Bone Anatomy and Physiology Lecture Notes

Flashcards to review key concepts related to bone structure, function, and remodeling.

Bone

Primary organs of the skeletal system; rigid framework of body.

Compact bone

Dense bone; relatively dense connective tissue; appears white, smooth, and solid; 80% of bone mass.

Spongy bone

Cancellous or trabecular bone; located internal to compact bone; appears porous (with red bone marrow); 20% of bone mass.

Cartilage

Semirigid connective tissue; more flexible than bone.

Hyaline cartilage

Attaches ribs to sternum; covers ends of some bones; cartilage within growth plates.

Fibrocartilage

Weight-bearing cartilage that withstands compression; located in intervertebral discs, pubic symphysis, and cartilage pads of knees.

Ligaments

Anchor bone to bone.

Tendons

Connect muscle to bone.

Movement (Function of Bones)

Bones serve as the attachment sites for skeletal muscles, soft tissues, and some organs; muscle contraction exerting a pull on the skeleton.

Hemopoiesis (Function of Bones)

Blood cell production occurs in red bone marrow.

Storage of mineral and energy reserves (Function of Bones)

Bone stores body’s reserve of calcium and phosphate -- released from bone into blood as needed; lipids stored in yellow bone marrow of adult bones.

Long bones

Greater in length than width; elongated, cylindrical shaft (diaphysis); most common bone shape; found in upper and lower limbs.

Short bones

Length nearly equal to width; carpal bones tarsals, sesamoid bones, patella.

Flat bones

Flat, thin surfaces, may be slightly curved; provide surfaces for muscle attachment; protect underlying soft tissues; locations: roof of skull, scapulae, sternum, ribs.

Irregular bones

Complex shapes vertebrae, ossa coxae, ethmoid, sphenoid.

Diaphysis

Elongated, usually cylindrical shaft of a long bone.

Epiphysis

Proximal and distal ends of a long bone.

Metaphysis

Region of mature bone between diaphysis and epiphysis.

Periosteum

Tough sheath covering outer surface of bone.

Nutrient foramen

Small opening or hole in bone; artery entrance and vein exit here.

Red bone marrow

Blood cell forming.

Yellow bone marrow

Product of red bone marrow degeneration as children mature; fatty substance; may convert back to red bone marrow during severe anemia (reduced erythrocytes).

Cells in Bone Connective Tissue

Bone is composed of cells and extracellular matrix; includes osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts.

Organic components of Bone Matrix

Osteon produced by osteoblasts, contains collagen protein and semisolid ground substance of proteoglycans and glycoproteins; gives bone tensile strength by resisting stretching; contributes to bone flexibility.

Inorganic components of Bone Matrix

Salt crystals, calcium phosphate, Ca3(PO4)2; crystals deposit around collagen fibers; harden matrix and account for rigidity of bones.

Bone resorption

Bone matrix is destroyed by substances released from osteoclasts; proteolytic enzymes released from lysosomes within osteoclasts chemically digest organic matrix components; freed calcium and phosphate ions enter the blood; occurs when blood calcium levels are low.

Calcitriol

Active form of Vitamin D3; stimulates absorption of calcium ions from small intestine into the blood.

Parathyroid hormone (PTH)

Secreted and released by parathyroid glands in response to reduced blood calcium levels; accelerates conversion to calcitriol by kidney.

Growth hormone

Most important hormone in stimulating epiphyseal plate activity in infancy and childhood.

Thyroid hormone

Modulates activity of growth hormone, ensuring proper proportions.

Testosterone and estrogens at puberty

Promote adolescent growth spurts and end growth by inducing epiphyseal plate closure.

Compact bone

Composed of small cylindrical structures—osteons (Haversian systems); basic functional and structural unit of mature compact bone.

Central canal

Center of osteon where blood vessels and nerves extend through open.

Osteocytes

Mature bone cells, maintain bone matrix; found in small spaces between concentric lamellae (lacunae).

Canaliculi

Tiny, interconnecting channels within bone; allow exchange of nutrients, minerals, gases, and wastes between blood vessels and osteocytes.

Bone Remodeling

Continues throughout adulthood; occurs at periosteal and endosteal surfaces of a bone; dependent upon the coordinated activities of osteoblasts, osteocytes, and osteoclasts; influenced by hormones and mechanical stress.

Decreased tensile strength of bone due to aging

Reduced rate of protein synthesis by osteoblasts; relative amount of inorganic material increases; become brittle and susceptible to fracture.

Bone loss of calcium and other minerals due to aging

Bones thinner and weaker; insufficient ossification.

Osteoporosis

Reduced bone mass; occurs in a significant percentage of older women and a smaller percentage of older men.

Fractures

Breaks in bone; result of unusual stress or sudden impact; increased incidence with age due to normal thinning and weakening of bone.

Stress fracture

Thin break caused by increased physical activity; bone experiences repetitive loads.

Pathologic fracture

Occurs in bone weakened by disease.

Simple fracture

Broken bone not penetrating skin.

Compound fracture

One or both ends of the bone pierce overlying skin.

Bone Fracture Repair

Four steps: (1) Fracture hematoma forms from clotted blood, (2) Fibrocartilaginous callus forms, (3) Hard (bony) callus forms, (4) Bone is remodeled.