Increase Blood Calcium Levels

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When blood calcium levels drop below normal, the body, in order to maintain its homeostatic calcium level, responds in various ways to increase those levels again. The body does this with the help of three hormones. The first one, PTH or parathyroid hormone, is secreted by the parathyroid gland. The only function of the parathyroid gland is to keep calcium within a certain range in the blood. The parathyroid gland consists of 4 tiny glands that are attached to the thyroid gland located in the neck. When blood calcium levels drop, the parathyroid gland, which has receptors that sense that drop, produces PTH in the chief cells and releases it into the blood. PTH then travels to bone and the kidneys. In bone, PTH binds to receptors on osteoclasts and causes them to release…show more content…
It is derived from cholesterol, which in the skin is converted to 7-Dehydrocholesterol. Once the skin is exposed to the sun, 7-dehydrocholesterol is further converted to cholecalciferol. This is an inactive form of vitamin D, which circulates to the liver for its first activation. Once there, the enzyme 25 hydroxylase attaches a hydroxyl group (OH) to the 25th carbon on the molecule and now it becomes 25-cholecalciferol. Once it leaves the liver, 25-cholecalciferol goes to the kidneys. When blood calcium levels are low, PTH activates another enzyme in the kidneys called 1 hydroxylase. This enzyme adds another hydroxyl group (OH) to the 1st carbon of 25-hydroxycalciferol that becomes the activated form of vitamin D known as 1,25-dihydroxycalciferol or calcitriol. The action of calcitriol is twofold. First, it decreases the kidney’s excretion of calcium. Second, it increases the reabsorption of calcium from the renal tubules. This in turn increases the amount of calcium in the blood. Calcitriol also plays another role in maintaining calcium. Like PTH, it stimulates the intestines to absorb more calcium from
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