Chapter 5 Skeletal System

Skeletal system: bones, joints, cartilages, ligaments

2 divisions: Axial and Appendicular

Bones – 206Functions

• 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