Every organ in our body feeds on blood. Without this, its proper functioning becomes impossible. At each point in time, organs need a certain amount of blood. Therefore, its entry to the tissues is not the same. This becomes possible due to the regulation of blood circulation. What is this process, its features will be discussed later.
General concept
In the process of changes in the functional activity of each organ and tissue, as well as their metabolic needs, regulation of blood circulation occurs. The physiology of the human body is such that this process is carried out in three main directions.
The first way to adapt to changing conditions is through vascular regulation. To measure this indicator, a blood quantity is determined in a certain time period. This, for example, may be a minute. This indicator is called minute blood volume (IOC). Such an amount is able to meet the needs of tissues in the process of metabolic reactions.
The second direction of ensuring regulatory processes is to maintain the necessary pressure in the aorta, as well as other large arteries. This is a driving force that provides sufficient blood flow at any given moment. Moreover, it should 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 between all organs and tissues. In this case, their blood demand is determined. For this, their activity, functional loads at the moment are taken into account. In such periods, the metabolic needs of tissues increase.
Regulation of blood circulation occurs under the influence of these three processes. They are inextricably linked. In accordance with this, the regulation of the heart, local and systemic blood flow takes place.
To calculate the IOC, it will be necessary to determine the amount of blood that the left or right heart ventricle ejects into the vascular system in a minute. Normally, this figure is about 5-6 l / min. Age-related features of blood circulation regulation 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 specific diameter and length. They practically do not change under the influence of various factors. Therefore, the regulation of blood movement occurs by changing its speed. It moves thanks to the work of the heart. This organ creates a pressure difference between the beginning and end of the bloodstream. Like all fluids, blood moves from high to low pressure. These extreme points are located in certain areas of the body. The highest pressure is determined in the aorta and pulmonary arteries. When blood passes through the whole body, it returns back to the heart. The lowest pressure is determined in the vena cava (lower, upper) and pulmonary veins.
The pressure drops gradually, since a lot of energy is spent on pushing blood through the capillary ducts. Also, blood flow during 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 is made possible by several other reasons. Among them, the main ones are:
- there are valves in the veins, which prevents the reverse movement of fluid;
- different pressure in the vessels at the starting and ending points;
- the existence of suction force when inhaling;
- skeletal muscle movement.
The 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 takes into account how loaded the organ or department is, how much oxygen it needs for proper operation. Central regulation is carried out under the influence of general adaptive reactions.
Local regulation
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 body as a whole. They have several differences.
Blood brings oxygen to the cells and takes away from them the waste elements of their vital functions. Local regulation processes are associated with maintaining basal vascular tone. Depending on the intensity of metabolism in a particular system, this indicator may vary.
The walls of the vessels are covered with smooth muscles. They are never relaxed. This tension is called muscle vascular 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. He received 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 a different excitement. This provokes the occurrence of rhythmic vibrations. When the membrane becomes hyperpolarized, spontaneous excitations disappear. At the same time, muscle contractions also disappear.
In the process of metabolism, substances are produced in the cells that have an active effect on the smooth muscles of blood vessels. This principle is called feedback. When the tone of precapillary sphincters increases, blood flow in such vessels decreases. The concentration of metabolic products increases. They contribute to the expansion of blood vessels, 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
The mechanisms of regulation of organ circulation are subject to two interrelated factors. On the one hand, there is central regulation in the body. However, for a number of organs with a high metabolic rate this is not enough. Therefore, local regulation mechanisms are pronounced here.
These organs include the kidneys, heart, and brain. In those tissues that do not have a high metabolic rate, such processes are less pronounced. Local regulatory mechanisms are necessary to maintain a stable speed and volume of blood flow. The more pronounced are the metabolic processes in the organ, the more it needs to maintain a stable influx and outflow of blood. Even with pressure fluctuations in the systemic circulation, a stable level is maintained in these parts of the body.
However, the local regulation mechanism is still insufficient to ensure rapid changes in blood flow and outflow. If only these processes existed in the body, they would not be able to provide the correct, timely adaptation to changing external conditions. Therefore, local regulation is necessarily added by the processes of central neurohumoral regulation of blood circulation.
Nerve endings are responsible for the processes of innervation of blood vessels and the heart. Receptors that are present in the system respond to different blood counts. The first category includes nerve endings that respond to pressure changes in the bed. They are called mechanoreceptors. If the chemical composition of the blood changes, other nerve endings respond to this. These are chemoreceptors.
Mechanoreceptors respond to stretching of the walls of blood vessels and a change in the speed of movement of fluid in them. They are able to distinguish between fluctuations in rising pressure or pulse jerks.
A single field of nerve endings, which is located in the vascular system, is angioreceptors. They accumulate in certain areas. These are reflexogenic zones. They are determined in the sinocarotid, aoral region, as well as in the vessels, which are concentrated in the pulmonary circle of blood circulation. With increasing pressure, mechanoreceptors create a volley of pulses. They disappear with a decrease in pressure. The threshold of excitation of mechanoreceptors is from 40 to 200 mm RT. Art.
Chemoreceptors respond to an increase or decrease in the concentration of hormones, nutrients inside the vessels. They transmit signals about the information collected to the central nervous system.
Central mechanisms
The blood circulation regulation center regulates the amount of ejection from the heart, as well as vascular tone. This process occurs due to the general work of nerve structures. They are also called the vasomotor center. It includes different levels of regulation. Moreover, there is a clear hierarchical subordination.
The center of blood circulation regulation is 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. Axons of these nerve cells form fibers that constrict blood vessels. Their impulses are supported by the structures above.
The bulbar level is a vasomotor center, which is located in the medulla oblongata. It is located at the bottom of the 4th ventricle. This is the main center of regulation of the circulatory process. It is divided into pressor, depressor parts.
The first of these zones is responsible for increasing pressure in the channel. Along with this, the frequency and strength of contractions of the heart muscle increase. This contributes to an increase in 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 site exerts a braking effect on neurons that belong to the pressor zone.
Other levels of regulation
Neuro-humoral regulation of blood circulation is provided by work of other levels. They occupy a higher position in the hierarchy system. 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 can be considered as a duplicate of the bulbar level.
There is also a cortical level of regulation. There are areas in the cerebral cortex that have a downward effect on the center located in the medulla oblongata. This process is the result of comparing data from higher receptor zones based on information from different receptors. This forms the realization of behavioral reactions, 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 consist of different components. Their relationship allows you to regulate blood flow in accordance with the existing needs of the body.
Neural 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 by three components:
- Sympathetic preganglionic neurons. Located in the lumbar region and the anterior horns of the spinal cord. They are also defined in the sympathetic ganglia.
- Parasympathetic preganglionic neurons. These are the nuclei of the vagus nerve. They are in the medulla oblongata. Also included are the nuclei of the pelvic nerve, which is located in the sacral region of the spinal cord.
- Efferent neurons of the metasympathetic nervous system. They are needed for the hollow organs of the visceral type. These neurons are located in the ganglia of the intramural type of their walls. This is the final path along which the central efferent influences move.
Almost all vessels are subject to innervation. This is uncharacteristic only for capillaries. The innervation of arteries corresponds to the innervation of veins. In the second case, the density of neurons is lower.
Neuro-humoral regulation of blood circulation is clearly traced to the very sphincters of capillaries. They end on the smooth muscle cells of these vessels. Nervous regulation of capillaries is manifested in the form of efferent innervation through the free diffusion of metabolites directed to the walls of blood vessels.
Endocrine regulation
The regulation of the circulatory system can be performed 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 vasoconstrictor effect is exerted by adrenaline on the arteries of the skin, kidneys, digestive organs, and lungs. Moreover, the same substance is capable of producing the opposite effect. Adrenaline dilates the vessels that pass in the muscles of the skeleton, in the smooth muscles of the bronchi. This process contributes to the redistribution of blood. With strong excitement, feelings, tension, blood flow increases in skeletal muscles, as well as in the heart and brain.
Norepinephrine also has an effect on blood vessels, allowing redistribution of blood. With an increase in the level of this substance, special receptors react to it. They can be of two types. Both species are present in vessels. They control the process of narrowing or expansion of the duct.
Considering the physiology of blood circulation regulation, other substances that affect the whole process should be considered. 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 the digestive tract. Vessels become more or less exposed to adrenaline and norepinephrine.
A substance such as vasopressin helps to narrow the walls of the arteries in the lungs and in the peritoneal organs. In this case, the vessels of the heart and brain respond 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. Renin affects this process. This substance has a strong vasoconstrictor 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 provided due to the presence of receptors sensitive to the substance only in arterioles at the entrance to the capillaries. They are located unevenly in the circulatory system. This explains the heterogeneity of the effects of the presented substance 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 may 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, norepinephrine, aldosterone. This enhances vasoconstrictor effects.
Local hormones (serotonin, histamine, bradykinin, etc.), as well as biologically active compounds, can also expand blood vessels.
Age-related reactions
There are age-related features of blood circulation regulation. In childhood and adulthood, they are significantly different. Also, this process is affected by a person’s fitness. In newborns, sympathetic and parasympathetic nerve endings are pronounced. Up to three years, the tonic effect of nerves on the heart predominates in children. The center of the vagus nerve is distinguished at this age by a low tone. It begins to affect blood circulation as early as 3-4 months. However, this process manifests itself brighter in more adulthood. . .
, . , . , , .