Chapter 7 - Skeletal System7.1 Introduction(p. 132)A.Bones are very active tissuesB.Each bone is made up of several types of tissues and is an organ.7.2 Bone Structure(p. 132)A.Bones differ in size and shape, yet are similar in several ways.B.Parts of a Long Bone (p. 132; Figs. 7.1-7.2)1.Expanded ends of bones that form joints with adjacent bones are calledepiphyses.2.Articular cartilages (hyaline cartilage) cover the epiphyses.3.The shaft of the bone is the diaphysis.4.A tough layer of vascular connective tissue, called the periosteum, covers thebone and is continuous with ligaments and tendons.5.A bone's shape makes possible its function; bony processes or grooves indicateplaces of attachment for muscles.6.Compact bone makes up the wall of the diaphysis; the epiphyses are filled withspongy bone to reduce the weight of the skeleton.7.The diaphysis contains a hollow medullary cavity that is lined with endosteumand filled with marrow.C.Microscopic Structure (p. 133; Fig. 7.3)1.Bone cells (osteocytes) are located within lacunae that lie in concentric circlesaround osteonic canals.2.Osteocytes communicate with each other by cellular processes in canaliculi.3.Intercellular material consists of collagen and inorganic salts.4.In compact bone, osteocytes and intercellular material are organized intoosteons that are cemented together.5.Osteonic canals contain blood vessels and nerve fibers, and extend longitudinallythrough bone.6.Osteonic canals are interconnected by transverse perforating canals.7.Unlike compact bone, the osteocytes and intercellular material in spongy boneare not arranged around osteonic canals.7.3 Bone Development and Growth(p. 134)A.Bones form by replacing connective tissue in the fetus.B.Some form within sheetlike layers of connective tissue (intramembranous bones), whileothersreplace masses of cartilage (endochondral bones).C.Intramembranous Bones (p. 134; Fig. 7.4)1.The flat bones of the skull form as intramembranous bones that develop fromlayers of connective tissue.2.Osteoblasts deposit bony tissue around themselves.3.Once osteoblasts deposit bone are located in lacunae, they are called osteocytes.4.Cells of the membranous connective tissue that lie outside the developing bonegive rise to the periosteum.D.Endochondral Bones (p. 134; Fig. 7.5)1.Most of the bones of the skeleton fall into this category.2.They first develop as hyaline cartilage models and are then replaced with bone.3.Cartilage is broken down in the diaphysis and progressively replaced with bonewhile the periosteum develops on the outside.
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