commonly in teens and young adults, but it can occur at any age. Even newborn babies can get acne.

The main sign of acne is the appearance of pimples (pustules) on the skin, like those in the photo above. Other signs of acne may include whiteheads, blackheads, nodules, and other lesions. Besides the face, acne can appear on the back, chest, neck, shoulders, upper arms, and buttocks. Acne can permanently scar the skin, especially if it isn’t treated appropriately. Besides its physical effects on the skin, acne can also lead to low self-esteem and depression.

Acne is caused by clogged, sebum-filled pores that provide a perfect environment for the growth of bacteria. The bacteria cause infection, and the immune system responds with inflammation. Inflammation, in turn, causes swelling and redness, and may be associated with the formation of pus. If the inflammation goes deep into the skin, it may form an acne nodule.

Mild acne often responds well to treatment with over-the-counter (OTC) products containing benzoyl peroxide or salicylic acid. Treatment with these products may take a month or two to clear up the acne. Once the skin clears, treatment generally needs to continue for some time to prevent future breakouts.

If acne fails to respond to OTC products, nodules develop, or acne is affecting self-esteem, a visit to a dermatologist is in order. A dermatologist can determine which treatment is best for a given patient. A dermatologist can also prescribe prescription medications (which are likely to be more effective than OTC products) and provide other medical treatments, such as laser light therapies or chemical peels.

What can you do to maintain healthy skin and prevent or reduce acne? Dermatologists recommend the following tips:

• Wash affected or acne-prone skin (such as the face) twice a day, and after sweating.
• Use your fingertips to apply a gentle, non-abrasive cleanser. Avoid scrubbing, which can make acne worse.
• Use only alcohol-free products and avoid any products that irritate the skin, such as harsh astringents or exfoliants.
• Rinse with lukewarm water, and avoid using very hot or cold water.
• Shampoo your hair regularly.
• Do not pick, pop, or squeeze acne. If you do, it will take longer to heal and is more likely to scar.
• Keep your hands off your face. Avoid touching your skin throughout the day.
• Stay out of the sun and tanning beds. Some acne medications make your skin very sensitive to UV light.

Attributions

Figure 10.4.1

Goose_bumps by EverJean on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.

Figure 10.4.2

Layers_of_the_Dermis by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 10.4.3

Fingerprint_detail_on_male_finger_in_Třebíč,_Třebíč_District by Frettie on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 10.4.4

Blausen_0802_Skin_Dermal Circulation by BruceBlaus on Wikimedia commons is used under a  CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license. 

Figure 10.4.5

Anatomy_The_Skin_-_NCI_Visuals_Online by Don Bliss (artist) /  National Cancer Institute (National Institutes of Health, with the ID 4604) is in the public domain (https://en.wikipedia.org/wiki/public_domain). 

Figure 10.4.6

Blausen_0809_Skin_TactileReceptors by BruceBlaus on Wikimedia commons is used under a  CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license. 

Figure 10.4.7

Akne-jugend by Ellywa on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/public_domain). (No machine-readable author provided. Ellywa assumed, based on copyright claims).

References

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 5.7 Layers of the dermis [digital image]. In Anatomy and Physiology (Section 5.1 Layers of the skin). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/5-1-layers-of-the-skin

Blausen.com staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

SciShow. (2016, October 26). How do you get rid of acne? YouTube. https://www.youtube.com/watch?v=FX-FwK0IIrE

Seeker. (2013, October 26). When you can't scratch away an itch. YouTube. https://www.youtube.com/watch?v=VcHQWMAClhQ&feature=emb_logo

As per caption.

Created by CK-12 Foundation/Adapted by Christine Miller

Arm Wrestling

It’s obvious that a sport like arm wrestling (Figure 12.4.1) depends on muscle contractions. Arm wrestlers must contract muscles in their hands and arms, and keep them contracted in order to resist the opposing force exerted by their opponent. The wrestler whose muscles can contract with greater force wins the match.

A muscle contraction is an increase in the tension or a decrease in the length of a muscle. Muscle tension is the force exerted by the muscle on a bone or other object. A muscle contraction is isometric if muscle tension changes, but muscle length remains the same. An example of isometric muscle contraction is holding a book in the same position. A muscle contraction is isotonic if muscle length changes, but muscle tension remains the same. An example of isotonic muscle contraction is raising a book by bending the arm at the elbow. The termination of a muscle contraction of either type occurs when the muscle relaxes and returns to its non-contracted tension or length.

To use our arm wrestling example, if both arm wrestlers have equal strength and they are pulling with all their might, but there is no movement, that is isometric muscle contraction.  However, as soon as one arm wrestler starts to win and is able to start pulling the opponents arm down, that is isotonic muscle contraction.

Excluding reflexes, all skeletal muscle contractions occur as a result of conscious effort originating in the brain. The brain sends electrochemical signals through the somatic nervous system to motor neurons that innervate muscle fibres (to review how the brain and neurons function, see the chapter Nervous System). A single motor neuron with multiple axon terminals is able to innervate multiple muscle fibres, thereby causing all of them to contract at the same time. The connection between a motor neuron axon terminal and a muscle fibre occurs at a site called a neuromuscular junction. This is a chemical synapse where a motor neuron transmits a signal to a muscle fibre to initiate a muscle contraction. The process by which a signal is transmitted at a neuromuscular junction is illustrated in Figure 12.4.2 below.

The sequence of events begins when an action potential is initiated in the cell body of a motor neuron, and the action potential is propagated along the neuron’s axon to the neuromuscular junction. Once the action potential reaches the end of the axon terminal, it causes the release of the neurotransmitter acetylcholine (ACh) from synaptic vesicles in the axon terminal. The ACh molecules diffuse across the synaptic cleft and bind to receptors on the muscle fibre, thereby initiating a muscle contraction.

Once the muscle fibre is stimulated by the motor neuron, actin and myosin protein filaments within the skeletal muscle fibre slide past each other to produce a contraction. The sliding filament theory is the most widely accepted explanation for how this occurs. According to this theory, muscle contraction is a cycle of molecular events in which thick myosin filaments repeatedly attach to and pull on thin actin filaments, so the filaments slide over one another, as illustrated in Figure 12.4.3. The actin filaments are attached to Z discs, each of which marks the end of a sarcomere. The sliding of the filaments pulls the Z discs of a sarcomere closer together, thus shortening the sarcomere. As this occurs, the muscle contracts.

Crossbridge Cycling

Crossbridge cycling is a sequence of molecular events that underlies the sliding filament theory. There are many projections from the thick myosin filaments, each of which consists of two myosin heads (you can see the projections and heads in Figures 12.4.3 and 12.4.4). Each myosin head has binding sites for ATP (or the products of ATP hydrolysis: ADP and Pi) and for actin. The thin actin filaments also have binding sites for the myosin heads. A crossbridge forms when a myosin head binds with an actin filament.

The process of crossbridge cycling is shown in the video "Muscle Contraction 3D" by 3DBiology (below), and in Figure 12.4.4. A crossbridge cycle begins when the myosin head binds to an actin filament. ADP and Pi are also bound to the myosin head at this stage. Next, a power stroke moves the actin filament inward toward the center of sarcomere, thereby shortening the sarcomere. At the end of the power stroke, ADP and Pi are released from the myosin head, leaving the myosin head attached just to the thin filament until another ATP binds to the myosin head. When ATP binds to the myosin head, it causes the myosin head to detach from the actin. ATP is once again split into ADP and Pi and the energy released is used to move the myosin head into a "cocked" position. Once in this position, the myosin head can bind to the actin filament again, and another crossbridge cycle begins.

 

Energy for Muscle Contraction

According to the sliding filament theory, ATP is needed to provide the energy for a muscle contraction. Where does this ATP come from? Actually, there are multiple potential sources, as illustrated in Figure 12.4.5 below.

1. As you can see from the first diagram, some ATP is already available in a resting muscle. As a muscle contraction starts, this ATP is used up in just a few seconds. More ATP is generated from creatine phosphate, but this ATP is used up rapidly as well. It’s gone in another 15 seconds or so.
2. Glucose from the blood and glycogen stored in muscle can then be used to make more ATP. Glycogen breaks down to form glucose, and each glucose molecule produces two molecules of ATP and two molecules of pyruvate. Pyruvate (as pyruvic acid) can be used in aerobic respiration if oxygen is available. Alternatively, pyruvate can be used in anaerobic respiration, if oxygen is not available. The latter produces lactic acid, which may contribute to muscle fatigue. Anaerobic respiration typically occurs only during strenuous exercise when so much ATP is needed that sufficient oxygen cannot be delivered to the muscle to keep up.
3. Resting or moderately active muscles can get most of the ATP they need for contractions by aerobic respiration. This process takes place in the mitochondria of muscle cells. In the process, glucose and oxygen react to produce carbon dioxide, water, and many molecules of ATP.

Basic research on muscle contraction, especially if it is interesting and hopeful, is often in the news, because muscle contractions are involved in so many different body processes and disorders, including heart failure and stroke.

• Heart failure is a chronic condition in which cardiac muscle cells cannot contract forcefully enough to keep body cells adequately supplied with oxygen. According to a 2016 report by the Heart and Stroke Foundation of Canada, 600,000 Canadians are living with heart failure and each year, 50,000 new cases are diagnosed.  Heart failure costs the Canadian medical system more than $2.8 billion annually.  In 2016, researchers at the University of Texas Southwestern Medical Center identified a potential new target for the development of drugs to increase the strength of cardiac muscle contractions in patients with heart failure. The UT researchers found a previously unidentified protein involved in muscle contraction. The protein, which is very small, turns off the “brake” on the heart so it pumps blood more vigorously. At the molecular level, the protein affects the calcium-ion pump that controls muscle contraction. The scientists also found the same protein in slow-twitch skeletal muscle fibres. Interestingly, the protein is encoded by a stretch of mRNA that had been dismissed by scientists as non-coding RNA, commonly referred to as “junk” RNA. According to one of the researchers, “We dipped into the RNA ‘junk’ pile and came up with a hidden treasure.” This result is likely to lead to searches for additional treasures that might be hiding in the RNA junk pile.
• A stroke occurs when a blood clot lodges in an artery in the brain and cuts off blood flow to part of the brain. Approximately 6% of deaths in Canada are due to stroke and while men and women experiences strokes almost equally, women are more likely to die from a stroke.  Damage from the clot associated with strokes would be reduced if the smooth muscles lining brain arteries relaxed following a stroke, because the arteries would dilate and allow greater blood flow to the brain. In a recent study undertaken at the Yale University School of Medicine, researchers determined that the muscles lining blood vessels in the brain actually contract after a stroke. This constricts the vessels, reduces blood flow to the brain, and appears to contribute to permanent brain damage. The hopeful takeaway of this finding is that it suggests a new target for stroke therapy.

Attributions

Figure 12.4.1

Armwrestling_Championships by Jnadler1 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

Figure 12.4.2

Motor_End_Plate_and_Innervation by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by 4.0) license.

Figure 12.4.3

Sliding_Filament_Model_of_Muscle_Contraction by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by 4.0) license.

Figure 12.4.4

Skeletal_Muscle_Contraction by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by 4.0) license.

Figure 12.4.5

Muscle_Metabolism by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by 4.0) license.

References

3DBiology. (2017). Muscle contraction 3D. YouTube. https://www.youtube.com/watch?v=GrHsiHazpsw

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 27). Figure 10.6 Motor end-plate and innervation [digital image].  In Anatomy and Physiology (Section 10.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-2-skeletal-muscle

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 27). Figure 10.10 The sliding filament model of muscle contraction [digital image].  In Anatomy and Physiology (Section 10.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-3-muscle-fiber-contraction-and-relaxation

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 27). Figure 10.11 Skeletal muscle contraction [digital image].  In Anatomy and Physiology (Section 10.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-3-muscle-fiber-contraction-and-relaxation

Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 27). Figure 10.12 Muscle metabolism [digital image].  In Anatomy and Physiology (Section 10.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-3-muscle-fiber-contraction-and-relaxation

Dorian Wilson. (2017, March 8). Aerobic vs anaerobic difference. YouTube.  https://www.youtube.com/watch?v=8Y_FdjI2v4I&feature=youtu.be

Heart and Stroke Foundation. (2016). 2016 Report on the health of Canadians: The burden of heart failure. https://www.heartandstroke.ca/-/media/pdf-files/canada/2017-heart-month/heartandstroke-reportonhealth-2016.ashx?la=en

Hill, R. A., Tong, L., Yuan, P., Murikinati, S., Gupta, S., & Grutzendler, J. (2015). Regional blood flow in the normal and ischemic brain is controlled by arteriolar smooth muscle cell contractility and not by capillary pericytes. Neuron, 87(1), 95–110. https://doi.org/10.1016/j.neuron.2015.06.001

UTSouthwestern Newsroom. (2016, January 14). Researchers find a small protein that plays a big role in heart muscle contraction [online article]. https://www.utsouthwestern.edu/newsroom/articles/year-2016/dworf-protein-olson.html

What we do. (n.d.). Heart and Stroke Foundation of Canada. https://www.heartandstroke.ca/what-we-do

Image shows a photo of a woman doing a yoga pose which involves a backbend.

Image shows a photo of a young man sitting and staring down at his cell phone

Image shows a photo of the bruise associated with a pulled hamstring. I large, dark purple and black bruise covers parts of lower back thigh, behind the knee and down into the calf.

Image shows two photos of the eyes of the same patient. In the first photo, the patient's right eyelid is drooping substantially. In the second photograph the same eyelid is drooping, but not as drastically.