True statement about calcium :
Correct Answer: Absorbed in upper small intestine
Description: A i.e. Absorbed in upper small intestineThe body of young adult contains - 1100gm (27.5mol) of Ca; 90% of it is in skeleton. The plasma calcium, is normally about 10gm/dL (5meq/ L, 2.5 mmol / L)Q, of which 50% is ionized. The remainder is bound ionically to negative charged proteins (predominantly albumin & immunoglobins) or loosly complexed with phosphate, citrate, sulphate. It is the free ionizedcalcium, that is a vital second messengerQ and necessary for blood coagulation, nerve conduction and muscle contractionQ.The level of plasma calcium at which fatal tetany occurs is still above the level at which clotting defect would occur.Since the extent of calcium binding by plasma protein is propoionate to the plasma protein level, it is impoant to know the plasma protein level when evaluating the total plasma calcium. An algorithm to correct for protein changes adjusts the totalserum calcium (in mg / dL) upward by 0.8 times the defecit in serum albumin (in gm/dl) or by 0.5 times the defect in serum immunoglobin (in g/dl). So corrected calcium concentration= Total calcium level (mg/dL) + 0.8 mg/dL (0.2MM) for every decrement in serum albumin of 1.0 gm/dL (below the reference value of 4.1 gm/dL of albumin).= Total calcium level (mg/dL) + 0.5 mg/dL for every decrement in serum immunoglobulin of 1gm/dL.PH affects the calcium level, for example tetany appear at much higher total Ca++ levels, if patient hyperventilates, increasing plasma pH. Plasma proteins are more ionized when the pH is high, providing more protein anion to bind with calcium thus reducing effective amount of ionized calcium. In same way acidosis increases ionized Ca++ levelsQ.Intestinal absorption of calcium involves both active (transcellular) and passive (pa racellular) mechanism. Passive absorption is nonsaturable & approximates 5% of intake, whereas active mechanism controlled by 1, 25, (OH)2 D, normally ranges from 20- 70%. Active absorption occurs mainly in proximal small bowel (duodenum & proximal jejunum)Q. Optical rates of Ca** absorption requires gastric acidQ. This is especially true for weakly dissociable calcium supplements as Ca CO3.Calcium interchange between plasma and rapidly exchangeable reservoir of bone is 500mmol per day. Whereas between plasma and stable pool of bone is only 7.5mmol/day. 98-99% of filtered calcium is reabsorbed - 60% of which occurs in PCT and remainder in ascending loop of Henle and distal tubule.Total diffusible calcium1.34- Ionized (Ca++)1.18- Complexed to HCO 3, citrate etc0.16Total nondiffusible (protein bound) calcium1.16- Bound to albumin0.92- Bound to globulin0.24Total plasma calcium2.50
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