Parathyroid hormones: role in the body, norm and pathology

Parathyroid hormones: role in the body, norm and pathology

The parathyroid glands are vital organs whose function is to produce and release parathyroid hormone (parathyrin) into the bloodstream. They were first described at the end of the 19th century (more precisely, in 1879) by the scientist from Sweden K. Sandstrom, who also gave them the name. You will learn about what kind of organs they are, about the features of their structure, as well as about the functions of the hormone they produce from our article.

Anatomy basics


Usually a person has 4 parathyroid glands located on the posterior surface of the thyroid gland. In some cases, their number can even reach 10.

The parathyroid glands are located along the posterior surface of the thyroid gland, outside its capsule, at the upper and lower poles. As a rule, there are 4-2 pairs of them, upper and lower, however, cases of a different number of these glands are known, sometimes there can be even 10-12 of them, while they are located in the thickness of the thyroid gland, in the mediastinum, behind the esophagus, in the pericardium, and so on. Further.

Usually, the upper pair of parathyroid glands is oval in shape, and the lower one is in the shape of a ball. Their dimensions are approximately 4-6 * 1.5-3 mm, the color is yellowish brown or reddish.

Their blood is fed by the branches of the thyroid artery, the outflow of blood is carried out into the veins of the thyroid gland, trachea and even the esophagus.

The parathyroid glands are innervated by the fibers of the superior laryngeal, recurrent and vagus nerves.

The structural unit of this organ is the parathyroid cell. Some of these cells have hormonal activity (they are able to produce hormones), and some are at rest. Parathyroid cells are not located in isolation, but form cords and clusters. On the periphery of each gland, other cells are determined – eosinophilic, which in fact are degenerating parathyroid cells. A thin capsule consisting of connective tissue covers the parathyroid glands. From it, deep into the gland between the parathyroid cells, partitions extend.

Parathyroid hormone – what is it?


Parathyroid hormone is a protein that is formed in the parathyroid glands from a precursor, proparathyroid hormone.

During the day, parathyroid hormone is released unevenly, its pulsating secretion has been proven. So, the maximum amount of this hormone is produced at night: after 3-4 hours from the beginning of sleep, its concentration in the blood exceeds that in the daytime by almost 3 times.

Functions of parathyroid hormone


The main function of this substance is the regulation of calcium metabolism in the body. At the same time, serum calcium is considered the leading regulator of parathyroid hormone release. So, with a decrease in the concentration of calcium in the blood, the glands produce the hormone in greater quantities, and, on the contrary, with hypercalcemia , its synthesis slows down. Hypercalcemia stimulates the transformation of parathyroid hormone into parathyroid hormone.

The production of parathyroid hormone is influenced not only by calcium, but also by magnesium. An increased concentration of this trace element in the blood activates, and a reduced concentration inhibits the hormone release processes.

The targets of parathyroid hormone (the organs on which it has the strongest effect) are the skeleton and kidneys. To a lesser extent, it affects the body’s tolerance to carbohydrates, the absorption of calcium in the intestine, the concentration of fats in the blood serum, the occurrence of itching of the skin, and so on.

How does this hormone regulate calcium metabolism? This happens in three ways:

Activation of vitamin D in the kidneys. This stimulates the formation of calcitriol from vitamin D, a hormone-like substance that promotes the absorption of calcium in the intestine and an increased intake of this trace element from food into the blood. If there is not enough vitamin D in the body, this effect of parathyroid hormone is not realized.
Strengthening the reabsorption (reabsorption) of calcium ions from the primary urine.
Stimulation of the activity of cells that destroy bone tissue – osteoclasts. Calcium, formed during the destruction of bone trabeculae, enters the bloodstream, which leads to an increase in its level there and to a decrease in the strength of the bone tissue. This increases the risk of fractures in humans.
It is worth noting that parathyroid hormone has all of the above effects only when its level in the blood is constantly increased. If it enters the blood sporadically, this has a positive effect on the bone tissue – the bone trabeculae and the bone as a whole become stronger.

In addition to calcium, this hormone affects other types of metabolism in the body, providing the following effects:

  • increases urinary excretion of phosphate;
  • increases urinary excretion of bicarbonate (urine pH shifts towards alkaline);
  • increases the volume of urine;
  • activates the processes of lipolysis in fat cells;
  • activates the processes of gluconeogenesis (the formation of glucose from non-carbohydrate compounds) in the kidneys;
  • changes blood flow in the intestinal vessels.


Blood test for parathyroid hormone


To determine the level of parathyroid hormone from the patient, venous blood is taken.

If you suspect some diseases, the doctor prescribes this analysis to the patient. Blood for research is taken from a vein. Special preparatory measures on the part of the patient are not required for this.

Indications


Indications for a blood test for parathyroid hormone are:

  • suspicion of osteoporosis , vertebral osteosclerosis, cystic formations in bone tissue;
  • pseudo-fractures of long tubular bones;
  • increased blood calcium levels;
  • a decrease in the level of calcium in the blood;
  • the presence of X-ray-positive calculi in the renal pelvis ;
  • neurofibromatosis ;
  • suspicion of multiple endocrine neoplasia.


What can affect the result of the study


A number of medications can distort the test result. When prescribing a study, the doctor must be aware of what medications his patient is taking, and take this into account when decoding the analysis, or ask the patient to refuse to take this or that drug for a few days.

So, the following medicines help to increase the level of parathyroid hormone:

  • cortisol;
  • nifedipine, verapamil;
  • cyclosporin A;
  • isoniazid ;
  • some antifungal drugs (such as ketoconazole);
  • estrogens.


The following drugs help to reduce its concentration in the blood:

  • proton pump blockers (famotidine, cimetidine);
  • magnesia (magnesium sulfate);
  • thiazide diuretics ;
  • some antibiotics (in particular, gentamicin);
  • glucocorticoids (prednisone);
  • combined oral contraceptives;
  • vitamin D.


Interpretation of the result


The normal level of parathyroid hormone in the blood varies depending on the laboratory, or rather, on the method by which it is determined in a particular laboratory. It is usually indicated on the analysis form. The level can be expressed in pmol / l or pg / ml, and one unit can be converted to another by simple mathematical calculations. To obtain pg / ml, the hormone concentration in pmol / l must be multiplied by 9.8.

If the level of parathyroid hormone exceeds the upper limit of the norm, this may be a sign of:

  • primary hyperparathyroidism ( hyperplasia or cancer of the parathyroid glands, multiple endocrine neoplasia);
  • secondary hyperparathyroidism (can occur with rickets , chronic nonspecific inflammatory bowel diseases ( Crohn’s disease and NUC ), chronic renal failure , hypovitaminosis D);
  • tertiary hyperparathyroidism (occurs with adenoma of the parathyroid glands , which developed against the background of long-standing secondary hyperparathyroidism );
  • pseudohyperparathyroidism (a condition that occurs as a result of a decrease in tissue sensitivity to parathyroid hormone);
  • Zollinger-Ellison syndrome .


A decrease in the concentration of this substance in the blood is a sign of:

  • primary hypoparathyroidism (failure of the parathyroid glands);
  • secondary hypoparathyroidism (occurs with a decrease in the level of magnesium in the blood, an increase in vitamin D, as a complication of surgery on the thyroid gland (when one or more parathyroid glands are removed or damaged with it), sarcoidosis);
  • active osteolysis (dissolution of bone fragments).


As a rule, suspecting a particular disease, the doctor prescribes a blood test not only for the level of parathyroid hormone, but also for the concentration of calcitonin (thyroid hormone, an antagonist (with the opposite effect) of parathyroid hormone), magnesium, vitamin D, or other studies that he deems necessary in a specific case.

Which doctor to contact


As with any other diseases of the endocrine organs, the pathology of the parathyroid glands requires observation and treatment by an endocrinologist. Additionally, the patient may need the help of an orthopedist, urologist, gastroenterologist, oncologist, nephrologist.

Conclusion


The hormone synthesized by the cells of the parathyroid glands is parathyroid hormone (another name is parathyrin). It has a protein nature and is released into the blood according to the circadian rhythm – its maximum is determined 3-4 hours after the onset of sleep. Its main function is the regulation of calcium metabolism in the body. Its level in the blood is somehow related to the level of calcium itself, the hormone calcitonin (hormone antagonist), magnesium, vitamin D.

It is possible to determine the concentration of parathyroid hormone in the blood in almost any laboratory. Venous blood will be taken for analysis. No special preparation for the study is required.

Depending on the result of the analysis, the doctor will confirm or deny the preliminary diagnosis, and the tactics of treating the disease that caused changes in the level of parathyroid hormone in the blood directly depends on this.

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