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44 Cards in this Set

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  • Back
What are the different forms of Ca in the body, and their relative percentages?
40% Protein-bound, 60% ultrafilterable (10% complexed to ions, 50% free ionized)
What is the only form of Ca which is biologically active?
free, ionized Ca (blood conc = ~5mg/dL)
What are the symptoms of hypocalcemia?
hyperreflexia, spontaneous twitching, muscle cramps, tingling & numbness
specifically: Chvostek sign (twitching of facial muscles upon tapping of facial nerve), Trousseau sign (carpopedal spasm upon inflation of bp cuff)
What are the symptoms of hypercalcemia?
constipation, polyuria, polydipsia, lethargy, coma, death
How does the ionized Ca concentration change when plasma protein concentration increases?
plasma prot inc is assoc w/inc in total Ca conc, however there IS NOT a change in ionized Ca conc (because changes are slow/chronic)
How does the ionized Ca concentration change in acidemia?
H and Ca compete for same binding spots on albumin, thus acidemia increases ionized Ca concentration
What is positive Ca balance?
Intestinal a/b excedes urinary e/c, excess Ca is deposited in bones (seen in kids)
What is negative Ca balance?
intestinal a/b is less than Ca e/c, and deficit comes from maternal bones (often in pregnant/lactating women)
Where is PTH synthesized?
chief cells of parathyroid glands
What is the stimulus for PTH secretion?
when serum Ca is low (less than 10mg/dL) - (it is actually the ionized Ca conc that specifically regulates PTH)
What effects do chronic changes in Ca concentration have on PTH?
alters transcription of gene, PTH synthesis and storage, and growth of PTH glands
What effect does Mg have on PTH?
low Mg stimulates PTH s/c, high Mg inhibits it, but severe Mg depletion also inhibits (seen in alcoholics)
On what 3 locations does PTH have an effect?
bone, intestine, kidney
What is the effect of PTH on bone?
acts on osteoblasts briefly, but then has long-lasting effects on osteoclasts, which increases bone resorption -> releases Ca AND phosphate into ECF
What is the urinary marker for increased bone resorption?
hydroxyproline (released from bone matrix)
What would be the effect if PTH ONLY acted on bone?
none! Ca and phosphate released in equal amounts, Ca is bound, no change in ionized Ca
What effect does PTH have on the kidney?
1. inhibits Ph r/a (inhibit Na-Ph cotransport in proximal tubule)
2. stimulates Ca r/a in distal tubule
What urinary markers are a result of PTH's actions on the proximal tubule?
phosphate ("phosphaturic effect"), and cAMP
What effect does PTH have on the intestine?
stimulates Ca r/a indirectly via production of 1,25-dihydroxycholecalciferol (active form of vit D) in kidney
What are the symptoms of primary hyperparathyroidism?
inc: PTH; vit D; bone resorption; urinary Ph, cAMP, AND CA (due to high filtered load)-can cause stones; serum Ca

dec: serum Ph
What is a common cause of primary hyperparathyroidism?
PTH secreting parathyroid adenoma
What is the difference between primary and secondary hyperparathyroidism?
parathyroid gland is normal, but excessive PTH is stimulated secondary to hypocalcemia (from vit D deficiency, or renal failure)

*serum Ca is low or normal, never high*
What are the symptoms of surgical hypoparathyroidism?
inc: serum Ph

dec: PTH, vit D, bone resorption, Ph e/c, cAMP e/c, serum Ca
What is a common treatment for surgical hypoparathyroidism?
oral Ca supplement and active vitamin D
What is the cause of pseudohypoparathyroidism?
defective G(s) protein for PTH in kidney and bone (inherited autosomal dominant)
What is another name for pseudohypoparathyroidism type Ia?
Albright's hereditary osteodystrophy
What are the physiologic changes in pseudohypoparathyroidism?
inc: PTH, serum Ph

dec: bone resorption, serum Ca, Ph e/c, cAMP e/c
What is the cause of humoral hypercalcemia of malignancy?
malignant tumor that secretes PTH-related peptide (PTH-rp) (mimics actions of PTH)
What are the physiologic changes in humoral hypercalcemia of malignancy?
inc: serum Ca, Ph e/c, bone resorption, vit D

dec: PTH, serum Ph
What are the common treatments for humoral hypercalcemia of malignancy?
furosemide (inhibits renal Ca r/a, increases Ca e/c), and bone inhibitors (eg etidronate)
What are the physiologic effects of chronic renal failure on Ca and Ph metabolism?
*cant produce active vitamin D*

inc: PTH (secondary), serum P (caused by dec P e/c), bone resorption (due to inc PTH) w/osteomalacia (dec vit D)

dec: vit D (caused by renal failure), serum Ca (caused by dec vit D), Ph e/c (dec GFR)
What does vitamin D deficiency in kids cause?
rickets (growth failure and skeletal deformities)
What does vitamin D deficiency in adults cause?
osteomalacia (new bone fails to mineralize -> bending and softening of weight-bearing bones)
Why is vitamin D critical to bone mineralization?
it provides Ca and Ph to ECF
What is the active form of vitamin D?
Where is the active form of vitamin D produced, and what enzyme is it catalyzed by?
kidney; 1alpha-hydroxylase
What stimulates 1alpha-hydroxylase activity?
low serum Ca, high PTH, low serum PH
What are the actions of 1,25-dihydroxycholecalciferol in the intestine?
increases intestinal Ca a/b (activates vit D-dependent Ca binding protein, calbindin D-28K)
How does PTH mediate the effects of 1,25-dihydroxycholecalciferol on the intestine?
PTH stimulates 1alpha-hydroxylase in the kidney to increase production of active vitamin D
What are the other actions of 1,25-dihydroxycholecalciferol?
increases intestinal Ph r/a, renal r/a of Ca and Ph, and bone resorption (to mineralize new bone)
By what type of cells is calcitonin synthesized?
parafollicular cells of the thyroid
What stimulates secretion of calcitonin?
inc serum Ca
What the primary action of calcitonin?
to inhibit osteoclastic bone resorption, which decreases serum Ca

note: does not participate in minute-to-minute regulation of plasma Ca
For what syndrome could calcitonin be used as treatment?