Parathyroid Hormone – A major regulator of calcium metabolism

Calcium (Ca) is an important microelement necessary for normal nerve conduction and muscle contraction. The flow of nerve impulses transmitted from one neuron to another in the nervous system is mediated by the change in cellular levels of calcium ion.

On the other hand, the muscle contraction is accomplished by slipping two proteins to each other – actin and myosin. To achieve this and reduce the muscle fiber, it is necessary to release calcium in the cage.

Each process in our body functions properly only and only under certain conditions. In this case, nerve conduction and muscle contraction depend on achieving a steady equilibrium of calcium levels in the blood (calcium homeostasis). Four are the main components responsible for this: calcium, phosphorus, vitamin D and parathyroid hormone (parathormone).

Parathyroid hormone is released from the parathyroid glands. They are usually four small glands located on the back of the thyroid gland. Their number and location may vary.

Although they are in close proximity to the thyroid gland, parathyroid glands have a radically different function. While the thyroid plays the role of regulator of the primary metabolism, parathyroid glands are the main regulator of calcium levels.

The most important and central role of parathyroid hormone is to maintain calcium levels within physiological limits, typically ranging between 2.12 – 2.62 mmol / l. Under normal circumstances, any oscillation beyond the norm affects the function of the parathyroid glands. If calcium levels are low, the production of parathormone is stimulated and vice versa – high levels of calcium suppress its secretion.

How does parathyroid hormone maintain calcium levels?

Target organs of the hormone are three – kidneys, bones and intestinal tract. Its effect on these three target organs aims to increase calcium levels.

At the kidney level, parathyroid hormone stimulates calcium reabsorption, i. e. The secreted calcium in the urine, prepared for disposal, is returned to the circulatory system. While calcium is a desirable element for parathyroid hormone, the other important microelement – phosphorus is not. Under the action of parathyroid hormone, phosphorus is excreted in the urine.

Calcium is a basic structural component of the bone with which it appears and its depot. Under hypocalcaemia (low calcium levels in the blood), bone hormone parathyroid hormone will enhance its resorption to increase calcium levels in the bloodstream. In physiological conditions, this would not result in a drastic reduction in calcium bone content, because other mechanisms would subsequently be added to compensate for the loss and restore the necessary balance.

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