what are the five functions of the skeletal system?
- 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
what is another name for bones?
what are the characteristics of bone 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
what are four general shapes of bones?
- flat (broad, scapula like)
- irregular (complex in shape, like a vertebra)
describe the long bone
- diaphysis is fromed of densely packed bone, epiphysis (end) is composed of spongy bone
- each bone has outer covering (periosteum) an innner (endosteum)
what is lamellae
bone cells are located in pockets of lacunae which are found between the sheets of matrix called lamellae
what are osteons?
repeating fuctional units of concetric cirecles of lamella surrounding a central canal
what are osteocytes?
mature cells that maintian bone structure by recycling calcium salts
what is different about spongy bones?
no osteons, the lamellae form rods called trabeculae
what is osteoclasts?
- large cells that secrete acid and enzymes that break down the matrix (osteolysis)
- break down bone for calcium
what are osteoblasts?
produce new bone through a process called ossification
what are two types of bone formation?
- intramembranous ossification
- endochondral ossification
what is similar about the two types of bone formation?
calcification (deposition of calcium salts)
describe the process of intramembrane ossification.
- 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
describe the process of endochondral ossification
- 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
why is there an epiphyseal line in endochondral ossification in adult bones?
- at puberty, bone growth accelerates due to sex hormone production
- osteoblasts produce bone faster than the epiphyseal cartilage can expand (eventually they close)
describe appositional growth and bone remodeling
- 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
why does osteoclast has a ruffled border?
increase surface area for release of H+ ions by active transport pumps (acidity gnawls away at the bone)
what are the requirements for bone growth?
- 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
how is the calcium balance regulated?
- parathyroid hormone (PTH) to raise calcium levels
- calcitonin to lower calcium levels in body fluids
what is osteoporosis
- loss of bone mass that impairs normal function and can lead to more fracture
- due to decline in circulating estrogen in women after menopause
what are the controllable and uncontrollable risksof osteoporosis?
- age and ethnicity
- anorexia and amenorrhea