Bones
A. Functions of Bones
1. Support. Provide a hard framework.
2. Protection of many vital organs.
3. Movement. Act as levers with skeletal muscles moving them. Joints control possible movements.
4. Mineral storage. Especially calcium and phosphate, critical minerals for cellular function. Continuous deposition and withdrawal. Exquisite control of Ca++ (calcium ions) levels necessary for function of nerves, muscles, blood coagulation and other functions. Most of Ca++ in body in bones. Osteoclasts & osteoblasts controlled by hormones which regulate blood levels of Ca++.
5. Blood cell formation. Certain bones have active marrow.
B. Structure
1. Compact-Dense outer layer, looks smooth and solid. Contains cylinder of concentric layers with central canals.
a. Haversian system = circles of bone (lamella) with central canal (Haversian canal)
b. Central canal contain blood vessels & nerves. Connected at right angles to network.
c. Perforating small canals - blood vessels & nerves go through lamellar bone to supply osteocytes. Connect to periosteum.
d. Osteocytes live in bone, maintain it. Live in holes called lacunae. Connect to each other and central canal via canaliculi, little canals. Pass nutrients, waste products
2. Spongy- honeycombed, open spaces. Same structure as compact but less regular.
Withstand maximum stress with least weight. In bone interiors & weird weight bearing bones like head of femur. Not organized in lamella. Trabeculae are arranged along lines of stress. Osteocytes interconnected by canaliculi. Nutrients reach osteocytes by diffusing through the canaliculi from capillaries. Osteoporosis - More bone resorption than deposition, very weak bone.
Skeletal System
A. Axial skeleton
Principal supportive structure of the body includes skull, vertebrae, sternum & ribs. Central column of the skeleton from which arms and legs & bones that help them hang.
B. Appendicular skeleton
Provides fairly freely movable frame for upper & lower limbs. Includes pectoral (shoulder) & pelvic (hip) girdles, arms, forearms, wrists, hands, thighs, legs & feet.
Joints
Bones -> framework; muscles -> power; joints provide mechanism that allows body to move
A joint is where 2 adjacent bones or cartilages or combination thereof meet.
Most joints movable, some not.
General Structure
1. Articular cartilage
2. Joint (synovial) cavity
3. Articular capsule - external layer = fibrous capsule, inner layer is a synovial membrane
4. Synovial fluid-occupies all free spaces within the joint capsule, fluid derived by filtration from blood flowing thorough the capillaries in the synovial membrane
5. Reinforcing ligaments
Skeletal System