Osseous Tissue PDF

Osseous Tissue Objectives Describe the functions of the skeletal system. Classify bones and identify the major markings. Identify cell types in bone and list their functions. Compare spongy and compact bone. Compare intramembranous and endochondral ossif...

Osseous Tissue Objectives Describe the functions of the skeletal system. Classify bones and identify the major markings. Identify cell types in bone and list their functions. Compare spongy and compact bone. Compare intramembranous and endochondral ossification. Discuss the effects of nutrition, hormones, exercise, and aging on the bones. Describe the types of fractures and certain skeletal system disorders. The skeletal system includes Bones of the skeleton Cartilages, ligaments, and other connective tissues that stabilize and connect Functions of the skeletal system Support and movement Storage of minerals and lipids/energy Blood cell production - hematopoiesis Protection Leverage A Classification of Bones Bone shapes Long bones – femur, humerus Short bones - carpals Flat bones - parietal, sternum Irregular bones – vertebra, pelvis Sesamoid bones– develop in tendon – patella and other variable bones of joints Sutural bones– variable skull bones Bone structure = two types of bone Compact bone (dense) Spongy bone (cancellous) A typical long bone includes Diaphysis - shaft Epiphyses - ends Metaphysis – union of above two Articular cartilage- hyaline cartilage covering of articulating end of bone Marrow cavity or medullary cavity– hollow center Filled with red or yellow marrow 36  Covered by periosteum Lined by endosteum at medullary cavity Bone Histology Osseous tissue Supporting tissue with a solid matrix Minerals deposited in lamellae Covered by periosteum Cells are widely scattered in a matrix of protein fibers (collagen) and a ground substance of calcium salts Cells in bone: Osteocytes = mature bone cells In lacunae Connected by canaliculi Osteoblasts synthesize new matrix = immature bone cells Osteogenesis Osteoclasts dissolve bone matrix Osteoprogenitor cells differentiate into osteoblasts Basic unit of compact bone is an Osteon or Haversian System Concentric lamellae around a central (Havesian) canal Canals contain blood vessels Perforating canals extend between adjacent osteons Interstitial lamellae fill-in space between osteons Circumferential lamellae cover bone Periosteum covers bone – two layers: outer fibrous and inner cellular Spongy bone contains trabeculae, an irregular lattice-work of ununited lamellae Compact bone located where stresses are limited in direction Spongy bone located where stresses are weaker or multi-directional Bone Development and Growth Ossification = converting other tissue to bone Calcification = depositing calcium salts within tissues Two major processes: Endochondral Ossification and Intramembranous Ossification 37 Endochondral ossification Hyaline cartilage model replaced by bone – See Figure in text Begins at Primary Ossification Center Chondrocytes hypertrophy and die, leaving spaces in diaphysis Blood vessels grow around perichondrium, osteoblasts develop, and lay down bone on surface Blood vessels penetrate into central region, medullary cavity forms Repeats at Secondary Ossification Center(s) in epiphysis All hyaline cartilage replaced except for articular cartilage, and epiphyseal/growth plate Continues to regulate bone length Timing of epiphyseal closure/ossification differs by site and gender Appositional growth increases bone diameter by laying down bone on surface Intramembranous ossification Bone forms directly without a hyaline cartilage model Few bones - skull, clavicles Bone is continually changing Remodeling from stress and exercise This is the process of replacement of old bone tissue by new. 25% replaced annually Distal femur replaced every 4 months Other bones (face) may never be fully replaced Hormone levels also influence bone remodeling Growth hormone and thyroxine increase bone mass Calcitonin (from thyroid gland) and PTH (from parathyroid glands) control blood calcium levels Calcitonin (CT) as blood Ca++ increases Increases osteoblast activity Increases bone Ca++ Decreases blood Ca++ Parathyroid Hormone (PTH) as blood Ca++ decreases Increases osteoclast activity Decreases bone Ca++ Increases blood Ca++ The skeleton is a calcium reserve 99 percent body’s calcium in the skeleton Calcium ion concentration maintained by bones, GI tract, and kidneys Calcitonin and PTH regulate blood calcium levels 38 Fracture repair Fracture hematoma External callus Internal callus Bone Markings (Surface Features) Are characteristic for each bone and each individual Markings include Elevations Projections Depressions Grooves and tunnels See table in text for terminology examples Aging and Disorders of the Skeletal System Effects of aging include Osteopenia – normal loss of bone Osteoporosis – severe loss of bone resulting in loss of function Risk factors include: age, sex, race, genetics, poor diet, lack of exercise Other Skeletal Disorders Kyphosis or hunchback Exaggerated thoracic curve – age, diet, rickets, genetics, posture, polio Lordosis or swayback Exaggerated lumbar curve - age, diet, genetics, poor posture Scolosis Abnormal lateral curve – genetic, polio Spina bifida Lamina of vertebra fail to unite at midline, mild to severe Herniated disc Nucleus pulposus bulges through annulus fribosus, compressing nerves Compression fracture of vertebrae Vertebral body height is compressed, requires decompression 39