How does the cardiovascular system work?

How does the human cardiovascular system work?
The human cardiovascular system is a complex and sensitive device that provides blood supply to all body organs and tissues. At the same time, the principles of the cardiovascular system are extremely simple: the heart performs the function of a pump that pumps blood, and the blood vessels play the role of pipelines that deliver blood from the heart to the organs and back. Such a comparison, of course, is approximate and reflects only the basic essence of the work of our heart and blood vessels, we will try to explain the more subtle mechanisms of functioning of this complex system of the body below.

The heart is the central pump of our body. Every minute, the heart pumps about 5 liters of blood. Inside the heart there are 4 cavities (chambers), separated from each other by partitions and valves. The work of the heart consists of cyclically alternating contractions (systole) and relaxations (diastole). During contraction (systole), the volume of the heart cavities decreases and blood is ejected from the heart into the system of blood vessels. During relaxation (diastole), the chambers of the heart expand and the heart fills with blood. During the relaxation phase, the valve that separates the heart from the system of blood vessels (aortic valve) closes, due to which the blood does not return to the heart, but begins to flow through the vessels.

Blood vessels are the pathways through which blood flows. There are several types of blood vessels in the human body: arteries, capillaries and veins.

Arteries (arterial vessels) look like tubes of different diameters with more or less thick walls. A characteristic feature of arterial vessels is that their walls have a large number of muscle fibers, thanks to which these vessels can contract and relax, which means that they can decrease and increase their diameter (lumen). Arteries are so called because arterial blood flows through them from the heart, that is, blood rich in oxygen. The speed of blood circulation in the arteries is very high (several meters per second). In the figure, the arteries are shown in red

Veins are blood vessels through which venous blood flows, that is, blood with a low oxygen content. Through the veins, blood returns from the organs to the heart. Like arteries, veins come in different diameters. The diameter of the veins varies depending on the volume of blood accumulated in them - the larger the volume of blood, the wider the lumen of the vein. Blood flows slowly through the veins (several centimeters per second). In the figure, the veins are shown in blue.

Capillaries are the smallest blood vessels in our body. The diameter of capillaries is measured in several microns, which can be compared to the diameter of human blood cells. The walls of capillaries are extremely thin. An exchange of gases and nutrients takes place between the blood and the tissues of our body through the capillary walls. The speed of blood flow through the capillaries is minimal.

Thus, the cardiovascular system of the body is a closed circle through which blood circulates from the heart to the organs and back - this is the so-called great circle of blood circulation. In addition to the large circle of blood circulation, there is also a small circle of blood circulation, which circulates blood between the lungs and the heart. In the lungs, blood is enriched with oxygen and gets rid of excess carbon dioxide.

Pulse and blood pressure
Pulse and blood pressure are the two most important indicators of the work of the cardiovascular system of our body. Below we will show what pulse and blood pressure are.

A pulse is an impulse that we feel when we feel the arteries passing near the surface of the body. A pulse wave is formed when blood is ejected from the heart at the moment of systole (contraction), while a shock wave is formed in the initial part of the aorta (the main arterial vessel of our body), which is transmitted along the walls of all arteries, and which we feel as a pulse. Normally, the pulse frequency and its rhythmicity correspond to the frequency and rhythmicity of heart contractions.

Arterial pressure is the pressure under which blood flows through arterial vessels. How is blood pressure formed? First, blood pressure depends on the volume of circulating blood. The total blood volume of an adult is approximately 5 liters, 2/3 of which flows through blood vessels. A decrease in the volume of circulating blood (BCC) leads to a decrease in blood pressure, and an increase in BCC leads to an increase in blood pressure.
Secondly, arterial pressure depends on the diameter of blood vessels through which blood flows. The smaller the diameter of the vessel, the greater the resistance to blood flow and the greater the arterial pressure.
Thirdly, blood pressure is determined by the work of the heart, the more intensively the heart works and the more blood it pumps per unit of time, the higher the blood pressure.
In medicine, it is customary to define two types of blood pressure: systolic and diastolic. Systolic blood pressure corresponds to the pressure in arterial vessels at the moment of contraction of the heart - it is the maximum indicator of blood pressure.
Diastolic pressure corresponds to the pressure in arterial vessels at the moment of diastole (relaxation) of the heart.
In the well-known formula of normal blood pressure 120/80 (read 120 by 80), the number 120 corresponds to the systolic pressure, and the number 80 to the diastolic pressure.

Blood pressure control systems
The level of blood pressure determines the degree of supply of nutrients and oxygen to the organs of the whole body. Even small changes in blood pressure can significantly affect the work of one or another organ. That is why the level of blood pressure in the body is under strict control and regulated with a high level of accuracy. Two main mechanisms are involved in blood pressure regulation: nervous and humoral.
The nervous mechanism of blood pressure control is carried out by the cerebral cortex, autonomic centers of the brain and sympathetic centers of the spinal cord. Thanks to the work of these nerve centers, nerve impulses are constantly sent to the arterial vessels, which, with the help of contraction or relaxation of the muscle fibers in the walls of the vessels, maintain the tone of the vessels (diameter of the vessels), and, accordingly, the blood pressure level at the required level.
The humoral mechanism of regulation includes the participation of a large number of hormones (adrenaline, noradrenaline, angiotensin, steroid hormones) that affect the main components of the human cardiovascular system: the work of the heart, the volume of circulating blood, the tone of blood vessels.
One of the most important components of the apparatus that regulates blood pressure is the renin-angiotensin system, in which the kidneys participate.
Knowledge of the basic mechanisms of the cardiovascular system will help the reader better understand the problems of arterial hypertension, understand the causes of this disease and the principles of its treatment.