Parathyroid glands are located on the anterolateral surface of the neck behind the thyroid gland and closely adheres to the back of the thyroid gland to the inferior poles of both lobes. Usually a person has four parathyroid glands, two on each side, but quite often there are different versions of the parathyroid glands. Fabric parathyroid glands consist of two types of cells. Some of them produce parathyroid hormone, the function of other yet unknown.
Parathyroid hormone - PTH or parathyrin is a complex protein substance. Effects of parathyroid hormone are aimed primarily at increasing concentrations of calcium and phosphate concentrations decrease in the blood.
Calcium in the human body plays a crucial role. Calcium ions are involved in many metabolic processes within the cells of all tissues of the human body. Calcium is involved in the transmission of nerve impulses from the nervous system to muscles and to the reduction in muscle tissue. He is one of the essential components of blood coagulation. More than 99% of the total stock of calcium in the body is in bone. In the adult human calcium is about one kilogram. Thanks to the calcium-bone becomes hard and durable.
About 99% is in bone calcium is in the form of crystals gidroksiappatita. It is sparingly soluble compounds and consists of a base (matrix) of bone tissue. The remaining 1% of calcium found in bone tissue in the form of salts of phosphorus, which dissolve easily and are a source of calcium entry into the blood by a sudden lack of it. The blood is always a certain amount of calcium. Half of it is related to protein or salt form, and the other half - it's free ionized calcium. These forms can be transformed into one another, but between them amounts to maintain a balance. The body always is a loss of calcium from the nails, hair, blood, otshelushivshihsya skin cells from the gastrointestinal tract and kidneys.
Regulate levels of calcium:
parathyrin (parathyroid hormone or parathyroid hormone), which increases blood calcium levels, while reducing the level of phosphate
derivatives of vitamin D (cholecalciferol) - lead to increased levels of calcium in the blood calcitonin produced by the parafollicular cells of the thyroid gland, which reduces the concentration of calcium in the blood plasma.
Parathyroid hormone or PTH parathyrin increases blood calcium levels by acting on bone, kidney and gastrointestinal tract.
In the skeletal system parathyroid hormone increases the yield of the bones of calcium dissolves easily, but its main effect is to accelerate the synthesis of enzymes that cause the breakdown of bone matrix. Bone basis under the influence of PTH undergoes resorption (resorption) and calcium ions are released into the blood.
In the kidney, PTH causes increased excretion of phosphates in the urine and increase the reabsorption of calcium, reducing its excretion in the urine. In addition, PTH increases the excretion of sodium and potassium excretion and reduces magnesium.
Another effect of PTH in the kidney - the conversion of vitamin D from the inactive to active form. In the gastrointestinal tract parathyrin increases calcium absorption in the intestine by means of the same vitamin D a necessary link in the regulation of calcium metabolism - a vitamin D and its derivatives. It is absorbed through the intestines, along with other substances or zhirorasvorimymi produced in the skin caused by ultraviolet light.
Further, vitamin D undergoes chemical reactions in the liver and kidneys and converted to an active metabolite, which is a true hormone. Under the influence of the active metabolite of vitamin D increases the amount of calcium in bone tissue, thereby increasing bone mass. In the kidney, vitamin D decreases the excretion of calcium in the urine, and in the gastrointestinal tract stimulates the active absorption of calcium and phosphate from food received.
Another component of the regulatory calcium metabolism is calcitonin - a hormone produced by parafollicular cells of the thyroid gland. In the end, calcitonin causes a decrease in calcium concentration in the blood, when it exceeds 2.5 mg / dL. In the skeletal system calcitonin prevents bone resorption and calcium excretion from it. In the kidney under the influence of calcitonin increased excretion of sodium, chloride, calcium and phosphate. In addition to the regulation of calcium metabolism are involved and other hormones: hormones of the adrenal cortex hormones.