Case Study: A Pain in the Foot<\/h1>\r\n<\/div>\r\nSophia loves wearing high heels when she goes out at night, like the stiletto heels shown in Figure 11.1.1. She knows they are not the most practical shoes, but she likes how they look.\r\n\r\nLately, she has been experiencing pain in the balls of her feet \u2014 the area just behind the toes. Even when she trades her heels for comfortable sneakers, it still hurts when she stands or walks.\r\n\r\nWhat could be going on? She searches online to try to find some answers. She finds a reputable source for foot pain information \u2014 a website from a professional organization of physicians that peer reviews the content by experts in the field. There, she reads about a condition called metatarsalgia<\/a>, which produces pain in the ball of the foot that sounds very similar to what she is experiencing.\r\n\r\nShe learns that a common cause of metatarsalgia is the wearing of high heels. Shoes like this push the foot into an abnormal position, resulting in excessive pressure being placed on the ball of the foot. Looking at the photograph above (Figure 11.1.1), you can imagine how much of the woman\u2019s body weight is focused on the ball of her foot, because of the shape of her high heels. If she were not wearing high heels, her weight would be more evenly distributed across her foot.\r\n\r\nAs she reads more about the hazards of high heels, Sophia learns that they can also cause foot deformities, such as hammertoes, bunions, and small cracks in bone called stress fractures. High heels may even contribute to the development of osteoarthritis of the knees at an early age.\r\n\r\nThese conditions caused by high heels are all problems of the [pb_glossary id=\"2906\"]skeletal system[\/pb_glossary], which includes [pb_glossary id=\"5913\"]bones[\/pb_glossary]\u00a0and [pb_glossary id=\"2815\"]connective tissues[\/pb_glossary]\u00a0that hold bones together and cushion them at joints (such as the knee). The skeletal system supports the body\u2019s weight and protects internal organs, but as you will learn as you read this chapter, it also carries out a variety of other important physiological functions.\r\n\r\nAt the end of the chapter, you will find out why high heels can cause these skeletal system problems, as well as the steps Sophia takes to recover from her foot pain and prevent long-term injury.\r\n\r\nChapter 11 Overview: Skeletal System<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you will learn about the structure, functions, growth, repair, and disorders of the skeletal system. Specifically you will learn about:\r\n\r\n \t- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\r\n \t
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\r\n \t
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\r\n \t
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\r\n \t
- The different types of bones in the skeletal system, based on shape and location.<\/li>\r\n \t
- How bones grow, remodel, and repair themselves.<\/li>\r\n \t
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\r\n \t
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
\r\n \t- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\r\n \t
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\r\n \t
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\r\n<\/ol>\r\n<\/div>\r\n \r\n
Attribution<\/h2>\r\nFigure 11.1.1<\/strong>\r\n\r\nHeels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReference<\/h2>\r\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>","rendered":"
<\/p>\n![\"11.1.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Heels-by-apostolos-vamvouras-_pdbqMcNWus-unsplash-scaled-e1591372330939-2.jpg\")
Figure 11.1.1 Fancy shoes can be a real pain in the….. foot.<\/em><\/figcaption><\/figure>\n\nCase Study: A Pain in the Foot<\/h1>\n<\/div>\n
Sophia loves wearing high heels when she goes out at night, like the stiletto heels shown in Figure 11.1.1. She knows they are not the most practical shoes, but she likes how they look.<\/p>\n
Lately, she has been experiencing pain in the balls of her feet \u2014 the area just behind the toes. Even when she trades her heels for comfortable sneakers, it still hurts when she stands or walks.<\/p>\n
What could be going on? She searches online to try to find some answers. She finds a reputable source for foot pain information \u2014 a website from a professional organization of physicians that peer reviews the content by experts in the field. There, she reads about a condition called metatarsalgia<\/a>, which produces pain in the ball of the foot that sounds very similar to what she is experiencing.<\/p>\nShe learns that a common cause of metatarsalgia is the wearing of high heels. Shoes like this push the foot into an abnormal position, resulting in excessive pressure being placed on the ball of the foot. Looking at the photograph above (Figure 11.1.1), you can imagine how much of the woman\u2019s body weight is focused on the ball of her foot, because of the shape of her high heels. If she were not wearing high heels, her weight would be more evenly distributed across her foot.<\/p>\n
As she reads more about the hazards of high heels, Sophia learns that they can also cause foot deformities, such as hammertoes, bunions, and small cracks in bone called stress fractures. High heels may even contribute to the development of osteoarthritis of the knees at an early age.<\/p>\n
These conditions caused by high heels are all problems of the skeletal system<\/a>, which includes bones<\/a>\u00a0and connective tissues<\/a>\u00a0that hold bones together and cushion them at joints (such as the knee). The skeletal system supports the body\u2019s weight and protects internal organs, but as you will learn as you read this chapter, it also carries out a variety of other important physiological functions.<\/p>\nAt the end of the chapter, you will find out why high heels can cause these skeletal system problems, as well as the steps Sophia takes to recover from her foot pain and prevent long-term injury.<\/p>\n
\n\nChapter 11 Overview: Skeletal System<\/span><\/h1>\n<\/header>\n\nIn this chapter, you will learn about the structure, functions, growth, repair, and disorders of the skeletal system. Specifically you will learn about:<\/p>\n
\n- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\n
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\n
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\n
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\n
- The different types of bones in the skeletal system, based on shape and location.<\/li>\n
- How bones grow, remodel, and repair themselves.<\/li>\n
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\n
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
As you read this chapter, think about the following questions:<\/p>\n
\n- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\n
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\n
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\n<\/ol>\n<\/div>\n
<\/p>\n
Attribution<\/h2>\n
Figure 11.1.1<\/strong><\/p>\nHeels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\nReference<\/h2>\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>\n
definition<\/span>Created by:\u00a0CK-12\/Adapted by Christine Miller<\/p>\n
\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Borrelia_hermsii_Bacteria_13758011613.jpg\")
Figure 4.3.1 A bacterium attacks a human erythrocyte. Both are cells.<\/em><\/figcaption><\/figure>\nBacteria\u00a0Attack!<\/h1>\n<\/div>\n
The colourful image in Figure 4.3.1 shows a bacterial cell (in green) attacking human red blood cells. The bacterium causes a disease called relapsing fever. The bacterial and human cells look very different in size and shape. Although all living cells have certain things in common \u2014 such as a plasma membrane and cytoplasm \u2014 different types of cells, even within the same organism, may have their own unique structures and functions. Cells with different functions generally have different shapes that suit them for their particular job. Cells vary not only in shape, but also in size, as this example shows. In most organisms, however, even the largest cells are no bigger than the period at the end of this sentence. Why are cells so small?<\/p>\n
\nExplaining Cell Size<\/h1>\n<\/div>\n
Most organisms, even very large ones, have microscopic cells. Why don't cells get bigger instead of remaining tiny and multiplying? Why aren't you one giant cell rolling around school? What limits cell size?<\/p>\n
Once you know how a cell functions, the answers to these questions are clear. To carry out life processes, a cell must be able to quickly pass substances in and out of the cell. For example, it must be able to pass\u00a0nutrients\u00a0and oxygen into the cell and waste products out of the cell. Anything that enters or leaves a cell must cross its outer surface. The size of a cell is limited by its need to pass substances across that outer surface.<\/p>\n
Look at the three cubes in Figure 4.3.2. A larger cube has less surface area relative to its volume than a smaller cube. This relationship also applies to cells \u2014 a larger cell has less surface area relative to its volume than a smaller cell. A cell with a larger volume also needs more nutrients and oxygen, and produces more waste. Because all of these substances must pass through the surface of the cell, a cell with a large volume will not have enough surface area to allow it to meet its needs. The <\/span>larger<\/em> the cell is, the <\/span>smaller<\/em> its ratio of surface area to volume, and the more difficult it will be for the cell to get rid of its waste and take in necessary substances. This is what limits the size of the cell.<\/span><\/p>\n <\/p>\n
<\/p>\n
<\/p>\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Cell-Size.png\")
Figure 4.3.2 Surface area to volume ratio.<\/em><\/figcaption><\/figure>\n\nCell Form and Function<\/h1>\n<\/div>\n
Cells with different functions often have varying shapes. The cells pictured below (Figure 4.3.3) are just a few examples of the many different shapes that human cells may have. Each type of cell\u00a0 has characteristics that help it do its job. The job of the nerve cell, for example, is to carry messages to other cells. The nerve cell has many long extensions that reach out in all directions, allowing it to pass messages to many other cells at once. Do you see the tail of each tiny sperm cell? Its tail helps a sperm cell \"swim\" through fluids in the female reproductive tract in order to reach an egg cell. The white blood cell has the job of destroying bacteria and other pathogens. It is a large cell that can engulf foreign invaders.<\/p>\n
\n\n<\/div>\n<\/div>\nFigure 4.3.3 Human cells may have many different shapes that help them to do their jobs.<\/em><\/p>\n<\/div>\n\nCells With and Without a\u00a0Nucleus<\/h1>\n<\/div>\n
The\u00a0nucleus<\/a>\u00a0is a basic\u00a0cell structure\u00a0present in many \u2014 but not\u00a0all \u2014<\/em>\u00a0living cells. The\u00a0nucleus<\/a>\u00a0of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane) and contains\u00a0DNA<\/a>. Based on whether or not they have a nucleus, there are two basic types of cells: prokaryotic<\/a> cells and eukaryotic<\/a> cells.<\/p>\nProkaryotic Cells<\/h2>\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/2000px-Average_prokaryote_cell-_en.svg_.png\")
Figure 4.3.3 Bacteria are prokaryotes, meaning they do not have a nucleus. Their DNA is contained in a region called the nucleoid.<\/em><\/figcaption><\/figure>\nProkaryotic<\/a> cells<\/strong> are cells without a nucleus. The DNA<\/a> in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane.\u00a0 In addition, these cells are typically smaller than eukaryotic cells and contain fewer organelles.\u00a0 Prokaryotic cells are found in single-celled organisms, such as the bacterium represented by the model in Figure 4.3.3. Organisms with prokaryotic cells are called prokaryotes<\/strong>. They were the first type of organisms to evolve, and they are still the most common organisms today.<\/p>\n\n <\/p>\n<\/div>\n
Eukaryotic Cells<\/h2>\n![\"Image](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Animal-Cell-1.png\")
Figure 4.3.4 Eukaryotic cells, like this animal cell, contain a nucleus and many other membrane-bound organelles.<\/em><\/figcaption><\/figure>\nEukaryotic<\/a> cells<\/strong> are cells that contain a nucleus<\/a>. A typical eukaryotic cell is represented by the model in Figure 4.3.4. Eukaryotic cells are usually larger than prokaryotic cells. They are found in some single-celled and all multicellular organisms. Organisms with eukaryotic cells are called eukaryotes<\/strong>, and they range from\u00a0fungi\u00a0to\u00a0humans.<\/p>\nBesides a nucleus, eukaryotic cells also contain other\u00a0organelles. An\u00a0organelle<\/a><\/strong>\u00a0is a structure within the cytoplasm that performs a specific job in the cell.\u00a0Organelles\u00a0called\u00a0mitochondria<\/a>, for example, provide\u00a0energy<\/a>\u00a0to the cell, and organelles called vesicles store substances in the cell. Organelles allow eukaryotic<\/a> cells to carry out more functions than prokaryotic<\/a> cells can.<\/p>\nInterestingly, scientists think that mitochondria were once free-living prokaryotes that infected (or were engulfed by) larger cells. The two organisms developed a symbiotic relationship that was beneficial to both of them, resulting in the smaller prokaryote becoming an organelle within the larger cell. This is called endosymbiotic theory, and it is supported by a lot of evidence, including the fact that mitochondria<\/a> have their own DNA<\/a> separate from the DNA in the nucleus of the eukaryotic cell. Endosymbiotic theory will be described in more detail in later sections, and it's also discussed in the video below.<\/p>\n\nhttps:\/\/www.youtube.com\/watch?v=FGnS-Xk0ZqU<\/p>\n
Endosymbiotic Theory, Amoeba Sisters, 2017.<\/p>\n
\n\n4.3 Summary<\/h1>\n<\/header>\n\n\n- Cells must be very small so they have a large enough surface area-to-volume ratio to maintain normal cell processes.<\/li>\n
- Cells with different functions often have different shapes.<\/li>\n
- Prokaryotic<\/a> cells do not have a nucleus. Eukaryotic <\/a>cells\u00a0do<\/em>\u00a0have a nucleus<\/a>, along with other\u00a0organelles<\/a>.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n\n\n
\n4.3 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Explain why most cells are very small.<\/li>\n
- Discuss variations in the form and function of cells.<\/li>\n
- \n\n
Chapter 11 Overview: Skeletal System<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nIn this chapter, you will learn about the structure, functions, growth, repair, and disorders of the skeletal system. Specifically you will learn about:\r\n\r\n \t- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\r\n \t
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\r\n \t
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\r\n \t
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\r\n \t
- The different types of bones in the skeletal system, based on shape and location.<\/li>\r\n \t
- How bones grow, remodel, and repair themselves.<\/li>\r\n \t
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\r\n \t
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
\r\n \t- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\r\n \t
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\r\n \t
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\r\n<\/ol>\r\n<\/div>\r\n \r\n
Attribution<\/h2>\r\nFigure 11.1.1<\/strong>\r\n\r\nHeels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\nReference<\/h2>\r\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>","rendered":"
<\/p>\nFigure 11.1.1 Fancy shoes can be a real pain in the….. foot.<\/em><\/figcaption><\/figure>\n\nCase Study: A Pain in the Foot<\/h1>\n<\/div>\n
Sophia loves wearing high heels when she goes out at night, like the stiletto heels shown in Figure 11.1.1. She knows they are not the most practical shoes, but she likes how they look.<\/p>\n
Lately, she has been experiencing pain in the balls of her feet \u2014 the area just behind the toes. Even when she trades her heels for comfortable sneakers, it still hurts when she stands or walks.<\/p>\n
What could be going on? She searches online to try to find some answers. She finds a reputable source for foot pain information \u2014 a website from a professional organization of physicians that peer reviews the content by experts in the field. There, she reads about a condition called metatarsalgia<\/a>, which produces pain in the ball of the foot that sounds very similar to what she is experiencing.<\/p>\nShe learns that a common cause of metatarsalgia is the wearing of high heels. Shoes like this push the foot into an abnormal position, resulting in excessive pressure being placed on the ball of the foot. Looking at the photograph above (Figure 11.1.1), you can imagine how much of the woman\u2019s body weight is focused on the ball of her foot, because of the shape of her high heels. If she were not wearing high heels, her weight would be more evenly distributed across her foot.<\/p>\n
As she reads more about the hazards of high heels, Sophia learns that they can also cause foot deformities, such as hammertoes, bunions, and small cracks in bone called stress fractures. High heels may even contribute to the development of osteoarthritis of the knees at an early age.<\/p>\n
These conditions caused by high heels are all problems of the skeletal system<\/a>, which includes bones<\/a>\u00a0and connective tissues<\/a>\u00a0that hold bones together and cushion them at joints (such as the knee). The skeletal system supports the body\u2019s weight and protects internal organs, but as you will learn as you read this chapter, it also carries out a variety of other important physiological functions.<\/p>\nAt the end of the chapter, you will find out why high heels can cause these skeletal system problems, as well as the steps Sophia takes to recover from her foot pain and prevent long-term injury.<\/p>\n
\n\nChapter 11 Overview: Skeletal System<\/span><\/h1>\n<\/header>\n\nIn this chapter, you will learn about the structure, functions, growth, repair, and disorders of the skeletal system. Specifically you will learn about:<\/p>\n
\n- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\n
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\n
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\n
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\n
- The different types of bones in the skeletal system, based on shape and location.<\/li>\n
- How bones grow, remodel, and repair themselves.<\/li>\n
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\n
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
As you read this chapter, think about the following questions:<\/p>\n
\n- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\n
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\n
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\n<\/ol>\n<\/div>\n
<\/p>\n
Attribution<\/h2>\n
Figure 11.1.1<\/strong><\/p>\nHeels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\nReference<\/h2>\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>\n
definition<\/span>Created by:\u00a0CK-12\/Adapted by Christine Miller<\/p>\n
\nFigure 4.3.1 A bacterium attacks a human erythrocyte. Both are cells.<\/em><\/figcaption><\/figure>\nBacteria\u00a0Attack!<\/h1>\n<\/div>\n
The colourful image in Figure 4.3.1 shows a bacterial cell (in green) attacking human red blood cells. The bacterium causes a disease called relapsing fever. The bacterial and human cells look very different in size and shape. Although all living cells have certain things in common \u2014 such as a plasma membrane and cytoplasm \u2014 different types of cells, even within the same organism, may have their own unique structures and functions. Cells with different functions generally have different shapes that suit them for their particular job. Cells vary not only in shape, but also in size, as this example shows. In most organisms, however, even the largest cells are no bigger than the period at the end of this sentence. Why are cells so small?<\/p>\n
\nExplaining Cell Size<\/h1>\n<\/div>\n
Most organisms, even very large ones, have microscopic cells. Why don't cells get bigger instead of remaining tiny and multiplying? Why aren't you one giant cell rolling around school? What limits cell size?<\/p>\n
Once you know how a cell functions, the answers to these questions are clear. To carry out life processes, a cell must be able to quickly pass substances in and out of the cell. For example, it must be able to pass\u00a0nutrients\u00a0and oxygen into the cell and waste products out of the cell. Anything that enters or leaves a cell must cross its outer surface. The size of a cell is limited by its need to pass substances across that outer surface.<\/p>\n
Look at the three cubes in Figure 4.3.2. A larger cube has less surface area relative to its volume than a smaller cube. This relationship also applies to cells \u2014 a larger cell has less surface area relative to its volume than a smaller cell. A cell with a larger volume also needs more nutrients and oxygen, and produces more waste. Because all of these substances must pass through the surface of the cell, a cell with a large volume will not have enough surface area to allow it to meet its needs. The <\/span>larger<\/em> the cell is, the <\/span>smaller<\/em> its ratio of surface area to volume, and the more difficult it will be for the cell to get rid of its waste and take in necessary substances. This is what limits the size of the cell.<\/span><\/p>\n <\/p>\n
<\/p>\n
<\/p>\nFigure 4.3.2 Surface area to volume ratio.<\/em><\/figcaption><\/figure>\n\nCell Form and Function<\/h1>\n<\/div>\n
Cells with different functions often have varying shapes. The cells pictured below (Figure 4.3.3) are just a few examples of the many different shapes that human cells may have. Each type of cell\u00a0 has characteristics that help it do its job. The job of the nerve cell, for example, is to carry messages to other cells. The nerve cell has many long extensions that reach out in all directions, allowing it to pass messages to many other cells at once. Do you see the tail of each tiny sperm cell? Its tail helps a sperm cell \"swim\" through fluids in the female reproductive tract in order to reach an egg cell. The white blood cell has the job of destroying bacteria and other pathogens. It is a large cell that can engulf foreign invaders.<\/p>\n
\n\n<\/div>\n<\/div>\nFigure 4.3.3 Human cells may have many different shapes that help them to do their jobs.<\/em><\/p>\n<\/div>\n\nCells With and Without a\u00a0Nucleus<\/h1>\n<\/div>\n
The\u00a0nucleus<\/a>\u00a0is a basic\u00a0cell structure\u00a0present in many \u2014 but not\u00a0all \u2014<\/em>\u00a0living cells. The\u00a0nucleus<\/a>\u00a0of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane) and contains\u00a0DNA<\/a>. Based on whether or not they have a nucleus, there are two basic types of cells: prokaryotic<\/a> cells and eukaryotic<\/a> cells.<\/p>\nProkaryotic Cells<\/h2>\nFigure 4.3.3 Bacteria are prokaryotes, meaning they do not have a nucleus. Their DNA is contained in a region called the nucleoid.<\/em><\/figcaption><\/figure>\nProkaryotic<\/a> cells<\/strong> are cells without a nucleus. The DNA<\/a> in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane.\u00a0 In addition, these cells are typically smaller than eukaryotic cells and contain fewer organelles.\u00a0 Prokaryotic cells are found in single-celled organisms, such as the bacterium represented by the model in Figure 4.3.3. Organisms with prokaryotic cells are called prokaryotes<\/strong>. They were the first type of organisms to evolve, and they are still the most common organisms today.<\/p>\n\n <\/p>\n<\/div>\n
Eukaryotic Cells<\/h2>\nFigure 4.3.4 Eukaryotic cells, like this animal cell, contain a nucleus and many other membrane-bound organelles.<\/em><\/figcaption><\/figure>\nEukaryotic<\/a> cells<\/strong> are cells that contain a nucleus<\/a>. A typical eukaryotic cell is represented by the model in Figure 4.3.4. Eukaryotic cells are usually larger than prokaryotic cells. They are found in some single-celled and all multicellular organisms. Organisms with eukaryotic cells are called eukaryotes<\/strong>, and they range from\u00a0fungi\u00a0to\u00a0humans.<\/p>\nBesides a nucleus, eukaryotic cells also contain other\u00a0organelles. An\u00a0organelle<\/a><\/strong>\u00a0is a structure within the cytoplasm that performs a specific job in the cell.\u00a0Organelles\u00a0called\u00a0mitochondria<\/a>, for example, provide\u00a0energy<\/a>\u00a0to the cell, and organelles called vesicles store substances in the cell. Organelles allow eukaryotic<\/a> cells to carry out more functions than prokaryotic<\/a> cells can.<\/p>\nInterestingly, scientists think that mitochondria were once free-living prokaryotes that infected (or were engulfed by) larger cells. The two organisms developed a symbiotic relationship that was beneficial to both of them, resulting in the smaller prokaryote becoming an organelle within the larger cell. This is called endosymbiotic theory, and it is supported by a lot of evidence, including the fact that mitochondria<\/a> have their own DNA<\/a> separate from the DNA in the nucleus of the eukaryotic cell. Endosymbiotic theory will be described in more detail in later sections, and it's also discussed in the video below.<\/p>\n\nhttps:\/\/www.youtube.com\/watch?v=FGnS-Xk0ZqU<\/p>\n
Endosymbiotic Theory, Amoeba Sisters, 2017.<\/p>\n
\n\n4.3 Summary<\/h1>\n<\/header>\n\n\n- Cells must be very small so they have a large enough surface area-to-volume ratio to maintain normal cell processes.<\/li>\n
- Cells with different functions often have different shapes.<\/li>\n
- Prokaryotic<\/a> cells do not have a nucleus. Eukaryotic <\/a>cells\u00a0do<\/em>\u00a0have a nucleus<\/a>, along with other\u00a0organelles<\/a>.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n\n\n
\n4.3 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- Explain why most cells are very small.<\/li>\n
- Discuss variations in the form and function of cells.<\/li>\n
- \n\n
- \r\n \t
- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\r\n \t
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\r\n \t
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\r\n \t
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\r\n \t
- The different types of bones in the skeletal system, based on shape and location.<\/li>\r\n \t
- How bones grow, remodel, and repair themselves.<\/li>\r\n \t
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\r\n \t
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n\r\n\r\nAs you read this chapter, think about the following questions:\r\n
- \r\n \t
- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\r\n \t
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\r\n \t
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\r\n<\/ol>\r\n<\/div>\r\n \r\n
Attribution<\/h2>\r\nFigure 11.1.1<\/strong>\r\n\r\nHeels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).\r\n
Reference<\/h2>\r\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>","rendered":"
<\/p>\n
Figure 11.1.1 Fancy shoes can be a real pain in the….. foot.<\/em><\/figcaption><\/figure>\n \nCase Study: A Pain in the Foot<\/h1>\n<\/div>\n
Sophia loves wearing high heels when she goes out at night, like the stiletto heels shown in Figure 11.1.1. She knows they are not the most practical shoes, but she likes how they look.<\/p>\n
Lately, she has been experiencing pain in the balls of her feet \u2014 the area just behind the toes. Even when she trades her heels for comfortable sneakers, it still hurts when she stands or walks.<\/p>\n
What could be going on? She searches online to try to find some answers. She finds a reputable source for foot pain information \u2014 a website from a professional organization of physicians that peer reviews the content by experts in the field. There, she reads about a condition called metatarsalgia<\/a>, which produces pain in the ball of the foot that sounds very similar to what she is experiencing.<\/p>\n
She learns that a common cause of metatarsalgia is the wearing of high heels. Shoes like this push the foot into an abnormal position, resulting in excessive pressure being placed on the ball of the foot. Looking at the photograph above (Figure 11.1.1), you can imagine how much of the woman\u2019s body weight is focused on the ball of her foot, because of the shape of her high heels. If she were not wearing high heels, her weight would be more evenly distributed across her foot.<\/p>\n
As she reads more about the hazards of high heels, Sophia learns that they can also cause foot deformities, such as hammertoes, bunions, and small cracks in bone called stress fractures. High heels may even contribute to the development of osteoarthritis of the knees at an early age.<\/p>\n
These conditions caused by high heels are all problems of the skeletal system<\/a>, which includes bones<\/a>\u00a0and connective tissues<\/a>\u00a0that hold bones together and cushion them at joints (such as the knee). The skeletal system supports the body\u2019s weight and protects internal organs, but as you will learn as you read this chapter, it also carries out a variety of other important physiological functions.<\/p>\n
At the end of the chapter, you will find out why high heels can cause these skeletal system problems, as well as the steps Sophia takes to recover from her foot pain and prevent long-term injury.<\/p>\n
\n\n Chapter 11 Overview: Skeletal System<\/span><\/h1>\n<\/header>\n
\nIn this chapter, you will learn about the structure, functions, growth, repair, and disorders of the skeletal system. Specifically you will learn about:<\/p>\n
- \n
- The components of the skeletal system, which includes bones, ligaments, and cartilage.<\/li>\n
- The functions of the skeletal system, including supporting and giving shape to the body; protecting internal organs; facilitating movement; producing blood cells; helping maintain homeostasis; and producing endocrine hormones.<\/li>\n
- The organization and functions of the two main divisions of the skeletal system: the axial skeletal system (which includes the skull, spine, and rib cage), and the appendicular skeletal system (which includes the limbs and girdles that attach the limbs to the axial skeleton).<\/li>\n
- The tissues and cells that make up bones, along with their specific functions, which include making new bone, breaking down bone, producing blood cells, and regulating mineral homeostasis.<\/li>\n
- The different types of bones in the skeletal system, based on shape and location.<\/li>\n
- How bones grow, remodel, and repair themselves.<\/li>\n
- The different types of joints between bones, where they are located, and the ways in which they allow different types of movement, depending on their structure.<\/li>\n
- The causes, risk factors, and treatments for the two most common disorders of the skeletal system \u2014 osteoporosis and osteoarthritis.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
As you read this chapter, think about the following questions:<\/p>\n
- \n
- Sophia suspects she has a condition called metatarsalgia. This term is related to the term \u201cmetatarsals.\u201d What are metatarsals, where are they located, and how do you think they are related to metatarsalgia?<\/li>\n
- High heels can cause stress fractures, which are small cracks in bone that usually appear after repeated mechanical stress, instead of after a significant acute injury. What other condition described in this chapter involves a similar process?<\/li>\n
- What are bunions and osteoarthritis of the knee? Why do you think they can be caused by wearing high heels?<\/li>\n<\/ol>\n<\/div>\n
<\/p>\n
Attribution<\/h2>\n
Figure 11.1.1<\/strong><\/p>\n
Heels by apostolos-vamvouras-_pdbqMcNWus<\/a> [photo] by Apostolos Vamvouras<\/a> on Unsplash<\/a> is used under the Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\n
Reference<\/h2>\n
Mayo Clinic Staff. (n.p.). Metatarsalgia [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/metatarsalgia\/symptoms-causes\/syc-20354790<\/p>\n
definition<\/span>Created by:\u00a0CK-12\/Adapted by Christine Miller<\/p>\n
\nFigure 4.3.1 A bacterium attacks a human erythrocyte. Both are cells.<\/em><\/figcaption><\/figure>\n Bacteria\u00a0Attack!<\/h1>\n<\/div>\n
The colourful image in Figure 4.3.1 shows a bacterial cell (in green) attacking human red blood cells. The bacterium causes a disease called relapsing fever. The bacterial and human cells look very different in size and shape. Although all living cells have certain things in common \u2014 such as a plasma membrane and cytoplasm \u2014 different types of cells, even within the same organism, may have their own unique structures and functions. Cells with different functions generally have different shapes that suit them for their particular job. Cells vary not only in shape, but also in size, as this example shows. In most organisms, however, even the largest cells are no bigger than the period at the end of this sentence. Why are cells so small?<\/p>\n
\nExplaining Cell Size<\/h1>\n<\/div>\n
Most organisms, even very large ones, have microscopic cells. Why don't cells get bigger instead of remaining tiny and multiplying? Why aren't you one giant cell rolling around school? What limits cell size?<\/p>\n
Once you know how a cell functions, the answers to these questions are clear. To carry out life processes, a cell must be able to quickly pass substances in and out of the cell. For example, it must be able to pass\u00a0nutrients\u00a0and oxygen into the cell and waste products out of the cell. Anything that enters or leaves a cell must cross its outer surface. The size of a cell is limited by its need to pass substances across that outer surface.<\/p>\n
Look at the three cubes in Figure 4.3.2. A larger cube has less surface area relative to its volume than a smaller cube. This relationship also applies to cells \u2014 a larger cell has less surface area relative to its volume than a smaller cell. A cell with a larger volume also needs more nutrients and oxygen, and produces more waste. Because all of these substances must pass through the surface of the cell, a cell with a large volume will not have enough surface area to allow it to meet its needs. The <\/span>larger<\/em> the cell is, the <\/span>smaller<\/em> its ratio of surface area to volume, and the more difficult it will be for the cell to get rid of its waste and take in necessary substances. This is what limits the size of the cell.<\/span><\/p>\n
<\/p>\n
<\/p>\n
<\/p>\n
Figure 4.3.2 Surface area to volume ratio.<\/em><\/figcaption><\/figure>\n \nCell Form and Function<\/h1>\n<\/div>\n
Cells with different functions often have varying shapes. The cells pictured below (Figure 4.3.3) are just a few examples of the many different shapes that human cells may have. Each type of cell\u00a0 has characteristics that help it do its job. The job of the nerve cell, for example, is to carry messages to other cells. The nerve cell has many long extensions that reach out in all directions, allowing it to pass messages to many other cells at once. Do you see the tail of each tiny sperm cell? Its tail helps a sperm cell \"swim\" through fluids in the female reproductive tract in order to reach an egg cell. The white blood cell has the job of destroying bacteria and other pathogens. It is a large cell that can engulf foreign invaders.<\/p>\n
\n\n<\/div>\n<\/div>\nFigure 4.3.3 Human cells may have many different shapes that help them to do their jobs.<\/em><\/p>\n<\/div>\n
\nCells With and Without a\u00a0Nucleus<\/h1>\n<\/div>\n
The\u00a0nucleus<\/a>\u00a0is a basic\u00a0cell structure\u00a0present in many \u2014 but not\u00a0all \u2014<\/em>\u00a0living cells. The\u00a0nucleus<\/a>\u00a0of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane) and contains\u00a0DNA<\/a>. Based on whether or not they have a nucleus, there are two basic types of cells: prokaryotic<\/a> cells and eukaryotic<\/a> cells.<\/p>\n
Prokaryotic Cells<\/h2>\n
Figure 4.3.3 Bacteria are prokaryotes, meaning they do not have a nucleus. Their DNA is contained in a region called the nucleoid.<\/em><\/figcaption><\/figure>\n Prokaryotic<\/a> cells<\/strong> are cells without a nucleus. The DNA<\/a> in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane.\u00a0 In addition, these cells are typically smaller than eukaryotic cells and contain fewer organelles.\u00a0 Prokaryotic cells are found in single-celled organisms, such as the bacterium represented by the model in Figure 4.3.3. Organisms with prokaryotic cells are called prokaryotes<\/strong>. They were the first type of organisms to evolve, and they are still the most common organisms today.<\/p>\n
\n<\/p>\n<\/div>\n
Eukaryotic Cells<\/h2>\n
Figure 4.3.4 Eukaryotic cells, like this animal cell, contain a nucleus and many other membrane-bound organelles.<\/em><\/figcaption><\/figure>\n Eukaryotic<\/a> cells<\/strong> are cells that contain a nucleus<\/a>. A typical eukaryotic cell is represented by the model in Figure 4.3.4. Eukaryotic cells are usually larger than prokaryotic cells. They are found in some single-celled and all multicellular organisms. Organisms with eukaryotic cells are called eukaryotes<\/strong>, and they range from\u00a0fungi\u00a0to\u00a0humans.<\/p>\n
Besides a nucleus, eukaryotic cells also contain other\u00a0organelles. An\u00a0organelle<\/a><\/strong>\u00a0is a structure within the cytoplasm that performs a specific job in the cell.\u00a0Organelles\u00a0called\u00a0mitochondria<\/a>, for example, provide\u00a0energy<\/a>\u00a0to the cell, and organelles called vesicles store substances in the cell. Organelles allow eukaryotic<\/a> cells to carry out more functions than prokaryotic<\/a> cells can.<\/p>\n
Interestingly, scientists think that mitochondria were once free-living prokaryotes that infected (or were engulfed by) larger cells. The two organisms developed a symbiotic relationship that was beneficial to both of them, resulting in the smaller prokaryote becoming an organelle within the larger cell. This is called endosymbiotic theory, and it is supported by a lot of evidence, including the fact that mitochondria<\/a> have their own DNA<\/a> separate from the DNA in the nucleus of the eukaryotic cell. Endosymbiotic theory will be described in more detail in later sections, and it's also discussed in the video below.<\/p>\n
\nhttps:\/\/www.youtube.com\/watch?v=FGnS-Xk0ZqU<\/p>\n
Endosymbiotic Theory, Amoeba Sisters, 2017.<\/p>\n
\n\n 4.3 Summary<\/h1>\n<\/header>\n
\n- \n
- Cells must be very small so they have a large enough surface area-to-volume ratio to maintain normal cell processes.<\/li>\n
- Cells with different functions often have different shapes.<\/li>\n
- Prokaryotic<\/a> cells do not have a nucleus. Eukaryotic <\/a>cells\u00a0do<\/em>\u00a0have a nucleus<\/a>, along with other\u00a0organelles<\/a>.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n\n\n
\n 4.3 Review Questions<\/span><\/h1>\n<\/header>\n
\n- \n
- Explain why most cells are very small.<\/li>\n
- Discuss variations in the form and function of cells.<\/li>\n
- \n\n