Increased parathyroid function. Parathyroid gland, its hormones and functions

A person has two pairs of parathyroid (parathyroid) glands located on the surface or inside. The gland includes the so-called main (“dark” and “light”) cells that have acidophilic protoplasm with oxyphilic inclusions in the protoplasm (they appear only after the age of 20 years, multiplying with age). The bulk of the gland is made up of "dark" cells. In the parenchyma of the gland, is the tubule system that contains a colloidal substance. The glands are well equipped with blood and lymph vessels, receive sympathetic (from the cervical ganglia) and parasympathetic ( nervus vagus) innervation.
Hormones of the parathyroid glands.  The parathyroid glands produce parathyroid hormone (parathyrin), which, along with thyroid calcitonin, regulates calcium metabolism in the body and maintains its level in the blood at a certain level. This is achieved by: a) resorption of calcium from bones b) reabsorption from the distal tubules of the nephron c) accelerated absorption from the intestine under the influence of the vitamin D metabolite that is formed in the kidneys. In parallel, parathyroid hormone causes the release of phosphate from mineral matterforming bone (hydroxyapatite) and inhibits the reabsorption of phosphates in the kidneys, thereby reducing their concentration in the blood.
  With insufficient function of the parathyroid glands, the calcium content in the blood significantly decreases (normally this indicator is 2.25-2.75 mmol / l). And vice versa, with hyperfunction of the glands, its increase is observed.
The mechanism of action of parathyroid hormone  on bone cells associated with specific membrane receptors. Due to the contact of the hormone with the receptor, adenylate cyclase activity increases, the content of cAMP increases, and Ca2 + entry into bone cells.
  An increase in the intracellular concentration of calcium leads to an acceleration of the transformation of progenitor cells into osteoblasts and osteoclasts, followed by the release of Ca2 + from bone tissue.
Regulation of the function of the parathyroid glands. The most important regulator of parathyroid hormone levels is the concentration of calcium in the blood. With hypocalcemia, the production of parathyroid hormone increases, with hypercalcemia, the decomposition of the hormone synthesized in the cells begins, and its concentration in the blood decreases. Stimulation of the parathyroid glands is also noted with the excitation of the adrenergic system, the mediators of which act through the a-adrenergic receptors of cell membranes.
  Blood calcium levels are especially important for the function of excitable structures. Its decrease is accompanied by an increase in the excitability of the neuromuscular system, the occurrence of involuntary tonic contractions of skeletal muscles. Spasmodic contractions of the respiratory and pharyngeal muscles can lead to death. This syndrome is called tetany and is a manifestation of hypoparathyroidism, a condition that develops as a result of removal of the parathyroid glands during thyroid surgery or autoimmune destruction of cells producing parathyroid hormone. With the development of tumors (adenomas) of the parathyroid glands, the level of calcium in the blood plasma can increase to 0.17 g / l (normal 0.1 g / l), causing the development of hyperparathyroidism. The patient is affected by bone damage, slowing of heart contractions (bradycardia), calcium deposits in blood vessels and kidneys. In many cases, kidney stones are the result of high activity of the parathyroid glands. A patient with hyperparathyroidism may die as a result of cardiac arrest after a meal rich in calcium.

The parathyroid or parathyroid gland is an accumulation of rounded bodies located along back wall  thyroid gland. Their number can be different - from two to seven to eight, in most cases - four, 4-8 mm long, and they are arranged in pairs (hence the name) along the upper and lower poles of the thyroid gland. The mass of all Taurus usually does not exceed 1.2 grams.

Unlike the thyroid, the parathyroid gland has a lighter color - pale pinkish in children and yellowish in adults. It is separated from surrounding organs by its own fibrous tissue.

Parathyroid function

This body has the most important function of regulating the phosphorus-calcium balance in the body through the production of a certain hormone. The functioning of the motor, nervous and bone systems of the body directly depends on the activity of the parathyroid gland.

When falling below acceptable level the parathyroid gland, through receptors sensitive to this element, begins to intensively release the so-called parathyroid hormone, or parathyrin, which, in turn, stimulates the release of a deficient trace element from bone tissue. Therefore, the main purpose of the parathyroid gland is to produce a hormone, the main catalyst for the balance of calcium in the body.

Signs of pathology

The body for malfunctions parathyroid glands  reacts with disturbances in the work of all its organs and systems. The first manifestations of violations of the optimal secretion of parathyroid hormone are, as a rule, pathologies of calcium-phosphorus metabolism in the body, which are manifested by symptoms characteristic of endocrine diseases:

• oppression nervous system;
• persistent fatigue;
• impaired appetite;
• weakness
• headaches;
• convulsive contractions of skeletal and smooth muscles due to insufficient production of parathyrin;
• increased muscle and nervous excitability.

When conditions worsen, the symptoms only increase due to damage to organs and tissues of the body: the musculoskeletal system suffers from myopathy and gout, the visual system is threatened by cataracts and calcium deposits in the cornea, and problems from cardiovascular system  manifested by calcification of blood vessels and heart, coupled with the progression of arrhythmias and hypertension.

A characteristic symptom is kidney damage with the presence of thirst, development urolithiasis. A febrile condition and an insufficient level of hemoglobin in the blood also indicates problems with this gland.

External manifestations of hormonal problems are yellowness and dryness of the skin, fungal infections, brittleness and dullness of hair, eczema or psoriasis, loss of eyelashes and eyebrows, sometimes cataracts, thinning of nails, subcutaneous calcifications in the area auricles, myositis, tooth damage.

Parathyroid diseases

Hyperparathyroidism  - a disease that occurs with excessive secretion of parathyrin, as a result of which hypercalcemia develops in the body. Hyperactivity of the glands is a very menacing disease. A high concentration of the hormone leads to an increased content of calcium in the blood and, consequently, to a decrease in its content in bone tissue, as a result of which there is a risk of osteoporosis, kidneys suffer.

The trigger mechanism for this disease is tissue hyperplasia, adenoma or oncology of the parathyroid glands, as well as other conditions that interfere with the normal functioning of the organ, such as long-term calcium deficiency, chronic renal failurelong-term lack of vitamin D. Treatment this disease  surgical, the prognosis is favorable in the vast majority of cases.

Hypoparathyroidism  - a disease in which an insufficient amount of parathyrin is reduced, which entails a decrease in calcium in the blood and contributes to the growth of neuromuscular excitation, up to psychosis.

Often hypoparathyroidism occurs with damage or accidental removal during surgery on this organ, with hemorrhage in the neck or with inflammatory processflowing in the gland. Also, this disease can provoke a lack of vitamin D in the body, improper absorption of calcium in the intestines, exposure to radiation or carbon monoxide poisoning.

The very first sign is muscle cramps, aggravated by stress, hypothermia or physical activity. The treatment of the disease is mainly hormonal.

Timely diagnosis

To identify pathological conditions of glandular tissues, laboratory and instrumental diagnostic methods are used. Laboratory include:

• determination of calcium level in urine;
• serum calcium and its ionized forms;
• amount of phosphates;
• concentration of parathyroid hormone.

However, the leading role in diagnosis today belongs to more accurate instrumental methods. Let's consider them in more detail.

1. Ultrasound examination is a safe, high-precision and painless technique, which in the vast majority (approximately 60-70 percent of cases) allows us to detect an increase in glands. It is actively applied at surgical interventions. However, with unchanged size, the gland is ineffective.
2. Computed tomography with contrast is a more sensitive method that allows you to see abnormalities in the parathyroid gland in 90% of studies.
3. MRI is a method in which nuclear magnetic resonance imaging is visualized. This examination is quite effective due to its high sensitivity, and the absence of ionizing radiation makes it very attractive due to safety.
4. Subtraction scintigraphy is the most accurate imaging technique to date. During the study, the patient is injected with radioactive isotopes, the radiation from which is converted by high-tech devices into information about the degree of pathology. The sensitivity of the method allows you to evaluate the effectiveness of the therapy in short periods of time, but it is not recommended for use in lactating and pregnant women and in severe conditions of patients.
5. X-ray research methods. They are mainly used to study the condition of bone tissue and malfunctions of the cardiovascular system.

It should be added that each of the diagnostic methods has both advantages and disadvantages, however, it is recommended to use several methods, especially for the initial diagnosis or treatment choice. Each case of the disease must be approached individually.

With controversial results of ultrasound or laboratory researchthat are attractive in terms of safety and low cost, scintigraphy should be resorted to.

Calcium Obeys Parathyroid Hormone

Main meaning parathyroid gland  for the body consists in the production of periotioid hormone, or paratinin. When the level of calcium in the blood drops to a critical level, hormone receptors that are sensitive to this, begin to intensively produce this hormone. Further, the hormone activates osteoclasts, which in turn extract calcium from bone tissue. As a result of this, the concentration of calcium ions in the blood increases, but the bones lose their stiffness and can begin to deform when there is a violation of calcium-phosphorus metabolism.

The hormone is the main regulator of maintaining calcium ions in the blood at the proper level through effects on the bones, intestines and kidneys.

The lower the level of calcium ions in the blood, the more intensively this hormone is secreted by the parathyroid gland, and vice versa.

During the day, its concentration in the body is different - during the most activity in the daytime, when metabolic processes are accelerated, it is maximum and, accordingly, at night it is minimal.

Symptoms taken by surprise?

When detecting the first signs of malfunctions in the parathyroid gland, it should be borne in mind that the lack of timely treatment can not go unnoticed for a health condition. Great development risks severe complicationssuch as osteoporosis, bone fractures, the occurrence of kidney stones, cardiovascular disease.

Pregnant women are especially at risk of developing fetal irregularities. Only an urgent visit to the endocrinologist is the right start to a return to health.

She is often hidden in her fabric. A person has two pairs of small oval-shaped glands.

Sometimes the parathyroid glands can also be located outside the thyroid gland. Their location, quantity and shape in vertebrates are very different. They contain 2 types of cells: main and oxyphilic. The cytoplasm of both types of cells contains secretory granules.

Parathyroid  - an independent organ of internal secretion. After its removal, while preserving the thyroid gland, convulsions and death occur.

The hormone of the parathyroid glands, parathyroid hormone, or parathyroidine, is a protein compound (albumose) containing nitrogen, iron and sulfur, acting only after subcutaneous administration, as it is destroyed by proteolytic enzymes, but can withstand heating to 100 ° C. The hormone is released continuously. It regulates the development of the skeleton and the deposition of calcium in the bone substance, as it promotes the binding of calcium to proteins and phosphates. At the same time, the hormone stimulates the function of osteoclasts that absorb bones. This leads to the release of calcium from the bones and an increase in its content in the blood. As a result normal level  the calcium content in the blood is 5-11 mg%.

Bones contain 99% the total  body calcium, 85% of all inorganic compounds of bones consists of phosphoric acid calcium. The hormone maintains at a certain level the content of the enzyme phosphatase, which is involved in the deposition of calcium phosphate in the bones.

The hormone reduces the phosphate content in the blood and increases their excretion in the urine. This causes the mobilization of calcium and phosphorus from the bones. After removal of the glands, the ability to remove calcium phosphate from the bones decreases sharply.

Therefore, an increase in blood calcium is due to increased excretion of phosphates in the urine.

Parathyroidin acts not directly on calcium metabolism, but through the liver. When the liver is not functioning, the introduction of parathyroidin into the blood does not increase the concentration of calcium in the blood. After removal of the parathyroid glands, the deamination process and the ability of the liver to convert ammonia to urea are disrupted. Therefore, animals that have removed the parathyroid glands do not tolerate protein food.

The hormone calcitonin is also formed in the glands, which reduces the Ca content in the blood. It stands out with hypercalcemia.

Parathyroid glands innervated by the sympathetic nerves and branches of the recurrent and laryngeal nerves.

The reflex regulation of the function of the parathyroid glands and their relationship with other endocrine glands are not well understood. After denervation of the glands, their function does not noticeably change. Better studied neurohumoral regulation. The main regulator of parathyroidin secretion is the level of calcium in the blood. An increase in blood calcium inhibits, and a decrease - stimulates the secretion of parathyroid hormone. A large increase in the parathyroid glands is observed with a diet poor in calcium.

After removal of the pituitary gland, the parathyroid glands atrophy. This allows us to conclude that the pituitary hormone enhances their function.

Hypofunction and hyperfunction of the parathyroid glands

Hypofunction of the parathyroid glands causes in humans tetany  (convulsive disease). The excitability of the nervous system increases, fibrillar contractions appear in individual muscle groups, which turn into prolonged convulsions. Convulsions can seize all the muscles of the body and due to convulsive contraction respiratory muscles  death by suffocation may occur. In cases of slowly developing tetany, development of teeth, hair and nails, and digestive disorders are observed.

In the parathyroid glands, tetany can be detected degenerative changes  or hemorrhage. Constantly observed decrease in calcium in the blood from 10 to 3-7 mg%. When tetany occurs in blood and urine, the amount of toxic products of protein breakdown (guanidine and its derivatives) increases due to depletion of calcium in the body, which leads to disruption of protein breakdown. Guanidine is found in meat. In chronic hypofunction of the glands, due to an increase in the excretion of calcium in the urine and insufficient release of calcium from the bones, its content in the blood is significantly reduced. On the contrary, the excretion of phosphorus in the urine decreases, and its content in the blood increases. Overexcitation of the nervous system passes into its inhibition. With hyperfunction of the glands, the calcium content in the blood increases to 18 mg% or more, and the phosphorus content decreases.

When the concentration of calcium in the blood becomes higher than 15 mg%, apathy and sleep occur, associated with the phenomenon of poisoning. Parathyroidin and Vitamin D act in the same direction to maintain a constant level of calcium in the blood. Vitamin D is often accompanied by hypertrophy of the parathyroid glands with their hyperfunction. In this case, an increase in parathyroidin intake compensates for vitamin D deficiency.

With chronic hyperfunction of the glands, the calcium content in the bones decreases, they are destroyed and become brittle, heart activity and digestion are upset, muscle strength is reduced.

With the growth of glandular tissue associated with their hyperfunction, excessive ossification appears and at the same time an increase in the calcium content in the blood (hypercalcemia), as well as vomiting, diarrhea, cardiac disorders, decreased nervous system excitability, apathy, and death occurs in severe cases. The excitability of the cerebral hemispheres temporarily increases, and then inhibition is enhanced.

With prolonged administration to young animals large quantities  parathyroid hormone of the parathyroid glands in them softens the bones due to the transition of calcium from bone tissue to the blood.

The parathyroid gland (in other words - parathyroid and parathyroid) is an endocrine organ, consisting of several small formations. They are located at the back of the thyroid gland, 2 at the top and bottom. In the human body, the parathyroid gland performs an essential function - it regulates the level of calcium in the blood and is responsible for full-fledged nervous activity and motor activity.

The location and size of the parathyroid glands

For the first time, the parathyroid gland was not found in humans, but ... in the Indian rhino - at the autopsy of a dead animal in 1850. The young British researcher Richard Owen managed to find and identify a huge organ compared to the human rhino - weighing as much as 8 grams. Since then, the rhinoceros has been the symbol of the most complicated surgery of the parathyroid glands.

The glory of the discovery of human "parathyroid glands" belongs to the Swedish professor Ivar Sandstrom, who discovered this organ in 1880 and thus launched a whole program to study the new endocrine gland.

The most important feature of the parathyroid gland – individual characteristics  buildings. At different people  meets different amount  of these organs, their localization, color and even size may differ. 80% of all inhabitants of the planet have 4 parathyroid glands, but normally their number can reach 8.

Traditionally, the upper pair of "parathyroid glands" is located in the upper part of the thyroid gland, beyond the borders of its capsule. And the lower one is inside the organ, under the capsule. But in medical practice there have been cases when parathyroid formations were located in the thymus gland (thymus) and near the main neurovascular bundle of the neck, near the carotid artery, on the front surface of the spinal column and behind the esophagus.

Outwardly, parathyroid organs look like lentil kernels. In children, they are pinkish in color, in adults - yellow-brown, with an admixture of red. Length varies between 4-8 mm, width 3-4, thickness - 2-4 mm. Each organ weighs an average of 0.5 grams, and in many cases the lower glands are slightly larger than the upper ones.

The structure of the parathyroid gland

Unlike others endocrine organs  - adrenal glands, pituitary or thymus, - “parathyroid glands” do not have a clear division into lobes or areas. Each gland is enclosed in a dense capsule, inside of which there is a parenchyma consisting of glandular cells of paratyrocytes.

Inside each of the parts of this organ, 5 types of parathyrocytes can be found: the main dark and main light cells, acidophilic, watery and transitional. All of them are connected in cords and clusters, separated by stroma of connective tissue. In these stroms are blood vessels  and nerve fibers, the thyroid arteries are responsible for the main blood supply to the parathyroid gland.

The structure of the parenchyma of the parathyroid glands is also very individual and can take one of three forms:

• Whole, without dividing into lobules (such a parenchyma is usually found in embryos and children, but is sometimes diagnosed in adults and elderly patients);
• Mesh, divided into equal groups of cells, but without a clear system (the most common variety, fixed in most patients);
• Alveolar, divided into fairly regular cells by connective tissue.

Sometimes there is a mixed variety, when a small section of a completely different structure suddenly appears in a parenchyma cell from one type of cell. This feature is also considered the norm.

Cell ratio different types  changes with age: in infants, the “parathyroid gland” consists of the main paratyrocytes, at 5-7 years old, oxyphilic cells appear, and after 20-25 years the number of fat cells increases.

Parathyroid function

Until the turn of the 19th-20th centuries, the function of the parathyroid glands was unknown and the surgeons even removed them during operations on the thyroid gland, not counting it as especially important. When it became clear that this was fatal, such operations were banned by law in France. And the famous American surgeon Robert Gross called these procedures "bloody massacre."

Over time, scientists have found that parathyroid gland plays a crucial role in the body. Namely, it regulates the level of calcium in a strictly defined framework, maintaining the optimal level of the mineral in the blood.

The main amount of Ca in the human body is in the skeleton - almost 99%. And only a small part is in the blood. But to maintain the life and work of basic systems, this 1% is incredibly important. As soon as the level of the mineral in the blood falls, the body immediately rushes to restore it, and the parathyroid gland does this.

The work of the parathyroid gland takes place in 3 stages:

1. The excretion of calcium in the urine is sharply reduced.
2. In the blood, the active form of vitamin D rises, which enhances the absorption of calcium into the blood with the help of the protein calmodulin.
3. The production of bone cells of osteoclasts, which destroy aging bone tissue and transfer Ca to the blood, is started.

Parathyroid hormone

Parathyroid gland is responsible for the synthesis and production of only one substance - parathyroid hormone. Its hormonal antagonist is the product of thyroid gland activity - thyrocalcitonin, which stimulates the production of osteoblast cells - the builders of bone tissue.

The function of the parathyroid gland in the body is due to the work of parathyroid hormone. As soon as the level of Ca in the blood drops below normal, the sensitive parathyroid receptors release parathyroid hormone. And he, in turn, increases the concentration of vitamin D and the production of osteoclasts.

The parathyroid gland is an organ with a very narrow specialization. Disruptions in the functioning of this endocrine gland can provoke 2 dangerous diseases  - hyperparathyroidism  (leads to hypercalcemia) and hypoparathyroidism. The consequences of excess calcium in the blood are memory impairment, weakness and drowsiness, depression and psychosis, as well as kidney problems. Too active osteoclast activity leads to softening of the bones and to osteoporosis. A mineral deficiency can cause cramps, numbness and spasm in the arms and legs, vision problems and impaired brain activity.

The parathyroid glands (parathyroid glands, epithelial bodies) are small glands of internal secretion of a reddish or yellow-brown color. In humans, they are usually represented by two pairs. The dimensions of each of them are approximately 0.6x0.3x0.15 cm, and the total mass is about 0.05-0.3 g. The parathyroid glands are closely adjacent to the posterior surface of the thyroid gland (Fig. 43). The upper pair of parathyroid glands, adjacent to the capsule of the lateral thyroid glands, is located on the border between the upper and middle third of the thyroid gland, at the level of the cricoid cartilage. The lower pair of parathyroid glands is localized at the lower pole of the thyroid gland. Sometimes the parathyroid glands can be located in the tissue of the thyroid or thymus gland, as well as in the pericardium.

Blood supply to the parathyroid glands is due to the branches of the lower thyroid artery, and innervation is carried out by the fibers of the sympathetic nervous system from the return and upper laryngeal nerves. The parathyroid glands consist of a parenchyma, partitioned into segments by connective tissue membranes with blood vessels. In the parenchyma, the main and acidophilic cells are distinguished. Among the main cells, the most numerous are round-shaped, small-sized cells containing a small amount of watery light cytoplasm and a well-stained nucleus. This type of main cell reflects an increase in the function of the parathyroid glands. Along with them, dark main cells are distinguished, which reflect the resting stage of the parathyroid glands. Acidophilic cells are located mainly on the periphery of the parathyroid glands. Acidophilic cells are considered as an involutional stage of the main cells. They are usually larger than its main cells, with a small dense nucleus. Transitional cells are transitional forms between the main and acidophilic cells. The parathyroid glands are vital formations. When all parathyroid glands are removed, death occurs.

Parathyroid hormone, which along with calcitonin and vitamin D (D-hormone) maintains a constant level of calcium in the blood, is a product of the intracecretory activity of the parathyroid glands (mainly the main and to a lesser extent acidophilic cells). It is a single chain polypeptide consisting of 84 amino acid residues (mol. M. Is approximately 9500 daltons, half-life is about 10 minutes).

The formation of parathyroid hormone occurs on the ribosomes in the form of preproparathormone. The latter is a polypeptide containing 115 amino acid residues. The preproparathormone moves to the region of the rough endoplasmic reticulum, where a peptide consisting of 25 amino acid residues is cleaved from it. As a result, proparathormone is formed, containing 90 amino acid residues and having a molecular weight of 10,200 daltons. The binding of proparathormone and its transfer into the cistern space of the endoplasmic reticulum is carried out by a secretory protein. The latter is formed in the main cells of the parathyroid glands. In the Golgi apparatus (lamellar complex), a polypeptide of 6 amino acid residues is cleaved from proparathormone. The latter provides transport of the hormone from the endoplasmic reticulum to the Golgi apparatus, which is the storage site of the hormone in secretory granules, from where it enters the bloodstream.

The most intense secretion of this hormone at night. It was established that the content of parathyroid hormone in the blood after 3-4 hours from the beginning of night sleep is 2.5-3 times higher than its average daily level. Parathyroid hormone maintains a constant level of ionized calcium in the blood by affecting the bones, kidneys and intestines (through vitamin D). Stimulation of parathyroid hormone secretion occurs with a decrease in blood calcium below 2 mmol / l (8 mg%). Parathyroid hormone helps to increase the calcium content in the extracellular fluid, as well as in the cytosol of the cells of the target organs (mainly the kidneys, skeleton bones, intestines). It is believed to be related to increased income  calcium through the cell membrane, as well as with the transition of its mitochondrial reserves into the cytosol.

Bone consists of a protein framework - matrix and minerals. Osteoblasts and osteoclasts provide the structure of bone tissue and a constant metabolism in it. Osteoblasts originate from undifferentiated mesenchyme cells. Osteoblasts are in a monolayer on the bone surface, in close contact with the osteoid. The osteoblast vital product is alkaline phosphatase. Osteoclasts are giant polynuclear cells. It is believed that they are formed by the fusion of mononuclear macrophages. Osteoclasts secrete acid phosphatase and proteolytic enzymes that cause collagen degradation, the destruction of hydroxyapatite and the removal of minerals from the matrix. The actions of osteoblasts and osteoclasts are consistent among themselves, despite the independence of their functions. This leads to normal skeleton remodeling. Osteoblasts take part in bone tissue neoplasm and its mineralization processes, and osteoclasts take part in bone resorption (resorption) processes. Osteoclasts do not alter the bone matrix. Their action is directed only to the mineralized bone.

With excessive production of parathyroid hormone, hypercalcemia occurs, mainly due to leaching of calcium from the bones. Along with the demineralization of bone tissue with a prolonged excess of parathyroid hormone, matrix destruction also occurs with an increase in the concentration of hydroxyproline in the blood plasma and its excretion in the urine. In bones and kidneys, parathyroid hormone activates the mediator of the cellular effects of this hormone - cyclic adenosine monophosphate (cAMP) by stimulating adenylate cyclase - an enzyme associated with the cell membrane. The latter accelerates the formation of cAMP. The interaction of parathyroid hormone with osteoblast receptors is accompanied by an increase in the level of alkaline phosphatase, the formation of new bone tissue with an increase in its mineralization. When parathyroid hormone activates osteoclasts, an increased synthesis of collagenase and other enzymes involved in the destruction of the matrix (for example, acid phosphatase) occurs in them. Under the influence of parathyroid hormone, the cAMP content in the kidneys increases and is accompanied by an increase in the excretion of cAMP in the urine. It was found that parathyroid hormone and cAMP increase the permeability of the proximal tubules of the kidneys. Parathyroid hormone increases the reabsorption of calcium in the distal tubules of the kidneys, resulting in a decrease in urinary calcium excretion.

Along with hypercalcemia, parathyroid hormone simultaneously contributes to a decrease in the phosphorus content in the blood by suppressing its reabsorption in the proximal renal tubules. The consequence of this is increased excretion of phosphorus in the urine. Parathyroid hormone also increases urinary excretion of chlorides, sodium, potassium, water, citrates and sulfates and causes alkalization of urine.

The functional activity of the parathyroid glands is mainly autoregulatory in nature and depends on the serum calcium content: with hypocalcemia, the production of parathyroid hormone increases, and with hypercalcemia it decreases. Calcium (ionized calcium) plays an important role in the life of the body. It reduces the excitability of the peripheral nervous system and the permeability of cell membranes, is an important plastic material for the formation of bone tissue, is involved in the regulation of blood coagulation, etc. The main reserves of calcium and phosphorus are found in bone tissue. The amount of calcium in bone tissue is 95-99% of its content in the body, and phosphorus - 66%. In a human body with a body weight of 70 kg, approximately 1120 g of calcium is contained. Daily requirement  in calcium, adults is 0.5-1 g.

In bones, calcium is in the form of calcium-phosphorus compounds that form crystals of hydroxyl apatite. Total Blood Calcium healthy people  is 2.4-2.9 mmol / l (9.6-11.6 mg%). Only ionized calcium, which in the blood serum contains 1.2 mmol / l (5 mg%), has biological activity; 1 mmol / l (4 mg%) of calcium in the blood is bound to protein, 0.5 mmol / l (2 mg%) of calcium is not ionized. The amount of calcium bound to the protein increases with a shift in the pH of the medium to the alkaline side. It has been established that parathyroid hormone regulates the content of ionized calcium and phosphorus in the blood, controlling its composite fraction - inorganic phosphorus. The serum phosphorus content in healthy people is 3.2-4.8 mmol / L (10-15 mg%), of which inorganic phosphorus is 0.97-1.6 mmol / L (3-5 mg%), lipid phosphorus - 2.6 mmol / L (8 mg%), phosphorus esters - 0.3 mmol / L (1 mg%).

The secretion of parathyroid hormone is stimulated by STH, prolactin, glucagon, catecholamines, as well as other biogenic amines (serotonin, histamine, dopamine). Magnesium ions also have a regulatory effect on the secretion of parathyroid hormone and the implementation of its specific action. The serum magnesium concentration is 0.99 mmol / L (2.4 mg%), and its ionized fraction is 0.53 mmol / L (1.3 mg%). With a high content of magnesium in the blood, stimulation occurs, and with a low - suppression of the secretion of parathyroid hormone. It has been established that with magnesium deficiency, cAMP synthesis is disrupted in the parathyroid glands and in the target organs of parathyroid hormone with the subsequent development of hypocalcemia.

In humans, calcitonin is synthesized, in addition to the thyroid gland, in the parathyroid glands and the thymus gland. Hypercalcemia (higher than 2.25 mmol / l), glkzhagon, cholecystokinin, gastrin is a stimulator of calcitonin secretion. The intracellular mediator of calcitonin secretion is cAMP. An increase in the intracellular mediator, cAMP, occurs when calcitonin interacts with receptors in bone tissue and in the kidneys.

In healthy people, parathyroid hormone and calcitonin are in dynamic equilibrium. Under the influence of parathyroid hormone, the calcium content in the blood rises, and under the influence of calcitonin it decreases. The hypocalcemic effect of calcitonin is associated with its direct effect on bone tissue and inhibition of resorptive processes in bones. Along with the hypocalcemic effect, calcitonin also contributes to a decrease in the phosphorus content in the blood. Hypophosphatemia occurs due to a decrease in the mobilization of phosphorus from the bone and direct stimulation of the absorption of phosphorus by the bone tissue. Biological effect  calcitonin is carried out not only due to its effect on bone tissue, but also on the kidneys. The interaction of calcitonin and parathyroid hormone in the bone tissue occurs mainly with osteoclasts, and with receptors in the kidneys - in various parts of the nephron. Calcitonin receptors are located in the distal tubules and the ascending part of the nephron loop, and parathyroid hormone receptors are located in the proximal tubules of the descending part of the nephron loop and distal tubules.

Along with parathyroid hormone and calcitonin, vitamin D3 also takes part in the regulation of calcium-phosphorus metabolism. Vitamin D3 (cholecalciferol) is formed in the skin from 7-dehydrocholesterol under ultraviolet radiation. The resulting vitamin D3 initially does not have biological activity. In order to become biologically active, it goes through two ways of hydroxylation - in the liver and kidneys. By the first hydroxylation, under the influence of the enzyme 25-hydroxylase, vitamin D. is converted in the liver to 25-hydroxy-cholecalciferol (25-OH-D3). Subsequently, in the kidneys, by re-hydroxylation under the influence of the enzyme 1-a-hydroxylase in the presence of calcitonin and parathyroid hormone, it is synthesized in 1,25- (OH) 2-D3 - biologically active vitamin D3 (D-hormone). The process of hydroxylation of vitamin D3 in the kidneys can take place in another way - under the influence of the enzyme 24-hydroxylase, as a result of which 24.25- (OH) -D is formed in the kidneys. The biological activity of the latter is below 1.25- (OH) 2-D3. The process of hydroxylation of vitamin D is carried out in the mitochondria. The accumulation of D-hormone in the cells of the proximal tubules of the kidneys and an increase in its content in the blood inhibit the synthesis of 1,25- (OH) 2-D3 while accelerating the synthesis of 24,25- (OH), - D3. This is due to the inhibitory effect of 1,25- (OH) 2-D3 on the activity of the enzyme 1-a-hydroxylase and its stimulating effect on the activity of 24-hydroxylase.

The way hydroxylation of vitamin D? (ergocalciferol) contained in plants in the body is the same as that of vitamin D3. As a result of hydroxylation of vitamin D, 1.25- (OH) 3-D2 is formed. The latter in biological activity is not inferior to 1.25- (OH) 2-D3.

Vitamin D circulates in the blood in complex with a-globulin. The latter is synthesized by the liver. Receptors for 1,25- (OH) 2-D3 are found in the intestines, kidneys, bones, skin, muscles, mammary and parathyroid glands. The biological effect of vitamin D is primarily manifested in the kidneys, intestines, and bones. 1,25- (OH) 2-D3 has a direct effect on the kidneys, helping to enhance tubular reabsorption of calcium and phosphates. In the intestine, the active metabolism of vitamin D contributes to increased absorption of calcium and phosphorus. Stimulation of calcium absorption in the intestine occurs by stimulating the synthesis of calcium-binding protein. The latter is a carrier of calcium through the membrane of the cells of the intestinal mucosa. The active metabolite of vitamin D in bone tissue helps normalize bone formation and mineralization by mobilizing calcium and using it in newly formed bone tissue. 1,25- (OH) 2-D3 also affects collagen synthesis. The latter takes part in the formation of a bone matrix. The active metabolite of vitamin D., thus, counteracts, along with parathyroid hormone, a decrease in extracellular calcium.

Parathyroid hormone, calcitonin and the active metabolite of vitamin D3 stimulate the secretion of ACTH, tyroliberin, prolactip and cortisol to varying degrees. Calcitonin has an inhibitory effect on the secretion of STH, insulin and glucagon. In addition, parathyroid hormone and calcitonin have a pronounced cardiotropic and vascular effect.

Glucocorticoids, growth hormone, thyroid hormones, glucagon and sex hormones also participate in the regulation of phosphorus-calcium metabolism. In contrast to parathyroid hormone, these hormones have a hypocalcemic effect. Glucocorticoids reduce the function of osteoblasts and the rate of formation of new bone tissue, increase bone resorption. In this case, the function of osteoclasts in bone tissue does not change or is somewhat enhanced. These hormones reduce calcium absorption in gastrointestinal tract  and increase urinary calcium excretion.

Growth hormone stimulates the activity of osteoblasts and bone-respiratory processes in the newly formed bone tissue, increases the excretion of calcium in the urine. In the previously formed bone, growth hormone stimulates the activity of osteoclasts and demineralization of bone tissue. This hormone also enhances the absorption of calcium in the intestine directly, affecting the intestinal mucosa, and indirectly, enhancing the synthesis of vitamin D.

At physiological concentrations, thyroid hormones equally stimulate the activity of both osteoblasts and osteoclasts, i.e. act on bone tissue in a balanced way. With an excess of thyroid hormones, there is an increase in calcium excretion in the urine, osteoclast activity predominates, bone resorption increases, and if there is a lack of it, the formation and maturation of bone tissue is delayed.

Estrogens stimulate the synthesis of parathyroid hormone and D-hormone. However, they reduce the sensitivity of bone tissue to parathyroid hormone. In addition, estrogens inhibit the activity of osteoclasts as a result of increased secretion of calcitonin.

Glucagon helps to reduce blood calcium levels through a direct effect on bones (a decrease in resorption processes) and indirectly through stimulation of calcitonin secretion.