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Parathyroid hormone (PTH) is a hormone produced by the parathyroid glands. It primarily affects the calcium and phosphate metabolism: parathyroid hormone increases the concentration of calcium in the blood, and at the same time its secretion results in an increase in the excretion of phosphates from the body. Dangerous consequences are caused by both the deficiency and excess of parathyroid hormone - but what can be the causes of abnormal levels of PTH in the body?

Parathyroid hormone(abbreviatedPTH ) is a polypeptide hormone made of 84 amino acids. Parathyroid glands (parathyroid glands), which in humans are located on both sides of the neck, directly under the lower and upper poles of the thyroid gland, deal with the production and secretion of parathyroid hormone. Typically humans have four parathyroid glands, but it is possible for a patient to have one or even eight parathyroid glands.

Parathyroid hormone: secretion

Parathyroid hormone is constitutively produced (permanently) within the parathyroid gland, but this hormone is not constantly secreted. The stimulus that causes PTH to be released is to lower blood calcium levels.

Parathyroid hormone: functions

The function of parathyroid hormone is to regulate the calcium-phosphate balance. This polypeptide primarily affects 3 human organs: bones, kidneys and intestines.

Parathyroid hormone, as mentioned above, is secreted in the event of hypocalcaemia - the role of PTH in this case is to increase the concentration of calcium in the blood. This is mainly due to the fact that parathyroid hormone acts on bones - this hormone, admittedly indirectly, but ultimately stimulates osteoclasts, i.e. bone cells that are responsible for its breakdown. Ultimately, from this specific "bank" of calcium, i.e. from the bone tissue, thanks to PTH, calcium is released from the bones and then its concentration in the blood increases.

Parathyroid hormone also works on the kidneys. Here, the operation of PTH is much more complicated. Well, first, the hormone increases the calcium reabsorption in the renal tubules. As a result, a much smaller amount of calcium ions is lost from the body along with urine. Another action of PTH is the inhibition of phosphate reabsorption.

It also increases calcium levelsin the blood - phosphate binds with calcium in the blood into various s alts, therefore when there is less phosphate in the blood, less calcium is bound to them - thanks to this, ultimately the concentration of calcium in the blood increases.

This, however, is not the end of the renal effects of parathyroid hormone - this substance also influences the formation of the active form of vitamin D3. PTH stimulates one of the enzymes, 1-alpha-hydroxylase, whose task is to transform vitamin D precursors into their biologically active forms.

Parathyroid hormone also affects the intestines, but not directly. Well, it is in the intestines that calcium is absorbed from food - it is understandable that when there is a calcium deficiency in the body, then the absorption of this element should be increased in the digestive tract. This is indeed the case, but the increase in calcium absorption in the intestine is due to vitamin D - which, in turn, is produced in the kidneys thanks to the action of PTH.

The hormone that has an opposite (antagonistic) effect in relation to PTH is calcitonin - this substance is produced by C cells of the thyroid gland.

Parathyroid hormone: blood PTH concentration test

Parathyroid hormone level testing is performed on a blood sample taken from the patient. As a general rule, no special preparation is required before this test is performed, and patients may be asked to come to the test on an empty stomach.

The norm of parathyroid hormonemay vary depending on the laboratory, but it is generally accepted that the normal concentration of parathyroid hormone in the blood is 10-60 pg / ml.

It should be added here that analyzing the level of parathyroid hormone alone does not allow for the assessment of the patient's he alth. In order to obtain a complete clinical picture, it is necessary to analyze the parathyroid hormone level result together with other test results, such as e.g. the level of calcium and phosphate in the body.

Testing parathyroid hormone is not one of the laboratory analyzes that are routinely ordered to patients - in order for a doctor to perform this test, there must be some premises for it. Usually, there are mainly symptoms that suggest abnormal levels of calcium in the body - both its deficiency and excess.

Parathyroid hormone: causes and effects of its excess in the body

A condition in which an excess of parathyroid hormone appears in the body may be caused by an overactive parathyroid gland. There are two types of this problem. Primary hyperparathyroidism may result from the presence of nodules in this organ that produce PTH. Increased levels of parathyroid hormone in the bodyit is then accompanied by another deviation, i.e. hypercalcemia (excess calcium in the blood).

The second problem with excess parathyroid hormone is secondary hypoparathyroidism. In her case - as above - there is an excess of PTH in the body, but the accompanying deviation is different, because it is hypocalcemia (lowering blood calcium levels). The condition may seem atypical, but it can be easily explained - in the case of secondary hyperparathyroidism in a patient - e.g. due to renal failure - calcium deficiency first appears. To remedy this, the body begins to produce increased amounts of parathyroid hormone - eventually an excess of this substance appears in the blood.

It is also possible that the excess of parathyroid hormone in the body will not result from parathyroid disorders. This possibility is related to the fact that some cancers - e.g. lung tumors or breast tumors - are able to secrete PTH alone or substances that act like parathyroid hormone. Excess parathyroid hormone can lead to many different problems. In patients with such a problem, nervous system disorders as well as cardiac arrhythmias may appear. Patients with excess PTH also have an increased risk of osteoporosis.

Parathyroid hormone: causes and effects of its deficiency in the body

The opposite state to the above-described condition, i.e. parathyroid hormone deficiency in the body, occurs in the case of hypoparathyroidism. This problem is much rarer than hyperparathyroidism, but it is possible that it may occur.

The most common causes of hypoparathyroidism are complications of head and neck procedures (most often it concerns total thyroidectomy, i.e. total removal of the thyroid gland). In the case of removal or damage of the parathyroid glands - due to the functions of parathyroid hormone - patients may suffer from deficiencies not only of PTH, but also of calcium or vitamin D.

Check:

Parathyroid cancer Repeated hypoparathyroidism (Albright's syndrome) Diet in hyperparathyroidism

Sources: 1. Materials of the Encyclopaedia Britannica, on-line access: https://www.britannica.com/science/parathormone2. H. Krauss, P. Sosnowski (eds)., Fundamentals of human physiology, Wyd. Scientific University of Medical Sciences in Poznań, 2009, Poznań 3. Interna Szczeklik 2016/2017, ed. P. Gajewski, publ. Practical Medicine

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