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How vessels work

So what is vegetative-vascular dystonia? In plain language, this is a violation of the tone of blood vessels - arteries, veins, capillaries - which occurred as a result of disturbances in the functioning of the autonomic nervous system. The human cardiovascular system is a clearly streamlined mechanism that is constantly in motion. The heart, contracting, pushes the blood into the aorta - the largest blood vessel, and then into the arteries. Arteries, in turn, also contract and relax in a certain rhythm, directing blood further throughout the body. This is due to the fact that the walls of the arteries have a muscular structure and thus compensate for the sharp shock of the heart so that the blood flows smoothly further.

Arteries branch as they move away from the heart, their diameter becomes smaller, and they pass into the so-called arterioles - the smallest vessels that are in front of the capillaries. They have a thick wall and a narrow clearance, and this structure allows them to resist the general blood flow - that is why arterioles are called resistance vessels, or resistive vessels.

And, finally, the last link in the delivery of gases, nutrients and trace elements to tissues is capillaries, which are short tubes with very thin walls that can no longer contract. There are a huge number of them in the body, and they are responsible for the metabolism between blood and interstitial fluid. After all, the blood passing through the capillary manages to exchange contents up to 40 times with the intercellular fluid. In the process of this, she gives up the substances necessary for the body and “collects” unnecessary ones. The better this metabolism proceeds, the more nutrition organs and tissues receive. Capillaries are called exchange vessels.

For normal nutrient delivery to tissues, maintaining a certain level of blood pressure is necessary. The amount of blood pressure depends on the force with which the blood presses on the walls of the vessels or on the flow of blood from the center to the periphery. In different vessels, the pressure value will be different. So, the blood pressure in the capillaries (capillary pressure) should be significantly lower than in large arteries. The height of blood pressure depends on the strength of the heart contractions and the volume of blood that is ejected into the aorta, as well as on the degree of contraction of the small arteries and capillaries; It is also important how flexible the large vessels are.

The pressure drop in large and small vessels is very large (compare: 120-150 mm Hg for the arteries and 10-15 mm Hg for the capillaries), despite the fact that they are all directly connected - some go into others. This is due to the fact that in the cardiovascular system there is a mechanism due to which the walls of arteries (vessels of the so-called muscle type) are reduced. This mechanism impedes the movement of blood from large vessels into the capillaries, so the pressure in both parts of the connected and unified cardiovascular system varies so much.

To understand the mechanism of blood vessels, we are most interested in resistive vessels, or vessels of resistance. They contain only 3% of the total volume of our blood, but they, due to their structure, play the main role in the occurrence of pressure drops in the body. The walls of arterioles and capillaries are constantly in good shape, but they can change the diameter of the lumen under the influence of neurohumoral influences. How does this happen? What causes the vessels to expand and contract?

First of all, these are the laws of hydrodynamics (or hemodynamics, i.e. blood movements). The muscle fiber of the vessel responds to the amount of blood that has entered the vessel. If there is a lot of it, the vessel expands. But since the sheath of resistive vessels does not stretch well, blood pressure on the vessel wall increases.

The narrowing or expansion of blood vessels largely depends on the intake of mineral substances - calcium, magnesium and potassium. For example, a lack of potassium leads to an increase in blood pressure; Also, a high content of free calcium in the blood can increase the resistance of the walls of blood vessels and, as a consequence, increase pressure.

The narrowing and expansion of blood vessels depends on the influence of hormones. Some substances, such as adrenaline and norepinephrine, produced by the adrenal medulla, have the ability to affect vascular contraction. The walls of the vessels of resistance are expanded and contracted by the sympathetic nervous system. It regulates the release of more or less adrenaline and norepinephrine, which also transmit nerve impulses in the receptors of the sympathetic nerves. The latter send an impulse to the tissues, including the walls of the resistance vessels.

An essential role in the regulation of the activity of the heart and blood vessels is played by special protein formations on the cell membrane - receptors, which are many in the walls of blood vessels and in the heart muscle.
Receptors respond even to minor changes in tissue metabolism, and if tissues are not adequately supplied with nutrients, receptors quickly transmit information about this to the cerebral cortex. Further, the corresponding impulses are sent from the central nervous system, which cause vasodilation, which ensures enhanced heart function, and also increases the supply of food to organs and tissues.

So, we see how complex even in a healthy person is the regulation of the heart and blood vessels. But what is the picture if functional disturbances occur in the cerebral cortex and nervous system?

In the human nervous system, such departments as the somatic nervous system and the autonomic nervous system are distinguished.

In the somatic nervous system, the central (brain and spinal cord) part and the peripheral (nerves extending from them to various organs) are distinguished.

VVD is associated with a disruption in the functioning of the autonomic part of the nervous system and arises from an imbalance between its parts - the sympathetic and parasympathetic departments. The sympathetic nervous system is involved in the regulation of the activity of internal organs and activates the processes associated with the decay of energy. A parasympathetic, on the contrary, activates the processes of accumulation of energy and substances in the body. Changes due to failures in the management of the tone of these departments lead to the development of VVD syndrome. Both increase and decrease in blood pressure (BP) are perhaps the most frequent manifestations of disorders of the physiological systems and internal organs, because pressure is always the result of accurately calculated joint activity of the heart and blood vessels.

In a healthy person, the cardiovascular system instantly responds to changing external conditions and provides all organs and systems with the nutrients necessary for them.

When they say that “all diseases are from nerves”, then this directly relates to the IRR. Often, the control of the activity of the heart and blood vessels through the nervous and hormonal systems is disturbed as a result of neurosis. This violation just received a special designation in medicine: "neurocirculatory dystonia."

The connection between the nervous system and the vascular apparatus is very close, therefore, using special devices that record the expansion and narrowing of blood vessels, one can determine excitement, anxiety or other human experiences (the principle of the lie detector is based on this principle).

However, with painful changes, the activity of the cardiovascular system is disturbed. These changes and disorders resulting from a particular harmful effect on the nervous system can be very diverse. Moreover, one and the same reason can cause disturbances both in the work of the heart, and in the work of blood vessels or of individual sections of the vascular system. Most often, these disorders, as already mentioned, are manifested in the form of an increase or decrease in blood pressure.

Take, for example, such a destructive factor as stress. Strong negative emotions (anger, fear, despair) cause an increase or decrease in blood pressure. These short-term malfunctions of blood pressure at first are quickly compensated by auto-regulation of the body. But if no protective measures are taken, and stress for everyday reasons is aggravated and becomes constant, a person may wear out these regulatory systems, that is, depressor (relaxing) mechanisms that are not designed for frequent and prolonged use.

If the effect of stress factors continues, the safety depressor apparatus begins to perceive another malfunction of the vessels as a habitual, constant phenomenon. The body "gets used" to the new conditions and adapts to them. As a result of violation of blood pressure, failures in other systems are becoming more significant and prolonged.

However, the nerve center, which is subjected to constant stress, can react in another way - not to stop resisting stress, but to increase resistance and create a “guard ring” around itself. This, of course, will well protect the “defending” nerve center, but it will deprive it of the ability to properly regulate the activities of the “organs” entrusted to it.

These are two options for the development of primary IRR. Both in the first and in the second case, the vascular tone is reduced, but in the first it is simply the lack of tone, and in the second - blocks and cramps. Accordingly, drug treatment of these two options should be carried out differently. In addition, there is a third mechanism of VVD associated with impaired neurohumoral regulation of cardiac activity. Often these three mechanisms can be combined.
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How vessels work

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