intro to physio

• support: bones provide attachments for soft tissues and organs
• storage: provided by the bones for calcium salts for body fluids; lipids stored in yellow marow for energy reserves
• blood cell production: occurs in the red marrow and results in increases in red blood cells, white blood cells and platelets
• protection: provided to soft tissues and organs by surrounding them with the skeleton
• movement: when skeletl muscles pull on the bones, movement occurs

osseous tissue

• bones are a supporting connetive tissue; bone cells are called osteocytes
• matrix made of extracellular protein fibers and a ground substance
• calcium phosphate: a salt deposited into the matrix comprises 2/3 of the weight of the 206 bones in the body

• long
• short
• flat (broad, scapula like)
• irregular (complex in shape, like a vertebra)

• diaphysis is fromed of densely packed bone, epiphysis (end) is composed of spongy bone
• each bone has outer covering (periosteum) an innner (endosteum)

bone cells are located in pockets of lacunae which are found between the sheets of matrix called lamellae

repeating fuctional units of concetric cirecles of lamella surrounding a central canal

mature cells that maintian bone structure by recycling calcium salts

no osteons, the lamellae form rods called trabeculae

• large cells that secrete acid and enzymes that break down the matrix (osteolysis) 
• break down bone for calcium

produce new bone through a process called ossification

• intramembranous ossification
• endochondral ossification

calcification (deposition of calcium salts)

• occurs during the fetal development
• osteoblasts differentiate and develop calcified matrix
• ossification begins around an ossification center
• new bone branches outward, develops blood supply
• spongy bone structures remodel into compact flat bones
• skull bones, mandible

• ossification of existin hyaline cartilage
• chondrocytes enlarge and matrix begins to calcify
• bone formation starts at the shaft surface as osteoblasts form
• blood vessels invade inner region of cartilage
• osteoblasts begin to break down spony bone in center (epiphyseal cartilages on the ends continue to enlarge)
• centers of the epiphyses begin to calcify

• at puberty, bone growth accelerates due to sex hormone production
• osteoblasts produce bone faster than the epiphyseal cartilage can expand (eventually they close)

• enlargement in the diameter of bones occurs as it is growing in length
• periosteum cells develop into osteoblasts, producing more matrix on the outer surface of the bone
• osteoclasts erode the inner surface, enlarging the marrow cavity

increase surface area for release of H+ ions by active transport pumps (acidity gnawls away at the bone)

• mineral supply (Calcium salts)
• vitamin D (involved in calcium metabolism)
• vitamin A and C (provide support for osteoblasts)
• growth hormone, sex hormones, thyroid hormone, and the calcium balancing hormones

• parathyroid hormone (PTH) to raise calcium levels
• calcitonin to lower calcium levels in body fluids

• loss of bone mass that impairs normal function and can lead to more fracture
• due to decline in circulating estrogen in women after menopause

• age and ethnicity
• anorexia and amenorrhea