Chapter 5 Skeletal System Skeletal system: bones, joints, cartilages, ligaments 2 divisions: Axial and Appendicular

Bones – 206 Functions Support/framework Protection Movement Storage – minerals (calcium and phosphorus), fats in internal cavities Blood cell formation – hematopoiesis – in marrow

Classification 2 types of bone (osseous) tissue –Compact – dense, looks smooth –Spongy – needlelike pieces, lots of space Divided into 4 groups based on shape –(1)Long bones Shaft with head at both ends Compact All limbs except wrist and ankles

–(2)Short bones Cube-shaped Spongy Ankles and wrists Sesamoid – form in tendons – ex. patella –(3)Flat bones Thin, flat, curved Compact layered around spongy Skull, ribs, sternum –(4)Irregular bones Don’t fit into other three Vertebrae, hip bones

Long Bone Structure Diaphysis – shaft –Compact bone –Periosteum – protective connective membrane –Perforating (Sharpey’s) fibers connect membrane and bone Epiphyses – ends –Thin compact layer around spongy –Covered by articular cartilage – decreases friction –In adults: epiphyseal line – bony tissue –In kids: epiphyseal plate – cartilage – causes lengthwise growth

Cavity –Yellow marrow (medullary cavity) In adults Fat deposits –Red marrow In kids Blood cell formation In adults this marrow is in spongy, flat bones

Bone Markings Where muscles, tendons, ligaments attach or where vessels and nerves pass –2 types: projections (processes) and depressions (cavities)

Microscopic Anatomy Osteocytes – mature bone cells Found in cavities called lacunae Lacunae form circles (lamellae) around a central canal (Haversian canal) which carries blood vessels and nerves Osteon (Haversian system) – each complex Canaliculi – canals that come off central canal and lead to lacunae Perforating (Volkmann’s) canals – run at right angles to shafts

Formation, growth, & remodeling Ossification – bone formation –2 steps Hyaline cartilage model is covered with bone matrix by osteoblasts (bone forming cells) Cartilage is broken down and leaves the medullary cavity By birth only cartilage regions left are: –Articular cartilage – covers ends – stays for life –Epiphyseal plates – area of longitudinal growth New cartilage is added on surface away from medullary cavity Cartilage closest to cavity is broken down and replaced by bone

Appositional growth – diameter increase –Osteoblasts in periosteum add bone to external diaphysis Growth controlled by growth hormone and sec hormones Bones remodel (change) because of: –Calcium levels in blood Decrease in calcium – PTH released – activates osteoclasts which break down bone to release calcium Increase in calcium – hypercalcemia – calcium deposits form –Pull of gravity and muscles Causes bones to become thicker and form projections for attachment

Fractures Closed (simple) fractures – clean break – under skin Open (compound) fractures – ends pierce skin Reduction – realignment Closed – placed/coaxed by hands Open – surgery

Repair –Hematoma forms –Break splinted by a fibrocartilage callus –Bony callus forms – replaces cartilage –Bone remodeling Types –Comminuted – many fragments – common in older people

–Compression – crushed –Depression – pressed inward – skull fracture –Impacted – ends forced into each other – falls –Spiral – twisting forces – sports –Greenstick – partial break – kids

Other Disorders Sprain – tendon/ligament damage Arthritis –Osteoarthritis (OA) – aka “wear and tear arthritis” –Rheumatoid arthritis (RA) – autoimmune – body’s immune system is attacking itself –Gouty arthritis – gout – uric acid builds up and is deposited in joints Osteoporosis – bone thinning

Joints aka articulations Functions –Hold bones together –Allow movement 2 ways to classify –(1)Function – amount of movement Synarthroses – immovable Amphiarthroses – slightly movable Diarthroses – freely movable

–(2)Structurally Fibrous –Joined by fibrous tissue –Synarthroses –Ex. skull sutures Cartilaginous –Joined by cartilage –Most amphiarthroses –Ex. pubic symphysis, intervertebral joints –A few synarthroses – epiphyeal plates, btw ribs and sternum

Synovial –Separated by a joint cavity w/ synovial fluid –Found in limbs –4 features »Articular cartilage over ends »Fibrous articular capsule »Joint cavity – enclosed by capsule »Contains synovial fluid »Reinforcing ligaments –May have bursae (fluid filled sacs) or a tendon sheath (completely wraps tendons in high friction areas)

Synovial joint types – based of shape –Plane – gliding – flat surfaces – wrist – nonaxial –Hinge – uniaxial – elbow, knee, fingers –Pivot – uniaxial – radioulnar joint, atlas and axis

–Condyloid – biaxial – side/side and back/forth Btw metacarpals and phalanges –Saddle – biaxial – carpometacarpal of thumb – twiddling –Ball and socket – multiaxial – shoulder, hip