Calcium is absorbed in the GI tract under the influence of:
A. Vitamin D
B. Glucose
C. HCl
D. Vitamin C
Correct Answer: A. Vitamin D
Calcium is absorbed in the GI tract under the influence of vitamin D in its biologically active form. Vitamin D also increases the intestinal absorption of calcium, as well as bone resorption and the tubular reabsorption of calcium. The effects on intestinal reabsorption of calcium and bone resorption seem to be due primarily to the active metabolite 1,25-DHCC, but other metabolites may contribute to some of the other effects on serum calcium.
Option B: Abnormal calcium regulation may contribute to reduced ?-cells function, thereby promoting altered glucose homeostasis. In vitro studies have also found that high cytosolic calcium may contribute to insulin resistance within adipocytes and skeletal muscle.
Option C: Oral calcium carbonate (0-5 g, pH 9-4) increased serum gastrin and gastric acid output with slight but insignificant change in serum calcium. A similar rise in serum calcium during an intravenous infusion of calcium gluconate failed to increase serum gastrin and gastric acid output.
Option D: Vitamin C blocks cells that break down our bones and helps us make more cells responsible for bone formation. It also regulates important bone-building minerals, like calcium, in our bodies. Most people can get enough vitamin C through diet alone.
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