Bone Mineral Disorders (Pedia) Flashcards
What percentage of body calcium is rapidly exchangable?
1%
What percentage of serum calcium is bound?
40% is bound to albumin
10% is bound to citrate, lactate, bicarbonate, phosphate, and sulfate
50% is biologically active
What are the “second messengers” involved in calcium transport?
cAMP, inositol, 1,4,5-triphosphate, and diacylglycerol
What is the molecular “pore” through which calcium enters the cell
alpha subunit
What are the functions of serum ionized calcium modulator?
signal transduction, cell to cell adhesion, clotting, muscular contraction, cardiac rhythmicity, enzyme action, synthesis and secretion of endocrine factors, cellular proliferation
How does the kidney contribute to the regulation of iCa?
transcellular reabsorption of calcium in the distal convoluted tubules
What portion of the PTH molecule binds to receptors in target organs?
amino terminus
What is the net effect of PTH?
- increased serum calcium
2. decreased serum phosphorus
What is the effect of calcitriol on intestinal absorption?
inc. absorption of calcium and phosphorus
What is the net effect of calcitriol?
increased serum calcium and phosphorus
Calcitonin is primarily secreted by?
parafollicular thyroid cells
What portion of vitamin D synthesis occurs in the liver?
hydroxylation (product is calcidiol)
Calcitonin is used as a marker for which type of malignancy?
medullary thyroid CA
In hypocalcemia, what are the values of total serum and ionized Ca?
Total serum Ca < 7.5 mg/dL
Ionized Ca < 1.2 mmol/L
What are the possible causes of pseudohypocalcemia?
hypoalbuminemia, alkalosis, elevated free fatty acids, lipid infusion, gadolinium contrast
What is the Chvostek sign?
contraction of the orbicularis oris when the masseter muscle is tapped
What is the Trosseau sign?
induced spasm when pressure is applied to the forearm
What are the chronic Ssx of hypocalcemia?
calcification of basal ganglia, cataracts, rickets and osteomalacia
What drugs can cause hypocalcemia?
biphosphanates, diuretics, citrate
What are the causes of transient, abnormal PTH secretion?
hypomagnesemia, critical illness, pregnancy, toxicity
What are the characteristic radiologic findings in hypocalcemic rickets?
widening and cupping of epiphyses, metaphyseal distortion from osteomalacia
What are the 3 forms of hypocalcemic rickets?
nutritional deficiency, vitamin D-dependent, vitamin D-resistant
What is pseudohypoparathyroidism?
resistance to PTH characterized by supranormal PTH levels
What is the first-line treatment for hypocalcemia?
10% calcium gluconate (not over 2 ml/kg in 10 minutes)
What are the maternal risk factors for neonatal hypocalcemia?
maternal diabetes mellitus and hyperparathyroidism, vitamin D or Mg deficiency
What are the causes of hypercalcemia?
excessive PTH production, altered calcium sensing, excessive PTH receptor activity
What are the treatments for severe hypercalcemia?
hydration, loop diuretics, hemodialysis, calcitonin, biphosphonates
