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35 Cards in this Set
- Front
- Back
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What are the three major tenants of calcium physiology?
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1) Calcium is absorbed through the gut
2) Calcium is excreted by the kidney 3) Calcium is stored in the bones |
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How does LOW free serum calcium affect parathyroid hormone levels?
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Low serum calcium stimulates parathyroid hormone release.
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How does HIGH serum calcium affect parathyroid hormone levels?
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High serum calcium inhibits the release of PTH.
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What are the two Ca absorptive pathways in the gut?
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1) Saturable - mediated by active Vit. D3
2) Non-saturable |
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Why is a daily supply of calcium so important?
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Because of the 200 ml obligatory Ca loss through normal renal function. If the obligatory loss of Ca is not supplied in the diet, it instead must come from the bones.
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What is the effect of active Vitamin D on calcium absorption in the gut?
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Increasing the level of active Vitamin D in the blood will increase Calcium absorption in the gut.
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How does PTH affect calcium levels in the blood?
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An increase in PTH favors osteoclast activity in the bones. Also, a rising PTH level decreases calcium excretion in the kidney.
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What are the three main regulators of calcium absorption?
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1) Diet
2) 1,25-(OH)2-Vitamin-D 3) Age |
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The blood concentration of <blank> is the most important factor in controlling the efficiency of absorbed calcium.
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The blood concentration of 1,25-hydroxy-Vitamin-D is the most important factor in controlling the efficiency of absorbed calcium.
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Is perspiration an important source of insensitive calcium loss?
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Perspiration can account for over 300 mg calcium losses in performing athletes.
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What is the main site of hormonal regulation of calcium resorption in the kidney?
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The Distal Convoluted Tubule is the main site of hormonally-controlled calcium resorption in the kidney.
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How does PTH affect calcium resorption in the kidney?
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PTH increases the number of open calcium channels in the DCT, thereby increasing the amount of calcium resorbed.
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If PTH and serum calcium is low, what will be the net effect of Ca and Vit. D treatment without PTH supplementation?
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No PTH -> Calcium excretion, high urinary calcium, renal calcification and kidney failure.
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Why is IVNS the cornerstone of therapy for high serum calcium?
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In the Proximal Convoluted Tubule, where calcium (and sodium) resorption is passive, Sodium loss (due to rehydration) will "drag out" calcium as well.
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What is the most common cause of hypercalcemia?
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Increased release of bone calcium is the most clinically relevant cause of hypercalcemia.
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What effect does acute acidosis have on free serum calcium levels?
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Acidosis will acutely increase free calcium from the total calcium pool, as there are more protons competing for charged moieties on carrier molecules.
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Where in the body are Calcium Receptors expressed?
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1) Parathyroid Gland - rising serum calcium depresses PTH release
2) Th Asc. Loop of Henle - extracts more Ca from urine if serum concn. is low, and vice versa. |
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How does high serum calcium -> nephrogenic diabetes incipidus?
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With very high serum Ca, the TALH calcium receptor signaling interferes with ADH. This results in dilute urine, dehydration and, paradoxically, increased Ca resorption in the PCT.
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Where is the inactive Vitamin D precursor converted to its active form?
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Two hydroxylation steps are needed:
1) Vit D -> 25-OH-Vit D: in the LIVER 2) 25-OH-Vit D -> 1,25-OH2-Vit D: in the KIDNEY |
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What affect does chronic kidney disease have on circulating Vitamin D?
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1) Less active Vit D hormone is produced, due to a loss of cellular enzyme
2) Decreased phosphate clearance leads to high blood phosphate levels, a suppression signal to the Vit. D converting enzyme. |
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How do glucocorticoids affect bone health?
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Glucocorticoids blunt the effect of Vitamin D hormone on intestinal cell gene transcription, lowering calcium intake from the diet.
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What effect does Vitamin D have on PTH secretion from the parathyroid gland?
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In the presence of hypercalcemia, Vitamin D may inhibit the release of PTH by the parathyroid gland. HOWEVER, Vitamin D may NOT inhibit PTH release if serum calcium is LOW.
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What three factors increase PTH secretion?
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1) Low serum calcium
2) Low levels of 1,25-OH2-Vit D 3) High levels of serum Phosphate |
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What two pathologies are most common in Renal Osteodystrophy?
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Renal Osteodystrophy is common in dialysis patients. Two types:
1) High PTH/Osteitis Fibrosa from high bone turnover 2) Chronic low PTH from excessive Ca and Vit D therapy lead to adynamic bone disease. |
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What is Paget's disease?
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Unusual disease characterized by patches of high bony turnover.
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What is the major characteristic of Osteoporosis?
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Osteoporosis is a disease characterized by decreased bone mineral density. OP is a problem with bone formation.
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What is the major characteristic of Osteomalacia? What bone substance is found in excess of normal?
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Osteomalacia is characterized by excessive unmineralized osteoid. Osteoid is then found in percentage excess of normal.
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Which is generally more symptomatic - HYPOcalcemia, or HYPERcalcemia?
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Generally HYPOcalcemia is much more symptomatic.
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What are the more common clinical signs of hypocalcemia?
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Neuro: numbness/tingling, irritability, brisk reflexes, seizures
MS: cramps, Trousseau's, spasms, tetany CV: long QT, CHF |
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Lower serum calcium leads to what result in muscles?
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Low serum calcium leads to increased muscle excitability and tetany. Hypocalcemia = Tetany!
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Does a lower serum calcium level mean more or less muscle excitability?
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A low serum calcium means more muscle excitability:
Hypocalcemia = Tetany! |
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A decline in serum phosphate will trigger what reaction in the kidney?
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Falling serum phosphate levels will trigger the conversion of 25-OH-VD to 1,25-OH2-VD in the kidney.
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What three ions are stored in the bone?
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Calcium, phosphate and bicarbonate.
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Is the body's ability to absorb gut calcium endless?
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No. The main calcium transporters in the gut may be saturated by high levels of dietary calcium.
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Besides Vitamin D, what four factors influence calcium absorption from the gut?
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1) Bioavailability and solubility (complex reasons)
2) Anion imbalance (sticky negatives in diet) 3) Stomach pH (low pH -> low absorption) 4) Amount of calcium per meal (saturation) |
