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bones and skeletal tissue.docx

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Biological Sciences
Kenneth Welch

Bones and Skeletal Tissue Skeletal Cartilage • Contains no blood vessels or nerves • Surrounded by the perichondrium (dense irregular CT) that resists outward expansion • Three types – hyaline, elastic, and fibrocartilage Hyaline Cartilage • Provides support, flexibility, and resilience • Is the most abundant skeletal cartilage • Is present in these cartilages: • Articular – covers the ends of long bones • Costal – connects the ribs to the sternum • Respiratory – makes up the larynx and reinforces air passages • Nasal – supports the nose Elastic Cartilage • Similar to hyaline cartilage but contains elastic fibers • Found in the external ear and the epiglottis Fibrocartilage • Highly compressed with great tensile strength • Contains collagen fibers • Found in menisci of the knee and in intervertebral discs Growth of Cartilage • Appositional – cells in the perichondrium secrete matrix against the external face of existing cartilage • Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within Bones and Cartilages of the Human Body Classification of Bones • Axial skeleton – bones of the skull, vertebral column, and rib cage • Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip Classification of Bones: By Shape • Long bones – longer than they are wide (e.g., humerus) Classification of Bones: By Shape • Short bones • Cube-shaped bones of the wrist and ankle • Bones that form within tendons (e.g., patella) Classification of Bones: By Shape • Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones) • Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones) Function of Bones • Support – form the framework that supports the body and cradles soft organs • Protection – provide a protective case for the brain, spinal cord, and vital organs • Movement – provide levers for muscles • Mineral storage – reservoir for minerals, especially calcium and phosphorus • Blood cell formation – hematopoiesis occurs within the marrow cavities of bones Gross Anatomy of Bones • Compact bone – dense outer layer • Spongy bone – honeycomb of trabeculae filled with yellow bone marrow Structure of Long Bone • Diaphysis • Tubular shaft that forms the axis of long bones • Composed of compact bone that surrounds the medullary cavity • Yellow bone marrow (fat) is contained in the medullary cavity • Epiphyses • Expanded ends of long bones • Exterior is compact bone, and the interior is spongy bone • Joint surface is covered with articular (hyaline) cartilage • Epiphyseal line separates the diaphysis from the epiphyses Bone Membranes • Periosteum – double-layered protective membrane • Outer fibrous layer is dense regular CT • Inner osteogenic layer is composed of osteoblasts and osteoclasts • Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina • Secured to underlying bone by Sharpey’s fibers • Endosteum – delicate membrane covering internal surfaces of bone Structure of Short, Irregular, and Flat Bones • Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside • Have no diaphysis or epiphyses • Contain bone marrow between the trabeculae Location of Hematopoietic Tissue (Red Marrow) • In infants • Found in the medullary cavity and all areas of spongy bone • In adults • Found in the diploë of flat bones, and the head of the femur and humerus Microscopic Structure of Bone: Compact Bone • Haversian system, or osteon – the structural unit of compact bone • Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen • Haversian, or central canal – central channel containing blood vessels and nerves • Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal • Osteocytes – mature bone cells • Lacunae – small cavities in bone that contain osteocytes • Canaliculi – hairlike canals that connect lacunae to each other and the central canal Chemical Composition of Bone: Organic • Osteoblasts – bone-forming cells • Osteocytes – mature bone cells • Osteoclasts – large cells that resorb or break down bone matrix • Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen Chemical Composition of Bone: Inorganic • Hydroxyapatites, or mineral salts • Sixty-five percent of bone by mass • Mainly calcium phosphates • Responsible for bone hardness and its resistance to compression Bone Markings • Bulges, depressions, and holes that serve as: • Sites of attachment for muscles, ligaments, and tendons • Joint surfaces • Conduits for blood vessels and nerves Bone Markings: Projections – Sites of Muscle and Ligament Attachment • Tuberosity – rounded projection • Crest – narrow, prominent ridge of bone • Trochanter – large, blunt, irregular surface • Line – narrow ridge of bone Bone Markings: Projections – Sites of Muscle and Ligament Attachment • Tubercle – small rounded projection • Epicondyle – raised area above a condyle • Spine – sharp, slender projection • Process – any bony prominence Bone Markings: Projections That Help to Form Joints • Head – bony expansion carried on a narrow neck • Facet – smooth, nearly flat articular surface • Condyle – rounded articular projection • Ramus – armlike bar of bone Bone Markings: Depressions and Openings • Meatus – canal-like passageway • Sinus – cavity within a bone • Fossa – shallow, basinlike depression • Groove – furrow • Fissure – narrow, slitlike opening • Foramen – round or oval opening through a bone Bone Development • Osteogenesis and ossification – the process of bone tissue formation, which leads to: • The formation of the bony skeleton in embryos • Bone growth until early adulthood • Bone thickness, remodeling, and repair Formation of the Bony Skeleton • Begins at week 8 of embryo development • Intramembranous ossification – bone develops from a fibrous membrane • Endochondral ossification – bone forms by replacing hyaline cartilage Intramembranous Ossification • Formation of most of the flat bones of the skull and the clavicles • Fibrous connective tissue membranes are formed by mesenchymal cells Stages of Intramembranous Ossification • An ossification center appears in the fibrous CT membrane • Bone matrix is secreted within the fibrous membrane • Woven bone and periosteum form • Bone collar of compact bone forms, and red marrow appears Endochondral Ossification • Begins in the second month of development • Uses hyaline cartilage “bones” as models for bone construction • Requires breakdown of hyaline cartilage prior to ossification Stages of Endochondral Ossification • Formation of bone collar • Cavitation of the hyaline cartilage • Invasion of internal cavities by the periosteal bud, and spongy bone formation • Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses • Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates Postnatal Bone Growth • Growth in length of long bones • Cartilage on the side of the epiphyseal plate closest to the epiphysis is relatively inactive • Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth • Cells of the epiphyseal plate proximal to the resti
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