Nutritional and metabolic disorders

What is osteopenia?

a failure of bone matrix formation

What is osteomalacia/rickets?

a failure of the bone matrix to mineralize

What is osteopenia/fibrous osteodystrophy?

a failure of the body to maintain a once normal bone matrix

Why is calcium and phosphorous homeostasis important in bone?

bone matrix is composed of hydroapatite (Ca₁₀(PO₄)₆(OH)₂), 99% of calcium and 85% of phosphorous in the body is stored in bone

What is the parathyroid hormone (PTH)?

low serum ionized Ca stimulates parathyroid chief cells to release this to increase Ca and decrease p

What is the effect of parathyroid hormone on bone?

high continuous doses increase RANKL which increases osteoclasts-resorption of Ca and P (kidneys later excrete the P but keep the Ca)

What is another term for active vitamin D?

calcitriol

What is calcitriol?

PTH, low P and low Ca stimulates conversion in the kidney by 1a-hydroxylase to increase Ca and P

What is the effect of calcitriol on bone?

promotes mineralization when their is an adequate supply of Ca/P or bone resorption when they’re deficient

What is calcitonin?

high serum ionized Ca stimulates thyroid C cells to release to decrease Ca (counterbalance of PTH and calcitriol)

What is the effect of calcitonin on bone?

inhibits osteoclasts action so decreases bone resorption and initiates osteocytes of Ca deposition

What is fibroblast growth factor 23 (FGF23)?

high serum P and calcitriol stimulated osteocytes to release to decrease P

What is osteoporosis/osteopenia?

decreased amount of bone with normal bone composition known as “bone atrophy”, results from an imbalance between bone and resorption and deposition causing a decrease in bone density and mass meaning its prone to pathologic fracture

What is the deference between osteroporosis and osteopenia?

osteopenia is a milder degree of bone loss compared to osteoporosis (clinical signs)

What are the causes of osteoporosis/osteopenia?

starvation, disuse, senility, hormonal, corticosteroid-induce, calcium deficiency

What is rickets/osteomalacia?

vitamin D and phosphorus deficiencies causes defective mineralization

Rickets affects what age group?

young growing animals; abnormal endochondral ossification at growth plate; defective bone formation

Osteopenia affects what age group?

adults; only affects osteoid formed during bone remodeling

What is rickets?

disease of the growing skeleton seen as failure in the active physis characterized by accumulation of unmineralized cartilage and osteoid at growth plate and metaphysis (soft easy to cut/saw bone); rachitic rosary

What is fibrous osteodystrophy (FOD)?

hyperparathyroidism (persistent elevation of PTH) causes excessive osteoclastic bone resorption with replacement by primitive fibro-osseous connective tissue leads to weakening of bone

What is primary hyperparathyroidism causes FOD?

autonomous release of PTH from the parathyroid gland (rare); adenomas

What is secondary hyperparathyroidism causes FOD?

reduction in plasma ionized calcium and high phosphorus levels cause the secretion of PTH (nutritional and renal forms)

What is nutritional hyperparathyroidism?

diets high in P and low in Ca (marked imbalances in dietary Ca:P ratios)

What is the correct Ca:P ratio in diets?

1:1 to 2:1

What is considered to be the classic example of nutrition al hyperparathyroidism?

bran disease

What is Bran Disease?

thickening of maxillary bones due to diets composed of primarily cereal grains, bran, oxalates (pasture grasses) which bind to calcium, meat (high in phosphorus), fruit (vitamin D deficiencies)

What is renal hyperparathyroidism?

seen in dogs and cats with chronic renal failure causing hyperphosphatemia and hypocalcemia; horses DO NOT get this!

What is scurvy?

guinea pigs and primates get due to a deficiency of vitamin C since its needed for formation of collagen (proline and lysine hydroxylation-stable triple helix formation, collagen cross-linking), defective collagen can lead to fragile blood vessels and bones

What is white muscle disease?

deficiency of vitamin E/selenium primarily affects type I oxidative fibers, cardiac muscle degeneration may also occur

What is white muscle disease seen as in sheep?

congenital lesions especially in tongue and neck muscles cause a high mortality in 2-4 weeks old lambs

What is white muscle disease seen as in cattle?

myocardial lesions mainly in left ventricle especially in 3-6 week old calves

What is white muscle disease seen as in pigs?

skeletal muscle lesions are less common but can have mulberry heart disease (pale myocardium with hemorrhages) or hepatosis dietetic (centrilobular to massive hepatic necrosis)

What is white muscle disease seen as in horse?

myocardial lesions especially on left ventricular wall or lesions on masticatory and tongue muscles