Skeletal System, Bone Structure, and Development

Flashcards covering the skeletal system's organs, bone shapes, microscopic structure, metabolic functions, and growth processes.

Skeletal System Organs

Includes the bones of the skeleton and the structures that connect bones to other structures including ligaments, tendons, and cartilages.

Long Bones

Bones consisting of a shaft with two ends; examples include the femur (thigh bone) and humerus (upper arm bone).

Short Bones

Cube-like bones such as the carpals (wrist bones) and tarsals (ankle bones).

Flat Bones

Thin and usually curved bones; examples include most skull bones, the sternum (breast bone), scapulae (shoulder blades), and ribs.

Irregular Bones

Bones that are not long, short, or flat, such as the vertebrae and auditory ossicles.

Sesamoid Bones

Bones that develop within a tendon; the patella is a human example.

Diaphysis

The shaft of a long bone consisting of a central medullary cavity filled with yellow marrow, surrounded by a thick collar of compact bone.

Epiphyses

The expanded ends of a long bone consisting mainly of spongy bone surrounded by a thin layer of compact bone.

Epiphyseal Line

The remnant of the epiphyseal disc or plate, which is cartilage at the junction of the diaphysis and epiphyses (growth plate).

Periosteum

The outer fibrous protective covering of the diaphysis, richly supplied with blood vessels, lymph vessels, and nerves; contains an osteogenic layer with osteoblasts and osteoclasts.

Nutrient Foramen

A perforating canal that allows blood vessels to enter and leave the bone.

Endosteum

The inner lining of the medullary cavity containing a layer of osteoblasts and osteoclasts.

Articular Cartilage

A pad of hyaline cartilage on the epiphyses where long bones join, acting as a "shock absorber."

Compact Bone

Solid, dense, and smooth bone tissue where the structural unit is the Osteon (Haversian system).

Osteon (Haversian System)

The structural unit of compact bone containing osteocytes in lacunae, concentric lamellae, and a central Haversian canal.

Canaliculi

Communicating canals within compact bone that connect the lacunae of osteocytes.

Perforating (Volkmann's) Canals

Canals that run at right angles to central canals, connecting the blood and nerve supply of adjacent osteons.

Spongy (Cancellous) Bone

Bone consisting of poorly organized trabeculae (small needle-like pieces) and open spaces filled with red bone marrow.

Hematopoiesis

The formation of all blood cells, occurring in the red marrow of spongy bone.

Hydroxyapatite

Primarily calcium phosphate with the formula $[Ca_3(PO_4)_2 \text{.} (OH)_2]$ which gives bone its hardness and rigidity.

Parathyroid Hormone (PTH)

Hormone secreted when blood calcium is low; stimulates osteoclast activity, causes kidneys to reabsorb $Ca^{2+}$, and increases intestinal absorption of calcium.

Calcitonin

Hormone secreted by the thyroid gland when blood calcium is high; inhibits bone resorption, increases osteoblast activity, and causes kidneys to secrete excess $Ca^{2+}$ into urine.

Intramembranous Bones

Bones where ossification forms on or within a fibrous connective tissue membrane, such as skull bones and clavicles.

Endochondral Bones

Bones where ossification occurs within a hyaline cartilage model; includes most bones of the skeleton.

Appositional Growth

The process by which bones grow in thickness or diameter.

Osteoclasts

Large multinucleated cells originating from monocytes that secrete lysosomal enzymes and acids to decompose calcium salts for bone resorption.

Osteoblasts

Bone-building cells that lay down bone matrix on calcified cartilage or outer surfaces.

Vitamin D

A nutrient that increases intestinal absorption of calcium; deficiency causes rickets in children and osteomalacia in adults.

Vitamin C

A nutrient required for collagen synthesis and bone matrix maintenance; deficiency causes scurvy.

Hypertrophy

The stimulation of bone growth resulting from physical stress and exercise.