Anatomy & Physiology: Skeletal System and Bones

206

Axial (80 bones): skull, hyoid, ear ossicles, vertebral column, ribs, sternum. Appendicular (126 bones): limbs plus the pectoral and pelvic girdles.

Support Protection of organs Movement (bones act as levers) Mineral storage (calcium, phosphate) Blood cell formation in red marrow Fat storage in yellow marrow

Long (femur), short (carpals), flat (sternum, skull bones), irregular (vertebrae), sesamoid (patella).

The shaft of a long bone: compact bone around the medullary cavity.

The end of a long bone: spongy bone covered by articular cartilage.

Hyaline cartilage growth plate where a long bone grows in length; it becomes the epiphyseal line when growth ends.

Dense connective tissue membrane covering bone (except at joints); holds osteoblasts, nerves and vessels and anchors tendons and ligaments.

The structural unit of compact bone: concentric lamellae around a central canal carrying blood vessels and nerves.

Osteoblasts build bone matrix. Osteoclasts break down (resorb) bone. Osteocytes are mature bone cells that maintain the matrix.

Compact bone: dense, organized into osteons, forms the outer layer. Spongy (cancellous) bone: a lattice of trabeculae, lighter, holds red marrow.

Intramembranous: bone forms directly from mesenchyme (flat skull bones, clavicle). Endochondral: bone replaces a hyaline cartilage model (most bones, such as the femur).

PTH raises it (activates osteoclasts). Calcitonin lowers it (inhibits osteoclasts). Vitamin D (calcitriol) raises it by increasing intestinal absorption.

Synarthrosis: immovable (skull sutures). Amphiarthrosis: slightly movable (pubic symphysis, intervertebral discs). Diarthrosis: freely movable (synovial joints).

Hinge: elbow, knee Pivot: atlas–axis, proximal radioulnar Ball-and-socket: shoulder, hip Saddle: thumb carpometacarpal Condyloid: wrist (radiocarpal) Plane (gliding): between carpals

Ligaments connect bone to bone. Tendons connect muscle to bone.

Cervical 7, thoracic 12, lumbar 5, sacrum (5 fused), coccyx (usually 4 fused).

First cervical vertebra; has no body and supports the skull, allowing the nodding motion.

Second cervical vertebra; its dens (odontoid process) is the pivot that lets the head turn side to side.

Ribs 1–7 are true ribs (attach directly to the sternum by their own cartilage). Ribs 8–12 are false ribs; 11 and 12 are floating ribs with no anterior attachment.

Frontal, occipital, sphenoid and ethmoid (one each); parietal and temporal (paired).

Membrane-covered soft spots between an infant's skull bones; let the skull compress during birth and allow brain growth.

U-shaped bone in the neck that does not articulate with any other bone; anchors the tongue.

The middle-ear ossicles: malleus, incus and stapes. The stapes is the smallest.

Clavicle and scapula.

Femur

Radius (lateral, thumb side) and ulna (medial, pinky side).

Tibia (medial, weight-bearing) and fibula (lateral, thin).

8 carpals, 5 metacarpals and 14 phalanges.

Loss of bone mass that leaves bones porous and fragile because resorption outpaces formation; common after menopause as estrogen falls.

Open (compound): bone breaks through the skin. Closed (simple): skin intact. Comminuted: bone shattered into three or more pieces. Greenstick: incomplete break, common in children.

Hematoma → fibrocartilaginous (soft) callus → bony (hard) callus → remodeling