What Is Homeostasis?<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary]<\/strong>\u00a0is 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\u00a0[pb_glossary id=\"5665\"]cells[\/pb_glossary], [pb_glossary id=\"2801\"]tissues[\/pb_glossary], [pb_glossary id=\"2803\"]organs[\/pb_glossary], and [pb_glossary id=\"2804\"]organ systems[\/pb_glossary]\u00a0throughout 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.\r\nSet Point and Normal Range<\/h2>\r\nFor any given variable, such as body\u00a0temperature\u00a0or\u00a0blood\u00a0glucose level, there is a particular\u00a0[pb_glossary id=\"2948\"]set point[\/pb_glossary]<\/strong>\u00a0that is the physiological optimum value.\u00a0The set point for\u00a0human body\u00a0temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain [pb_glossary id=\"5761\"]homeostasis[\/pb_glossary] 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\u00a0[pb_glossary id=\"2949\"]normal range[\/pb_glossary]<\/strong>. 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).\r\n\r\nA good analogy for set point, normal range, and maintenance of homeostasis is driving.\u00a0 When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane \u2014 this is analogous to the [pb_glossary id=\"2948\"]set point[\/pb_glossary].\u00a0 Sometimes, you are not driving in the exact<\/em> centre of the lane, but you are still within your lines, so you are in the equivalent of the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].\u00a0 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.\u00a0 You'd move left if you were too close to the shoulder, or right if too close to the centre line \u2014 which is analogous to our next concept, [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary] to maintain [pb_glossary id=\"5761\"]homeostasis[\/pb_glossary].\r\nMaintaining Homeostasis<\/h2>\r\n[pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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.\r\n\r\n \t- The\u00a0[pb_glossary id=\"2950\"]stimulus[\/pb_glossary]<\/strong>\u00a0is 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.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2951\"]sensor[\/pb_glossary]<\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5951\"]control centre[\/pb_glossary]<\/strong> 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.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5979\"]effector[\/pb_glossary]<\/strong> 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.<\/li>\r\n<\/ol>\r\nEach 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 [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary]. Biological examples of positive feedback are much less common.\r\n\r\n \r\n\r\n \r\n\r\n[caption id=\"attachment_2954\" align=\"aligncenter\" width=\"777\"]
![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Negative_Feedback_Loops-2.jpg\")
Figure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em>[\/caption]\r\n\r\n\r\n\r\nNegative Feedback<\/span>\r\n\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary]<\/strong>, feedback serves to reduce an excessive response and keep a variable within the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.\r\nBody Temperature<\/h2>\r\nBody temperature regulation involves [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary], whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.\r\n\r\n[caption id=\"attachment_2963\" align=\"aligncenter\" width=\"725\"]![\"Homeostasis](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Body-Temperature-Homeostasis-2.jpg\")
Figure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em>[\/caption]\r\n\r\n\r\n\r\nCooling Down<\/span>\r\n\r\n<\/div>\r\nThe human body\u2019s temperature regulatory centre is the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the [pb_glossary id=\"2948\"]set point[\/pb_glossary], it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\r\n \t
- 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\u00a0heat\u00a0with it.<\/li>\r\n \t
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\r\n<\/ul>\r\n
Heating Up<\/h3>\r\nWhen the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\r\n \t
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary]\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary]\u00a0may also be stimulated to secrete the\u00a0hormone [pb_glossary id=\"5875\"]adrenaline[\/pb_glossary]. This hormone causes the breakdown of [pb_glossary id=\"327\"]glycogen[\/pb_glossary] (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to [pb_glossary id=\"5451\"]glucose[\/pb_glossary], which can be used as an energy source. This catabolic chemical process is [pb_glossary id=\"5513\"]exothermic[\/pb_glossary], or heat producing.<\/li>\r\n<\/ul>\r\n
Blood Glucose<\/h2>\r\nIn controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.\r\n\r\n \t- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\r\n \t
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\r\n<\/ul>\r\n\r\n\r\n \r\n\r\n[caption id=\"attachment_331\" align=\"aligncenter\" width=\"632\"]
![\"Diagram](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Homeostasis_of_blood_sugar-2.png\")
Figure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em>[\/caption]\r\n\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4\r\nHomeostasis and Negative\/Positive Feedback, Amoeba Sisters, 2017.<\/p>\r\n\r\n
Positive Feedback<\/h1>\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2962\"]positive feedback loop[\/pb_glossary]<\/strong>, 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.\r\nBlood Clotting<\/h2>\r\n[caption id=\"attachment_2967\" align=\"aligncenter\" width=\"754\"]![\"Positive](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Positive_Feedback_Diagram_Blood_Clotting-2.png\")
Figure 7.8.5 The diagram demonstrates positive feedback, using the example of blood clotting in the body. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot. Every time the blood clot builds up more, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely healed and the positive feedback loop has ended. The graph represents the number of platelets aiding in the formation of the blood clot. The exponential form of the graph represents the positive feedback mechanism.<\/em>[\/caption]\r\n\r\nWhen 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.\r\nChildbirth<\/h2>\r\nFigure 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 [pb_glossary id=\"3093\"]oxytocin[\/pb_glossary]<\/strong>\u00a0to the\u00a0pituitary gland,\u00a0which 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\u00a0nerve impulses\u00a0to the brain, and the entire process stops.\r\n\r\n[caption id=\"attachment_2966\" align=\"aligncenter\" width=\"714\"]![\"Positive](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Pregnancy-Positive_Feedback-2.jpg\")
Figure 7.8.6 Normal childbirth is driven by a positive feedback loop.\u00a0<\/em>[\/caption]\r\n\r\n\r\n\r\nNormal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed end point, rather than a return to a normal set point as in homeostasis.\r\n\r\n<\/div>\r\n\r\nWhen Homeostasis Fails<\/h1>\r\n<\/div>\r\nHomeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do,\u00a0[pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]<\/strong>\u00a0may 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 \u2014 or even death.\u00a0[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nNormal aging may bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control systems, which makes the body more susceptible to disease.\u00a0Older 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.\r\n\r\nFeature: My Human Body<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nOf the two types of diabetes, [pb_glossary id=\"2970\"]type 2 diabetes[\/pb_glossary] is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes<\/a> 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.\r\n\r\nYou 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.\r\n\r\nThe 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\u2019s how:\r\n\r\n \t- Lose\u00a0weight.<\/strong> Any\u00a0weight\u00a0loss is beneficial. Losing as little as\u00a0seven\u00a0per cent of your\u00a0weight\u00a0may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.<\/li>\r\n \t
- Exercise\u00a0regularly.<\/strong>\u00a0You should try to\u00a0exercise\u00a0for 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\u00a0blood pressure\u00a0and improve your\u00a0heart\u00a0health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.<\/li>\r\n \t
- Adopt a healthy diet.<\/strong> 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.<\/li>\r\n \t
- Control stress.<\/strong>\u00a0Stress can increase your blood glucose and also raise your\u00a0blood pressure\u00a0and risk of\u00a0heart\u00a0disease. When you feel stressed out, do\u00a0breathing\u00a0exercises or take a brisk walk or jog.\u00a0Try to replace stressful thoughts with more calming ones.<\/li>\r\n \t
- Establish a support system.<\/strong>\u00a0Enlist 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.<\/li>\r\n<\/ul>\r\n\r\n
\r\n7.8 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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 homeostasis.<\/li>\r\n \t
- For any given variable, such as body temperature, there is a particular [pb_glossary id=\"2948\"]set point[\/pb_glossary] that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].<\/li>\r\n \t
- Homeostasis is generally maintained by a [pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary] that includes a [pb_glossary id=\"2950\"]stimulus[\/pb_glossary], [pb_glossary id=\"2951\"]sensor[\/pb_glossary], [pb_glossary id=\"5951\"]control centre[\/pb_glossary], and [pb_glossary id=\"5979\"]effector[\/pb_glossary]. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.<\/li>\r\n \t
- [pb_glossary id=\"2962\"]Positive feedback loops[\/pb_glossary]\u00a0are not common in biological systems. Positive feedback serves to intensify a response until an end point is reached. Positive feedback loops control blood clotting and childbirth.<\/li>\r\n \t
- Sometimes homeostatic mechanisms fail, resulting in [pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control system,\u00a0which makes\u00a0the elderly more susceptible to disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"547\"]<\/li>\r\n \t
- [h5p id=\"548\"]<\/li>\r\n \t
- Compare and contrast negative and positive feedback loops.<\/li>\r\n \t
- Explain how negative feedback controls body temperature.<\/li>\r\n \t
- Give two examples of physiological processes controlled by positive feedback loops.<\/li>\r\n \t
- During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer.\u00a0What do you think might be the evolutionary benefit of the milk production regulation mechanism\u00a0you described?<\/li>\r\n \t
- Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.<\/li>\r\n \t
- The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the\u00a0pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.\r\n
\r\n \t- What is the stimulus in this system? Explain your answer.<\/li>\r\n \t
- What is the control centre in this system? Explain your answer.<\/li>\r\n \t
- In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Explore More<\/span><\/h1>\r\n<\/header>https:\/\/www.youtube.com\/watch?v=LSgEJSlk6W4\r\nHomeostasis - What Is Homeostasis - What Is Set Point For Homeostasis - Homeostasis In The Human Body, Whats Up Dude, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM\r\n
GCSE Biology - Homeostasis #38, Cognito, 2018.<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nAttributions<\/h2>\r\nFigure 7.8.1<\/strong>\r\n\r\nNest_Thermostat<\/a> by Amanitamano<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en) license.\r\n\r\nFigure 7.8.2<\/strong>\r\n\r\nNegative_Feedback_Loops<\/a>\u00a0by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\n\r\nFigure 7.8.3<\/strong>\r\n\r\nBody Temperature Homeostasis<\/a>\u00a0by OpenStax College, Biology<\/a> is used under a CC BY 4.0<\/a> license.\r\n\r\nFigure 7.8.4<\/strong>\r\n\r\nHomeostasis_of_blood_sugar<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a \u00a0CC0 1.0 Universal Public Domain Dedication<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) license.\r\n\r\nFigure 7.8.5<\/strong>\r\n\r\nPositive_Feedback_Diagram_Blood_Clotting<\/a> by Elliottuttle<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0 <\/a>\u00a0(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 7.8.6<\/strong>\r\n\r\nPregnancy-Positive_Feedback<\/a> by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2017, September 7). Homeostasis and negative\/positive feedback. YouTube. https:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4&feature=youtu.be<\/p>\r\n
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\u00a0<\/span>1.10<\/span>\u00a0<\/span>Negative feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/p>\r\nBetts, 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 <\/span>1.11<\/span>\u00a0<\/span>Positive feedback loop<\/span>\u00a0<\/span>normal childbirth is driven by a positive feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/span><\/p>\r\nCognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM&feature=youtu.be<\/p>\r\n
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<\/p>\r\n
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<\/span>, Biology <\/em>(Section 33.3). https:\/\/cnx.org\/contents\/GFy_h8cu@10.8:BP24ZReh@7\/Homeostasis<\/p>\r\nWhats 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<\/p>","rendered":"
<\/p>\n![\"\"](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Nest_Thermostat-2.jpg\")
Figure 7.8.1\u00a0 A thermostat controls a complex system to maintain a steady temperature in our homes.\u00a0<\/em><\/figcaption><\/figure>\nSteady as She Goes<\/h1>\n
This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature \u2014 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 \u2014 including the human body\u2014 maintain a steady state called homeostasis.<\/p>\n
\nWhat Is Homeostasis?<\/h1>\n<\/div>\n
Homeostasis<\/a><\/strong>\u00a0is 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\u00a0cells<\/a>, tissues<\/a>, organs<\/a>, and organ systems<\/a>\u00a0throughout 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.<\/p>\nSet Point and Normal Range<\/h2>\n
For any given variable, such as body\u00a0temperature\u00a0or\u00a0blood\u00a0glucose level, there is a particular\u00a0set point<\/a><\/strong>\u00a0that is the physiological optimum value.\u00a0The set point for\u00a0human body\u00a0temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain homeostasis<\/a> 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\u00a0normal range<\/a><\/strong>. 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).<\/p>\nA good analogy for set point, normal range, and maintenance of homeostasis is driving.\u00a0 When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane \u2014 this is analogous to the set point<\/a>.\u00a0 Sometimes, you are not driving in the exact<\/em> centre of the lane, but you are still within your lines, so you are in the equivalent of the normal range<\/a>.\u00a0 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.\u00a0 You’d move left if you were too close to the shoulder, or right if too close to the centre line \u2014 which is analogous to our next concept, negative feedback<\/a> to maintain homeostasis<\/a>.<\/p>\nMaintaining Homeostasis<\/h2>\n
Homeostasis<\/a> 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.<\/p>\n\n- The\u00a0stimulus<\/a><\/strong>\u00a0is 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.<\/li>\n
- The\u00a0sensor<\/a><\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\n
- The\u00a0control centre<\/a><\/strong> 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.<\/li>\n
- The\u00a0effector<\/a><\/strong> 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.<\/li>\n<\/ol>\n
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<\/a>. Biological examples of positive feedback are much less common.<\/p>\n <\/p>\n
<\/p>\nFigure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em><\/figcaption><\/figure>\n\nNegative Feedback<\/span><\/p>\n<\/div>\nIn a\u00a0negative feedback loop<\/a><\/strong>, feedback serves to reduce an excessive response and keep a variable within the normal range<\/a>.\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.<\/p>\nBody Temperature<\/h2>\n
Body temperature regulation involves negative feedback<\/a>, whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.<\/p>\nFigure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em><\/figcaption><\/figure>\n\nCooling Down<\/span><\/p>\n<\/div>\nThe human body\u2019s temperature regulatory centre is the hypothalamus<\/a> in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point<\/a>, it sets into motion the following responses:<\/p>\n\n- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\n
- 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\u00a0heat\u00a0with it.<\/li>\n
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\n<\/ul>\n
Heating Up<\/h3>\n
When the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:<\/p>\n
\n- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\n
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\n
- The\u00a0thyroid gland<\/a>\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\n
- The\u00a0adrenal glands<\/a>\u00a0may also be stimulated to secrete the\u00a0hormone adrenaline<\/a>. This hormone causes the breakdown of glycogen (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to glucose<\/a>, which can be used as an energy source. This catabolic chemical process is exothermic<\/a>, or heat producing.<\/li>\n<\/ul>\n
Blood Glucose<\/h2>\n
In controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.<\/p>\n
\n- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\n
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\n<\/ul>\n\n
<\/p>\nFigure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em><\/figcaption><\/figure>\n <\/p>\n
Maintaining Homeostasis<\/h2>\r\n[pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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.\r\n\r\n \t- The\u00a0[pb_glossary id=\"2950\"]stimulus[\/pb_glossary]<\/strong>\u00a0is 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.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2951\"]sensor[\/pb_glossary]<\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5951\"]control centre[\/pb_glossary]<\/strong> 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.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5979\"]effector[\/pb_glossary]<\/strong> 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.<\/li>\r\n<\/ol>\r\nEach 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 [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary]. Biological examples of positive feedback are much less common.\r\n\r\n \r\n\r\n \r\n\r\n[caption id=\"attachment_2954\" align=\"aligncenter\" width=\"777\"] Figure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em>[\/caption]\r\n\r\n\r\n\r\nNegative Feedback<\/span>\r\n\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary]<\/strong>, feedback serves to reduce an excessive response and keep a variable within the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.\r\n
Body Temperature<\/h2>\r\nBody temperature regulation involves [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary], whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.\r\n\r\n[caption id=\"attachment_2963\" align=\"aligncenter\" width=\"725\"] Figure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em>[\/caption]\r\n\r\n\r\n\r\nCooling Down<\/span>\r\n\r\n<\/div>\r\nThe human body\u2019s temperature regulatory centre is the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the [pb_glossary id=\"2948\"]set point[\/pb_glossary], it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\r\n \t
- 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\u00a0heat\u00a0with it.<\/li>\r\n \t
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\r\n<\/ul>\r\n
Heating Up<\/h3>\r\nWhen the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\r\n \t
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary]\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary]\u00a0may also be stimulated to secrete the\u00a0hormone [pb_glossary id=\"5875\"]adrenaline[\/pb_glossary]. This hormone causes the breakdown of [pb_glossary id=\"327\"]glycogen[\/pb_glossary] (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to [pb_glossary id=\"5451\"]glucose[\/pb_glossary], which can be used as an energy source. This catabolic chemical process is [pb_glossary id=\"5513\"]exothermic[\/pb_glossary], or heat producing.<\/li>\r\n<\/ul>\r\n
Blood Glucose<\/h2>\r\nIn controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.\r\n\r\n \t- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\r\n \t
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\r\n<\/ul>\r\n\r\n\r\n \r\n\r\n[caption id=\"attachment_331\" align=\"aligncenter\" width=\"632\"] Figure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em>[\/caption]\r\n\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4\r\n
Homeostasis and Negative\/Positive Feedback, Amoeba Sisters, 2017.<\/p>\r\n\r\n
Positive Feedback<\/h1>\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2962\"]positive feedback loop[\/pb_glossary]<\/strong>, 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.\r\nBlood Clotting<\/h2>\r\n[caption id=\"attachment_2967\" align=\"aligncenter\" width=\"754\"] Figure 7.8.5 The diagram demonstrates positive feedback, using the example of blood clotting in the body. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot. Every time the blood clot builds up more, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely healed and the positive feedback loop has ended. The graph represents the number of platelets aiding in the formation of the blood clot. The exponential form of the graph represents the positive feedback mechanism.<\/em>[\/caption]\r\n\r\nWhen 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.\r\nChildbirth<\/h2>\r\nFigure 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 [pb_glossary id=\"3093\"]oxytocin[\/pb_glossary]<\/strong>\u00a0to the\u00a0pituitary gland,\u00a0which 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\u00a0nerve impulses\u00a0to the brain, and the entire process stops.\r\n\r\n[caption id=\"attachment_2966\" align=\"aligncenter\" width=\"714\"] Figure 7.8.6 Normal childbirth is driven by a positive feedback loop.\u00a0<\/em>[\/caption]\r\n\r\n\r\n\r\nNormal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed end point, rather than a return to a normal set point as in homeostasis.\r\n\r\n<\/div>\r\n\r\nWhen Homeostasis Fails<\/h1>\r\n<\/div>\r\nHomeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do,\u00a0[pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]<\/strong>\u00a0may 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 \u2014 or even death.\u00a0[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nNormal aging may bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control systems, which makes the body more susceptible to disease.\u00a0Older 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.\r\n\r\nFeature: My Human Body<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nOf the two types of diabetes, [pb_glossary id=\"2970\"]type 2 diabetes[\/pb_glossary] is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes<\/a> 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.\r\n\r\nYou 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.\r\n\r\nThe 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\u2019s how:\r\n\r\n \t- Lose\u00a0weight.<\/strong> Any\u00a0weight\u00a0loss is beneficial. Losing as little as\u00a0seven\u00a0per cent of your\u00a0weight\u00a0may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.<\/li>\r\n \t
- Exercise\u00a0regularly.<\/strong>\u00a0You should try to\u00a0exercise\u00a0for 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\u00a0blood pressure\u00a0and improve your\u00a0heart\u00a0health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.<\/li>\r\n \t
- Adopt a healthy diet.<\/strong> 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.<\/li>\r\n \t
- Control stress.<\/strong>\u00a0Stress can increase your blood glucose and also raise your\u00a0blood pressure\u00a0and risk of\u00a0heart\u00a0disease. When you feel stressed out, do\u00a0breathing\u00a0exercises or take a brisk walk or jog.\u00a0Try to replace stressful thoughts with more calming ones.<\/li>\r\n \t
- Establish a support system.<\/strong>\u00a0Enlist 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.<\/li>\r\n<\/ul>\r\n\r\n
\r\n7.8 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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 homeostasis.<\/li>\r\n \t
- For any given variable, such as body temperature, there is a particular [pb_glossary id=\"2948\"]set point[\/pb_glossary] that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].<\/li>\r\n \t
- Homeostasis is generally maintained by a [pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary] that includes a [pb_glossary id=\"2950\"]stimulus[\/pb_glossary], [pb_glossary id=\"2951\"]sensor[\/pb_glossary], [pb_glossary id=\"5951\"]control centre[\/pb_glossary], and [pb_glossary id=\"5979\"]effector[\/pb_glossary]. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.<\/li>\r\n \t
- [pb_glossary id=\"2962\"]Positive feedback loops[\/pb_glossary]\u00a0are not common in biological systems. Positive feedback serves to intensify a response until an end point is reached. Positive feedback loops control blood clotting and childbirth.<\/li>\r\n \t
- Sometimes homeostatic mechanisms fail, resulting in [pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control system,\u00a0which makes\u00a0the elderly more susceptible to disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"547\"]<\/li>\r\n \t
- [h5p id=\"548\"]<\/li>\r\n \t
- Compare and contrast negative and positive feedback loops.<\/li>\r\n \t
- Explain how negative feedback controls body temperature.<\/li>\r\n \t
- Give two examples of physiological processes controlled by positive feedback loops.<\/li>\r\n \t
- During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer.\u00a0What do you think might be the evolutionary benefit of the milk production regulation mechanism\u00a0you described?<\/li>\r\n \t
- Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.<\/li>\r\n \t
- The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the\u00a0pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.\r\n
\r\n \t- What is the stimulus in this system? Explain your answer.<\/li>\r\n \t
- What is the control centre in this system? Explain your answer.<\/li>\r\n \t
- In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Explore More<\/span><\/h1>\r\n<\/header>https:\/\/www.youtube.com\/watch?v=LSgEJSlk6W4\r\nHomeostasis - What Is Homeostasis - What Is Set Point For Homeostasis - Homeostasis In The Human Body, Whats Up Dude, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM\r\n
GCSE Biology - Homeostasis #38, Cognito, 2018.<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nAttributions<\/h2>\r\nFigure 7.8.1<\/strong>\r\n\r\nNest_Thermostat<\/a> by Amanitamano<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en) license.\r\n\r\nFigure 7.8.2<\/strong>\r\n\r\nNegative_Feedback_Loops<\/a>\u00a0by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\n\r\nFigure 7.8.3<\/strong>\r\n\r\nBody Temperature Homeostasis<\/a>\u00a0by OpenStax College, Biology<\/a> is used under a CC BY 4.0<\/a> license.\r\n\r\nFigure 7.8.4<\/strong>\r\n\r\nHomeostasis_of_blood_sugar<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a \u00a0CC0 1.0 Universal Public Domain Dedication<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) license.\r\n\r\nFigure 7.8.5<\/strong>\r\n\r\nPositive_Feedback_Diagram_Blood_Clotting<\/a> by Elliottuttle<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0 <\/a>\u00a0(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 7.8.6<\/strong>\r\n\r\nPregnancy-Positive_Feedback<\/a> by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2017, September 7). Homeostasis and negative\/positive feedback. YouTube. https:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4&feature=youtu.be<\/p>\r\n
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\u00a0<\/span>1.10<\/span>\u00a0<\/span>Negative feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/p>\r\nBetts, 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 <\/span>1.11<\/span>\u00a0<\/span>Positive feedback loop<\/span>\u00a0<\/span>normal childbirth is driven by a positive feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/span><\/p>\r\nCognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM&feature=youtu.be<\/p>\r\n
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<\/p>\r\n
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<\/span>, Biology <\/em>(Section 33.3). https:\/\/cnx.org\/contents\/GFy_h8cu@10.8:BP24ZReh@7\/Homeostasis<\/p>\r\nWhats 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<\/p>","rendered":"
<\/p>\nFigure 7.8.1\u00a0 A thermostat controls a complex system to maintain a steady temperature in our homes.\u00a0<\/em><\/figcaption><\/figure>\nSteady as She Goes<\/h1>\n
This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature \u2014 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 \u2014 including the human body\u2014 maintain a steady state called homeostasis.<\/p>\n
\nWhat Is Homeostasis?<\/h1>\n<\/div>\n
Homeostasis<\/a><\/strong>\u00a0is 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\u00a0cells<\/a>, tissues<\/a>, organs<\/a>, and organ systems<\/a>\u00a0throughout 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.<\/p>\nSet Point and Normal Range<\/h2>\n
For any given variable, such as body\u00a0temperature\u00a0or\u00a0blood\u00a0glucose level, there is a particular\u00a0set point<\/a><\/strong>\u00a0that is the physiological optimum value.\u00a0The set point for\u00a0human body\u00a0temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain homeostasis<\/a> 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\u00a0normal range<\/a><\/strong>. 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).<\/p>\nA good analogy for set point, normal range, and maintenance of homeostasis is driving.\u00a0 When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane \u2014 this is analogous to the set point<\/a>.\u00a0 Sometimes, you are not driving in the exact<\/em> centre of the lane, but you are still within your lines, so you are in the equivalent of the normal range<\/a>.\u00a0 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.\u00a0 You’d move left if you were too close to the shoulder, or right if too close to the centre line \u2014 which is analogous to our next concept, negative feedback<\/a> to maintain homeostasis<\/a>.<\/p>\nMaintaining Homeostasis<\/h2>\n
Homeostasis<\/a> 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.<\/p>\n\n- The\u00a0stimulus<\/a><\/strong>\u00a0is 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.<\/li>\n
- The\u00a0sensor<\/a><\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\n
- The\u00a0control centre<\/a><\/strong> 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.<\/li>\n
- The\u00a0effector<\/a><\/strong> 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.<\/li>\n<\/ol>\n
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<\/a>. Biological examples of positive feedback are much less common.<\/p>\n <\/p>\n
<\/p>\nFigure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em><\/figcaption><\/figure>\n\nNegative Feedback<\/span><\/p>\n<\/div>\nIn a\u00a0negative feedback loop<\/a><\/strong>, feedback serves to reduce an excessive response and keep a variable within the normal range<\/a>.\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.<\/p>\nBody Temperature<\/h2>\n
Body temperature regulation involves negative feedback<\/a>, whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.<\/p>\nFigure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em><\/figcaption><\/figure>\n\nCooling Down<\/span><\/p>\n<\/div>\nThe human body\u2019s temperature regulatory centre is the hypothalamus<\/a> in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point<\/a>, it sets into motion the following responses:<\/p>\n\n- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\n
- 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\u00a0heat\u00a0with it.<\/li>\n
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\n<\/ul>\n
Heating Up<\/h3>\n
When the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:<\/p>\n
\n- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\n
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\n
- The\u00a0thyroid gland<\/a>\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\n
- The\u00a0adrenal glands<\/a>\u00a0may also be stimulated to secrete the\u00a0hormone adrenaline<\/a>. This hormone causes the breakdown of glycogen (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to glucose<\/a>, which can be used as an energy source. This catabolic chemical process is exothermic<\/a>, or heat producing.<\/li>\n<\/ul>\n
Blood Glucose<\/h2>\n
In controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.<\/p>\n
\n- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\n
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\n<\/ul>\n\n
<\/p>\nFigure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em><\/figcaption><\/figure>\n <\/p>\n
Figure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em>[\/caption]\r\n\r\nBody Temperature<\/h2>\r\nBody temperature regulation involves [pb_glossary id=\"2955\"]negative feedback[\/pb_glossary], whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.\r\n\r\n[caption id=\"attachment_2963\" align=\"aligncenter\" width=\"725\"] Figure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em>[\/caption]\r\n\r\n\r\n\r\nCooling Down<\/span>\r\n\r\n<\/div>\r\nThe human body\u2019s temperature regulatory centre is the [pb_glossary id=\"2937\"]hypothalamus[\/pb_glossary] in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the [pb_glossary id=\"2948\"]set point[\/pb_glossary], it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\r\n \t
- 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\u00a0heat\u00a0with it.<\/li>\r\n \t
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\r\n<\/ul>\r\n
Heating Up<\/h3>\r\nWhen the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:\r\n\r\n \t- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\r\n \t
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary]\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary]\u00a0may also be stimulated to secrete the\u00a0hormone [pb_glossary id=\"5875\"]adrenaline[\/pb_glossary]. This hormone causes the breakdown of [pb_glossary id=\"327\"]glycogen[\/pb_glossary] (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to [pb_glossary id=\"5451\"]glucose[\/pb_glossary], which can be used as an energy source. This catabolic chemical process is [pb_glossary id=\"5513\"]exothermic[\/pb_glossary], or heat producing.<\/li>\r\n<\/ul>\r\n
Blood Glucose<\/h2>\r\nIn controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.\r\n\r\n \t- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\r\n \t
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\r\n<\/ul>\r\n\r\n\r\n \r\n\r\n[caption id=\"attachment_331\" align=\"aligncenter\" width=\"632\"] Figure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em>[\/caption]\r\n\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4\r\n
Homeostasis and Negative\/Positive Feedback, Amoeba Sisters, 2017.<\/p>\r\n\r\n
Positive Feedback<\/h1>\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2962\"]positive feedback loop[\/pb_glossary]<\/strong>, 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.\r\nBlood Clotting<\/h2>\r\n[caption id=\"attachment_2967\" align=\"aligncenter\" width=\"754\"] Figure 7.8.5 The diagram demonstrates positive feedback, using the example of blood clotting in the body. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot. Every time the blood clot builds up more, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely healed and the positive feedback loop has ended. The graph represents the number of platelets aiding in the formation of the blood clot. The exponential form of the graph represents the positive feedback mechanism.<\/em>[\/caption]\r\n\r\nWhen 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.\r\nChildbirth<\/h2>\r\nFigure 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 [pb_glossary id=\"3093\"]oxytocin[\/pb_glossary]<\/strong>\u00a0to the\u00a0pituitary gland,\u00a0which 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\u00a0nerve impulses\u00a0to the brain, and the entire process stops.\r\n\r\n[caption id=\"attachment_2966\" align=\"aligncenter\" width=\"714\"] Figure 7.8.6 Normal childbirth is driven by a positive feedback loop.\u00a0<\/em>[\/caption]\r\n\r\n\r\n\r\nNormal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed end point, rather than a return to a normal set point as in homeostasis.\r\n\r\n<\/div>\r\n\r\nWhen Homeostasis Fails<\/h1>\r\n<\/div>\r\nHomeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do,\u00a0[pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]<\/strong>\u00a0may 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 \u2014 or even death.\u00a0[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nNormal aging may bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control systems, which makes the body more susceptible to disease.\u00a0Older 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.\r\n\r\nFeature: My Human Body<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nOf the two types of diabetes, [pb_glossary id=\"2970\"]type 2 diabetes[\/pb_glossary] is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes<\/a> 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.\r\n\r\nYou 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.\r\n\r\nThe 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\u2019s how:\r\n\r\n \t- Lose\u00a0weight.<\/strong> Any\u00a0weight\u00a0loss is beneficial. Losing as little as\u00a0seven\u00a0per cent of your\u00a0weight\u00a0may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.<\/li>\r\n \t
- Exercise\u00a0regularly.<\/strong>\u00a0You should try to\u00a0exercise\u00a0for 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\u00a0blood pressure\u00a0and improve your\u00a0heart\u00a0health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.<\/li>\r\n \t
- Adopt a healthy diet.<\/strong> 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.<\/li>\r\n \t
- Control stress.<\/strong>\u00a0Stress can increase your blood glucose and also raise your\u00a0blood pressure\u00a0and risk of\u00a0heart\u00a0disease. When you feel stressed out, do\u00a0breathing\u00a0exercises or take a brisk walk or jog.\u00a0Try to replace stressful thoughts with more calming ones.<\/li>\r\n \t
- Establish a support system.<\/strong>\u00a0Enlist 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.<\/li>\r\n<\/ul>\r\n\r\n
\r\n7.8 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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 homeostasis.<\/li>\r\n \t
- For any given variable, such as body temperature, there is a particular [pb_glossary id=\"2948\"]set point[\/pb_glossary] that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].<\/li>\r\n \t
- Homeostasis is generally maintained by a [pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary] that includes a [pb_glossary id=\"2950\"]stimulus[\/pb_glossary], [pb_glossary id=\"2951\"]sensor[\/pb_glossary], [pb_glossary id=\"5951\"]control centre[\/pb_glossary], and [pb_glossary id=\"5979\"]effector[\/pb_glossary]. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.<\/li>\r\n \t
- [pb_glossary id=\"2962\"]Positive feedback loops[\/pb_glossary]\u00a0are not common in biological systems. Positive feedback serves to intensify a response until an end point is reached. Positive feedback loops control blood clotting and childbirth.<\/li>\r\n \t
- Sometimes homeostatic mechanisms fail, resulting in [pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control system,\u00a0which makes\u00a0the elderly more susceptible to disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [h5p id=\"547\"]<\/li>\r\n \t
- [h5p id=\"548\"]<\/li>\r\n \t
- Compare and contrast negative and positive feedback loops.<\/li>\r\n \t
- Explain how negative feedback controls body temperature.<\/li>\r\n \t
- Give two examples of physiological processes controlled by positive feedback loops.<\/li>\r\n \t
- During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer.\u00a0What do you think might be the evolutionary benefit of the milk production regulation mechanism\u00a0you described?<\/li>\r\n \t
- Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.<\/li>\r\n \t
- The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the\u00a0pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.\r\n
\r\n \t- What is the stimulus in this system? Explain your answer.<\/li>\r\n \t
- What is the control centre in this system? Explain your answer.<\/li>\r\n \t
- In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n7.8 Explore More<\/span><\/h1>\r\n<\/header>https:\/\/www.youtube.com\/watch?v=LSgEJSlk6W4\r\nHomeostasis - What Is Homeostasis - What Is Set Point For Homeostasis - Homeostasis In The Human Body, Whats Up Dude, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM\r\n
GCSE Biology - Homeostasis #38, Cognito, 2018.<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nAttributions<\/h2>\r\nFigure 7.8.1<\/strong>\r\n\r\nNest_Thermostat<\/a> by Amanitamano<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en) license.\r\n\r\nFigure 7.8.2<\/strong>\r\n\r\nNegative_Feedback_Loops<\/a>\u00a0by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\n\r\nFigure 7.8.3<\/strong>\r\n\r\nBody Temperature Homeostasis<\/a>\u00a0by OpenStax College, Biology<\/a> is used under a CC BY 4.0<\/a> license.\r\n\r\nFigure 7.8.4<\/strong>\r\n\r\nHomeostasis_of_blood_sugar<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a \u00a0CC0 1.0 Universal Public Domain Dedication<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) license.\r\n\r\nFigure 7.8.5<\/strong>\r\n\r\nPositive_Feedback_Diagram_Blood_Clotting<\/a> by Elliottuttle<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0 <\/a>\u00a0(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 7.8.6<\/strong>\r\n\r\nPregnancy-Positive_Feedback<\/a> by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\nReferences<\/h2>\r\n
Amoeba Sisters. (2017, September 7). Homeostasis and negative\/positive feedback. YouTube. https:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4&feature=youtu.be<\/p>\r\n
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\u00a0<\/span>1.10<\/span>\u00a0<\/span>Negative feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/p>\r\nBetts, 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 <\/span>1.11<\/span>\u00a0<\/span>Positive feedback loop<\/span>\u00a0<\/span>normal childbirth is driven by a positive feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/span><\/p>\r\nCognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM&feature=youtu.be<\/p>\r\n
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<\/p>\r\n
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<\/span>, Biology <\/em>(Section 33.3). https:\/\/cnx.org\/contents\/GFy_h8cu@10.8:BP24ZReh@7\/Homeostasis<\/p>\r\nWhats 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<\/p>","rendered":"
<\/p>\nFigure 7.8.1\u00a0 A thermostat controls a complex system to maintain a steady temperature in our homes.\u00a0<\/em><\/figcaption><\/figure>\nSteady as She Goes<\/h1>\n
This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature \u2014 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 \u2014 including the human body\u2014 maintain a steady state called homeostasis.<\/p>\n
\nWhat Is Homeostasis?<\/h1>\n<\/div>\n
Homeostasis<\/a><\/strong>\u00a0is 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\u00a0cells<\/a>, tissues<\/a>, organs<\/a>, and organ systems<\/a>\u00a0throughout 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.<\/p>\nSet Point and Normal Range<\/h2>\n
For any given variable, such as body\u00a0temperature\u00a0or\u00a0blood\u00a0glucose level, there is a particular\u00a0set point<\/a><\/strong>\u00a0that is the physiological optimum value.\u00a0The set point for\u00a0human body\u00a0temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain homeostasis<\/a> 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\u00a0normal range<\/a><\/strong>. 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).<\/p>\nA good analogy for set point, normal range, and maintenance of homeostasis is driving.\u00a0 When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane \u2014 this is analogous to the set point<\/a>.\u00a0 Sometimes, you are not driving in the exact<\/em> centre of the lane, but you are still within your lines, so you are in the equivalent of the normal range<\/a>.\u00a0 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.\u00a0 You’d move left if you were too close to the shoulder, or right if too close to the centre line \u2014 which is analogous to our next concept, negative feedback<\/a> to maintain homeostasis<\/a>.<\/p>\nMaintaining Homeostasis<\/h2>\n
Homeostasis<\/a> 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.<\/p>\n\n- The\u00a0stimulus<\/a><\/strong>\u00a0is 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.<\/li>\n
- The\u00a0sensor<\/a><\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\n
- The\u00a0control centre<\/a><\/strong> 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.<\/li>\n
- The\u00a0effector<\/a><\/strong> 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.<\/li>\n<\/ol>\n
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<\/a>. Biological examples of positive feedback are much less common.<\/p>\n <\/p>\n
<\/p>\nFigure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em><\/figcaption><\/figure>\n\nNegative Feedback<\/span><\/p>\n<\/div>\nIn a\u00a0negative feedback loop<\/a><\/strong>, feedback serves to reduce an excessive response and keep a variable within the normal range<\/a>.\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.<\/p>\nBody Temperature<\/h2>\n
Body temperature regulation involves negative feedback<\/a>, whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.<\/p>\nFigure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em><\/figcaption><\/figure>\n\nCooling Down<\/span><\/p>\n<\/div>\nThe human body\u2019s temperature regulatory centre is the hypothalamus<\/a> in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point<\/a>, it sets into motion the following responses:<\/p>\n\n- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\n
- 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\u00a0heat\u00a0with it.<\/li>\n
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\n<\/ul>\n
Heating Up<\/h3>\n
When the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:<\/p>\n
\n- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\n
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\n
- The\u00a0thyroid gland<\/a>\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\n
- The\u00a0adrenal glands<\/a>\u00a0may also be stimulated to secrete the\u00a0hormone adrenaline<\/a>. This hormone causes the breakdown of glycogen (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to glucose<\/a>, which can be used as an energy source. This catabolic chemical process is exothermic<\/a>, or heat producing.<\/li>\n<\/ul>\n
Blood Glucose<\/h2>\n
In controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.<\/p>\n
\n- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\n
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\n<\/ul>\n\n
<\/p>\nFigure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em><\/figcaption><\/figure>\n <\/p>\n
- \r\n \t
- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\r\n \t
- 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\u00a0heat\u00a0with it.<\/li>\r\n \t
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\r\n<\/ul>\r\n
Heating Up<\/h3>\r\nWhen the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:\r\n
- \r\n \t
- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\r\n \t
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"2958\"]thyroid gland[\/pb_glossary]\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"5869\"]adrenal glands[\/pb_glossary]\u00a0may also be stimulated to secrete the\u00a0hormone [pb_glossary id=\"5875\"]adrenaline[\/pb_glossary]. This hormone causes the breakdown of [pb_glossary id=\"327\"]glycogen[\/pb_glossary] (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to [pb_glossary id=\"5451\"]glucose[\/pb_glossary], which can be used as an energy source. This catabolic chemical process is [pb_glossary id=\"5513\"]exothermic[\/pb_glossary], or heat producing.<\/li>\r\n<\/ul>\r\n
Blood Glucose<\/h2>\r\nIn controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.\r\n
- \r\n \t
- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\r\n \t
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\r\n<\/ul>\r\n\r\n\r\n \r\n\r\n[caption id=\"attachment_331\" align=\"aligncenter\" width=\"632\"] Figure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em>[\/caption]\r\n\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4\r\n
Homeostasis and Negative\/Positive Feedback, Amoeba Sisters, 2017.<\/p>\r\n\r\n
Positive Feedback<\/h1>\r\n<\/div>\r\nIn a\u00a0[pb_glossary id=\"2962\"]positive feedback loop[\/pb_glossary]<\/strong>, 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.\r\n
Blood Clotting<\/h2>\r\n[caption id=\"attachment_2967\" align=\"aligncenter\" width=\"754\"]
Figure 7.8.5 The diagram demonstrates positive feedback, using the example of blood clotting in the body. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot. Every time the blood clot builds up more, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely healed and the positive feedback loop has ended. The graph represents the number of platelets aiding in the formation of the blood clot. The exponential form of the graph represents the positive feedback mechanism.<\/em>[\/caption]\r\n\r\nWhen 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.\r\nChildbirth<\/h2>\r\nFigure 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 [pb_glossary id=\"3093\"]oxytocin[\/pb_glossary]<\/strong>\u00a0to the\u00a0pituitary gland,\u00a0which 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\u00a0nerve impulses\u00a0to the brain, and the entire process stops.\r\n\r\n[caption id=\"attachment_2966\" align=\"aligncenter\" width=\"714\"]
Figure 7.8.6 Normal childbirth is driven by a positive feedback loop.\u00a0<\/em>[\/caption]\r\n\r\n\r\n\r\nNormal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed end point, rather than a return to a normal set point as in homeostasis.\r\n\r\n<\/div>\r\n\r\nWhen Homeostasis Fails<\/h1>\r\n<\/div>\r\nHomeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do,\u00a0[pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]<\/strong>\u00a0may 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 \u2014 or even death.\u00a0[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nNormal aging may bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control systems, which makes the body more susceptible to disease.\u00a0Older 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.\r\n
\r\nFeature: My Human Body<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"2969\"]Diabetes[\/pb_glossary]\u00a0is 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.\r\n\r\nOf the two types of diabetes, [pb_glossary id=\"2970\"]type 2 diabetes[\/pb_glossary] is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes<\/a> 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.\r\n\r\nYou 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.\r\n\r\nThe 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\u2019s how:\r\n
- \r\n \t
- Lose\u00a0weight.<\/strong> Any\u00a0weight\u00a0loss is beneficial. Losing as little as\u00a0seven\u00a0per cent of your\u00a0weight\u00a0may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.<\/li>\r\n \t
- Exercise\u00a0regularly.<\/strong>\u00a0You should try to\u00a0exercise\u00a0for 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\u00a0blood pressure\u00a0and improve your\u00a0heart\u00a0health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.<\/li>\r\n \t
- Adopt a healthy diet.<\/strong> 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.<\/li>\r\n \t
- Control stress.<\/strong>\u00a0Stress can increase your blood glucose and also raise your\u00a0blood pressure\u00a0and risk of\u00a0heart\u00a0disease. When you feel stressed out, do\u00a0breathing\u00a0exercises or take a brisk walk or jog.\u00a0Try to replace stressful thoughts with more calming ones.<\/li>\r\n \t
- Establish a support system.<\/strong>\u00a0Enlist 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.<\/li>\r\n<\/ul>\r\n
\r\n\r\n 7.8 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [pb_glossary id=\"5761\"]Homeostasis[\/pb_glossary] 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 homeostasis.<\/li>\r\n \t
- For any given variable, such as body temperature, there is a particular [pb_glossary id=\"2948\"]set point[\/pb_glossary] that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the [pb_glossary id=\"2949\"]normal range[\/pb_glossary].<\/li>\r\n \t
- Homeostasis is generally maintained by a [pb_glossary id=\"2956\"]negative feedback loop[\/pb_glossary] that includes a [pb_glossary id=\"2950\"]stimulus[\/pb_glossary], [pb_glossary id=\"2951\"]sensor[\/pb_glossary], [pb_glossary id=\"5951\"]control centre[\/pb_glossary], and [pb_glossary id=\"5979\"]effector[\/pb_glossary]. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.<\/li>\r\n \t
- [pb_glossary id=\"2962\"]Positive feedback loops[\/pb_glossary]\u00a0are not common in biological systems. Positive feedback serves to intensify a response until an end point is reached. Positive feedback loops control blood clotting and childbirth.<\/li>\r\n \t
- Sometimes homeostatic mechanisms fail, resulting in [pb_glossary id=\"2968\"]homeostatic imbalance[\/pb_glossary]. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the\u00a0efficiency\u00a0of the body\u2019s control system,\u00a0which makes\u00a0the elderly more susceptible to disease.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 7.8 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- [h5p id=\"547\"]<\/li>\r\n \t
- [h5p id=\"548\"]<\/li>\r\n \t
- Compare and contrast negative and positive feedback loops.<\/li>\r\n \t
- Explain how negative feedback controls body temperature.<\/li>\r\n \t
- Give two examples of physiological processes controlled by positive feedback loops.<\/li>\r\n \t
- During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer.\u00a0What do you think might be the evolutionary benefit of the milk production regulation mechanism\u00a0you described?<\/li>\r\n \t
- Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.<\/li>\r\n \t
- The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the\u00a0pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.\r\n
- \r\n \t
- What is the stimulus in this system? Explain your answer.<\/li>\r\n \t
- What is the control centre in this system? Explain your answer.<\/li>\r\n \t
- In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer.<\/li>\r\n<\/ol>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 7.8 Explore More<\/span><\/h1>\r\n<\/header>https:\/\/www.youtube.com\/watch?v=LSgEJSlk6W4\r\n
Homeostasis - What Is Homeostasis - What Is Set Point For Homeostasis - Homeostasis In The Human Body, Whats Up Dude, 2017.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM\r\n
GCSE Biology - Homeostasis #38, Cognito, 2018.<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\nAttributions<\/h2>\r\nFigure 7.8.1<\/strong>\r\n\r\nNest_Thermostat<\/a> by Amanitamano<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/deed.en) license.\r\n\r\nFigure 7.8.2<\/strong>\r\n\r\nNegative_Feedback_Loops<\/a>\u00a0by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\n\r\nFigure 7.8.3<\/strong>\r\n\r\nBody Temperature Homeostasis<\/a>\u00a0by OpenStax College, Biology<\/a> is used under a CC BY 4.0<\/a> license.\r\n\r\nFigure 7.8.4<\/strong>\r\n\r\nHomeostasis_of_blood_sugar<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a \u00a0CC0 1.0 Universal Public Domain Dedication<\/a> (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en) license.\r\n\r\nFigure 7.8.5<\/strong>\r\n\r\nPositive_Feedback_Diagram_Blood_Clotting<\/a> by Elliottuttle<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0 <\/a>\u00a0(https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\nFigure 7.8.6<\/strong>\r\n\r\nPregnancy-Positive_Feedback<\/a> by OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) license.\r\n
References<\/h2>\r\n
Amoeba Sisters. (2017, September 7). Homeostasis and negative\/positive feedback. YouTube. https:\/\/www.youtube.com\/watch?v=Iz0Q9nTZCw4&feature=youtu.be<\/p>\r\n
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\u00a0<\/span>1.10<\/span>\u00a0<\/span>Negative feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/p>\r\n
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 <\/span>1.11<\/span>\u00a0<\/span>Positive feedback loop<\/span>\u00a0<\/span>normal childbirth is driven by a positive feedback loop [digital image\/ diagram]. <\/span>\u00a0In Anatomy and Physiology<\/em> (Section 1.5). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-5-homeostasis<\/span><\/p>\r\n
Cognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https:\/\/www.youtube.com\/watch?v=XMsJ-3qRVJM&feature=youtu.be<\/p>\r\n
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<\/p>\r\n
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<\/span>, Biology <\/em>(Section 33.3). https:\/\/cnx.org\/contents\/GFy_h8cu@10.8:BP24ZReh@7\/Homeostasis<\/p>\r\n
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<\/p>","rendered":"
<\/p>\n
Figure 7.8.1\u00a0 A thermostat controls a complex system to maintain a steady temperature in our homes.\u00a0<\/em><\/figcaption><\/figure>\n Steady as She Goes<\/h1>\n
This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature \u2014 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 \u2014 including the human body\u2014 maintain a steady state called homeostasis.<\/p>\n
\nWhat Is Homeostasis?<\/h1>\n<\/div>\n
Homeostasis<\/a><\/strong>\u00a0is 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\u00a0cells<\/a>, tissues<\/a>, organs<\/a>, and organ systems<\/a>\u00a0throughout 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.<\/p>\n
Set Point and Normal Range<\/h2>\n
For any given variable, such as body\u00a0temperature\u00a0or\u00a0blood\u00a0glucose level, there is a particular\u00a0set point<\/a><\/strong>\u00a0that is the physiological optimum value.\u00a0The set point for\u00a0human body\u00a0temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain homeostasis<\/a> 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\u00a0normal range<\/a><\/strong>. 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).<\/p>\n
A good analogy for set point, normal range, and maintenance of homeostasis is driving.\u00a0 When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane \u2014 this is analogous to the set point<\/a>.\u00a0 Sometimes, you are not driving in the exact<\/em> centre of the lane, but you are still within your lines, so you are in the equivalent of the normal range<\/a>.\u00a0 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.\u00a0 You’d move left if you were too close to the shoulder, or right if too close to the centre line \u2014 which is analogous to our next concept, negative feedback<\/a> to maintain homeostasis<\/a>.<\/p>\n
Maintaining Homeostasis<\/h2>\n
Homeostasis<\/a> 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.<\/p>\n
- \n
- The\u00a0stimulus<\/a><\/strong>\u00a0is 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.<\/li>\n
- The\u00a0sensor<\/a><\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\n
- The\u00a0control centre<\/a><\/strong> 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.<\/li>\n
- The\u00a0effector<\/a><\/strong> 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.<\/li>\n<\/ol>\n
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<\/a>. Biological examples of positive feedback are much less common.<\/p>\n
<\/p>\n
<\/p>\n
Figure 7.8.2 Maintaining homeostasis through feedback requires a stimulus, sensor, control centre, and effector.<\/em><\/figcaption><\/figure>\n \nNegative Feedback<\/span><\/p>\n<\/div>\n
In a\u00a0negative feedback loop<\/a><\/strong>, feedback serves to reduce an excessive response and keep a variable within the normal range<\/a>.\u00a0Two\u00a0processes controlled by negative feedback\u00a0are\u00a0body temperature regulation and control of\u00a0blood\u00a0glucose.<\/p>\n
Body Temperature<\/h2>\n
Body temperature regulation involves negative feedback<\/a>, whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.<\/p>\n
Figure 7.8.3 Homeostasis of body temperature is maintained by negative feedback loops.<\/em><\/figcaption><\/figure>\n \nCooling Down<\/span><\/p>\n<\/div>\n
The human body\u2019s temperature regulatory centre is the hypothalamus<\/a> in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point<\/a>, it sets into motion the following responses:<\/p>\n
- \n
- Blood vessels\u00a0in the skin dilate (vasodilation) to allow more\u00a0blood\u00a0from the warm body core to flow close to the surface of the body, so\u00a0heat can be radiated into\u00a0the environment.<\/li>\n
- 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\u00a0heat\u00a0with it.<\/li>\n
- Breathing\u00a0becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases\u00a0heat\u00a0loss from the lungs.<\/li>\n<\/ul>\n
Heating Up<\/h3>\n
When the brain\u2019s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:<\/p>\n
- \n
- Blood vessels\u00a0in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.<\/li>\n
- As temperature falls lower, random signals to\u00a0skeletal muscles\u00a0are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.<\/li>\n
- The\u00a0thyroid gland<\/a>\u00a0may be stimulated by the brain (via the pituitary gland) to secrete more thyroid\u00a0hormone. This hormone increases metabolic activity and heat production in\u00a0cells\u00a0throughout the body.<\/li>\n
- The\u00a0adrenal glands<\/a>\u00a0may also be stimulated to secrete the\u00a0hormone adrenaline<\/a>. This hormone causes the breakdown of glycogen (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to glucose<\/a>, which can be used as an energy source. This catabolic chemical process is exothermic<\/a>, or heat producing.<\/li>\n<\/ul>\n
Blood Glucose<\/h2>\n
In controlling\u00a0the blood glucose level, certain endocrine\u00a0cells\u00a0in the\u00a0pancreas\u00a0(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.<\/p>\n
- \n
- If the blood glucose level rises above the normal range, pancreatic beta cells release the\u00a0hormone\u00a0insulin 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.<\/li>\n
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone\u00a0glucagon<\/strong>\u00a0into 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.<\/li>\n<\/ul>\n\n
<\/p>\n
Figure 7.8.4 Your liver plays an important role in balancing blood sugar levels. Glycogen in your liver can either collect glucose out of your blood stream to lower blood sugar, or release glucose into the bloodstream to increase blood sugar.\u00a0 This happens through a negative feedback loop.<\/em><\/figcaption><\/figure>\n <\/p>\n
- The\u00a0adrenal glands<\/a>\u00a0may also be stimulated to secrete the\u00a0hormone adrenaline<\/a>. This hormone causes the breakdown of glycogen (the\u00a0carbohydrate\u00a0used for\u00a0energy\u00a0storage in animals) to glucose<\/a>, which can be used as an energy source. This catabolic chemical process is exothermic<\/a>, or heat producing.<\/li>\n<\/ul>\n
- The\u00a0sensor<\/a><\/strong> monitors the values of the variable and sends data on it to the control centre.<\/li>\n
- The\u00a0stimulus<\/a><\/strong>\u00a0is 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.<\/li>\n
- Exercise\u00a0regularly.<\/strong>\u00a0You should try to\u00a0exercise\u00a0for 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\u00a0blood pressure\u00a0and improve your\u00a0heart\u00a0health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.<\/li>\r\n \t
- Lose\u00a0weight.<\/strong> Any\u00a0weight\u00a0loss is beneficial. Losing as little as\u00a0seven\u00a0per cent of your\u00a0weight\u00a0may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.<\/li>\r\n \t
![Nest_Thermostat<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Nest_Thermostat.JPG\"){kind=link}
![Negative_Feedback_Loops<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:105_Negative_Feedback_Loops.jpg\"){kind=link}
![Homeostasis_of_blood_sugar<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Homeostasis_of_blood_sugar.png\"){kind=link}
![Positive_Feedback_Diagram_Blood_Clotting<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Positive_Feedback_Diagram_(2).svg\"){kind=link}
![Pregnancy-Positive_Feedback<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:106_Pregnancy-Positive_Feedback.jpg\"){kind=link}