Chapter 5 Skeletal System Skeletal system bones joints

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 sex 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