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Ch 6 skeletal system (6.3 (ossification 2 patterns (Endochondral…

- - - - when a bone forms on or within a fibrous CT membrane
      - Flat bones are formed in this manner
    - - when bone is formed from hyaline cartilage model
      - most bone formed in this manner
      - primary ossification center hardens as fetus and infant
      - secondary ossificatio center develop in child and harden during adolescence and early adulthood
- - - - the bone in the legs and pelvis support the trunk
      - the atlas (1st vertebra) supports the skull,etc
    - - the skull protects the brain
      - the rib cage protects the heart and lungs,etc
    - - skeletal muscles attached to bones and tendons
      - serves as a lever to move bone
    - - all blood cells are formed in the red marrow of certain bones
    - - calcium
      - phosphorus
      - others
      - also a means of calcium homostasis
    - - yellow marrow in the shaft of long bones
      - serves as an important chemical energy reserve
- - - - diaphysis = shaft consist of a central medullary cavity (filled with yellow marrow). surrounded by a thick collar of compact bone.
      - epiphyses: expanded ends. Consist mainly of spongy bone surrounded by a thin layer of compact bone.
      - epiphyseal line: remnant of epiphyses disk/ plate. cartilage at the junction of the diaphysis and epiphyses (growth plate)
      - Periosteum: outer,fibrous, protective covering of diaphysis
        
        richly supplied with blood and lymph vessels nerves ( nutrition): Nutrient foramen=performing canal allowing blood vessels to enter and leave bone.
        
        osteogenic layer contains osteoblast and osteoclast
        
        serves as insertion for tendons and ligaments
      - endosteum : inner lining of medullary cavity . conatains layer of osteoblast and osteoclast
      - articular cartilage: pad of hyamine cartilage on the epiphyses where long bone articulate or join. Shock absorbers
      - covered by peristeum covered compact bone
      - surrounding endosteum spongy bone
      - looks like a sandwich (Two layers of compact bone)( hematopoietic tissues(Red marrow) located in the spongy bone within the epiphyses of long and flat bones
    - - form bone matrix by secreting collagen
      - can't undergo mitosis
    - - mature bone cells derived from osteoblast
      - principle bone cells
      - can't undergo mitosis
      - maintain daily cellular activities
    - - functions in bone resorption(bone destruction)
      - important in development, growth, maintenance and bone repair
    - - primarily collagen gives bone its high tensile strength
      - contains glycolipids and glycoproteina
    - - hydroxyapatite
        
        calcium phosphate gives bone its hardness or rigidity
    - - solid dense smooth
      - structural unit
        
        harversion system or osteon
      - elongated cylinders cemented together to form the long axis of a bone
      - components of haversian system
        
        osteoscytes lie in the lacunaw that have laid down a matrix of collagen and calcium salts in concentric lamelle around a central harversian canal containing blood vessels and nerves
      - communicating canals within compact bone
        
        canaliculi connect the lacunae of osteocytes
        
        volkmann's canal connect the blood & nerve supply of adjacent harversian system together
        
        runs at right angles to and connects addjacent harversian canals
    - - consist of poorly organized trabeculae ( Small needle like pieces of bone)
      - lots of open space between them
      - nourished by diffusion form nearby haversian canals
- - - - distal femur is replace every 4 month
      - diaphysis may not be fully replaced during one's life
    - - secrets lysomal enzymes that digest the organic matrix
      - secrete acids that decompose calcium salts into Ca++ and PO4- ions, which can then enter blood
    - - invloves 2 hormones (negitive feedback)
        
        parathyroid hormone (PTH), secreted by parathyroid glands when blood calcium levels are low
        
        simulates osteoclast activity (resorption of bone occurs) releases Ca++ into blood
        
        Causes kidney tubules to reabsorbs Ca++ back into blood causes intestinal muscosa to increase dietary absorption of Ca++
        
        Causes an increase in blood calcium levels (back to normal)
        
        Calcitonin secrets the thyroid gland when blood calcium levels are high
        
        inhibits bone resorption increases osteoblast activity
        
        causes kidney tubules to secrete excess Ca++ into the urine
        
        decrease in blood calcium levels back to normal
    - - calcium
      - phosphorus
      - magnesium ( normal osteoblast)
      - boron inhibits calcium loss
      - manganese (need for new matrix)
    - - vitamin D increases absorption of dietary calcium and retards urine loss (causes rickets in children and osteomalcia adults
      - Vitamin C helps maintain bone matrix causes scurvy
      - Vitamin A required for bone reabsorption controls the activity, distribution and cordination of osteoblast and osteoclast
      - Viatmin B12 may play a role in osteoblast activity
    - - Human Growth Hormone
        
        secreted by pituitary gland
        
        responsible for the general growth of all tissues, stimulates reproduction of cartilage cells at epiphyseal plate
      - Sex hormones
        
        estrogen + androgen (Testosterone)
        
        degenerates cartilage cells in epiphyseal plate
        
        aid in osteoblast activity
        
        estrogen effect is greater than androgen effect thyroid hormones
        
        T3 = triiodothyronine
        
        T4=thyroxine
        
        stimulates replacement of cartilage by bone in epiphyseal plate
- - - - after menopause female lose bone more rapidly
      - by age 70 bone loss between sexes is similar
    - - osteoporosis
        
        severe bone loss
        
        affects normal function
        
        over age 45, occurs in : 29% of women
        
        after menopause risk goes up
        
        because of less estrogen being produced
        
        18% of men less common in men under 60
        
        because of androgen are still produced