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44 Cards in this Set
- Front
- 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)
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What is the only form of Ca which is biologically active?
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free, ionized Ca (blood conc = ~5mg/dL)
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What are the symptoms of hypocalcemia?
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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) |
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What are the symptoms of hypercalcemia?
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constipation, polyuria, polydipsia, lethargy, coma, death
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How does the ionized Ca concentration change when plasma protein concentration increases?
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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)
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How does the ionized Ca concentration change in acidemia?
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H and Ca compete for same binding spots on albumin, thus acidemia increases ionized Ca concentration
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What is positive Ca balance?
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Intestinal a/b excedes urinary e/c, excess Ca is deposited in bones (seen in kids)
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What is negative Ca balance?
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intestinal a/b is less than Ca e/c, and deficit comes from maternal bones (often in pregnant/lactating women)
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Where is PTH synthesized?
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chief cells of parathyroid glands
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What is the stimulus for PTH secretion?
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when serum Ca is low (less than 10mg/dL) - (it is actually the ionized Ca conc that specifically regulates PTH)
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What effects do chronic changes in Ca concentration have on PTH?
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alters transcription of gene, PTH synthesis and storage, and growth of PTH glands
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What effect does Mg have on PTH?
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low Mg stimulates PTH s/c, high Mg inhibits it, but severe Mg depletion also inhibits (seen in alcoholics)
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On what 3 locations does PTH have an effect?
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bone, intestine, kidney
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What is the effect of PTH on bone?
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acts on osteoblasts briefly, but then has long-lasting effects on osteoclasts, which increases bone resorption -> releases Ca AND phosphate into ECF
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What is the urinary marker for increased bone resorption?
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hydroxyproline (released from bone matrix)
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What would be the effect if PTH ONLY acted on bone?
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none! Ca and phosphate released in equal amounts, Ca is bound, no change in ionized Ca
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What effect does PTH have on the kidney?
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1. inhibits Ph r/a (inhibit Na-Ph cotransport in proximal tubule)
2. stimulates Ca r/a in distal tubule |
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What urinary markers are a result of PTH's actions on the proximal tubule?
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phosphate ("phosphaturic effect"), and cAMP
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What effect does PTH have on the intestine?
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stimulates Ca r/a indirectly via production of 1,25-dihydroxycholecalciferol (active form of vit D) in kidney
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What are the symptoms of primary hyperparathyroidism?
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inc: PTH; vit D; bone resorption; urinary Ph, cAMP, AND CA (due to high filtered load)-can cause stones; serum Ca
dec: serum Ph |
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What is a common cause of primary hyperparathyroidism?
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PTH secreting parathyroid adenoma
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What is the difference between primary and secondary hyperparathyroidism?
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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* |
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What are the symptoms of surgical hypoparathyroidism?
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inc: serum Ph
dec: PTH, vit D, bone resorption, Ph e/c, cAMP e/c, serum Ca |
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What is a common treatment for surgical hypoparathyroidism?
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oral Ca supplement and active vitamin D
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What is the cause of pseudohypoparathyroidism?
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defective G(s) protein for PTH in kidney and bone (inherited autosomal dominant)
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What is another name for pseudohypoparathyroidism type Ia?
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Albright's hereditary osteodystrophy
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What are the physiologic changes in pseudohypoparathyroidism?
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inc: PTH, serum Ph
dec: bone resorption, serum Ca, Ph e/c, cAMP e/c |
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What is the cause of humoral hypercalcemia of malignancy?
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malignant tumor that secretes PTH-related peptide (PTH-rp) (mimics actions of PTH)
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What are the physiologic changes in humoral hypercalcemia of malignancy?
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inc: serum Ca, Ph e/c, bone resorption, vit D
dec: PTH, serum Ph |
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What are the common treatments for humoral hypercalcemia of malignancy?
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furosemide (inhibits renal Ca r/a, increases Ca e/c), and bone inhibitors (eg etidronate)
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What are the physiologic effects of chronic renal failure on Ca and Ph metabolism?
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*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) |
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What does vitamin D deficiency in kids cause?
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rickets (growth failure and skeletal deformities)
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What does vitamin D deficiency in adults cause?
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osteomalacia (new bone fails to mineralize -> bending and softening of weight-bearing bones)
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Why is vitamin D critical to bone mineralization?
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it provides Ca and Ph to ECF
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What is the active form of vitamin D?
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1,25-dihydroxycholecalciferol
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Where is the active form of vitamin D produced, and what enzyme is it catalyzed by?
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kidney; 1alpha-hydroxylase
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What stimulates 1alpha-hydroxylase activity?
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low serum Ca, high PTH, low serum PH
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What are the actions of 1,25-dihydroxycholecalciferol in the intestine?
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increases intestinal Ca a/b (activates vit D-dependent Ca binding protein, calbindin D-28K)
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How does PTH mediate the effects of 1,25-dihydroxycholecalciferol on the intestine?
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PTH stimulates 1alpha-hydroxylase in the kidney to increase production of active vitamin D
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What are the other actions of 1,25-dihydroxycholecalciferol?
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increases intestinal Ph r/a, renal r/a of Ca and Ph, and bone resorption (to mineralize new bone)
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By what type of cells is calcitonin synthesized?
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parafollicular cells of the thyroid
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What stimulates secretion of calcitonin?
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inc serum Ca
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What the primary action of calcitonin?
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to inhibit osteoclastic bone resorption, which decreases serum Ca
note: does not participate in minute-to-minute regulation of plasma Ca |
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For what syndrome could calcitonin be used as treatment?
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hypercalcemia
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