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Five primary function of skeletal system

Support, storage of minerals & lipids, blood cell production, protection, leverage

Six bone shapes

Sutural, irregular, short, flat, long, sesamoid

Long bone

Fairly long & slendar, located in the arm, forearm, thigh, leg, palms, soles,fingers & toes, fermur is the largest and heaviset bone

Sesamoid bone

Small,flat & shaped somehat like a seame seed, located near joints at the knee, hands and feet

Sutural bone

Small flat, irregularly shaped bones between the flat bones of the skull

Irregular bone

Complex shapes with short, flat, notched or ridged surfaces. Spinal vertebrae, pelvis, some skull bones.

Short bone

Are small and boxy. Found in carpal and tarsal bones

Flat bone

Are thin, parallel surfaces, parietal bones of the skull, protection for underlying soft tissue. Found in sternum, rib, and scapulae.


Wide part of each end, articulation with the bones, mostly spongy (cancellous) bone, covered witht the compact bone (cortex).


The shaft, a heavy wall of compact bone or dense, a central space called medullary cavity


Where diaphysis and epiphysis meet


Within cranium, the layer of spongy bone between the layers of compact bone

Four type of cells

Osteocytes, osteoblasts, osteoclasts, osteoprogenitor cells


Mature bone cells, live in lacunae, between layer (lamellae) of matrix, does not divide,
Function: Maintain proteins & minerals content of matrix, help repair damaged bone


Immature bone cells that screte matrix compound (osteogenesis), osteoid matrix produced but not yet calcified to form bone, surround by bone become osteocytes.

Osteoprogenitor cell

Assist in fracture repair, located in endosteum, the inner, cellular layer of periosteum Mesenchymal stem cell (partially differentiated squamous), divide to become osteoblasts


Secrete acids, protein, and digesting enzymes, giant multinucleate cells, dissolve bone matrix and released stored minerals(osteolysis), are derived from cells that produce macrophages, found in small depression on the endosteal surfaces


Osteocytes are arranged in concentric lamellae, around the central canal containing blood vessels.

Perforating canal

Perpendicular to the central canal, carry blood vessels into bone and marrow.

Spongy bone

Does not have osteons, open networks of trabeculae, red bone marrow is found between trabeculae of spongy & blood vessels, supplies nutrients to osteocytes, trabeculae has no blood vessels, yellow bone marrow stored fats.


Process of depositing calcium salts, occurs during bone ossifications and other tissues


Ossifies bone that originate as hyline cartilage

Effects of Exercise on bone

Minerals recycling allow bone to adapt to stress, heavily stress bones becomes thicken & stronger, a lack of exercis can cause weak bone

Calcium homeostatis

Skeleton calcium reserve, bones store calcium & other minerals, calcium is the most adundant, calcium ion vital to membranes, neuron, muscle cells, especially the heart.

calcium regulation

Calcium ions in body fluid must be closely regulated, homeostasis is maintained by calcitonin & parathyroid hormone which control storage

Calcitonin & parathyroid hormone

Bones (where calcium is stored)
Digestive tract (absorbed calcium)
kidneys (excreted calcium)

Parathyroid hormone

Increases calcium ions levels by: stimulating osteoclasts, increasing intestinal absorption of calcium, decreasing calcium excretion of kidney


Secreted by "C" cells (parafollicular cells) in thyroid, decreases calcium ions levels by: inhibiting osteoclast activity, increasing calcium excretion at kidney.

Calcium phosphate

About two-thirds of bone matrix is.

Collagen fiber

About one-third of bone matrix is protein.

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