{"id":4985,"date":"2015-10-28T15:56:13","date_gmt":"2015-10-28T15:56:13","guid":{"rendered":"https:\/\/opentextbc.ca\/biology\/chapter\/19-2-bone\/"},"modified":"2021-03-04T00:08:22","modified_gmt":"2021-03-04T00:08:22","slug":"19-2-bone","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/biology\/chapter\/19-2-bone\/","title":{"raw":"19.2\u00a0Bone","rendered":"19.2\u00a0Bone"},"content":{"raw":"<div class=\"section module\" title=\"38.2.\u00a0Bone\" xml:lang=\"en\">\n<div class=\"titlepage\">\n<div class=\"abstract\">\n<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\nBy the end of this section, you will be able to:\n<div class=\"itemizedlist\">\n<ul class=\"itemizedlist\">\n \t<li class=\"listitem\">Classify the different types of bones in the skeleton<\/li>\n \t<li class=\"listitem\">Explain the role of the different cell types in bone<\/li>\n \t<li class=\"listitem\">Explain how bone forms during development<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm54620432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1241294\"> <\/span><strong>Bone<a id=\"id804519\" class=\"indexterm\" href=\"\"><\/a><\/strong>, or <strong><span id=\"m44789-autoid-cnx2dbk-id1241303\"> <\/span>osseous tissue<a id=\"id804532\" class=\"indexterm\" href=\"\"><\/a><\/strong>, is a connective tissue that constitutes the endoskeleton. It contains specialized cells and a matrix of mineral salts and collagen fibers.\n\n<span id=\"m44789-fs-idm84548880\"> <\/span>The mineral salts primarily include hydroxyapatite, a mineral formed from calcium phosphate. <span id=\"m44789-autoid-cnx2dbk-id1241314\"> <\/span><strong>Calcification<a id=\"id804555\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the process of deposition of mineral salts on the collagen fiber matrix that crystallizes and hardens the tissue. The process of calcification only occurs in the presence of collagen fibers.\n\n<span id=\"m44789-fs-idm96433616\"> <\/span>The bones of the human skeleton are classified by their shape: long bones, short bones, flat bones, sutural bones, sesamoid bones, and irregular bones (Figure 19.16).\n\n[caption id=\"attachment_1255\" align=\"aligncenter\" width=\"500\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_01.jpg\"><img class=\"wp-image-4977\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1.jpg\" alt=\"Figure\u00a038.16.\u00a0 Shown are different types of bones: flat, irregular, long, short, and sesamoid.\" width=\"500\" height=\"535\"><\/a> Figure 19.16. Shown are different types of bones: flat, irregular, long, short, and sesamoid.[\/caption]\n\n<div id=\"m44789-fig-ch38_02_01\" class=\"figure\" title=\"Figure\u00a038.16.\u00a0\">\n\n<span id=\"m44789-fs-idp48592256\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1241365\"> <\/span><strong>Long bones<\/strong> are longer than they are wide and have a shaft and two ends. The <strong><span id=\"m44789-autoid-cnx2dbk-id1241368\"> <\/span>diaphysis<\/strong>, or central shaft, contains bone marrow in a marrow cavity. The rounded ends, the <span id=\"m44789-autoid-cnx2dbk-id1268435\"> <\/span><strong>epiphyses<\/strong>, are covered with articular cartilage and are filled with red bone marrow, which produces blood cells (Figure 19.17). Most of the limb bones are long bones\u2014for example, the femur, tibia, ulna, and radius. Exceptions to this include the patella and the bones of the wrist and ankle.\n\n[caption id=\"attachment_1256\" align=\"aligncenter\" width=\"300\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_02.jpg\"><img class=\"wp-image-4978\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02.jpg\" alt=\"Figure\u00a038.17.\u00a0 The long bone is covered by articular cartilage at either end and contains bone marrow (shown in yellow in this illustration) in the marrow cavity.\" width=\"300\" height=\"413\"><\/a> Figure 19.17.\u00a0<br>The long bone is covered by articular cartilage at either end and contains bone marrow (shown in yellow in this illustration) in the marrow cavity.[\/caption]\n\n<div id=\"m44789-fig-ch38_02_02\" class=\"figure\" title=\"Figure\u00a038.17.\u00a0\">\n\n<span id=\"m44789-fs-idm152546016\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268483\"> <\/span><strong>Short bones<\/strong>, or cuboidal bones, are bones that are the same width and length, giving them a cube-like shape. For example, the bones of the wrist (carpals) and ankle (tarsals) are short bones (<a class=\"xref target-figure\" title=\"Figure\u00a038.16.\u00a0\" href=\"#attachment_1255\">Figure 19.16<\/a>).\n\n<span id=\"m44789-fs-idp18280432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268500\"> <\/span><strong>Flat bones<\/strong> are thin and relatively broad bones that are found where extensive protection of organs is required or where broad surfaces of muscle attachment are required. Examples of flat bones are the sternum (breast bone), ribs, scapulae (shoulder blades), and the roof of the skull (<a class=\"xref target-figure\" title=\"Figure\u00a038.16.\u00a0\" href=\"#attachment_1255\">Figure 19.16<\/a>).\n\n<span id=\"m44789-fs-idm124655504\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268517\"> <\/span><strong>Irregular bones<a id=\"id804781\" class=\"indexterm\" href=\"\"><\/a><\/strong> are bones with complex shapes. These bones may have short, flat, notched, or ridged surfaces. Examples of irregular bones are the vertebrae, hip bones, and several skull bones.\n\n<span id=\"m44789-fs-idp6133120\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268527\"> <\/span><strong>Sesamoid bones<\/strong> are small, flat bones and are shaped similarly to a sesame seed. The patellae are sesamoid bones (Figure 19.18). Sesamoid bones develop inside tendons and may be found near joints at the knees, hands, and feet.\n\n[caption id=\"attachment_1257\" align=\"aligncenter\" width=\"250\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_03.jpg\"><img class=\"wp-image-4979\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03.jpg\" alt=\"Figure\u00a038.18.\u00a0 The patella of the knee is an example of a sesamoid bone.\" width=\"250\" height=\"250\"><\/a> Figure 19.18.\u00a0<br>The patella of the knee is an example of a sesamoid bone.[\/caption]\n\n<div id=\"m44789-fig-ch38_02_03\" class=\"figure\" title=\"Figure\u00a038.18.\u00a0\">\n\n<span id=\"m44789-fs-idm124049840\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1305692\"> <\/span><strong>Sutural bones<\/strong><a id=\"id804863\" class=\"indexterm\" href=\"\"><\/a> are small, flat, irregularly shaped bones. They may be found between the flat bones of the skull. They vary in number, shape, size, and position.\n<div class=\"section\" title=\"Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm5626320\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idp1203136\"> <\/span>Bones are considered organs because they contain various types of tissue, such as blood, connective tissue, nerves, and bone tissue. Osteocytes, the living cells of bone tissue, form the mineral matrix of bones. There are two types of bone tissue: compact and spongy.\n<div class=\"section\" title=\"Compact Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm149839456\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Compact Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idp54336560\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1305729\"> <\/span><strong>Compact bone<\/strong> (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. It provides protection and strength to bones. Compact bone tissue consists of units called osteons or Haversian systems. <span id=\"m44789-autoid-cnx2dbk-id1305735\"> <\/span><strong>Osteons<\/strong> are cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi, which transport blood. They are aligned parallel to the long axis of the bone. Each osteon consists of <span id=\"m44789-autoid-cnx2dbk-id1305740\"> <\/span><strong>lamellae<\/strong>, which are layers of compact matrix that surround a central canal called the Haversian canal. The <span id=\"m44789-autoid-cnx2dbk-id1305745\"> <\/span><strong>Haversian canal<\/strong> <strong>(osteonic canal)<\/strong> contains the bone\u2019s blood vessels and nerve fibers (Figure 19.19). Osteons in compact bone tissue are aligned in the same direction along lines of stress and help the bone resist bending or fracturing. Therefore, compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions.\n\n<\/div>\n<\/div>\n<div id=\"m44789-fs-idm6377616\" class=\"note art-connection\">\n<div class=\"title\">\n<div class=\"title\">\n\n[caption id=\"attachment_1258\" align=\"aligncenter\" width=\"350\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_04.png\"><img class=\"wp-image-4980\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04.png\" alt=\"Figure_38_02_04\" width=\"350\" height=\"310\"><\/a> Figure 19.19.\u00a0 Compact bone tissue consists of osteons that are aligned parallel to the long axis of the bone, and the Haversian canal that contains the bone\u2019s blood vessels and nerve fibers. The inner layer of bones consists of spongy bone tissue. The small dark ovals in the osteon represent the living osteocytes. (credit: modification of work by NCI, NIH)[\/caption]\n\n<\/div>\n<div class=\"body\">\n<div id=\"m44789-fig-ch38_02_04\" class=\"figure\" title=\"Figure\u00a038.19.\u00a0\">\n\n<span id=\"m44789-fs-idm52317584\"> <\/span>Which of the following statements about bone tissue is false?\n<div class=\"orderedlist\">\n<ol class=\"orderedlist\">\n \t<li class=\"listitem\">Compact bone tissue is made of cylindrical osteons that are aligned such that they travel the length of the bone.<\/li>\n \t<li class=\"listitem\">Haversian canals contain blood vessels only.<\/li>\n \t<li class=\"listitem\">Haversian canals contain blood vessels and nerve fibers.<\/li>\n \t<li class=\"listitem\">Spongy tissue is found on the interior of the bone, and compact bone tissue is found on the exterior.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Spongy Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idp27296784\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Spongy Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm1194288\"> <\/span>Whereas compact bone tissue forms the outer layer of all bones, <span id=\"m44789-autoid-cnx2dbk-id1411214\"> <\/span><strong>spongy bone<a id=\"id805094\" class=\"indexterm\" href=\"\"><\/a><\/strong> or cancellous bone forms the inner layer of all bones. Spongy bone tissue does not contain osteons that constitute compact bone tissue. Instead, it consists of <span id=\"m44789-autoid-cnx2dbk-id1411220\"> <\/span><strong>trabeculae<a id=\"id805109\" class=\"indexterm\" href=\"\"><\/a><\/strong>, which are lamellae that are arranged as rods or plates. Red bone marrow is found between the trabuculae. Blood vessels within this tissue deliver nutrients to osteocytes and remove waste. The red bone marrow of the femur and the interior of other large bones, such as the ileum, forms blood cells.\n\n<span id=\"m44789-fs-idm202492784\"> <\/span>Spongy bone reduces the density of bone and allows the ends of long bones to compress as the result of stresses applied to the bone. Spongy bone is prominent in areas of bones that are not heavily stressed or where stresses arrive from many directions. The epiphyses of bones, such as the neck of the femur, are subject to stress from many directions. Imagine laying a heavy framed picture flat on the floor. You could hold up one side of the picture with a toothpick if the toothpick was perpendicular to the floor and the picture. Now drill a hole and stick the toothpick into the wall to hang up the picture. In this case, the function of the toothpick is to transmit the downward pressure of the picture to the wall. The force on the picture is straight down to the floor, but the force on the toothpick is both the picture wire pulling down and the bottom of the hole in the wall pushing up. The toothpick will break off right at the wall.\n\n<span id=\"m44789-fs-idp54392224\"> <\/span>The neck of the femur is horizontal like the toothpick in the wall. The weight of the body pushes it down near the joint, but the vertical diaphysis of the femur pushes it up at the other end. The neck of the femur must be strong enough to transfer the downward force of the body weight horizontally to the vertical shaft of the femur (Figure 19.20).\n\n[caption id=\"attachment_1259\" align=\"aligncenter\" width=\"300\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_05.jpg\"><img class=\"wp-image-4981\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05.jpg\" alt=\"Figure\u00a038.20.\u00a0 Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.\" width=\"300\" height=\"290\"><\/a> Figure 19.20.\u00a0<br>Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.[\/caption]\n\n<div id=\"m44789-fig-ch38_02_05\" class=\"figure\" title=\"Figure\u00a038.20.\u00a0\">\n<div id=\"m44789-fs-idm221406720\" class=\"note interactive\">\n<h2 class=\"title\"><span class=\"cnx-gentext-tip-t\">Concept in Action\n<\/span><\/h2>\n<div class=\"body\">\n<div class=\"mediaobject\"><span id=\"m44789-fs-idm203119296\"> <\/span><img src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/muscle_tissue.png\" alt=\"QR Code representing a URL\" width=\"120\"><\/div>\n<span id=\"m44789-fs-idp21378560\"> <\/span>View <a class=\"link\" href=\"http:\/\/openstaxcollege.org\/l\/muscle_tissue\" target=\"\" rel=\"noopener noreferrer\">micrographs<\/a> of musculoskeletal tissues as you review the anatomy.\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Cell Types in Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h3 id=\"m44789-fs-idm176180400\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Cell Types in Bones<\/span><\/span><\/h3>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm202474080\"> <\/span>Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. <span id=\"m44789-autoid-cnx2dbk-id1410999\"> <\/span><strong>Osteoblasts<a id=\"id805265\" class=\"indexterm\" href=\"\"><\/a><\/strong> are bone cells that are responsible for bone formation. Osteoblasts synthesize and secrete the organic part and inorganic part of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts become trapped in these secretions and differentiate into less active osteocytes. <span id=\"m44789-autoid-cnx2dbk-id1411005\"> <\/span><strong>Osteoclasts<a id=\"id805281\" class=\"indexterm\" href=\"\"><\/a><\/strong> are large bone cells with up to 50 nuclei. They remove bone structure by releasing lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, help regulate calcium concentrations in body fluids. Bone may also be resorbed for remodeling, if the applied stresses have changed. <span id=\"m44789-autoid-cnx2dbk-id1411011\"> <\/span><strong>Osteocytes<a id=\"id805297\" class=\"indexterm\" href=\"\"><\/a><\/strong> are mature bone cells and are the main cells in bony connective tissue; these cells cannot divide. Osteocytes maintain normal bone structure by recycling the mineral salts in the bony matrix. <span id=\"m44789-autoid-cnx2dbk-id1411016\"> <\/span><strong>Osteoprogenitor cells<\/strong><a id=\"id805312\" class=\"indexterm\" href=\"\"><\/a> are squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. Osteoprogenitor cells are important in the repair of fractures.\n\n<\/div>\n<div class=\"section\" title=\"Development of Bone\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm53592688\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Development of Bone<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm105573872\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441281\"> <\/span><strong>Ossification<\/strong><a id=\"id805342\" class=\"indexterm\" href=\"\"><\/a>, or osteogenesis, is the process of bone formation by osteoblasts. Ossification is distinct from the process of calcification; whereas calcification takes place during the ossification of bones, it can also occur in other tissues. Ossification begins approximately six weeks after fertilization in an embryo. Before this time, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from fibrous membranes is called intramembranous ossification; development from hyaline cartilage is called endochondral ossification. Bone growth continues until approximately age 25. Bones can grow in thickness throughout life, but after age 25, ossification functions primarily in bone remodeling and repair.\n\n<\/div>\n<div class=\"section\" title=\"Intramembranous Ossification\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm174168672\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Intramembranous Ossification<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm94647152\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441305\"> <\/span><strong>Intramembranous ossification<\/strong><a id=\"id805384\" class=\"indexterm\" href=\"\"><\/a> is the process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells form a template of the future bone. They then differentiate into osteoblasts at the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of the bone or osteoid continues to form around blood vessels, forming spongy bone. Connective tissue in the matrix differentiates into red bone marrow in the fetus. The spongy bone is remodeled into a thin layer of compact bone on the surface of the spongy bone.\n<div class=\"section\" title=\"Endochondral Ossification\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idp5890240\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Endochondral Ossification<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm73220656\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441328\"> <\/span><strong>Endochondral ossification<\/strong>\n\n<\/div>\n<a id=\"id805417\" class=\"indexterm\" href=\"\"><\/a> is the process of bone development from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed through endochondral ossification.\n\n<span id=\"m44789-fs-idm82508496\"> <\/span>In long bones, chondrocytes form a template of the hyaline cartilage diaphysis. Responding to complex developmental signals, the matrix begins to calcify. This calcification prevents diffusion of nutrients into the matrix, resulting in chondrocytes dying and the opening up of cavities in the diaphysis cartilage. Blood vessels invade the cavities, and osteoblasts and osteoclasts modify the calcified cartilage matrix into spongy bone. Osteoclasts then break down some of the spongy bone to create a marrow, or medullary, cavity in the center of the diaphysis. Dense, irregular connective tissue forms a sheath (periosteum) around the bones. The periosteum assists in attaching the bone to surrounding tissues, tendons, and ligaments. The bone continues to grow and elongate as the cartilage cells at the epiphyses divide.\n\n<span id=\"m44789-fs-idp83840768\"> <\/span>In the last stage of prenatal bone development, the centers of the epiphyses begin to calcify. Secondary ossification centers form in the epiphyses as blood vessels and osteoblasts enter these areas and convert hyaline cartilage into spongy bone. Until adolescence, hyaline cartilage persists at the <span id=\"m44789-autoid-cnx2dbk-id1441355\"> <\/span><strong>epiphyseal plate<\/strong> (growth plate), which is the region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones (Figure 19.21).\n\n[caption id=\"attachment_1261\" align=\"aligncenter\" width=\"600\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_06.jpg\"><img class=\"wp-image-4983\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1.jpg\" alt=\"Figure\u00a038.21.\u00a0 Endochondral ossification is the process of bone development from hyaline cartilage. The periosteum is the connective tissue on the outside of bone that acts as the interface between bone, blood vessels, tendons, and ligaments.\" width=\"600\" height=\"221\"><\/a> Figure 19.21.\u00a0<br>Endochondral ossification is the process of bone development from hyaline cartilage. The periosteum is the connective tissue on the outside of bone that acts as the interface between bone, blood vessels, tendons, and ligaments.[\/caption]\n\n<\/div>\n<div class=\"section\" title=\"Growth of Bone\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm9225328\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Growth of Bone<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm28445664\"> <\/span>Long bones continue to lengthen, potentially until adolescence, through the addition of bone tissue at the epiphyseal plate. They also increase in width through appositional growth.\n<div class=\"section\" title=\"Lengthening of Long Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm142383552\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Lengthening of Long Bones<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm135847152\"> <\/span>Chondrocytes on the epiphyseal side of the epiphyseal plate divide; one cell remains undifferentiated near the epiphysis, and one cell moves toward the diaphysis. The cells, which are pushed from the epiphysis, mature and are destroyed by calcification. This process replaces cartilage with bone on the diaphyseal side of the plate, resulting in a lengthening of the bone.\n\n<span id=\"m44789-fs-idp26325616\"> <\/span>Long bones stop growing at around the age of 18 in females and the age of 21 in males in a process called epiphyseal plate closure. During this process, cartilage cells stop dividing and all of the cartilage is replaced by bone. The epiphyseal plate fades, leaving a structure called the epiphyseal line or epiphyseal remnant, and the epiphysis and diaphysis fuse.\n\n<\/div>\n<div class=\"section\" title=\"Thickening of Long Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm82277824\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Thickening of Long Bones<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm166160432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1238828\"> <\/span><strong>Appositional growth<a id=\"id805585\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the increase in the diameter of bones by the addition of bony tissue at the surface of bones. Osteoblasts at the bone surface secrete bone matrix, and osteoclasts on the inner surface break down bone. The osteoblasts differentiate into osteocytes. A balance between these two processes allows the bone to thicken without becoming too heavy.\n\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Bone Remodeling and Repair\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm123932544\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Bone Remodeling and Repair<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<span id=\"m44789-fs-idm131512688\"> <\/span>Bone renewal continues after birth into adulthood. <span id=\"m44789-autoid-cnx2dbk-id1238852\"> <\/span><strong>Bone remodeling<a id=\"id805618\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the replacement of old bone tissue by new bone tissue. It involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Normal bone growth requires vitamins D, C, and A, plus minerals such as calcium, phosphorous, and magnesium. Hormones such as parathyroid hormone, growth hormone, and calcitonin are also required for proper bone growth and maintenance.\n\n<span id=\"m44789-fs-idp30486048\"> <\/span>Bone turnover rates are quite high, with five to seven percent of bone mass being recycled every week. Differences in turnover rate exist in different areas of the skeleton and in different areas of a bone. For example, the bone in the head of the femur may be fully replaced every six months, whereas the bone along the shaft is altered much more slowly.\n\n<span id=\"m44789-fs-idp37830768\"> <\/span>Bone remodeling allows bones to adapt to stresses by becoming thicker and stronger when subjected to stress. Bones that are not subject to normal stress, for example when a limb is in a cast, will begin to lose mass. A fractured or broken bone undergoes repair through four stages:\n<div class=\"orderedlist\">\n<ol class=\"orderedlist\">\n \t<li class=\"listitem\">Blood vessels in the broken bone tear and hemorrhage, resulting in the formation of clotted blood, or a hematoma, at the site of the break. The severed blood vessels at the broken ends of the bone are sealed by the clotting process, and bone cells that are deprived of nutrients begin to die.<\/li>\n \t<li class=\"listitem\">Within days of the fracture, capillaries grow into the hematoma, and phagocytic cells begin to clear away the dead cells. Though fragments of the blood clot may remain, fibroblasts and osteoblasts enter the area and begin to reform bone. Fibroblasts produce collagen fibers that connect the broken bone ends, and osteoblasts start to form spongy bone. The repair tissue between the broken bone ends is called the fibrocartilaginous callus, as it is composed of both hyaline and fibrocartilage (<a class=\"xref target-figure\" title=\"Figure\u00a038.22.\u00a0\" href=\"#attachment_1262\">Figure 19.22<\/a>). Some bone spicules may also appear at this point.<\/li>\n \t<li class=\"listitem\">The fibrocartilaginous callus is converted into a bony callus of spongy bone. It takes about two months for the broken bone ends to be firmly joined together after the fracture. This is similar to the endochondral formation of bone, as cartilage becomes ossified; osteoblasts, osteoclasts, and bone matrix are present.<\/li>\n \t<li class=\"listitem\">The bony callus is then remodelled by osteoclasts and osteoblasts, with excess material on the exterior of the bone and within the medullary cavity being removed. Compact bone is added to create bone tissue that is similar to the original, unbroken bone. This remodeling can take many months, and the bone may remain uneven for years.<\/li>\n<\/ol>\n[caption id=\"attachment_1262\" align=\"aligncenter\" width=\"250\"]<a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_07.jpg\"><img class=\"wp-image-4984\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07.jpg\" alt=\"Figure_38_02_07\" width=\"250\" height=\"349\"><\/a> Figure 19.22.\u00a0 After this bone is set, a callus will knit the two ends together. (credit: Bill Rhodes)[\/caption]\n\n<\/div>\n<div id=\"m44789-fs-idm44816880\" class=\"note scientific\">\n<div class=\"title\">\n<h2>Scientific Method Connection<\/h2>\n<div class=\"body\">\n<div class=\"title\"><b>Decalcification of Bones<\/b><\/div>\n<span class=\"bold\"><strong>Question:<\/strong><\/span> What effect does the removal of calcium and collagen have on bone structure?\n\n<span id=\"m44789-fs-idp104238304\"> <\/span><span class=\"bold\"><strong>Background:<\/strong><\/span> Conduct a literature search on the role of calcium and collagen in maintaining bone structure. Conduct a literature search on diseases in which bone structure is compromised.\n\n<span id=\"m44789-fs-idm134949776\"> <\/span><span class=\"bold\"><strong>Hypothesis:<\/strong><\/span> Develop a hypothesis that states predictions of the flexibility, strength, and mass of bones that have had the calcium and collagen components removed. Develop a hypothesis regarding the attempt to add calcium back to decalcified bones.\n\n<span id=\"m44789-fs-idm145583472\"> <\/span><span class=\"bold\"><strong>Test the hypothesis:<\/strong><\/span> Test the prediction by removing calcium from chicken bones by placing them in a jar of vinegar for seven days. Test the hypothesis regarding adding calcium back to decalcified bone by placing the decalcified chicken bones into a jar of water with calcium supplements added. Test the prediction by denaturing the collagen from the bones by baking them at 250\u00b0C for three hours.\n\n<span id=\"m44789-fs-idm106711968\"> <\/span><span class=\"bold\"><strong>Analyze the data:<\/strong><\/span> Create a table showing the changes in bone flexibility, strength, and mass in the three different environments.\n\n<span id=\"m44789-fs-idm126442896\"> <\/span><span class=\"bold\"><strong>Report the results:<\/strong><\/span> Under which conditions was the bone most flexible? Under which conditions was the bone the strongest?\n\n<span id=\"m44789-fs-idp57222480\"> <\/span><span class=\"bold\"><strong>Draw a conclusion:<\/strong><\/span> Did the results support or refute the hypothesis? How do the results observed in this experiment correspond to diseases that destroy bone tissue?\n\n<\/div>\n<\/div>\n<h2>Summary<\/h2>\nBone, or osseous tissue, is connective tissue that includes specialized cells, mineral salts, and collagen fibers. The human skeleton can be divided into long bones, short bones, flat bones, and irregular bones. Compact bone tissue is composed of osteons and forms the external layer of all bones. Spongy bone tissue is composed of trabeculae and forms the inner part of all bones. Four types of cells compose bony tissue: osteocytes, osteoclasts, osteoprogenitor cells, and osteoblasts. Ossification is the process of bone formation by osteoblasts. Intramembranous ossification is the process of bone development from fibrous membranes. Endochondral ossification is the process of bone development from hyaline cartilage. Long bones lengthen as chondrocytes divide and secrete hyaline cartilage. Osteoblasts replace cartilage with bone. Appositional growth is the increase in the diameter of bones by the addition of bone tissue at the surface of bones. Bone remodeling involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Bone repair occurs in four stages and can take several months.\n<div class=\"section\">\n<div class=\"body\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n \t<li>The Haversian canal:\n<ol>\n \t<li>is arranged as rods or plates<\/li>\n \t<li>contains the bone\u2019s blood vessels and nerve fibers<\/li>\n \t<li>is responsible for the lengthwise growth of long bones<\/li>\n \t<li>synthesizes and secretes matrix<\/li>\n<\/ol>\n<\/li>\n \t<li>The epiphyseal plate:\n<ol>\n \t<li>is arranged as rods or plates<\/li>\n \t<li>contains the bone\u2019s blood vessels and nerve fibers<\/li>\n \t<li>is responsible for the lengthwise growth of long bones<\/li>\n \t<li>synthesizes and secretes bone matrix<\/li>\n<\/ol>\n<\/li>\n \t<li>The cells responsible for bone resorption are ________.\n<ol>\n \t<li>osteoclasts<\/li>\n \t<li>osteoblasts<\/li>\n \t<li>fibroblasts<\/li>\n \t<li>osteocytes<\/li>\n<\/ol>\n<\/li>\n \t<li>Compact bone is composed of ________.\n<ol>\n \t<li>trabeculae<\/li>\n \t<li>compacted collagen<\/li>\n \t<li>osteons<\/li>\n \t<li>calcium phosphate only<\/li>\n<\/ol>\n<\/li>\n \t<li>What are the major differences between spongy bone and compact bone?<\/li>\n \t<li>What are the roles of osteoblasts, osteocytes, and osteoclasts?<\/li>\n<\/ol>\n<strong>Answers<\/strong>\n<ol>\n \t<li>B<\/li>\n \t<li>C<\/li>\n \t<li>A<\/li>\n \t<li>C<\/li>\n \t<li>Compact bone tissue forms the hard external layer of all bones and consists of osteons. Compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions. Spongy bone tissue forms the inner layer of all bones and consists of trabeculae. Spongy bone is prominent in areas of bones that are not heavily stressed or at which stresses arrive from many directions.<\/li>\n \t<li>Osteocytes function in the exchange of nutrients and wastes with the blood. They also maintain normal bone structure by recycling the mineral salts in the bony matrix. Osteoclasts remove bone tissue by releasing lysosomal enzymes and acids that dissolve the bony matrix. Osteoblasts are bone cells that are responsible for bone formation.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc multiple-choice\">\n<div class=\"cnx-eoc free-response\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44789-fs-idm136908720\" class=\"exercise\">\n<div class=\"body\">\n<div id=\"m44789-fs-idm207789456\" class=\"solution labeled\">\n<div class=\"body\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Control of Muscle Tension\">\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<div class=\"glossary\" title=\"Glossary\">\n<dl>\n \t<dt><strong>appositional growth<\/strong><\/dt>\n \t<dd>increase in the diameter of bones by the addition of bone tissue at the surface of bones<\/dd>\n \t<dt><strong>bone remodeling<\/strong><\/dt>\n \t<dd>replacement of old bone tissue by new bone tissue<\/dd>\n \t<dt><strong>bone<\/strong><\/dt>\n \t<dd>(also, osseous tissue) connective tissue that constitutes the endoskeleton<\/dd>\n \t<dt><strong>calcification<\/strong><\/dt>\n \t<dd>process of deposition of mineral salts in the collagen fiber matrix that crystallizes and hardens the tissue<\/dd>\n \t<dt><strong>compact bone<\/strong><\/dt>\n \t<dd>forms the hard external layer of all bones<\/dd>\n \t<dt><strong>diaphysis<\/strong><\/dt>\n \t<dd>central shaft of bone, contains bone marrow in a marrow cavity<\/dd>\n \t<dt><strong>endochondral ossification<\/strong><\/dt>\n \t<dd>process of bone development from hyaline cartilage<\/dd>\n \t<dt><strong>epiphyseal plate<\/strong><\/dt>\n \t<dd>region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones<\/dd>\n \t<dt><strong>epiphysis<\/strong><\/dt>\n \t<dd>rounded end of bone, covered with articular cartilage and filled with red bone marrow, which produces blood cells<\/dd>\n \t<dt><strong>flat bone<\/strong><\/dt>\n \t<dd>thin and relatively broad bone found where extensive protection of organs is required or where broad surfaces of muscle attachment are required<\/dd>\n \t<dt><strong>Haversian canal<\/strong><\/dt>\n \t<dd>contains the bone\u2019s blood vessels and nerve fibers<\/dd>\n \t<dt><strong>intramembranous ossification<\/strong><\/dt>\n \t<dd>process of bone development from fibrous membranes<\/dd>\n \t<dt><strong>irregular bone<\/strong><\/dt>\n \t<dd>bone with complex shapes; examples include vertebrae and hip bones<\/dd>\n \t<dt><strong>lamella<\/strong><\/dt>\n \t<dd>layer of compact tissue that surrounds a central canal called the Haversian canal<\/dd>\n \t<dt><strong>long bone<\/strong><\/dt>\n \t<dd>bone that is longer than wide, and has a shaft and two ends<\/dd>\n \t<dt><strong>osseous tissue<\/strong><\/dt>\n \t<dd>connective tissue that constitutes the endoskeleton<\/dd>\n \t<dt><strong>ossification<\/strong><\/dt>\n \t<dd>(also, osteogenesis) process of bone formation by osteoblasts<\/dd>\n \t<dt><strong>osteoblast<\/strong><\/dt>\n \t<dd>bone cell responsible for bone formation<\/dd>\n \t<dt><strong>osteoclast<\/strong><\/dt>\n \t<dd>large bone cells with up to 50 nuclei, responsible for bone remodeling<\/dd>\n \t<dt><strong>osteocyte<\/strong><\/dt>\n \t<dd>mature bone cells and the main cell in bone tissue<\/dd>\n \t<dt><strong>osteon<\/strong><\/dt>\n \t<dd>cylindrical structure aligned parallel to the long axis of the bone<\/dd>\n \t<dt><strong>sesamoid bone<\/strong><\/dt>\n \t<dd>small, flat bone shaped like a sesame seed; develops inside tendons<\/dd>\n \t<dt><strong>short bone<\/strong><\/dt>\n \t<dd>bone that has the same width and length, giving it a cube-like shape<\/dd>\n \t<dt><strong>spongy bone tissue<\/strong><\/dt>\n \t<dd>forms the inner layer of all bones<\/dd>\n \t<dt><strong>suture bone<\/strong><\/dt>\n \t<dd>small, flat, irregularly shaped bone that forms between the flat bones of the cranium<\/dd>\n \t<dt><strong>trabeculae<\/strong><\/dt>\n \t<dd>lamellae that are arranged as rods or plates<\/dd>\n<\/dl>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc summary\">\n<div class=\"section\">\n<div class=\"section\">\n<div class=\"body\">\n\n<span id=\"m44789-fs-idm153514432\">\u00a0<\/span>\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>","rendered":"<div class=\"section module\" title=\"38.2.\u00a0Bone\" xml:lang=\"en\">\n<div class=\"titlepage\">\n<div class=\"abstract\">\n<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to:<\/p>\n<div class=\"itemizedlist\">\n<ul class=\"itemizedlist\">\n<li class=\"listitem\">Classify the different types of bones in the skeleton<\/li>\n<li class=\"listitem\">Explain the role of the different cell types in bone<\/li>\n<li class=\"listitem\">Explain how bone forms during development<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm54620432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1241294\"> <\/span><strong>Bone<a id=\"id804519\" class=\"indexterm\" href=\"\"><\/a><\/strong>, or <strong><span id=\"m44789-autoid-cnx2dbk-id1241303\"> <\/span>osseous tissue<a id=\"id804532\" class=\"indexterm\" href=\"\"><\/a><\/strong>, is a connective tissue that constitutes the endoskeleton. It contains specialized cells and a matrix of mineral salts and collagen fibers.<\/p>\n<p><span id=\"m44789-fs-idm84548880\"> <\/span>The mineral salts primarily include hydroxyapatite, a mineral formed from calcium phosphate. <span id=\"m44789-autoid-cnx2dbk-id1241314\"> <\/span><strong>Calcification<a id=\"id804555\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the process of deposition of mineral salts on the collagen fiber matrix that crystallizes and hardens the tissue. The process of calcification only occurs in the presence of collagen fibers.<\/p>\n<p><span id=\"m44789-fs-idm96433616\"> <\/span>The bones of the human skeleton are classified by their shape: long bones, short bones, flat bones, sutural bones, sesamoid bones, and irregular bones (Figure 19.16).<\/p>\n<figure id=\"attachment_1255\" aria-describedby=\"caption-attachment-1255\" style=\"width: 500px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_01.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4977\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1.jpg\" alt=\"Figure\u00a038.16.\u00a0 Shown are different types of bones: flat, irregular, long, short, and sesamoid.\" width=\"500\" height=\"535\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1.jpg 956w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1-280x300.jpg 280w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1-768x823.jpg 768w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1-65x70.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1-225x241.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/10\/Figure_38_02_01-956x1024-1-350x375.jpg 350w\" sizes=\"auto, (max-width: 500px) 100vw, 500px\" \/><\/a><figcaption id=\"caption-attachment-1255\" class=\"wp-caption-text\">Figure 19.16. Shown are different types of bones: flat, irregular, long, short, and sesamoid.<\/figcaption><\/figure>\n<div id=\"m44789-fig-ch38_02_01\" class=\"figure\" title=\"Figure\u00a038.16.\u00a0\">\n<p><span id=\"m44789-fs-idp48592256\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1241365\"> <\/span><strong>Long bones<\/strong> are longer than they are wide and have a shaft and two ends. The <strong><span id=\"m44789-autoid-cnx2dbk-id1241368\"> <\/span>diaphysis<\/strong>, or central shaft, contains bone marrow in a marrow cavity. The rounded ends, the <span id=\"m44789-autoid-cnx2dbk-id1268435\"> <\/span><strong>epiphyses<\/strong>, are covered with articular cartilage and are filled with red bone marrow, which produces blood cells (Figure 19.17). Most of the limb bones are long bones\u2014for example, the femur, tibia, ulna, and radius. Exceptions to this include the patella and the bones of the wrist and ankle.<\/p>\n<figure id=\"attachment_1256\" aria-describedby=\"caption-attachment-1256\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_02.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4978\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02.jpg\" alt=\"Figure\u00a038.17.\u00a0 The long bone is covered by articular cartilage at either end and contains bone marrow (shown in yellow in this illustration) in the marrow cavity.\" width=\"300\" height=\"413\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02.jpg 544w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02-218x300.jpg 218w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02-65x89.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02-225x310.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_02-350x482.jpg 350w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-1256\" class=\"wp-caption-text\">Figure 19.17.\u00a0<br \/>The long bone is covered by articular cartilage at either end and contains bone marrow (shown in yellow in this illustration) in the marrow cavity.<\/figcaption><\/figure>\n<div id=\"m44789-fig-ch38_02_02\" class=\"figure\" title=\"Figure\u00a038.17.\u00a0\">\n<p><span id=\"m44789-fs-idm152546016\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268483\"> <\/span><strong>Short bones<\/strong>, or cuboidal bones, are bones that are the same width and length, giving them a cube-like shape. For example, the bones of the wrist (carpals) and ankle (tarsals) are short bones (<a class=\"xref target-figure\" title=\"Figure\u00a038.16.\u00a0\" href=\"#attachment_1255\">Figure 19.16<\/a>).<\/p>\n<p><span id=\"m44789-fs-idp18280432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268500\"> <\/span><strong>Flat bones<\/strong> are thin and relatively broad bones that are found where extensive protection of organs is required or where broad surfaces of muscle attachment are required. Examples of flat bones are the sternum (breast bone), ribs, scapulae (shoulder blades), and the roof of the skull (<a class=\"xref target-figure\" title=\"Figure\u00a038.16.\u00a0\" href=\"#attachment_1255\">Figure 19.16<\/a>).<\/p>\n<p><span id=\"m44789-fs-idm124655504\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268517\"> <\/span><strong>Irregular bones<a id=\"id804781\" class=\"indexterm\" href=\"\"><\/a><\/strong> are bones with complex shapes. These bones may have short, flat, notched, or ridged surfaces. Examples of irregular bones are the vertebrae, hip bones, and several skull bones.<\/p>\n<p><span id=\"m44789-fs-idp6133120\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1268527\"> <\/span><strong>Sesamoid bones<\/strong> are small, flat bones and are shaped similarly to a sesame seed. The patellae are sesamoid bones (Figure 19.18). Sesamoid bones develop inside tendons and may be found near joints at the knees, hands, and feet.<\/p>\n<figure id=\"attachment_1257\" aria-describedby=\"caption-attachment-1257\" style=\"width: 250px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_03.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4979\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03.jpg\" alt=\"Figure\u00a038.18.\u00a0 The patella of the knee is an example of a sesamoid bone.\" width=\"250\" height=\"250\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03.jpg 544w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03-300x300.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03-150x150.jpg 150w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03-65x65.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03-225x225.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_03-350x350.jpg 350w\" sizes=\"auto, (max-width: 250px) 100vw, 250px\" \/><\/a><figcaption id=\"caption-attachment-1257\" class=\"wp-caption-text\">Figure 19.18.\u00a0<br \/>The patella of the knee is an example of a sesamoid bone.<\/figcaption><\/figure>\n<div id=\"m44789-fig-ch38_02_03\" class=\"figure\" title=\"Figure\u00a038.18.\u00a0\">\n<p><span id=\"m44789-fs-idm124049840\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1305692\"> <\/span><strong>Sutural bones<\/strong><a id=\"id804863\" class=\"indexterm\" href=\"\"><\/a> are small, flat, irregularly shaped bones. They may be found between the flat bones of the skull. They vary in number, shape, size, and position.<\/p>\n<div class=\"section\" title=\"Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm5626320\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idp1203136\"> <\/span>Bones are considered organs because they contain various types of tissue, such as blood, connective tissue, nerves, and bone tissue. Osteocytes, the living cells of bone tissue, form the mineral matrix of bones. There are two types of bone tissue: compact and spongy.<\/p>\n<div class=\"section\" title=\"Compact Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm149839456\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Compact Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idp54336560\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1305729\"> <\/span><strong>Compact bone<\/strong> (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. It provides protection and strength to bones. Compact bone tissue consists of units called osteons or Haversian systems. <span id=\"m44789-autoid-cnx2dbk-id1305735\"> <\/span><strong>Osteons<\/strong> are cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi, which transport blood. They are aligned parallel to the long axis of the bone. Each osteon consists of <span id=\"m44789-autoid-cnx2dbk-id1305740\"> <\/span><strong>lamellae<\/strong>, which are layers of compact matrix that surround a central canal called the Haversian canal. The <span id=\"m44789-autoid-cnx2dbk-id1305745\"> <\/span><strong>Haversian canal<\/strong> <strong>(osteonic canal)<\/strong> contains the bone\u2019s blood vessels and nerve fibers (Figure 19.19). Osteons in compact bone tissue are aligned in the same direction along lines of stress and help the bone resist bending or fracturing. Therefore, compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions.<\/p>\n<\/div>\n<\/div>\n<div id=\"m44789-fs-idm6377616\" class=\"note art-connection\">\n<div class=\"title\">\n<div class=\"title\">\n<figure id=\"attachment_1258\" aria-describedby=\"caption-attachment-1258\" style=\"width: 350px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_04.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4980\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04.png\" alt=\"Figure_38_02_04\" width=\"350\" height=\"310\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04.png 469w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04-300x265.png 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04-65x58.png 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04-225x199.png 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_04-350x310.png 350w\" sizes=\"auto, (max-width: 350px) 100vw, 350px\" \/><\/a><figcaption id=\"caption-attachment-1258\" class=\"wp-caption-text\">Figure 19.19.\u00a0 Compact bone tissue consists of osteons that are aligned parallel to the long axis of the bone, and the Haversian canal that contains the bone\u2019s blood vessels and nerve fibers. The inner layer of bones consists of spongy bone tissue. The small dark ovals in the osteon represent the living osteocytes. (credit: modification of work by NCI, NIH)<\/figcaption><\/figure>\n<\/div>\n<div class=\"body\">\n<div id=\"m44789-fig-ch38_02_04\" class=\"figure\" title=\"Figure\u00a038.19.\u00a0\">\n<p><span id=\"m44789-fs-idm52317584\"> <\/span>Which of the following statements about bone tissue is false?<\/p>\n<div class=\"orderedlist\">\n<ol class=\"orderedlist\">\n<li class=\"listitem\">Compact bone tissue is made of cylindrical osteons that are aligned such that they travel the length of the bone.<\/li>\n<li class=\"listitem\">Haversian canals contain blood vessels only.<\/li>\n<li class=\"listitem\">Haversian canals contain blood vessels and nerve fibers.<\/li>\n<li class=\"listitem\">Spongy tissue is found on the interior of the bone, and compact bone tissue is found on the exterior.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Spongy Bone Tissue\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idp27296784\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Spongy Bone Tissue<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm1194288\"> <\/span>Whereas compact bone tissue forms the outer layer of all bones, <span id=\"m44789-autoid-cnx2dbk-id1411214\"> <\/span><strong>spongy bone<a id=\"id805094\" class=\"indexterm\" href=\"\"><\/a><\/strong> or cancellous bone forms the inner layer of all bones. Spongy bone tissue does not contain osteons that constitute compact bone tissue. Instead, it consists of <span id=\"m44789-autoid-cnx2dbk-id1411220\"> <\/span><strong>trabeculae<a id=\"id805109\" class=\"indexterm\" href=\"\"><\/a><\/strong>, which are lamellae that are arranged as rods or plates. Red bone marrow is found between the trabuculae. Blood vessels within this tissue deliver nutrients to osteocytes and remove waste. The red bone marrow of the femur and the interior of other large bones, such as the ileum, forms blood cells.<\/p>\n<p><span id=\"m44789-fs-idm202492784\"> <\/span>Spongy bone reduces the density of bone and allows the ends of long bones to compress as the result of stresses applied to the bone. Spongy bone is prominent in areas of bones that are not heavily stressed or where stresses arrive from many directions. The epiphyses of bones, such as the neck of the femur, are subject to stress from many directions. Imagine laying a heavy framed picture flat on the floor. You could hold up one side of the picture with a toothpick if the toothpick was perpendicular to the floor and the picture. Now drill a hole and stick the toothpick into the wall to hang up the picture. In this case, the function of the toothpick is to transmit the downward pressure of the picture to the wall. The force on the picture is straight down to the floor, but the force on the toothpick is both the picture wire pulling down and the bottom of the hole in the wall pushing up. The toothpick will break off right at the wall.<\/p>\n<p><span id=\"m44789-fs-idp54392224\"> <\/span>The neck of the femur is horizontal like the toothpick in the wall. The weight of the body pushes it down near the joint, but the vertical diaphysis of the femur pushes it up at the other end. The neck of the femur must be strong enough to transfer the downward force of the body weight horizontally to the vertical shaft of the femur (Figure 19.20).<\/p>\n<figure id=\"attachment_1259\" aria-describedby=\"caption-attachment-1259\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_05.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4981\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05.jpg\" alt=\"Figure\u00a038.20.\u00a0 Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.\" width=\"300\" height=\"290\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05.jpg 544w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05-300x290.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05-65x63.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05-225x217.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_05-350x338.jpg 350w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-1259\" class=\"wp-caption-text\">Figure 19.20.\u00a0<br \/>Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.<\/figcaption><\/figure>\n<div id=\"m44789-fig-ch38_02_05\" class=\"figure\" title=\"Figure\u00a038.20.\u00a0\">\n<div id=\"m44789-fs-idm221406720\" class=\"note interactive\">\n<h2 class=\"title\"><span class=\"cnx-gentext-tip-t\">Concept in Action<br \/>\n<\/span><\/h2>\n<div class=\"body\">\n<div class=\"mediaobject\"><span id=\"m44789-fs-idm203119296\"> <\/span><img decoding=\"async\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/muscle_tissue.png\" alt=\"QR Code representing a URL\" width=\"120\" \/><\/div>\n<p><span id=\"m44789-fs-idp21378560\"> <\/span>View <a class=\"link\" href=\"http:\/\/openstaxcollege.org\/l\/muscle_tissue\" target=\"\" rel=\"noopener noreferrer\">micrographs<\/a> of musculoskeletal tissues as you review the anatomy.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Cell Types in Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h3 id=\"m44789-fs-idm176180400\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Cell Types in Bones<\/span><\/span><\/h3>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm202474080\"> <\/span>Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. <span id=\"m44789-autoid-cnx2dbk-id1410999\"> <\/span><strong>Osteoblasts<a id=\"id805265\" class=\"indexterm\" href=\"\"><\/a><\/strong> are bone cells that are responsible for bone formation. Osteoblasts synthesize and secrete the organic part and inorganic part of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts become trapped in these secretions and differentiate into less active osteocytes. <span id=\"m44789-autoid-cnx2dbk-id1411005\"> <\/span><strong>Osteoclasts<a id=\"id805281\" class=\"indexterm\" href=\"\"><\/a><\/strong> are large bone cells with up to 50 nuclei. They remove bone structure by releasing lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, help regulate calcium concentrations in body fluids. Bone may also be resorbed for remodeling, if the applied stresses have changed. <span id=\"m44789-autoid-cnx2dbk-id1411011\"> <\/span><strong>Osteocytes<a id=\"id805297\" class=\"indexterm\" href=\"\"><\/a><\/strong> are mature bone cells and are the main cells in bony connective tissue; these cells cannot divide. Osteocytes maintain normal bone structure by recycling the mineral salts in the bony matrix. <span id=\"m44789-autoid-cnx2dbk-id1411016\"> <\/span><strong>Osteoprogenitor cells<\/strong><a id=\"id805312\" class=\"indexterm\" href=\"\"><\/a> are squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. Osteoprogenitor cells are important in the repair of fractures.<\/p>\n<\/div>\n<div class=\"section\" title=\"Development of Bone\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm53592688\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Development of Bone<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm105573872\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441281\"> <\/span><strong>Ossification<\/strong><a id=\"id805342\" class=\"indexterm\" href=\"\"><\/a>, or osteogenesis, is the process of bone formation by osteoblasts. Ossification is distinct from the process of calcification; whereas calcification takes place during the ossification of bones, it can also occur in other tissues. Ossification begins approximately six weeks after fertilization in an embryo. Before this time, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from fibrous membranes is called intramembranous ossification; development from hyaline cartilage is called endochondral ossification. Bone growth continues until approximately age 25. Bones can grow in thickness throughout life, but after age 25, ossification functions primarily in bone remodeling and repair.<\/p>\n<\/div>\n<div class=\"section\" title=\"Intramembranous Ossification\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm174168672\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Intramembranous Ossification<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm94647152\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441305\"> <\/span><strong>Intramembranous ossification<\/strong><a id=\"id805384\" class=\"indexterm\" href=\"\"><\/a> is the process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells form a template of the future bone. They then differentiate into osteoblasts at the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of the bone or osteoid continues to form around blood vessels, forming spongy bone. Connective tissue in the matrix differentiates into red bone marrow in the fetus. The spongy bone is remodeled into a thin layer of compact bone on the surface of the spongy bone.<\/p>\n<div class=\"section\" title=\"Endochondral Ossification\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idp5890240\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Endochondral Ossification<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm73220656\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1441328\"> <\/span><strong>Endochondral ossification<\/strong><\/p>\n<\/div>\n<p><a id=\"id805417\" class=\"indexterm\" href=\"\"><\/a> is the process of bone development from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed through endochondral ossification.<\/p>\n<p><span id=\"m44789-fs-idm82508496\"> <\/span>In long bones, chondrocytes form a template of the hyaline cartilage diaphysis. Responding to complex developmental signals, the matrix begins to calcify. This calcification prevents diffusion of nutrients into the matrix, resulting in chondrocytes dying and the opening up of cavities in the diaphysis cartilage. Blood vessels invade the cavities, and osteoblasts and osteoclasts modify the calcified cartilage matrix into spongy bone. Osteoclasts then break down some of the spongy bone to create a marrow, or medullary, cavity in the center of the diaphysis. Dense, irregular connective tissue forms a sheath (periosteum) around the bones. The periosteum assists in attaching the bone to surrounding tissues, tendons, and ligaments. The bone continues to grow and elongate as the cartilage cells at the epiphyses divide.<\/p>\n<p><span id=\"m44789-fs-idp83840768\"> <\/span>In the last stage of prenatal bone development, the centers of the epiphyses begin to calcify. Secondary ossification centers form in the epiphyses as blood vessels and osteoblasts enter these areas and convert hyaline cartilage into spongy bone. Until adolescence, hyaline cartilage persists at the <span id=\"m44789-autoid-cnx2dbk-id1441355\"> <\/span><strong>epiphyseal plate<\/strong> (growth plate), which is the region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones (Figure 19.21).<\/p>\n<figure id=\"attachment_1261\" aria-describedby=\"caption-attachment-1261\" style=\"width: 600px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_06.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4983\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1.jpg\" alt=\"Figure\u00a038.21.\u00a0 Endochondral ossification is the process of bone development from hyaline cartilage. The periosteum is the connective tissue on the outside of bone that acts as the interface between bone, blood vessels, tendons, and ligaments.\" width=\"600\" height=\"221\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1.jpg 1024w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1-300x111.jpg 300w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1-768x284.jpg 768w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1-65x24.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1-225x83.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_06-1024x378-1-350x129.jpg 350w\" sizes=\"auto, (max-width: 600px) 100vw, 600px\" \/><\/a><figcaption id=\"caption-attachment-1261\" class=\"wp-caption-text\">Figure 19.21.\u00a0<br \/>Endochondral ossification is the process of bone development from hyaline cartilage. The periosteum is the connective tissue on the outside of bone that acts as the interface between bone, blood vessels, tendons, and ligaments.<\/figcaption><\/figure>\n<\/div>\n<div class=\"section\" title=\"Growth of Bone\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm9225328\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Growth of Bone<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm28445664\"> <\/span>Long bones continue to lengthen, potentially until adolescence, through the addition of bone tissue at the epiphyseal plate. They also increase in width through appositional growth.<\/p>\n<div class=\"section\" title=\"Lengthening of Long Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm142383552\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Lengthening of Long Bones<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm135847152\"> <\/span>Chondrocytes on the epiphyseal side of the epiphyseal plate divide; one cell remains undifferentiated near the epiphysis, and one cell moves toward the diaphysis. The cells, which are pushed from the epiphysis, mature and are destroyed by calcification. This process replaces cartilage with bone on the diaphyseal side of the plate, resulting in a lengthening of the bone.<\/p>\n<p><span id=\"m44789-fs-idp26325616\"> <\/span>Long bones stop growing at around the age of 18 in females and the age of 21 in males in a process called epiphyseal plate closure. During this process, cartilage cells stop dividing and all of the cartilage is replaced by bone. The epiphyseal plate fades, leaving a structure called the epiphyseal line or epiphyseal remnant, and the epiphysis and diaphysis fuse.<\/p>\n<\/div>\n<div class=\"section\" title=\"Thickening of Long Bones\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm82277824\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Thickening of Long Bones<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm166160432\"> <\/span><span id=\"m44789-autoid-cnx2dbk-id1238828\"> <\/span><strong>Appositional growth<a id=\"id805585\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the increase in the diameter of bones by the addition of bony tissue at the surface of bones. Osteoblasts at the bone surface secrete bone matrix, and osteoclasts on the inner surface break down bone. The osteoblasts differentiate into osteocytes. A balance between these two processes allows the bone to thicken without becoming too heavy.<\/p>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Bone Remodeling and Repair\">\n<div class=\"titlepage\">\n<div>\n<div>\n<h2 id=\"m44789-fs-idm123932544\"><span class=\"cnx-gentext-section cnx-gentext-autogenerated\"><span class=\"cnx-gentext-section cnx-gentext-t\">Bone Remodeling and Repair<\/span><\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<p><span id=\"m44789-fs-idm131512688\"> <\/span>Bone renewal continues after birth into adulthood. <span id=\"m44789-autoid-cnx2dbk-id1238852\"> <\/span><strong>Bone remodeling<a id=\"id805618\" class=\"indexterm\" href=\"\"><\/a><\/strong> is the replacement of old bone tissue by new bone tissue. It involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Normal bone growth requires vitamins D, C, and A, plus minerals such as calcium, phosphorous, and magnesium. Hormones such as parathyroid hormone, growth hormone, and calcitonin are also required for proper bone growth and maintenance.<\/p>\n<p><span id=\"m44789-fs-idp30486048\"> <\/span>Bone turnover rates are quite high, with five to seven percent of bone mass being recycled every week. Differences in turnover rate exist in different areas of the skeleton and in different areas of a bone. For example, the bone in the head of the femur may be fully replaced every six months, whereas the bone along the shaft is altered much more slowly.<\/p>\n<p><span id=\"m44789-fs-idp37830768\"> <\/span>Bone remodeling allows bones to adapt to stresses by becoming thicker and stronger when subjected to stress. Bones that are not subject to normal stress, for example when a limb is in a cast, will begin to lose mass. A fractured or broken bone undergoes repair through four stages:<\/p>\n<div class=\"orderedlist\">\n<ol class=\"orderedlist\">\n<li class=\"listitem\">Blood vessels in the broken bone tear and hemorrhage, resulting in the formation of clotted blood, or a hematoma, at the site of the break. The severed blood vessels at the broken ends of the bone are sealed by the clotting process, and bone cells that are deprived of nutrients begin to die.<\/li>\n<li class=\"listitem\">Within days of the fracture, capillaries grow into the hematoma, and phagocytic cells begin to clear away the dead cells. Though fragments of the blood clot may remain, fibroblasts and osteoblasts enter the area and begin to reform bone. Fibroblasts produce collagen fibers that connect the broken bone ends, and osteoblasts start to form spongy bone. The repair tissue between the broken bone ends is called the fibrocartilaginous callus, as it is composed of both hyaline and fibrocartilage (<a class=\"xref target-figure\" title=\"Figure\u00a038.22.\u00a0\" href=\"#attachment_1262\">Figure 19.22<\/a>). Some bone spicules may also appear at this point.<\/li>\n<li class=\"listitem\">The fibrocartilaginous callus is converted into a bony callus of spongy bone. It takes about two months for the broken bone ends to be firmly joined together after the fracture. This is similar to the endochondral formation of bone, as cartilage becomes ossified; osteoblasts, osteoclasts, and bone matrix are present.<\/li>\n<li class=\"listitem\">The bony callus is then remodelled by osteoclasts and osteoblasts, with excess material on the exterior of the bone and within the medullary cavity being removed. Compact bone is added to create bone tissue that is similar to the original, unbroken bone. This remodeling can take many months, and the bone may remain uneven for years.<\/li>\n<\/ol>\n<figure id=\"attachment_1262\" aria-describedby=\"caption-attachment-1262\" style=\"width: 250px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2015\/03\/Figure_38_02_07.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4984\" src=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07.jpg\" alt=\"Figure_38_02_07\" width=\"250\" height=\"349\" srcset=\"https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07.jpg 544w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07-215x300.jpg 215w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07-65x91.jpg 65w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07-225x314.jpg 225w, https:\/\/opentextbc.ca\/biology\/wp-content\/uploads\/sites\/96\/2021\/03\/Figure_38_02_07-350x489.jpg 350w\" sizes=\"auto, (max-width: 250px) 100vw, 250px\" \/><\/a><figcaption id=\"caption-attachment-1262\" class=\"wp-caption-text\">Figure 19.22.\u00a0 After this bone is set, a callus will knit the two ends together. (credit: Bill Rhodes)<\/figcaption><\/figure>\n<\/div>\n<div id=\"m44789-fs-idm44816880\" class=\"note scientific\">\n<div class=\"title\">\n<h2>Scientific Method Connection<\/h2>\n<div class=\"body\">\n<div class=\"title\"><b>Decalcification of Bones<\/b><\/div>\n<p><span class=\"bold\"><strong>Question:<\/strong><\/span> What effect does the removal of calcium and collagen have on bone structure?<\/p>\n<p><span id=\"m44789-fs-idp104238304\"> <\/span><span class=\"bold\"><strong>Background:<\/strong><\/span> Conduct a literature search on the role of calcium and collagen in maintaining bone structure. Conduct a literature search on diseases in which bone structure is compromised.<\/p>\n<p><span id=\"m44789-fs-idm134949776\"> <\/span><span class=\"bold\"><strong>Hypothesis:<\/strong><\/span> Develop a hypothesis that states predictions of the flexibility, strength, and mass of bones that have had the calcium and collagen components removed. Develop a hypothesis regarding the attempt to add calcium back to decalcified bones.<\/p>\n<p><span id=\"m44789-fs-idm145583472\"> <\/span><span class=\"bold\"><strong>Test the hypothesis:<\/strong><\/span> Test the prediction by removing calcium from chicken bones by placing them in a jar of vinegar for seven days. Test the hypothesis regarding adding calcium back to decalcified bone by placing the decalcified chicken bones into a jar of water with calcium supplements added. Test the prediction by denaturing the collagen from the bones by baking them at 250\u00b0C for three hours.<\/p>\n<p><span id=\"m44789-fs-idm106711968\"> <\/span><span class=\"bold\"><strong>Analyze the data:<\/strong><\/span> Create a table showing the changes in bone flexibility, strength, and mass in the three different environments.<\/p>\n<p><span id=\"m44789-fs-idm126442896\"> <\/span><span class=\"bold\"><strong>Report the results:<\/strong><\/span> Under which conditions was the bone most flexible? Under which conditions was the bone the strongest?<\/p>\n<p><span id=\"m44789-fs-idp57222480\"> <\/span><span class=\"bold\"><strong>Draw a conclusion:<\/strong><\/span> Did the results support or refute the hypothesis? How do the results observed in this experiment correspond to diseases that destroy bone tissue?<\/p>\n<\/div>\n<\/div>\n<h2>Summary<\/h2>\n<p>Bone, or osseous tissue, is connective tissue that includes specialized cells, mineral salts, and collagen fibers. The human skeleton can be divided into long bones, short bones, flat bones, and irregular bones. Compact bone tissue is composed of osteons and forms the external layer of all bones. Spongy bone tissue is composed of trabeculae and forms the inner part of all bones. Four types of cells compose bony tissue: osteocytes, osteoclasts, osteoprogenitor cells, and osteoblasts. Ossification is the process of bone formation by osteoblasts. Intramembranous ossification is the process of bone development from fibrous membranes. Endochondral ossification is the process of bone development from hyaline cartilage. Long bones lengthen as chondrocytes divide and secrete hyaline cartilage. Osteoblasts replace cartilage with bone. Appositional growth is the increase in the diameter of bones by the addition of bone tissue at the surface of bones. Bone remodeling involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Bone repair occurs in four stages and can take several months.<\/p>\n<div class=\"section\">\n<div class=\"body\">\n<div class=\"textbox exercises\">\n<h3>Exercises<\/h3>\n<ol>\n<li>The Haversian canal:\n<ol>\n<li>is arranged as rods or plates<\/li>\n<li>contains the bone\u2019s blood vessels and nerve fibers<\/li>\n<li>is responsible for the lengthwise growth of long bones<\/li>\n<li>synthesizes and secretes matrix<\/li>\n<\/ol>\n<\/li>\n<li>The epiphyseal plate:\n<ol>\n<li>is arranged as rods or plates<\/li>\n<li>contains the bone\u2019s blood vessels and nerve fibers<\/li>\n<li>is responsible for the lengthwise growth of long bones<\/li>\n<li>synthesizes and secretes bone matrix<\/li>\n<\/ol>\n<\/li>\n<li>The cells responsible for bone resorption are ________.\n<ol>\n<li>osteoclasts<\/li>\n<li>osteoblasts<\/li>\n<li>fibroblasts<\/li>\n<li>osteocytes<\/li>\n<\/ol>\n<\/li>\n<li>Compact bone is composed of ________.\n<ol>\n<li>trabeculae<\/li>\n<li>compacted collagen<\/li>\n<li>osteons<\/li>\n<li>calcium phosphate only<\/li>\n<\/ol>\n<\/li>\n<li>What are the major differences between spongy bone and compact bone?<\/li>\n<li>What are the roles of osteoblasts, osteocytes, and osteoclasts?<\/li>\n<\/ol>\n<p><strong>Answers<\/strong><\/p>\n<ol>\n<li>B<\/li>\n<li>C<\/li>\n<li>A<\/li>\n<li>C<\/li>\n<li>Compact bone tissue forms the hard external layer of all bones and consists of osteons. Compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions. Spongy bone tissue forms the inner layer of all bones and consists of trabeculae. Spongy bone is prominent in areas of bones that are not heavily stressed or at which stresses arrive from many directions.<\/li>\n<li>Osteocytes function in the exchange of nutrients and wastes with the blood. They also maintain normal bone structure by recycling the mineral salts in the bony matrix. Osteoclasts remove bone tissue by releasing lysosomal enzymes and acids that dissolve the bony matrix. Osteoblasts are bone cells that are responsible for bone formation.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc multiple-choice\">\n<div class=\"cnx-eoc free-response\">\n<div class=\"section empty\">\n<div class=\"section\">\n<div class=\"body\">\n<div id=\"m44789-fs-idm136908720\" class=\"exercise\">\n<div class=\"body\">\n<div id=\"m44789-fs-idm207789456\" class=\"solution labeled\">\n<div class=\"body\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"section\" title=\"Control of Muscle Tension\">\n<div class=\"glossary\" title=\"Glossary\">\n<div class=\"titlepage\">\n<div class=\"bcc-box bcc-success\">\n<h3>Glossary<\/h3>\n<div class=\"glossary\" title=\"Glossary\">\n<dl>\n<dt><strong>appositional growth<\/strong><\/dt>\n<dd>increase in the diameter of bones by the addition of bone tissue at the surface of bones<\/dd>\n<dt><strong>bone remodeling<\/strong><\/dt>\n<dd>replacement of old bone tissue by new bone tissue<\/dd>\n<dt><strong>bone<\/strong><\/dt>\n<dd>(also, osseous tissue) connective tissue that constitutes the endoskeleton<\/dd>\n<dt><strong>calcification<\/strong><\/dt>\n<dd>process of deposition of mineral salts in the collagen fiber matrix that crystallizes and hardens the tissue<\/dd>\n<dt><strong>compact bone<\/strong><\/dt>\n<dd>forms the hard external layer of all bones<\/dd>\n<dt><strong>diaphysis<\/strong><\/dt>\n<dd>central shaft of bone, contains bone marrow in a marrow cavity<\/dd>\n<dt><strong>endochondral ossification<\/strong><\/dt>\n<dd>process of bone development from hyaline cartilage<\/dd>\n<dt><strong>epiphyseal plate<\/strong><\/dt>\n<dd>region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones<\/dd>\n<dt><strong>epiphysis<\/strong><\/dt>\n<dd>rounded end of bone, covered with articular cartilage and filled with red bone marrow, which produces blood cells<\/dd>\n<dt><strong>flat bone<\/strong><\/dt>\n<dd>thin and relatively broad bone found where extensive protection of organs is required or where broad surfaces of muscle attachment are required<\/dd>\n<dt><strong>Haversian canal<\/strong><\/dt>\n<dd>contains the bone\u2019s blood vessels and nerve fibers<\/dd>\n<dt><strong>intramembranous ossification<\/strong><\/dt>\n<dd>process of bone development from fibrous membranes<\/dd>\n<dt><strong>irregular bone<\/strong><\/dt>\n<dd>bone with complex shapes; examples include vertebrae and hip bones<\/dd>\n<dt><strong>lamella<\/strong><\/dt>\n<dd>layer of compact tissue that surrounds a central canal called the Haversian canal<\/dd>\n<dt><strong>long bone<\/strong><\/dt>\n<dd>bone that is longer than wide, and has a shaft and two ends<\/dd>\n<dt><strong>osseous tissue<\/strong><\/dt>\n<dd>connective tissue that constitutes the endoskeleton<\/dd>\n<dt><strong>ossification<\/strong><\/dt>\n<dd>(also, osteogenesis) process of bone formation by osteoblasts<\/dd>\n<dt><strong>osteoblast<\/strong><\/dt>\n<dd>bone cell responsible for bone formation<\/dd>\n<dt><strong>osteoclast<\/strong><\/dt>\n<dd>large bone cells with up to 50 nuclei, responsible for bone remodeling<\/dd>\n<dt><strong>osteocyte<\/strong><\/dt>\n<dd>mature bone cells and the main cell in bone tissue<\/dd>\n<dt><strong>osteon<\/strong><\/dt>\n<dd>cylindrical structure aligned parallel to the long axis of the bone<\/dd>\n<dt><strong>sesamoid bone<\/strong><\/dt>\n<dd>small, flat bone shaped like a sesame seed; develops inside tendons<\/dd>\n<dt><strong>short bone<\/strong><\/dt>\n<dd>bone that has the same width and length, giving it a cube-like shape<\/dd>\n<dt><strong>spongy bone tissue<\/strong><\/dt>\n<dd>forms the inner layer of all bones<\/dd>\n<dt><strong>suture bone<\/strong><\/dt>\n<dd>small, flat, irregularly shaped bone that forms between the flat bones of the cranium<\/dd>\n<dt><strong>trabeculae<\/strong><\/dt>\n<dd>lamellae that are arranged as rods or plates<\/dd>\n<\/dl>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"cnx-eoc summary\">\n<div class=\"section\">\n<div class=\"section\">\n<div class=\"body\">\n<p><span id=\"m44789-fs-idm153514432\">\u00a0<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":90,"menu_order":46,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":"cc-by"},"chapter-type":[],"contributor":[],"license":[57],"class_list":["post-4985","chapter","type-chapter","status-publish","hentry","license-cc-by"],"part":4958,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4985","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/users\/90"}],"version-history":[{"count":1,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4985\/revisions"}],"predecessor-version":[{"id":4986,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4985\/revisions\/4986"}],"part":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/parts\/4958"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapters\/4985\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/media?parent=4985"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/pressbooks\/v2\/chapter-type?post=4985"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/contributor?post=4985"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/biology\/wp-json\/wp\/v2\/license?post=4985"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}