Hypoparathyroidism

Hypoparathyroidism is a condition where a marked decrease, reduction or diminished secretion of parathyroid hormones is noted. This disorder occurs less frequently than hyperparathyroidism. A genetic factor is sometimes involved in the occurrence of this disorder where the kidneys develop insensitivity to parathyroid hormones leading to a condition known aspseudohypoparathyroidism (HPH).

Parathyroid glands are small nodular endocrine tissue located at the posterior surface of the thyroid glands. There are around 2-8 glands found on the on the thyroid lobes. However, typically four to six are found. These glands are responsible for the production ofparathyroid hormones. The chief cells of parathyroid glands synthesize this peptide hormone that is also called aparathormone (PTH). Only few of these hormones are stored because after it is synthesized, secretion follows immediately. The main function of parathormone (PTH) is to regulate the serum calcium level. That is why this is the most important regulator of maintaining the blood homeostasis in relation to calcium level. The secretion of PTH is relatively dependent on calcium concentration. Very low degree of serum calcium stimulates the parathyroid glands to synthesize and increase the secretion of parathormone. Normal serum calcium level is 9-11 mg/dl. Any drop below the minimum range

Increase levels of parathormones would increase calcium levels. Thus, PTH is also called a hypercalcemic hormone. The one that acts opposite to PTH is called calcitonin which is secreted by the thyroid glands that causes increase deposition of calcium in the bones and low in the blood plasma. Thereby, calcitonin is called a hypocalcemic hormone. The feedback interaction between these two hormones is very vital in achieving calcium homeostasis in blood.

Increase levels of parathormones would increase calcium levels. Thus, PTH is also called a hypercalcemic hormone. The one that acts opposite to PTH is called calcitonin which is secreted by the thyroid glands that causes increase deposition of calcium in the bones and low in the blood plasma. Thereby, calcitonin is called a hypocalcemic hormone. The feedback interaction between these two hormones is very vital in achieving calcium homeostasis in blood.

The mechanisms on how calcium is elevated with increase PTH secretion are the following:

Result: release of calcium deposited in bones

When calcium levels drop parathyroid hormones activates osteoclasts inside the bone. Osteoclasts are cells that stimulate bone cell destruction. This is primarily done by the body to cause a breakdown in the bone matrix so that calcium from the bone will be released to the blood, making more calcium available.

Result: decrease phosphate levels

Increase parathormone secretion due to low calcium level triggers the body to undergo another mechanism which is the escalation of phosphate elimination in kidneys. This is effective in maintaining calcium in plasma because when calcium and phosphate are both elevated, they are incorporated into the bones. Presence of calcium alone does not have this effect, therefore, elimination of phosphate would prevent calcium bone deposition and the calcium released from the bones remains in the extracellular fluid (ECF).

Result: increase calcium in extracellular fluid (ECF)

Result: increase calcium absorption in the intestinal tract

This mechanism will lead to the addition of calcium in the blood plasma from the diet or food intake of a person. Vitamin D is a fat soluble vitamin that is needed for the absorption of calcium. Without this vitamin, calcium will not be used by the body. If a person’s diet contains enough calcium such as milk products, green leafy vegetables, shrimp, salmon, clams, tofu, legumes and fortified orange juice he/she will just excrete the calcium on the condition that vitamin D is lacking. Foods rich in Vitamin D are dairy products, eggs, and fatty fish. Once PTH is present this vitamin found in the gastrointestinal tract will be activated thereby, increasing calcium absorption.

Etiology

A resulting low calcium concentration in the plasma (hypocalcemia) due to the mentioned etiological factors can cause extreme weakness, defective muscular function and altered mental processes.

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