Chapter 6 Osseous Tissue and Bone Structure I An Introduction to the Skeletal System p 180 Objective Describe the functions of the skeletal system The skeletal system includes bones of the skeleton cartilages ligaments and other stabilizing connective tissues The 5 primary functions of the skeletal system are 1 Support 2 Storage of minerals calcium and lipids yellow marrow 3 Blood cell production red marrow 4 Protection 5 Leverage force of motion II The Gross Anatomy of Bones p 180 Objectives 1 Classify bones according to shapes and internal tissues 2 Identify the major types of bone markings Bone Shapes p 180 The 6 major bone shapes are 1 Long bones 2 Flat bones 3 Sutural bones 4 Irregular bones 5 Short bones 6 Sesamoid bones Figure 6 1a Long bones are long and thin They are found in arms legs hands feet fingers and toes Figure 6 1b Flat bones are thin with parallel surfaces They are found in the skull sternum ribs and scapula Figure 6 1c Sutural bones are small irregular bones between the flat bones of the skull Figure 6 1d Irregular bones are complex shapes such as spinal vertebrae and pelvic bones Figure 6 1e Short bones are small and thick including ankle and wrist bones Figure 6 1f Sesamoid bones are small flat bones that develop inside tendons near joints of knees hands and feet Bone Markings p 181 The surface features of bones include depressions or grooves where tendons ligaments and neighboring bones attach and tunnels where blood and nerves enter the bone Table 6 1 describes 19 types of surface features and their functions Bone Structure p 183 Figure 6 2a The femur is a long bone The long shaft is the diaphysis The wide part at each end where the femur articulates with other bones is the epiphysis The area where the two connect is the metaphysis The heavy wall of the diaphysis is made of compact or dense bone Inside is a central space called the marrow cavity The epiphysis is made mostly of spongy cancellous bone with an open network structure covered with a thin layer of compact bone called the cortex Figure 6 2b The parietal bone of the skull is a flat bone consisting of a sandwich of spongy bone between 2 layers of compact bone III Bone Histology p 184 Objectives 1 Identify cell types and functions in bone 2 Compare structures and functions of compact bone and spongy bone Osseous tissue is dense supportive connective tissue containing specialized cells The matrix of bone tissue is solid because of the calcium salts deposited around protein fibers in its ground substance The 4 characteristics of bone tissue are 1 Dense matrix containing deposits of calcium salts 2 The matrix contains bone cells within lacunae which are organized around blood vessels 3 Canaliculi form pathways for blood vessels to exchange nutrients and wastes 4 Outer surfaces of bones are covered by periosteum consisting of outer fibrous and inner cellular layers The Matrix of Bone p 184 Two thirds of bone matrix is made of calcium phosphate Ca3 PO4 2 which reacts with calcium hydroxide Ca OH 2 to form crystals of hydroxyapatite Ca10 PO4 6 OH 2 which incorporates other calcium salts and ions as it crystallizes About 1 3 of bone is protein fibers collagen Bone cells are only about 2 of bone mass The Cells of Bone p 184 Bone contains 4 types of cells 1 osteocytes 2 osteoblasts 3 osteoprogenitor cells 4 osteoclasts Figure 6 3a Osteocytes are mature bone cells that maintain the bone matrix Each osteocyte lives in a lacuna between layers lamellae of matrix Canaliculi through the lamellae allow osteocytes to connect at gap junctions between cytoplasmic extensions Osteocytes do not divide The main functions of osteocytes are 1 To maintain the protein and mineral content of the matrix 2 To help repair damaged bone can revert to osteoblast or osteoprogenitor Osteoblasts are immature bone cells that secrete the matrix by the process of osteogenesis secretion of proteins and other inorganic compounds of the matrix Before calcium salts are deposited forming bone the matrix is called osteoid When osteoblasts are surrounded by bone they become osteocytes Osteoprogenitor cells are mesenchymal stem cells that divide to produce osteoblasts Located in the inner cellular layer of periosteum endosteum Assist in repairing bone fractures Osteoclasts are giant mutlinucleate cells that secrete acids and protein digesting enzymes which dissolve bone matrix and release stored minerals the process of osteolysis Osteoclasts are derived from the stem cells that produce macrophages Bone building and bone recycling must be kept in balance When osteoclasts break down bone faster than osteocytes build bone bones become weak Bones get stronger with exercise which causes osteocytes to build bone The Structure of Compact Bone p 185 Figure 6 5 The basic unit of mature compact bone is a longitudinal unit called the osteon in which osteocytes are arranged in concentric circles concentric lamellae around a central canal containing blood vessels Perpendicular to the central canal are perforating canals which carry blood vessels deep into the bone and bone marrow All osteons in long bones run the length of the bone strengthening the bone in that direction A layer of circumferential lamellae wraps around the circumference of the long bone and binds all together The Structure of Spongy Bone p 186 Figure 6 6 Spongy bone does not have osteons Its matrix forms an open network of trabeculae Spongy bone has no blood vessels in its trabeculae The space between trabeculae is filled with another tissue red bone marrow which has blood vessels and supplies nutrients to the osteocytes Red bone marrow is red because it forms red blood cells In other bones spongy bone may hold yellow bone marrow which is yellow because it stores fat Figure 6 7 The femur transfers weight from the hip joint along its length to the knee joint causing stretching or tension on the outside of the shaft lateral and compression on the inside medial The Periosteum and Endosteum p 188 Figure 6 8 The periosteum covers all bones except the parts of joints enclosed within the joint capsule It has an outer fibrous layer and an inner cellular layer The collagen fibers of the periosteum connect the collagen fibers of the bone with those of joint capsules attached tendons and ligaments perforating fibers The periosteum has 3 functions 1 isolates bone from surrounding tissues 2 provides a route for circulatory and nervous supply 3 participates in bone growth and repair Figure 6 8b