Parathyroid glands: functions and pathologies

They are small glands located in the neck that regulate calcium levels in the body.

Parathyroids are four endocrine glands, which secrete hormones into the blood.

From a functional point of view they are completely independent of the thyroid, but are so called for their close proximity to the latter; They are in fact positioned at the posterior wall of the thyroid.

Parathyroids are distinguished into upper and lower according to their location.

They are extremely small glands, each varying in size between those of a grain of rice and those of a lentil and weighing between 10 and 60 milligrams.

How they work

The main task of parathyroids is to control the distribution of calcium in the body.

To regulate the functioning of the parathyroids are in fact the variations, even minimal, of the concentration of calcium in the blood (calcemia) compared to its normal values (included in the adult subject between 8.5 and 10.5 mg / dl).

The cells that make up the parathyroids are equipped with specific receptors that continuously detect serum calcium and trigger the activity of the glands in case of decrease in plasma calcium levels or, vice versa, inhibit it if these rise.

The activation of the parathyroids when the serum calcium is too low results in the production of parathyroid hormone (or parathyroid hormone) which, once introduced into circulation, reaches the organs at the level of which it acts to bring the amount of calcium back into the normal range.

The target organs of parathyroid hormone are mainly:

• the skeleton, where it stimulates the resorption of bone tissue with consequent release of calcium contained in it
• the kidneys, where it limits the elimination of calcium with the urine (simultaneously increasing that of phosphorus) and where it induces the conversion of vitamin D into its active form, which has the effect, in turn, of stimulating the absorption of calcium taken with food in the intestine.

Why they are essential

The importance of the proper functioning of the parathyroids lies in the fact that calcium is involved in a number of fundamental physiological processes:

• Together with phosphorus, it is the main element of the mineral component of bone tissue
• intervenes in the mechanisms of conduction of electrical impulses along the nerves and in those of activation of muscle contraction
• It acts as a regulator of the reactions that take place in the cells of many organs and as a modulator of the activity of various enzymes.

For this reason, a dysfunction of the parathyroids, which involves an excessive or insufficient production of parathyroid hormone, can have multiple negative effects, sometimes even serious.

What happens if they work too much or too little

The most frequent alteration of parathyroid activity is the release of an excessive amount of parathyroid hormone, which is called “hyperparathyroidism”.

This condition can originate from a pathological process affecting the parathyroids: the most common is parathyroid adenoma, a circumscribed benign tumor that can develop in one or more glands.

Rarer causes are diffuse parathyroid hyperplasia (with uniform enlargement of all glands), parathyroid carcinoma and multiple endocrine neoplasia (an inherited syndrome affecting several endocrine glands).

When the excessive secretion of parathyroid hormone derives from one of these diseases we speak of “primitive” hyperparathyroidism, to distinguish it from the “secondary” type that is determined instead by phenomena external to the glands: vitamin D deficiency, chronic renal failure, malabsorption of nutrients in the intestine can cause constant hypocalcemia that induces the parathyroids to continuously release large amounts of the hormone.

The harmful effects of hyperparathyroidism are due to chronic hypercalcemia, which causes:

• disorders of the nervous system (depression, difficulty concentrating, widespread pain)
• abnormalities of muscle activity (hypostenia)
• alterations of bone tissue (osteopenia, fibrous-cystic osteopathy)
• kidney stones
• deposition of calcium in the vascular walls (atherosclerosis).

A little less common is the condition of hypoparathyroidism caused in most cases by surgical removal of the parathyroids (necessary in the presence of diseases affecting the glands themselves or adjacent structures) or more rarely by an inflammatory process of autoimmune nature or by a congenital disease.

The symptoms of hypoparathyroidism are related to low levels of calcium in the blood, which primarily determine a state of neuromuscular hyperexcitability (muscle spasms, accentuation of tendon reflexes, sensitivity disorders).

If they occur acutely, both the increase and decrease in blood levels of calcium provoke serious clinical pictures (parathyrotoxic crisis in the first case, tetanus syndrome in the second), which require immediate hospitalization.

Diagnosis and treatment of parathyroid dysfunction

The main diagnostic tests indicated for the classification of a parathyroid dysfunction are:

• laboratory tests evaluating the endocrine activity of the parathyroids and the metabolism of calcium and phosphorus (blood determination of the parathyroid hormone, measurement of the concentrations of the two minerals in the blood and urine)
• radiological investigations that allow to visualize the state of the glands (ultrasound, scintigraphy, magnetic resonance imaging)
• radiological investigations that evaluate the possible effects of dysfunction on the skeletal system (radiography, bone densitometry).

As far as treatment is concerned, in case of primary hyperparathyroidism, surgical removal of the diseased gland(s) or, if the intervention is not feasible, medical therapy aimed at limiting bone damage (with drugs for osteoporosis) is required.

In case of secondary hyperparathyroidism, the correction of nutrient deficiencies that determine it or, especially in the presence of renal failure, the administration of drugs capable of modulating the activity of parathyroid cell receptors (calcium-mimetics) is indicated.

Finally, in case of hypoparathyroidism, calcium and vitamin D supplementation is necessary.