Every organ of our body feeds on blood. Without this, its proper functioning becomes impossible. Organs need a certain amount of blood at any given time. Therefore, its delivery to the tissues is not the same. This is made possible by the regulation of blood circulation. What is this process, its features will be discussed further.
General concept
In the process of changes in the functional activity of each organ and tissue, as well as their metabolic needs, blood circulation is regulated. The physiology of the human body is such that this process is carried out in three main directions.
The first way to adjust to changing conditions is regulation through the vascular system. To measure this indicator, the amount of blood in a certainperiod. For example, this could be a minute. This indicator is called the minute volume of blood (MOV). Such an amount is able to meet the needs of tissues in the process of metabolic reactions.
The second way to ensure the processes of regulation is to maintain the necessary pressure in the aorta, as well as other large arteries. This is the driving force that ensures sufficient blood flow at any given moment. Moreover, it must move at a certain speed.
The third direction is the volume of blood, which is determined in the systemic vessels at a given time. It is distributed among all organs and tissues. At the same time, their need for blood is determined. For this, their activity, functional loads at the moment are taken into account. During such periods, the metabolic requirements of tissues increase.
The regulation of blood circulation occurs under the influence of these three processes. They are inextricably linked. In accordance with this, the regulation of the work of the heart, local and systemic blood flow occurs.
To calculate the IOC, you need to determine the amount of blood that ejects the left or right heart ventricle into the vascular system per minute. Normally, this figure is about 5-6 l / minute. Age-related features of the regulation of blood circulation are compared with other norms.
Blood movement
Regulation of cerebral circulation, as well as all organs and tissues of the body occurs through the movement of blood through the vessels. Veins, arteries and capillaries have a certain diameter and length. They arepractically do not change under the influence of various factors. Therefore, the regulation of blood movement occurs by changing its speed. It moves due to the work of the heart. This organ creates a pressure difference between the beginning and end of the vascular bed. Like all fluids, blood moves from an area of high pressure to an area of low pressure. These extreme points are located in certain areas of the body. The highest pressure is determined in the aorta and pulmonary arteries. As the blood travels through the entire body, it returns back to the heart. The lowest pressure is determined in hollow (lower, upper) and pulmonary veins.
The pressure drops gradually, as much energy is spent pushing blood through the capillary ducts. Also, the blood flow in the process of movement experiences resistance. It is determined by the diameter of the lumen of the blood vessels, as well as the viscosity of the blood itself. Movement becomes possible due to several other reasons. Among them, the main ones are:
- veins have valves to prevent backflow of fluid;
- different pressure in the vessels at the start and end points;
- existence of suction force when inhaling;
- skeletal muscle movement.
Mechanisms of regulation of blood circulation are usually divided into local and central. In the first case, this process occurs in organs, local tissues. In this case, it is taken into account how the organ or department is loaded, how much oxygen it needs for proper operation. Central regulation is carried out under the influencegeneral adaptive responses.
Local regulations
If we consider the regulation of blood circulation briefly, it can be noted that this process occurs both at the level of individual organs and in the whole body. They have several differences.
Blood brings oxygen to the cells and takes away from them the spent elements of their vital activity. The processes of local regulation are associated with the maintenance of basal vascular tone. Depending on the intensity of metabolism in a particular system, this indicator may vary.
The walls of blood vessels are covered with smooth muscles. They are never relaxed. This tension is called vascular muscle tone. It is provided by two mechanisms. This is myogenic and neurohumoral regulation of blood circulation. The first of these mechanisms is the main one in maintaining vascular tone. Even if there are absolutely no external influences on the system, the residual tone is still preserved. It got the name basal.
This process is provided by the spontaneous activity of vascular smooth muscle cells. This voltage is transmitted through the system. Each cell transmits another excitation. This provokes the occurrence of rhythmic oscillations. When the membrane becomes hyperpolarized, spontaneous excitations disappear. At the same time, muscle contractions also disappear.
In the process of metabolism, cells produce substances that have an active effect on the smooth muscles of blood vessels. This principle is called feedback. When the tone of the precapillary sphinctersincreases, blood flow in such vessels decreases. The concentration of metabolic products increases. They help dilate blood vessels and increase blood flow. This process is repeated cyclically. It belongs to the category of local regulation of blood circulation in organs and tissues.
Local and central regulation
Mechanisms of regulation of organ circulation are subject to two interrelated factors. On the one hand, there is a central regulation in the body. However, for a number of organs with a high rate of metabolic processes, this is not enough. Therefore, local mechanisms of regulation are clearly expressed here.
These organs include the kidneys, heart and brain. In those tissues that do not have a high level of metabolism, such processes are less pronounced. Local regulatory mechanisms are necessary to maintain a stable rate and volume of blood flow. The more pronounced the processes of metabolism in the body, the more it needs to maintain a stable inflow and outflow of blood. Even with pressure fluctuations in the systemic circulation, its stable level is maintained in these parts of the body.
However, the local regulatory mechanism is still insufficient to ensure a rapid change in blood inflow and outflow. If only these processes existed in the body, they would not be able to provide correct, timely adaptation to changing external conditions. Therefore, local regulation is necessarily added by the processes of central neurohumoral regulation of blood circulation.
Nervousendings are responsible for the processes of innervation of blood vessels and the heart. The receptors that are present in the system respond to different blood parameters. The first category includes nerve endings that respond to changes in pressure in the channel. They are called mechanoreceptors. If the chemical composition of the blood changes, other nerve endings react to it. These are chemoreceptors.
Mechanoreceptors respond to the stretching of the walls of blood vessels and changes in the speed of fluid movement in them. They are able to distinguish between rising pressure fluctuations or pulse jerks.
The single field of nerve endings, which is located in the vascular system, is made up of angioreceptors. They accumulate in certain areas. These are the reflex zones. They are determined in the carotid sinus, aoral region, as well as in the vessels that are concentrated in the pulmonary circulation of blood. When the pressure rises, mechanoreceptors create a volley of impulses. They disappear when the pressure drops. The excitation threshold of mechanoreceptors is from 40 to 200 mm Hg. st.
Chemoreceptors respond to an increase or decrease in the concentration of hormones, nutrients inside the vessels. They transmit signals about the collected information to the central nervous system.
Central gears
Center for regulation of blood circulation regulates the amount of ejection from the heart, as well as vascular tone. This process occurs due to the overall work of the nervous structures. They are also called the vasomotor center. It includes different levels of regulation. Moreover, there is a clear hierarchical subordination.
Centerregulation of blood circulation is located in the hypothalamus. The subordinate structures of the vasomotor system are located in the spinal cord and brain, as well as in the cerebral cortex. There are several levels of regulation. They have blurry borders.
The spinal level is the neurons that are located in the lumbar and lateral horns of the thoracic spinal cord. The axons of these nerve cells form fibers that narrow the vessels. Their impulses are supported by underlying structures.
The bulbar level is a vasomotor center located in the medulla oblongata. It is located at the bottom of the 4th ventricle. This is the main center of regulation of the blood circulation process. It is divided into pressor, depressor parts.
The first of these zones is responsible for increasing the pressure in the channel. At the same time, the frequency and strength of contractions of the heart muscle increase. This contributes to an increase in the IOC. The depressor zone performs the opposite function. It reduces pressure in the arteries. At the same time, the activity of the heart muscle also decreases. Reflexively, this area inhibits neurons that belong to the pressor zone.
Other levels of regulation
Nervous-humoral regulation of blood circulation is provided by the work of other levels. They occupy a higher position in the hierarchy. Thus, the hypothalamic level of regulation affects the vasomotor center. This influence is downward. In the hypothalamus, the pressor and depressor zones are also distinguished. This iscan be considered as a duplicate of the bulbar level.
There is also a cortical level of regulation. There are zones in the cerebral cortex that have a downward effect on the center located in the medulla oblongata. This process is the result of a comparison of data received from higher receptor zones based on information from various receptors. This forms the realization of behavioral responses, the cardiovascular component of emotions.
The listed mechanisms form the central link. However, there is another mechanism of neurohumoral regulation. It is called the efferent link. All parts of this mechanism enter into a complex interaction with each other. They are made up of different components. Their relationship allows you to regulate blood flow in accordance with the existing needs of the body.
Nerve mechanism
Nervous regulation of blood circulation is part of the efferent link of the global system that controls these processes. This process is carried out through three components:
- Sympathetic preganglionic neurons. Located in the lumbar region and anterior horns of the spinal cord. They are also found in the sympathetic ganglia.
- Parasympathetic preganglionic neurons. These are the nuclei of the vagus nerve. They are located in the medulla oblongata. Also included are the nuclei of the pelvic nerve, which is located in the sacral spinal cord.
- Efferent neurons of the metasympathetic nervous system. They are needed for hollow organs of the visceral type. These neuronsare located in the ganglia of the intramural type of their walls. This is the final path along which the central efferent influences travel.
Practically all vessels are subject to innervation. This is uncharacteristic only for capillaries. The innervation of the arteries corresponds to the innervation of the veins. In the second case, the density of neurons is less.
Nervous-humoral regulation of blood circulation is clearly traced to the very sphincters of capillaries. They terminate on the smooth muscle cells of these vessels. The nervous regulation of capillaries is manifested in the form of efferent innervation through the free diffusion of metabolites directed towards the vessel walls.
Endocrine regulation
The regulation of the circulatory system can be carried out through endocrine mechanisms. The main role in this process is played by hormones that are produced in the brain and cortical layers of the adrenal glands, the pituitary gland (posterior lobe), and the juxtaglomerular renal apparatus.
The vasoconstrictive effect of adrenaline on the arteries of the skin, kidneys, digestive organs, lungs. At the same time, the same substance is capable of producing the opposite effect. Adrenaline dilates the vessels that pass in the skeletal muscles, in the smooth muscles of the bronchi. This process contributes to the redistribution of blood. With strong excitement, feelings, tension, blood flow increases in the skeletal muscles, as well as in the heart and brain.
Norepinephrine also has an effect on blood vessels, allowing redistribution of blood. When the level of this substance rises, special receptors react to it. They can be of two types. Both varieties are present in vessels. They control the narrowing or widening of the duct.
Considering the physiology of the regulation of blood circulation, we should also consider other substances that affect the entire process. One of them is aldosterone. It is produced by the adrenal glands. It affects the sensitivity of the walls of blood vessels. This process is controlled by changing the absorption of sodium by the kidneys, salivary glands, and also by the gastrointestinal tract. Vessels become more or less affected by adrenaline and norepinephrine.
Such a substance as vasopressin, contributes to the narrowing of the walls of arteries in the lungs and in the organs of the peritoneum. At the same time, the vessels of the heart and brain react to this by expansion. Vasopressin also performs the function of redistributing blood in the body.
Other components of endocrine regulation
Regulation of blood circulation of the endocrine type is possible with the participation of other mechanisms. One of them provides a substance such as angiotensin-II. It is formed during the breakdown of angiotensin-I enzymes. This process is influenced by renin. This substance has a strong vasoconstrictive effect. Moreover, it is much more powerful than the consequences of the release of norepinephrine into the blood. However, unlike this substance, angiotensin-II does not provoke the release of blood from the depot.
This action is ensured by the presence of substance-sensitive receptors only in the arterioles at the entrance to the capillaries. They are located unevenly in the circulatory system. This explains the heterogeneity of the impact of the presentedsubstances in different parts of the body. Thus, a decrease in blood flow with an increase in the concentration of angiotensin-II is determined in the skin, intestine, and kidneys. In this case, the vessels expand in the brain, heart, and also the adrenal glands. In the muscles, the change in blood flow in this case will be insignificant. If the doses of angiotensin are very large, the vessels in the brain and heart can narrow. This substance, in combination with renin, forms a separate regulatory system.
Angiotensin can also have an indirect effect on the endocrine system as well as the autonomic nervous system. This substance stimulates the production of adrenaline, noradrenaline, aldosterone. This enhances the vasoconstrictive effects.
Local hormones (serotonin, histamine, bradykinin, etc.), as well as biologically active compounds, can also expand blood vessels.
Age Reactions
Distinguish age-related features of the regulation of blood circulation. In childhood and adulthood, they differ significantly. Also, this process is influenced by the training of a person. In newborns, sympathetic and parasympathetic nerve endings are pronounced. Up to three years in children, the tonic influence of the nerves on the heart predominates. The center of the vagus nerve is distinguished at this age by low tone. It begins to affect blood circulation as early as 3-4 months. However, this process is more pronounced in adulthood. This becomes noticeable at school age. During this period, the baby's heart rate drops.
Having considered the features of the regulation of blood circulation, we can conclude that this process is complex. Many factors and mechanisms affect it. This allows you to clearly respond to any changes in the environment, regulate the flow of vital substances to the organs, which are currently more loaded.
