Parathyroid gland features of functioning and development. Diseases of the parathyroid glands. Macro construction and dimensions
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 above and below. In the human body, the parathyroid gland performs essential function- regulates the level of calcium in the blood and is responsible for the full nervous activity and motor activity.
Location and size of the parathyroid glands
For the first time, the parathyroid gland was found not in a person, but in ... an Indian rhinoceros - during the autopsy of a deceased animal in 1850. A young British researcher, Richard Owen, managed to find and identify a huge, in comparison with a human, organ in a rhinoceros - weighing as much as 8 grams. Since then, the rhinoceros has been the symbol of the most complex surgery of the parathyroid glands.
The glory of the discovery of the human "parathyroid glands" belongs to the Swedish professor Ivar Sandstrom, who in 1880 discovered this organ and thus launched a whole program to study a new endocrine gland.
The most important feature near thyroid 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 boundaries of its capsule. And the lower one is inside the organ, under the capsule. But in medical practice there were cases when parathyroid formations were in thymus(thymus) and next to the main neurovascular bundle of the neck, near carotid artery, on the front surface spinal column and behind the esophagus.
Outwardly, the parathyroid organs look like lentils. In children, they are pinkish in color, in adults - yellow-brown, with an admixture of red. The length varies within 4-8 mm, width 3-4, thickness - 2-4 mm. Each organ weighs an average of 0.5 grams, and lower glands in many cases slightly larger than the upper ones.
The structure of the parathyroid gland
Unlike others endocrine organs- adrenal glands, pituitary gland or thymus, - "parathyroid glands" do not have a clear division into lobes or regions. Each gland is enclosed in a dense capsule, inside which is a parenchyma consisting of glandular cells of parathyrocytes.
Within 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 into strands and clusters, separated by stromas from connective tissue. These stromas contain 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 division into lobules (such a parenchyma is usually found in embryos and children, but is sometimes diagnosed in adults and elderly patients);
- Reticulated, 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 also a mixed variety, when a small area 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 parathyrocytes, at 5-7 years old, oxiphilic cells appear, and after 20-25 years, the number of fat cells increases.
Functions of the parathyroid gland
Until the turn of the 19th-20th centuries, the function of the parathyroid glands was unknown, and surgeons even removed them during operations on the thyroid gland, not considering them especially important. When it became clear that this would lead to fatal consequences, such operations were banned by law in France. And the famous American surgeon Robert Gross called such procedures "carnage".
Over time, scientists have found that the parathyroid gland plays a critical role in the body. Namely, it regulates the level of calcium within strictly defined limits, maintaining optimal level minerals in the blood.
The main amount of Ca in human body is in the skeleton - almost 99%. And only a small part is in the blood. But to keep the core systems alive and functioning, that 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 it.
The work of the parathyroid gland takes place in 3 stages:
- The excretion of calcium in the urine is sharply reduced.
- The active form of vitamin D increases in the blood, which enhances the absorption of calcium into the blood with the help of calmodulin protein.
- The production of osteoclast bone cells is launched, which destroy aging bone tissue and transport Ca into the blood.
parathyroid hormone
The parathyroid gland is responsible for the synthesis and production of only one substance - parathyroid hormone. Its hormonal antagonist is the product of the activity of the thyroid gland - thyrocalcitonin, which stimulates the production of osteoblast cells - builders 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 falls below normal, the sensitive receptors of the “parathyroid gland” throw parathyroid hormone out. And it, in turn, increases the concentration of vitamin D and the production of osteoclasts.
The parathyroid gland is an organ with a very narrow specialization. Disruption of this endocrine gland can cause 2 the most 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 much activity of osteoclasts leads to softening of the bones and to osteoporosis. A lack of the mineral can cause cramps, numbness and spasm in the arms and legs, vision problems, and brain disorders.
The parathyroid gland is an organ located on the thyroid gland and related to endocrine system. The gland is often referred to as the parathyroid gland. Despite its small size, the parathyroid gland has a huge impact on the functioning of the human body.
Brief anatomy and histology
The parathyroid gland is a round or oval, slightly flattened parenchymal organ. Its normal dimensions are:
- length - from 0.2 to 0.8 cm;
- width - from 0.3 to 0.4 cm;
- thickness - from 0.15 to 0.3 cm.
In the human body there are from 2 to 8 of these glands, but more often there are 4 of them. Not only their number is variable, but also the location. The parathyroid glands can be located in the thickness of the thyroid gland, on its posterior surface, next to the thymus, behind the esophagus, etc. It is very important for endocrinologists to know these features.
Adults have yellow parathyroid glands, therefore similar to those located nearby lymph nodes. In children, the glands are pinkish.
Histology revealed that each parathyroid gland has its own capsule, from which connective tissue strands extend deep into blood vessels and nerves. Around these layers of connective tissue are secretory cells that secrete hormones that regulate the growth and development of the body, muscle contraction, etc.
How did you learn about the role of the parathyroid gland?
The study of the parathyroid glands began relatively recently. They were first discovered in the rhinoceros in the middle of the 19th century, and a few years later in humans. It was the lack of knowledge about these organs that caused the failures associated with resection of the thyroid gland. Previously, such operations resulted in lethal outcome due to convulsions associated with a violation of the concentration of calcium ions.
And only after the structure of the parathyroid gland, its histology and functions were established, it became clear that it is important body, which should regulate calcium metabolism.
A little about the role of calcium
Calcium is a macronutrient found mainly in bone tissue and teeth and has an impact on a variety of processes in the human body. He is involved in:
- building bones and teeth;
- contraction of skeletal and smooth muscles;
- glowing blood;
- conducting a nerve impulse;
- work of the heart;
- regulation of cell membrane permeability.
That's why correct exchange calcium, regulated including by the parathyroid gland, is important for normal functioning organism.
Functions of the parathyroid glands
The parathyroid glands belong to the endocrine system, that is, their function is to secrete hormones into the blood:
- parathyrin;
- calcitonin;
- biogenic amines (serotonin, histamine, etc.).
It is the first two that determine leading role parathyroid glands - normalization of calcium metabolism.
Parathormone
Parathormone, or parathyrin, is the main biologically active substance secreted by the parathyroid gland. It refers to polypeptides. The effect of this hormone is shown in the table.
The peak concentration of the hormone occurs at nighttime sleep. At the third hour of sleep, its content in the blood is approximately 3 times higher than daytime levels. Parathyroid hormone begins to be released when the concentration of calcium ions decreases to 2 mmol / l.
Stimulate the secretion of parathyrin hormones such as growth hormone, glucagon, biogenic amines, prolactin, and magnesium ions.
Calcitonin, like parathyroid hormone, is a peptide hormone. It is a parathyrin antagonist because:
- reduces reabsorption reverse suction) calcium in the kidneys;
- impairs the absorption of calcium in the intestines from food;
- blocks osteoclasts;
- slows down secretion growth hormone, insulin and glucagon.
The release of calcitonin occurs with an increase in the concentration of calcium in the blood over 2.25 mmol / l, as well as under the influence of cholecystokinin and gastrin. But the secretion of this active substance parathyroid is not so significant, it is produced in other organs.
Variants of dysfunction of the parathyroid glands
The dependence of physiology on the parathyroid glands is clearly visible in violation of their work. The classification of dysfunctions of these organs includes two types.
- hyperparathyroidism;
- hypoparathyroidism.
The first state is increased secretion parathyrin. The classification of hyperparathyroidism also includes 3 varieties.
- Primary hyperfunction is caused by such diseases of the parathyroid gland as adenoma, cancer, etc.
- Secondary hyperparathyroidism occurs due to kidney failure, lack of vitamin D, poor absorption nutrients in the intestines, bone destruction.
- Tertiary hyperparathyroidism is a condition in which the parathyroid glands become enlarged. It develops against the background of long-term secondary hyperparathyroidism.
Hyperfunction has the following clinical manifestations:
- frequent urination;
- constant thirst;
- nausea, lack of appetite, gas formation;
- elevated arterial pressure and heart pains and arrhythmias;
- decreased muscle tone;
- osteoporosis;
- pain in the spine, arms, legs;
- loss of teeth;
- deformation skeletal system;
- increased concentration total calcium in the blood up to 3.5 mmol / l.
Hypoparathyroidism - insufficient production of parathyrin. This condition is associated more often with accidental removal of the parathyroid glands during operations on thyroid gland, with swelling or hemorrhage resulting from injury or surgical intervention in the neck, with inflammation of the parathyroid glands.
The classification of this state includes 2 forms: latent (hidden) and manifest. They differ in the severity of symptoms. Hypoparathyroidism has the following manifestations:
- seizures that can last for hours
- dryness skin, dermatitis;
- fragility of nails and fragility of teeth;
- cataract;
- frequent numbness in the limbs.
Parathyrin deficiency has negative impact to a chair due to spasm in smooth muscle, for hair growth.
Thus, the parathyroid glands are organs that play important role. They control calcium metabolism, which is involved in many life processes. Removal of the glands is dangerous, and the increase and decrease in the secretion of their hormone leads to unpleasant symptoms significantly reducing the quality of human life.
A person has two pairs of parathyroid (parathyroid) glands located on the surface or inside. The composition of the gland includes the so-called basic ("dark" and "light") cells, which 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 a system of tubules that contains a colloidal substance. The glands are well equipped with blood and lymphatic vessels, receive sympathetic (from the cervical ganglia) and parasympathetic ( nervus vagus) innervation.
Hormones of the parathyroid glands. The parathyroid glands produce parathormone (parathyrin), which, along with thyroid calcitonin, regulates calcium metabolism in the body and maintains its content in the blood at a certain level. This is achieved due to: a) resorption of calcium from the bones b) reabsorption from the distal tubules of the nephron c) acceleration of absorption from the intestine under the influence of the vitamin D metabolite, which is formed in the kidneys. In parallel, parathyroid hormone causes the release of phosphate from mineral matter, which forms bone (hydroxyapatite) and inhibits the reabsorption of phosphates in the kidneys, thus reducing their concentration in the blood.
With insufficient function of the parathyroid glands, the calcium content in the blood is significantly reduced (normally this figure is 2.25-2.75 mmol / l). Conversely, with hyperfunction of the glands, its increase is observed.
The mechanism of action of parathyroid hormone on the bone cells associated with specific membrane receptors. Due to the contact of the hormone with the receptor, the activity of adenylate cyclase increases, the content of cAMP and the entry of Ca2 + into bone cells increase.
An increase in intracellular calcium concentration 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 the level of parathyroid hormone is the concentration of calcium in the blood. With hypocalcemia, the production of parathyroid hormone increases, with hypercalcemia, the breakdown of the hormone synthesized in the cells begins, and its concentration in the blood decreases. Stimulation of the parathyroid glands is also noted when the adrenergic system is excited, the mediators of which act through the a-adrenergic receptors of cell membranes.
The level of calcium in the blood is 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 the 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 the removal of the parathyroid glands during thyroid surgery or autoimmune destruction of cells that produce parathyroid hormone. With the development of tumors (adenomas) of the parathyroid glands, the level of calcium in the blood plasma can rise to 0.17 g / l (normally 0.1 g / l), causing the development of hyperparathyroidism. The patient suffers from damage to the bones, slowing of heart contractions (bradycardia), calcium deposits in the 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 calcium-rich meal.
The human body is a complex structure in which the work of all organs is interconnected, and destructive disorders of one of them lead to a violation of the overall balance. The parathyroid gland belongs to the category internal secretion and is part of the systems that organize the metabolism in the body. Despite this, until the beginning of the 20th century, it was not known to medical science.
What is a parathyroid gland?
The parathyroid gland has a small size of 4 - 8 mm, and 1 - 3 mm in height, the shape is round or oval. The color depends on the age of the person, at first it is pinkish, with time it turns into a pale yellow.
Her body is covered fibrous tissue through which it is nourished by blood. They are located on the front of the neck, in the upper and lower parts of the thyroid gland. Their number and location vary from person to person.
The typical arrangement of the parathyroid glands is in pairs. Normally, there should be from 2 to 6 pairs. Usually - these are 2 pairs, their location can be:
- thymus
- spine
- wall of the esophagus
- neurovascular cervical bundle
The variability in number and location complicates the detection of the organ, which creates difficulties for surgeons during the operation.
Role in the body
For a long time doctors did not know about the existence of the parathyroid gland and operations on the thyroid gland ended in death.
Traumatization or removal of these glands during surgery leads to sharp decline calcium in the blood, since its main function is to maintain the phosphorus-calcium balance in the body. It affects nerve impulses and joints.
The regulation of calcium concentration is carried out through the production of a specific hormone - which consists of 84 amino acid residues. This organ has sensitive receptors that respond to fluctuations in the calcium content in the blood, and, in accordance with the values obtained, regulates the level of hormone intake into the body.
It has an impact in three directions:
- In the kidneys, it accumulates the active form of vitamin D in the kidneys. The intestinal walls produce more calmodulin, which stimulates the absorption of calcium into the blood.
- Decreases the concentration of calcium in the urine
- Promotes the transfer of calcium from the bone structure to the blood.
The activity of the hormone varies depending on the time of day: in the light - the concentration increases, in the dark - decreases. In addition, the hormones that the gland produces are involved in the transmission nerve impulses muscles and provide correct formation bone tissue.
Symptoms of parathyroid dysfunction and its diagnosis
Important! The main analysis that allows you to reliably judge the quality of the work of the parathyroid gland is a blood test. It determines the content of parathyroid hormones.
The first manifestations of imbalance are identical to the symptoms of diseases of the endocrine system:
- decrease in working capacity
- limb numbness
- jumps in blood pressure
- increased irritability
- depressive states
An imbalance in the production of parathyroid hormones affects the entire body, affecting all organs and systems with which they interact. It can be manifested by the development of such diseases as gout, cataracts, progressive arrhythmia, urolithiasis.
Hormone production disorders are reflected in appearance human: hair becomes brittle, their loss intensifies, appear skin diseases, nails and teeth deteriorate, skeletal muscles become inflamed.
At the first suspicion of an imbalance in the functioning of the parathyroid gland, it is necessary to undergo an examination. AT without fail are held laboratory research: for this donate blood and urine. Standard tests:
- determination of calcium and phosphate in urine
- the level of parathyroid hormones
- serum and ionized calcium levels
Most accurate results diagnostics of the state of the gland give instrumental methods. With their help, the presence of pathologies, the general functional state are determined.
Usually, doctors use several methods at once to improve the accuracy and double-check the results obtained, and based on the generalized data, they make a diagnosis.
Diseases
All diseases are associated with a violation of the production of parathyroid hormone. Their level may be excessive or vice versa insufficient.
Hyperparathyroidism
Too much hormone is called hyperparathyroidism. This condition leads to an increase in the proportion of calcium in the blood and a decrease in bone tissue. AT advanced cases diseases, can cause coma.
The parathyroid glands, or it would be more correct to call them the parathyroid glands, are an independent paired organ internal secretion. It consists of two pairs of small oval-shaped endocrine glands. They are located on the back surface of the thyroid gland itself, at its lower and upper poles.
The parathyroid gland synthesizes two parathyroid glands - these are parathyroid hormone (PTH) and calcitonin.
We found out what hormones the parathyroid gland synthesizes. Now let's talk about the functions for which they are responsible. Parathyroid hormones are of great importance for the body.
Parathyroid hormone (PTH) is a protein compound that contains iron, nitrogen and sulfur. This hormone is constantly being synthesized.
- With its participation, the formation of the skeleton and the accumulation of calcium in the bones are carried out - important element providing bone strength.
- In addition, this secretion of the parathyroid gland stimulates the function of osteoclasts, which are responsible for the removal of calcium from bone tissue into the blood. This process allows you to maintain the right balance between the calcium content in the bones and blood. Moreover, it contains about 99% calcium, and in the blood serum it is only 1%.
- Calcium ions are involved in the transmission of nerve impulses, contractile activity muscle tissue. Calcium is important component in the blood coagulation system and activates the action of certain enzymes.
Calcitonin is responsible for reducing the concentration of calcium in the blood and is not synthesized constantly, but only with hypercalcemia.
Thus, parathyroid hormones and their functions for the human body are indispensable. They take part in important metabolic processes.
The action of parathyroid hormone on other organs
We found out that parathyroid hormones are important for the skeletal system. Now let us dwell on their action on other organs.
- This hormone exerts its influence on the urinary system. Some calcium is excreted from the body with the kidneys. This process occurs under the control of parathyroid hormone.
- Parathyroid hormone aids in the absorption of calcium from small intestine into the blood.
- This hormone reduces the deposition of calcium in the lens of the eye.
Hypofunction of the parathyroid gland
The hormones of the parathyroid gland with its hypofunction are produced in insufficient quantities. The inhibited activity of the parathyroid gland causes the so-called tetany, or convulsive illness. At the same time, excitability nervous system rises significantly. In some muscles, fibrillar contractions are periodically observed, turning into prolonged convulsions. AT severe cases convulsions spread to all muscle groups, including respiratory ones, as a result of which the patient dies from asphyxia (suffocation).
In the case of a gradual slow progression of tetany, patients may experience disorders associated with the digestive system, dental problems, as well as poor growth hair and nails.
Parathyroid hormones maintain normal calcium levels in the blood. Normally, it ranges from 2.1 to 2.5 mmol / l. With tetany, the level of calcium in the blood serum does not rise above 2.12 mmol / l. This is manifested not only by muscle cramps, such patients are nervous and often suffer from insomnia.
Hyperfunction of the parathyroid gland
The hormones of the parathyroid gland with its hyperfunction are synthesized in excess. This can occur with hyperactivity of some of the sections of this endocrine gland. It leads to serious violations associated with an imbalance of calcium in the blood serum. This condition is called hyperparathyroidism and can lead to pathological processes:
- Parathyroid osteodystrophy.
- Hypercalcemia.
Symptoms of hyperparathyroidism
Primary are non-specific:
- Apathy, lethargy, weakness.
- Bad mood.
- Nausea and decreased or lack of appetite.
- Constipation.
- Pain in joints and bones.
One of the options for hyperparathyroidism can be chronic hyperfunction of the glands, while the level of calcium in the bones decreases, and in the blood, on the contrary, increases. The bones of such patients become brittle, disorder occurs digestive system and there are problems associated with the cardiovascular system.
Hyperfunction may appear due to the growth of a separate section of the parathyroid gland. In the blood of such patients is determined excess amount calcium and excessive ossification of the skeleton. Patients may have indigestion (diarrhea, vomiting). On the part of the nervous system, there is reduced excitability, apathy. At further development diseases may appear curvature of the skeleton (deformation chest and spine). Patients lose a lot of weight in a few months - up to 10-15 kg in 3-4 months. There may be temporary excitability, which is later replaced by lethargy. Such a state requires immediate treatment, because in advanced severe cases, this can result in the death of the patient. In case of appearance similar symptoms you should immediately consult a doctor, preferably an endocrinologist.
Treatment of disorders of the parathyroid gland
We found out what function the parathyroid hormones perform. Violations in the work of this endocrine gland need to be corrected. Hypofunction is treated much easier. The patient needs to be given a series of medicines and adjust the diet, and it is also recommended to take sunbathing. This will improve the absorption of calcium by the body, because. this requires vitamin D, which our skin produces under the influence of ultraviolet radiation.
Treatment of hyperfunction of this organ is carried out only surgically. In this case, only the overgrown area of the parathyroid gland is removed. This organ cannot be completely removed, because this will lead to uncontrolled convulsions and death of the patient.
Parathyroid hormones and their effect on the body are very important. In time to identify problems associated with the work of the thyroid and parathyroid glands, will help preventive examinations and dispensary. If necessary, the doctor will prescribe an ultrasound. With the help of such an examination, it will not be difficult for a specialist to identify the problem in time.
