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Skeletal System Functions

Support, protection, leverage, movement, hemopoiesis, storage

Classification of bones by shape

Long, short, flat, irregular, sesamoid, and sutural bones

Long bones

Slightly curved for strength, levers (femur, arm and forearm, for example)

Short bones

Weight transfer - small and boxy (carpal and tarsal bones)

Flat bones

Thin, roughly parallel surfaces, for muscle attachment and protection (roof of skull, sternum, rips, scapula)

Irregular bones

For muscle attachment, complex shapes and notched or ridged surfaces (vertebrae, pelvic bones)

Sesamoid bones

Stress, develops within tendons (patella)

Sutural or wormian bones

small, flat irregularly shaped bones between flat bones of the skull. Individual variations on size, position and number of bones

Anatomy of a long bone

Epiphysis, Metaphysis, Diaphysis (shaft), Spongy bone, compact bone, marrow cavity


The ends of long bones, consist largely of spongy bone covered by a thin layer (cortex) of compact bone


Narrow zone where diaphysis and epiphysis are connected


tubular shaft in middle of bone

Spongy bone

Forms an open network of struts and plates called trabeculae, makes up the interior of the bone (stress from many directions), red marrow found here

Compact bone

Relatively solid bone always located on the surface of the bone where it forms a sturdy protective layer (stress in one direction)

Marrow (medullar) cavity

central space within the diaphysis

Bone marrow

loose connective tissue, yellow bone marrow is full of fat cells, red bone marrow mixture of mature and immature red and white blood cells and the stem cells that produce them. Yellow is energy reserve, red important site of blood cell formation

4 cells within bone

Osteoprogenitor, osteoblasts, osteocytes, osteoclasts


Form osteoblasts, undifferentiated, inner layer of periosteum (the endosteum) spongy bone


Form bone through osteogenesis, make and release proteins and other organic components of the matrix


Mature cells, develop from osteoblasts, control day-to-day activities (each occupies a lacuna, a pocket sandwiched between layers of matrix


Resorb bone, release Ca2+ and PO42- into blood (this erosion is called osteolysis)


Covers bone, not at articulations


Lines marrow cavity, central canals, surrounds trabeculae


process of converting other tissues to bone


process of depositing calcium salts into tissues

Intramembranous Calcification

Begins when osteoblasts differentiate within connective tissue, produces dermal bones (cranial, facial, sesamoid bones)

Endochondral Ossification

Embryo about the 4th week, hyaline cartilage skeleton is replaced by bone, most of skeleton is formed this way. Increases bone length

Epiphyseal plate

Narrow cartilaginous region separates epiphysis and diaphysis in a growing bone, in adults you can see where the plate used to be in "epiphyseal lines"

Appositional growth

bone diameter increases

Hormonal Regulation of Bone Growth

Before puberty, hGH (human growth hormone), insulin-like growth factors (IGFs), thyroid hormone, insulin. At puberty, increase in testosterone, estrogens


Organic and mineral components of bone are continuously recycled and renewed, especially in response to weight-bearing stress/exercise

Loss of mass in bone

Caused by no stress, lack of Ca2+, lack of osteoblast activity, increase in osteoclast activity (age, exercise, hormones, Calcium and phosphate ion absorption and excretion, genetic and environmental factors

Calcium is required for homeostatis

Muscle cells contraction, neurons, hormone secretion from glands, tight junctions, blood clotting


Comes from kidneys, promotes calcium and phosphate absoption along digestive tract

Effects of Diet on Bone

Vitamin A & K stimulates osteoblasts, C synthesis of collagen, osteoblast differentiation, Vitamin K and B12, protein synthesis

Immediate control of free Ca2+ levels

Blood calcium drops, parathyroid senses, secretes PTH to increase plasma calcium


parathyroid hormone. Stimulates osteoclasts to resorb bone, kidneys decrease calcium secretion, phospate still excreted. Stimulates osteocytes

Regulation of calcium levels over time

intestinal absorption and renal excretion or reabsoption. Promotes formation and action of calcitriol (intestinal absorption of calcium and phosphate, stimulates osteoclast activity, stimulates kidneys to reabsorb more calcium)

Calcitonin function

decreases the calcium concentration

Complete absence of PTH for a few days

results in death, usually asphyxiation

Vitamin D Deficiency

Impairs calcium absorption, PTH maintains levels at expense of bone, Rickets causes bones to become soft and deformed (bow legged), osteomalacia in adults

Simple or closed fractures

doesn't break through skin

Open or compound fractures

ends pierce through skin

Impacted fractures

one end of break driven into other end

Comminuted fractures

shatter the affected area into a multitude of bony fragments

Greenstick fractures

Only one side of the shaft is broken, and the other is bent (children whose bones aren't fully developed)

Pott's fractures

occurs at the ankle and affects both bones of the leg

Colle's fractures

break in the distal portion of the radium, typically the result of reaching out to cushion a fall

Displaced fractures

produce new and abnormal bone arrangements

Spiral fractures

produced by twisting stresses that spread along the length of the bone

Pathologic fractures

From weakening caused by disease, e.g. bone cancer

Stress fractures

Tiny fractures caused by repeated stress, e.g. running

Transverse fractures

breaks a shaft bone across its long axis

Epiphyseal fractures

occur where bone matrix is undergoing calcification and chondrocytes are dying. Can cause stopping of growth

Compression fractures

occur where vertebrae subjected to extreme stresses, such as landing on your seat when you fall

Aging and the Skeletal system

Physical activity decreases, bones lose mass, decrease protein synthesis (bones brittle, more likely to break), decreasing size and reiliency of intervertebral discs causes some height loss, Osteoporosis


Post-menopausal females decrease in estrogen, decrease osteoblast activity (osteoclasts more active?), inadequate exercise and diet, 10x more common in women


Any projection or bump


An extension of a bone making an angle with the rest of the structure


Large rough projection where tendons and ligaments attach


Smaller rough projection where tendons and ligaments attach


small rounded projection where tendons and ligaments attach


Prominent ridge where tendons and ligaments attach


A low ridge where tendons and ligaments attach


A pointed process where tendons and ligaments attach


Expanded articular end of an epiphysis, separated from the shaft by the neck (formed for articulation with adjacent bones)


Narrow connection between the epiphysis and the diaphysis (formed for articulation with adjacent bones)


smooth rounded articular process (formed for articulation with adjacent bones)


Smooth grooved articular process shaped like a pulley (formed for articulation with adjacent bones)


Small flat articular surface (formed for articulation with adjacent bones)


A shallow depression


A narrow groove


Rounded passageway for blood vessels or nerves


Passageway through the substance of a bone


Elongate cleft

Sinus or antrum

Chamber within a bone, normally filled with air


Inflammation of bone marrow, bacterial

Supernumerary bone

Extra bone, often a finger or toe

Rheumatoid arthritis

Chronic, joint inflammation, swelling stiffness and pain, cartilage changes can result in crippling deformity

Cleft palate

Palate, portion of lower face doesn't form properly


noninflammatory, degeneration of bones and joints

Osteogenic sarcoma

worst bone cancer, can metastasize to lungs, usually starts in long bones


Too much hGH


Too little hGH


Over secretion of hGH in adult, growth especially in face and hands

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