![\"11.2.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Skull_and_Crossbones.svg_-2.png\")
Figure 11.2.1 Bones can be quite jolly.<\/em>[\/caption]\r\n\r\nSkull and Cross-Bones<\/h1>\r\n<\/div>\r\nThe skull and cross-bones\u00a0symbol has been used for a very long time to represent death, perhaps because after death and decomposition, bones are all that remain. Many people think of bones as dead, dry, and brittle. These adjectives may correctly describe the bones of a preserved skeleton, but the bones of a living human being are very much alive. Living bones are also strong and flexible. Bones are the major organs of the [pb_glossary id=\"2906\"]skeletal system[\/pb_glossary].\r\n\r\nOverview of the Skeleton System<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"2906\"]skeletal system[\/pb_glossary]<\/strong>\u00a0is the organ system that provides an internal framework for the\u00a0human body. Why do you need a skeletal system? Try to imagine what you would look like without it. You would be a soft, wobbly pile of skin containing\u00a0muscles\u00a0and internal organs, but no bones. You might look something like a very large slug. Not that you would be able to see yourself \u2014 folds of skin would droop down over your\u00a0eyes\u00a0and block your\u00a0vision, because of your lack of skull bones. You could push the skin out of the way, if you could only move your arms, but you need bones for that, as well!\r\nComponents of the Skeletal System<\/h2>\r\nIn adults, the skeletal system includes 206 bones, many of which are shown in Figure 10.2.2 below. Bones are organs made of supportive connective tissues, mainly the tough protein collagen. Bones contain blood vessels, nerves, and other tissues, and they are hard and rigid, due to deposits of calcium and other mineral salts within their living tissues. Spots where two or more bones meet are called [pb_glossary id=\"3949\"]joints[\/pb_glossary]. Many joints allow bones to move like levers. Your elbow, for example, is a joint that allows you to bend and straighten your arm.\r\n\r\n[caption id=\"attachment_3950\" align=\"aligncenter\" width=\"1190\"]![\"11.2.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Skeleton-2.jpg\")
Figure 11.2.2 The adult skeleton contains 206 bones. A newborn infant has 270 bones, but many of them fuse together by adulthood.<\/em>[\/caption]\r\n\r\n\r\n\r\nBesides bones, the skeletal system includes cartilage and ligaments.<\/span>\r\n\r\n<\/div>\r\n\r\n \t- [pb_glossary id=\"3951\"]Cartilage[\/pb_glossary]<\/strong> is a type of dense connective tissue, made of tough protein fibres. It is strong, but flexible and very smooth. It covers the ends of bones at joints, providing a smooth surface for bones to move over.<\/li>\r\n \t
- [pb_glossary id=\"3952\"]Ligaments[\/pb_glossary]<\/strong> are bands of dense fibrous connective tissue that hold bones together. They keep the bones of the skeleton in place.<\/li>\r\n<\/ul>\r\n
Axial and Appendicular Skeletons<\/h2>\r\nThe skeleton is traditionally divided into two major parts: the axial skeleton and the appendicular skeleton, both of which are pictured below (Figure 10.2.3 and Figure 10.2.4 respectively).\r\n\r\n \t- The\u00a0[pb_glossary id=\"3953\"]axial skeleton[\/pb_glossary]<\/strong> forms the axis of the body. It includes the skull, vertebral column (spine), and rib cage. The bones of the axial skeleton \u2014 along with ligaments and\u00a0muscles\u00a0\u2014 allow the\u00a0human body\u00a0to maintain its upright posture. The axial skeleton also transmits\u00a0weight from the head, trunk, and upper extremities down the back to the lower extremities. In addition, the bones protect the brain and organs in the chest.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_3955\" align=\"aligncenter\" width=\"246\"]
![\"11.2.3](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Axial_skeleton_diagram_blank.svg_-2.png\")
Figure 11.2.3 The axial skeleton.<\/em>[\/caption]\r\n\r\n \t- The\u00a0[pb_glossary id=\"3954\"]appendicular skeleton[\/pb_glossary]<\/strong>\u00a0forms the appendages and their attachments to the axial skeleton. It includes the bones of the arms and legs, hands and feet, and shoulder and pelvic girdles. The bones of the appendicular skeleton make possible\u00a0locomotion\u00a0and other movements of the appendages. They also protect the major organs of digestion, excretion, and\u00a0reproduction.<\/li>\r\n<\/ul>\r\n\r\n\r\n[caption id=\"attachment_3956\" align=\"aligncenter\" width=\"296\"]
![\"11.2.4](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Appendicular_skeleton_diagram_blank.svg_-2.png\")
Figure 11.2.4 The appendicular skeleton.<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\n[h5p id=\"591\"]\r\nFunctions of the Skeletal System<\/h1>\r\n<\/div>\r\nThe skeletal system has many different functions that are necessary for human survival. Some of the functions, such as supporting the body, are relatively obvious. Other functions are less obvious but no less important.\u00a0Three tiny bones (hammer, anvil, and stirrup) inside the middle [pb_glossary id=\"5977\"]ear[\/pb_glossary], for example, transfer\u00a0sound waves\u00a0into the inner ear.\r\nSupport, Shape, and Protection<\/h2>\r\nThe skeleton supports the body and gives it shape. Without the rigid bones of the skeletal system, the\u00a0human body\u00a0would be just a bag of soft tissues, as described above. The bones of the skeleton are very hard and provide protection to the delicate tissues of internal organs. For example, the [pb_glossary id=\"3957\"]skull[\/pb_glossary] encloses and protects the soft tissues of the [pb_glossary id=\"5915\"]brain[\/pb_glossary], and the [pb_glossary id=\"3958\"]vertebral column[\/pb_glossary] protects the [pb_glossary id=\"2818\"]nervous tissues[\/pb_glossary]\u00a0of the [pb_glossary id=\"3010\"]spinal cord[\/pb_glossary]. The vertebral column, [pb_glossary id=\"5601\"]ribcage[\/pb_glossary], and sternum (breast bone) protect the [pb_glossary id=\"2987\"]heart[\/pb_glossary], [pb_glossary id=\"2990\"]lungs[\/pb_glossary], and major [pb_glossary id=\"5835\"]blood vessels[\/pb_glossary]. Providing protection to these latter internal organs requires the bones to be able to expand and contract. The ribs and the cartilage that connects them to the sternum and vertebrae are capable of small shifts that allow breathing and other internal organ movements.\r\nMovement<\/h2>\r\n[caption id=\"attachment_3960\" align=\"alignright\" width=\"338\"]![\"11.2.5](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Animation_triceps_biceps-2.gif\")
Figure 11.2.5 Bones that meet at the elbow and shoulder joint include the scapula, humerus, radius and ulna. These bones provide attachment surfaces for muscles that move the bones at the joint.<\/em>[\/caption]\r\n\r\nThe bones of the skeleton provide attachment surfaces for skeletal muscles. When the muscles contract, they pull on and move the bones. Figure 11.2.5, for example, shows the muscles attached to the bones at the elbow and shoulder. They help stabilize the joint and allow the arm to bend at these two joints. The bones at joints act like levers moving at a fulcrum point, and the muscles attached to the bones apply the force needed for movement.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\nHematopoiesis<\/h2>\r\n[pb_glossary id=\"3961\"]Hematopoiesis[\/pb_glossary]<\/strong>\u00a0is the process by which\u00a0blood\u00a0cells\u00a0are produced. This process occurs in a tissue called [pb_glossary id=\"3962\"]red marrow[\/pb_glossary], which is found inside some bones, including the [pb_glossary id=\"3963\"]pelvis[\/pb_glossary], [pb_glossary id=\"5601\"]ribs[\/pb_glossary], and [pb_glossary id=\"3964\"]vertebrae[\/pb_glossary]. Red marrow synthesizes red blood cells, white blood cells, and platelets. Billions of these blood cells are produced inside the bones every day.\r\nMineral Storage and\u00a0Homeostasis<\/h2>\r\nAnother function of the skeletal system is storing\u00a0minerals, especially [pb_glossary id=\"3965\"]calcium[\/pb_glossary] and [pb_glossary id=\"3966\"]phosphorus[\/pb_glossary]. This storage function is related to the role of bones in maintaining mineral\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary]. Just the right levels of calcium and other minerals are needed in the\u00a0blood\u00a0for normal functioning of the body. When mineral levels in the blood are too high, bones absorb some of the minerals and store them as mineral salts, which is why bones are so hard. When blood levels of minerals are too low, bones release some of the minerals back into the blood. Bone minerals are alkaline (basic), so their release into the blood\u00a0buffers\u00a0the blood against excessive acidity (low pH), whereas their absorption back into bones buffers the blood against excessive alkalinity (high pH). In this way, bones help maintain acid-base\u00a0homeostasis in the blood.\r\n\r\nAnother way that bones help maintain\u00a0homeostasis\u00a0is by acting as an endocrine organ. One endocrine\u00a0hormone\u00a0secreted by bone\u00a0cells\u00a0is\u00a0[pb_glossary id=\"3967\"]osteocalcin[\/pb_glossary],<\/strong>\u00a0which helps regulate\u00a0blood\u00a0[pb_glossary id=\"5451\"]glucose[\/pb_glossary] and fat\u00a0deposition. It increases [pb_glossary id=\"2590\"]insulin[\/pb_glossary] secretion, as well as\u00a0cell's sensitivity\u00a0to insulin. In addition, it boosts the number of insulin-producing\u00a0cells\u00a0and reduces fat stores.\r\n\r\nSexual Dimorphism of the Human Skeleton<\/h1>\r\n<\/div>\r\nThe human skeleton is not as [pb_glossary id=\"3906\"]sexually dimorphic[\/pb_glossary] as that of many other primate species, although human female skeletons tend to be smaller and less robust than human male skeletons within a given population. There are also subtle differences between males and females in the morphology of the skull, teeth, longs bones, and pelvis. The greatest difference is in the pelvis, because the female pelvis is adapted for child birth.\u00a0 Take a look at the pelvises in Figure 11.2.6 and 11.2.7.\u00a0 How are they different?\r\n
Overview of the Skeleton System<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"2906\"]skeletal system[\/pb_glossary]<\/strong>\u00a0is the organ system that provides an internal framework for the\u00a0human body. Why do you need a skeletal system? Try to imagine what you would look like without it. You would be a soft, wobbly pile of skin containing\u00a0muscles\u00a0and internal organs, but no bones. You might look something like a very large slug. Not that you would be able to see yourself \u2014 folds of skin would droop down over your\u00a0eyes\u00a0and block your\u00a0vision, because of your lack of skull bones. You could push the skin out of the way, if you could only move your arms, but you need bones for that, as well!\r\nComponents of the Skeletal System<\/h2>\r\nIn adults, the skeletal system includes 206 bones, many of which are shown in Figure 10.2.2 below. Bones are organs made of supportive connective tissues, mainly the tough protein collagen. Bones contain blood vessels, nerves, and other tissues, and they are hard and rigid, due to deposits of calcium and other mineral salts within their living tissues. Spots where two or more bones meet are called [pb_glossary id=\"3949\"]joints[\/pb_glossary]. Many joints allow bones to move like levers. Your elbow, for example, is a joint that allows you to bend and straighten your arm.\r\n\r\n[caption id=\"attachment_3950\" align=\"aligncenter\" width=\"1190\"] Figure 11.2.2 The adult skeleton contains 206 bones. A newborn infant has 270 bones, but many of them fuse together by adulthood.<\/em>[\/caption]\r\n\r\n\r\n\r\nBesides bones, the skeletal system includes cartilage and ligaments.<\/span>\r\n\r\n<\/div>\r\n\r\n \t- [pb_glossary id=\"3951\"]Cartilage[\/pb_glossary]<\/strong> is a type of dense connective tissue, made of tough protein fibres. It is strong, but flexible and very smooth. It covers the ends of bones at joints, providing a smooth surface for bones to move over.<\/li>\r\n \t
- [pb_glossary id=\"3952\"]Ligaments[\/pb_glossary]<\/strong> are bands of dense fibrous connective tissue that hold bones together. They keep the bones of the skeleton in place.<\/li>\r\n<\/ul>\r\n
Axial and Appendicular Skeletons<\/h2>\r\nThe skeleton is traditionally divided into two major parts: the axial skeleton and the appendicular skeleton, both of which are pictured below (Figure 10.2.3 and Figure 10.2.4 respectively).\r\n\r\n \t- The\u00a0[pb_glossary id=\"3953\"]axial skeleton[\/pb_glossary]<\/strong> forms the axis of the body. It includes the skull, vertebral column (spine), and rib cage. The bones of the axial skeleton \u2014 along with ligaments and\u00a0muscles\u00a0\u2014 allow the\u00a0human body\u00a0to maintain its upright posture. The axial skeleton also transmits\u00a0weight from the head, trunk, and upper extremities down the back to the lower extremities. In addition, the bones protect the brain and organs in the chest.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_3955\" align=\"aligncenter\" width=\"246\"] Figure 11.2.3 The axial skeleton.<\/em>[\/caption]\r\n
\r\n \t- The\u00a0[pb_glossary id=\"3954\"]appendicular skeleton[\/pb_glossary]<\/strong>\u00a0forms the appendages and their attachments to the axial skeleton. It includes the bones of the arms and legs, hands and feet, and shoulder and pelvic girdles. The bones of the appendicular skeleton make possible\u00a0locomotion\u00a0and other movements of the appendages. They also protect the major organs of digestion, excretion, and\u00a0reproduction.<\/li>\r\n<\/ul>\r\n\r\n\r\n[caption id=\"attachment_3956\" align=\"aligncenter\" width=\"296\"] Figure 11.2.4 The appendicular skeleton.<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\n[h5p id=\"591\"]\r\n
Functions of the Skeletal System<\/h1>\r\n<\/div>\r\nThe skeletal system has many different functions that are necessary for human survival. Some of the functions, such as supporting the body, are relatively obvious. Other functions are less obvious but no less important.\u00a0Three tiny bones (hammer, anvil, and stirrup) inside the middle [pb_glossary id=\"5977\"]ear[\/pb_glossary], for example, transfer\u00a0sound waves\u00a0into the inner ear.\r\nSupport, Shape, and Protection<\/h2>\r\nThe skeleton supports the body and gives it shape. Without the rigid bones of the skeletal system, the\u00a0human body\u00a0would be just a bag of soft tissues, as described above. The bones of the skeleton are very hard and provide protection to the delicate tissues of internal organs. For example, the [pb_glossary id=\"3957\"]skull[\/pb_glossary] encloses and protects the soft tissues of the [pb_glossary id=\"5915\"]brain[\/pb_glossary], and the [pb_glossary id=\"3958\"]vertebral column[\/pb_glossary] protects the [pb_glossary id=\"2818\"]nervous tissues[\/pb_glossary]\u00a0of the [pb_glossary id=\"3010\"]spinal cord[\/pb_glossary]. The vertebral column, [pb_glossary id=\"5601\"]ribcage[\/pb_glossary], and sternum (breast bone) protect the [pb_glossary id=\"2987\"]heart[\/pb_glossary], [pb_glossary id=\"2990\"]lungs[\/pb_glossary], and major [pb_glossary id=\"5835\"]blood vessels[\/pb_glossary]. Providing protection to these latter internal organs requires the bones to be able to expand and contract. The ribs and the cartilage that connects them to the sternum and vertebrae are capable of small shifts that allow breathing and other internal organ movements.\r\nMovement<\/h2>\r\n[caption id=\"attachment_3960\" align=\"alignright\" width=\"338\"] Figure 11.2.5 Bones that meet at the elbow and shoulder joint include the scapula, humerus, radius and ulna. These bones provide attachment surfaces for muscles that move the bones at the joint.<\/em>[\/caption]\r\n\r\nThe bones of the skeleton provide attachment surfaces for skeletal muscles. When the muscles contract, they pull on and move the bones. Figure 11.2.5, for example, shows the muscles attached to the bones at the elbow and shoulder. They help stabilize the joint and allow the arm to bend at these two joints. The bones at joints act like levers moving at a fulcrum point, and the muscles attached to the bones apply the force needed for movement.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\nHematopoiesis<\/h2>\r\n[pb_glossary id=\"3961\"]Hematopoiesis[\/pb_glossary]<\/strong>\u00a0is the process by which\u00a0blood\u00a0cells\u00a0are produced. This process occurs in a tissue called [pb_glossary id=\"3962\"]red marrow[\/pb_glossary], which is found inside some bones, including the [pb_glossary id=\"3963\"]pelvis[\/pb_glossary], [pb_glossary id=\"5601\"]ribs[\/pb_glossary], and [pb_glossary id=\"3964\"]vertebrae[\/pb_glossary]. Red marrow synthesizes red blood cells, white blood cells, and platelets. Billions of these blood cells are produced inside the bones every day.\r\nMineral Storage and\u00a0Homeostasis<\/h2>\r\nAnother function of the skeletal system is storing\u00a0minerals, especially [pb_glossary id=\"3965\"]calcium[\/pb_glossary] and [pb_glossary id=\"3966\"]phosphorus[\/pb_glossary]. This storage function is related to the role of bones in maintaining mineral\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary]. Just the right levels of calcium and other minerals are needed in the\u00a0blood\u00a0for normal functioning of the body. When mineral levels in the blood are too high, bones absorb some of the minerals and store them as mineral salts, which is why bones are so hard. When blood levels of minerals are too low, bones release some of the minerals back into the blood. Bone minerals are alkaline (basic), so their release into the blood\u00a0buffers\u00a0the blood against excessive acidity (low pH), whereas their absorption back into bones buffers the blood against excessive alkalinity (high pH). In this way, bones help maintain acid-base\u00a0homeostasis in the blood.\r\n\r\nAnother way that bones help maintain\u00a0homeostasis\u00a0is by acting as an endocrine organ. One endocrine\u00a0hormone\u00a0secreted by bone\u00a0cells\u00a0is\u00a0[pb_glossary id=\"3967\"]osteocalcin[\/pb_glossary],<\/strong>\u00a0which helps regulate\u00a0blood\u00a0[pb_glossary id=\"5451\"]glucose[\/pb_glossary] and fat\u00a0deposition. It increases [pb_glossary id=\"2590\"]insulin[\/pb_glossary] secretion, as well as\u00a0cell's sensitivity\u00a0to insulin. In addition, it boosts the number of insulin-producing\u00a0cells\u00a0and reduces fat stores.\r\n\r\nSexual Dimorphism of the Human Skeleton<\/h1>\r\n<\/div>\r\nThe human skeleton is not as [pb_glossary id=\"3906\"]sexually dimorphic[\/pb_glossary] as that of many other primate species, although human female skeletons tend to be smaller and less robust than human male skeletons within a given population. There are also subtle differences between males and females in the morphology of the skull, teeth, longs bones, and pelvis. The greatest difference is in the pelvis, because the female pelvis is adapted for child birth.\u00a0 Take a look at the pelvises in Figure 11.2.6 and 11.2.7.\u00a0 How are they different?\r\n
Figure 11.2.2 The adult skeleton contains 206 bones. A newborn infant has 270 bones, but many of them fuse together by adulthood.<\/em>[\/caption]\r\n\r\n\r\n\r\nBesides bones, the skeletal system includes cartilage and ligaments.<\/span>\r\n\r\n<\/div>\r\n
- \r\n \t
- [pb_glossary id=\"3951\"]Cartilage[\/pb_glossary]<\/strong> is a type of dense connective tissue, made of tough protein fibres. It is strong, but flexible and very smooth. It covers the ends of bones at joints, providing a smooth surface for bones to move over.<\/li>\r\n \t
- [pb_glossary id=\"3952\"]Ligaments[\/pb_glossary]<\/strong> are bands of dense fibrous connective tissue that hold bones together. They keep the bones of the skeleton in place.<\/li>\r\n<\/ul>\r\n
Axial and Appendicular Skeletons<\/h2>\r\nThe skeleton is traditionally divided into two major parts: the axial skeleton and the appendicular skeleton, both of which are pictured below (Figure 10.2.3 and Figure 10.2.4 respectively).\r\n
- \r\n \t
- The\u00a0[pb_glossary id=\"3953\"]axial skeleton[\/pb_glossary]<\/strong> forms the axis of the body. It includes the skull, vertebral column (spine), and rib cage. The bones of the axial skeleton \u2014 along with ligaments and\u00a0muscles\u00a0\u2014 allow the\u00a0human body\u00a0to maintain its upright posture. The axial skeleton also transmits\u00a0weight from the head, trunk, and upper extremities down the back to the lower extremities. In addition, the bones protect the brain and organs in the chest.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_3955\" align=\"aligncenter\" width=\"246\"] Figure 11.2.3 The axial skeleton.<\/em>[\/caption]\r\n
- \r\n \t
- The\u00a0[pb_glossary id=\"3954\"]appendicular skeleton[\/pb_glossary]<\/strong>\u00a0forms the appendages and their attachments to the axial skeleton. It includes the bones of the arms and legs, hands and feet, and shoulder and pelvic girdles. The bones of the appendicular skeleton make possible\u00a0locomotion\u00a0and other movements of the appendages. They also protect the major organs of digestion, excretion, and\u00a0reproduction.<\/li>\r\n<\/ul>\r\n\r\n\r\n[caption id=\"attachment_3956\" align=\"aligncenter\" width=\"296\"] Figure 11.2.4 The appendicular skeleton.<\/em>[\/caption]\r\n\r\n<\/div>\r\n\r\n\r\n[h5p id=\"591\"]\r\n
Functions of the Skeletal System<\/h1>\r\n<\/div>\r\nThe skeletal system has many different functions that are necessary for human survival. Some of the functions, such as supporting the body, are relatively obvious. Other functions are less obvious but no less important.\u00a0Three tiny bones (hammer, anvil, and stirrup) inside the middle [pb_glossary id=\"5977\"]ear[\/pb_glossary], for example, transfer\u00a0sound waves\u00a0into the inner ear.\r\n
Support, Shape, and Protection<\/h2>\r\nThe skeleton supports the body and gives it shape. Without the rigid bones of the skeletal system, the\u00a0human body\u00a0would be just a bag of soft tissues, as described above. The bones of the skeleton are very hard and provide protection to the delicate tissues of internal organs. For example, the [pb_glossary id=\"3957\"]skull[\/pb_glossary] encloses and protects the soft tissues of the [pb_glossary id=\"5915\"]brain[\/pb_glossary], and the [pb_glossary id=\"3958\"]vertebral column[\/pb_glossary] protects the [pb_glossary id=\"2818\"]nervous tissues[\/pb_glossary]\u00a0of the [pb_glossary id=\"3010\"]spinal cord[\/pb_glossary]. The vertebral column, [pb_glossary id=\"5601\"]ribcage[\/pb_glossary], and sternum (breast bone) protect the [pb_glossary id=\"2987\"]heart[\/pb_glossary], [pb_glossary id=\"2990\"]lungs[\/pb_glossary], and major [pb_glossary id=\"5835\"]blood vessels[\/pb_glossary]. Providing protection to these latter internal organs requires the bones to be able to expand and contract. The ribs and the cartilage that connects them to the sternum and vertebrae are capable of small shifts that allow breathing and other internal organ movements.\r\n
Movement<\/h2>\r\n[caption id=\"attachment_3960\" align=\"alignright\" width=\"338\"]
Figure 11.2.5 Bones that meet at the elbow and shoulder joint include the scapula, humerus, radius and ulna. These bones provide attachment surfaces for muscles that move the bones at the joint.<\/em>[\/caption]\r\n\r\nThe bones of the skeleton provide attachment surfaces for skeletal muscles. When the muscles contract, they pull on and move the bones. Figure 11.2.5, for example, shows the muscles attached to the bones at the elbow and shoulder. They help stabilize the joint and allow the arm to bend at these two joints. The bones at joints act like levers moving at a fulcrum point, and the muscles attached to the bones apply the force needed for movement.\r\n\r\n \r\n\r\n\r\n \r\n\r\n<\/div>\r\nHematopoiesis<\/h2>\r\n[pb_glossary id=\"3961\"]Hematopoiesis[\/pb_glossary]<\/strong>\u00a0is the process by which\u00a0blood\u00a0cells\u00a0are produced. This process occurs in a tissue called [pb_glossary id=\"3962\"]red marrow[\/pb_glossary], which is found inside some bones, including the [pb_glossary id=\"3963\"]pelvis[\/pb_glossary], [pb_glossary id=\"5601\"]ribs[\/pb_glossary], and [pb_glossary id=\"3964\"]vertebrae[\/pb_glossary]. Red marrow synthesizes red blood cells, white blood cells, and platelets. Billions of these blood cells are produced inside the bones every day.\r\n
Mineral Storage and\u00a0Homeostasis<\/h2>\r\nAnother function of the skeletal system is storing\u00a0minerals, especially [pb_glossary id=\"3965\"]calcium[\/pb_glossary] and [pb_glossary id=\"3966\"]phosphorus[\/pb_glossary]. This storage function is related to the role of bones in maintaining mineral\u00a0[pb_glossary id=\"5761\"]homeostasis[\/pb_glossary]. Just the right levels of calcium and other minerals are needed in the\u00a0blood\u00a0for normal functioning of the body. When mineral levels in the blood are too high, bones absorb some of the minerals and store them as mineral salts, which is why bones are so hard. When blood levels of minerals are too low, bones release some of the minerals back into the blood. Bone minerals are alkaline (basic), so their release into the blood\u00a0buffers\u00a0the blood against excessive acidity (low pH), whereas their absorption back into bones buffers the blood against excessive alkalinity (high pH). In this way, bones help maintain acid-base\u00a0homeostasis in the blood.\r\n\r\nAnother way that bones help maintain\u00a0homeostasis\u00a0is by acting as an endocrine organ. One endocrine\u00a0hormone\u00a0secreted by bone\u00a0cells\u00a0is\u00a0[pb_glossary id=\"3967\"]osteocalcin[\/pb_glossary],<\/strong>\u00a0which helps regulate\u00a0blood\u00a0[pb_glossary id=\"5451\"]glucose[\/pb_glossary] and fat\u00a0deposition. It increases [pb_glossary id=\"2590\"]insulin[\/pb_glossary] secretion, as well as\u00a0cell's sensitivity\u00a0to insulin. In addition, it boosts the number of insulin-producing\u00a0cells\u00a0and reduces fat stores.\r\n
\r\nSexual Dimorphism of the Human Skeleton<\/h1>\r\n<\/div>\r\nThe human skeleton is not as [pb_glossary id=\"3906\"]sexually dimorphic[\/pb_glossary] as that of many other primate species, although human female skeletons tend to be smaller and less robust than human male skeletons within a given population. There are also subtle differences between males and females in the morphology of the skull, teeth, longs bones, and pelvis. The greatest difference is in the pelvis, because the female pelvis is adapted for child birth.\u00a0 Take a look at the pelvises in Figure 11.2.6 and 11.2.7.\u00a0 How are they different?\r\n
- The\u00a0[pb_glossary id=\"3954\"]appendicular skeleton[\/pb_glossary]<\/strong>\u00a0forms the appendages and their attachments to the axial skeleton. It includes the bones of the arms and legs, hands and feet, and shoulder and pelvic girdles. The bones of the appendicular skeleton make possible\u00a0locomotion\u00a0and other movements of the appendages. They also protect the major organs of digestion, excretion, and\u00a0reproduction.<\/li>\r\n<\/ul>\r\n
- [pb_glossary id=\"3952\"]Ligaments[\/pb_glossary]<\/strong> are bands of dense fibrous connective tissue that hold bones together. They keep the bones of the skeleton in place.<\/li>\r\n<\/ul>\r\n
![\"11.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Male-pelvisGray241-2.png\")
Figure 11.2.6 The male pelvis.[\/caption]<\/td>\r\n![\"11.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Female-pelvisGray242-2.png\")
Figure 11.2.7 The female pelvis[\/caption]<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n![\"11.2.1](\"https:\/\/commons.wikimedia.org\/wiki\/File:Skull_and_Crossbones.svg\")
![Skeleton<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:801_Appendicular_Skeleton.jpg\"){kind=link}
![Axial_skeleton_diagram_blank.svg<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Axial_skeleton_diagram_blank.svg\"){kind=link}
![Axial skeleton diagram.svg<\/a>, by Mariana Ruiz Villarreal [](\"https:\/\/commons.wikimedia.org\/wiki\/File:Axial_skeleton_diagram.svg\"){kind=link}
![Appendicular_skeleton_diagram_blank.svg<\/a> by by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Appendicular_skeleton_diagram_blank.svg\"){kind=link}
![Appendicular_skeleton_diagram.svg<\/a>, by Mariana Ruiz Villarreal [](\"https:\/\/commons.wikimedia.org\/wiki\/File:Appendicular_skeleton_diagram.svg\"){kind=link}
![Animation_triceps_biceps<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Animation_triceps_biceps.gif\"){kind=link}
![Male pelvisGray241<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Gray241.png\"){kind=link}