How does blood from the arteries get into the veins? Physiology of blood circulation. Blood and blood circulation

For the normal operation of all organs and systems of the human body, it is vitally important to constantly supply them with nutrients and oxygen, as well as the timely removal of disintegration products and waste products. The implementation of these important processes is ensured by the constant circulation of blood. In this article, we will look at the human circulatory system, and also describe how blood from the arteries enters the veins, how it circulates through the blood vessels and how the main organ of the circulatory system, the heart, works.

The study of blood circulation from antiquity to the 17th century

Human blood circulation has been of interest to many scientists for centuries. Even ancient scholars, Hippocrates and Aristotle, assumed that all organs are somehow interconnected. They believed that the circulation of a man consists of two separate systems that do not unite with each other. Of course, their ideas were wrong. They were refuted by the Roman physician Claudius Galen, who proved experimentally that blood moves his heart not only through the veins, but also through the arteries. Until the XVII century, scientists were of the opinion that the blood comes from the right into the left atrium through the septum. Only in 1628 was a breakthrough: English anatomist William Garvey in his work "Anatomical study of the movement of the heart and blood in animals" introduced his new theory of blood circulation. He experimentally proved that it moves along the arteries from the ventricles of the heart, and then returns through the veins to the atria and can not be indefinitely produced in the liver. William Harvey was the first to quantify the cardiac output. On the basis of his work, a modern scheme of human circulation, including two circles, was created.

Further studies of the circulatory system

For a long time an important question remained unclear: "How the blood from the arteries gets into the veins." Only at the end of the XVII century Marcello Malpighi discovered special links of blood vessels - capillaries, which connect veins and arteries.

Later, many scientists (Steven Hales, Daniel Bernoulli, Euler, Poiseille, etc.) worked on the problem of blood circulation, including measured venous, arterial blood pressure, the volume of the chambers of the heart, the elasticity of arteries and other parameters. In 1843, scientist Jan Purkine offered the scientific community the hypothesis that a systolic decrease in the volume of the heart has a suction effect on the anterior edge of the left lung. In 1904 IP Pavlov made an important contribution to science, proving that there are four pumps in the heart, and not two, as previously thought. At the end of the twentieth century, it was possible to prove why the pressure in the cardiovascular system is above atmospheric pressure.

The physiology of the circulation: veins, capillaries and arteries

Thanks to all the scientific researches we now know that the blood constantly moves along special hollow tubes, which have a different diameter. They do not interrupt and pass to others, thereby forming a single closed circulatory system. In total, three types of vessels are known: arteries, veins, capillaries. All of them are different in structure. Arteries are the vessels that provide the flow of blood to the organs from the heart. Inside, they are lined with a single-layered epithelium, and externally have a connective tissue membrane. The middle layer of the arterial wall consists of smooth muscles. The largest vessel is the aorta. In organs and tissues, arteries are divided into smaller vessels, called arterioles. They, in turn, branch onto capillaries, which consist of a single-layer epithelial tissue and are located in the spaces between the cells. Capillaries have special pores through which water, oxygen, glucose and other substances are transported into the tissue fluid. How does blood from the arteries get into the veins? From the organs it goes, deprived of oxygen and enriched with carbon dioxide, and is directed through the capillaries into the venules. Then it returns to the right atrium along the lower, upper hollow and coronary veins. The veins are more superficial and have special semilunar valves that facilitate the movement of blood.

Circles of blood circulation

All the vessels, uniting, form two circles, which are called large and small. The first ensures the saturation of the organs and tissues of the body with oxygen-rich blood. The large circle of blood circulation is as follows: the left atrium simultaneously with the right decreases, thereby ensuring the flow of blood into the left ventricle. From there, the blood is sent to the aorta, from which it continues to move along other arteries and arterioles going in different directions to the tissues of the whole organism. Then the blood returns through the veins and goes to the right atrium.

Blood and circulation: a small circle

The second circle of blood circulation starts in the right ventricle and ends in the left atrium. Through it, the blood circulates through the lungs. The physiology of the circulation in the small circle is as follows. The contraction of the right ventricle ensures the direction of the blood into the pulmonary trunk, which branches up to an extensive network of pulmonary capillaries. Blood, entering them, is saturated with oxygen through ventilation of the lungs, and then returns to the left atrium. It can be concluded that two circles of blood circulation ensure the movement of blood: first, it travels along a large circle to the tissues and back, and then along a small circle into the lungs, where it is saturated with oxygen. There is a blood circulation of the person due to rhythmic cardiac work and pressure difference in arteries and veins.

Circulatory system: heart

The human circulatory system includes, in addition to arterial, venous vessels and capillaries, the heart. It is a muscular organ, hollow inside and having a conical shape. The heart, located in the chest cavity, is freely located in the pericardial bag, consisting of connective tissue. The bag provides constant moisturizing of the heart surface, and also supports its free contractions. The heart wall is formed of three layers: endocardium (inner), myocardium (middle) and epicardium (external). The structure of the heart muscle somewhat resembles the striated muscles, but has one distinctive feature - the ability to automatically contract regardless of external conditions. This is the so-called automata. It becomes possible due to the special nerve cells that are in the muscle and produce rhythmic stimulation.

Structure of the heart

The internal structure of the heart is as follows. It is divided into two halves, the left and the right, a solid partition. Each such half has two departments - the atrium and the ventricle. They are connected by a hole provided with a valvular valve that opens towards the ventricle. In the left half of the heart, this valve has two valves, and in the right - three. In the right atrium, blood comes from the upper, lower hollow, and coronal veins of the heart, and to the left - from the four pulmonary veins. The right ventricle gives rise to a pulmonary trunk, which, subdivided into two branches, transports blood to the lungs. The left ventricle directs blood along the left arch of the aorta. At the boundaries of the ventricles, the pulmonary trunk and the aorta, there are semilunar valves with three leaves on each. They close the lumen of the pulmonary trunk and aorta, as well as pass the blood into the vessels and prevent the reverse flow of blood into the ventricles.

Three phases of cardiac muscle work

Alternation of contractions and relaxation of the heart muscle allows blood to circulate in two circles of the circulation. There are three phases in the work of the heart:

• Atrial contraction;
• Contraction of the ventricles (aka systole);
• Relaxation of the ventricles and atria (otherwise diastole).

A cardiac cycle is the period from one to another atrial contraction. All cardiac activity consists of cycles, with each of them being composed of systole and diastole. The heart muscle is reduced approximately 70-75 times in one minute (if the body is at rest), that is about 100 thousand times in one day. At the same time, it pumps over 10,000 liters of blood. Such a high performance is created by increased blood supply to the heart muscle, as well as by a large number of metabolic processes in it. The nervous system, in particular its vegetative department, regulates the work of the heart. Some sympathetic fibers increase contractions during stimulation, others - parasympathetic fibers - on the contrary, weaken and slow heart activity. In addition to the nervous system, the humoral function also regulates the work of the heart. For example, adrenaline accelerates its work, and the high content of potassium inhibits it.

The concepts of the pulse

Pulse is the rhythmic fluctuations in the diameter of the vessels (arterial), which are caused by cardiac activity. Movement of blood along the arteries, including the aorta, is carried out at a speed of 500 mm / s. In thin vessels, capillaries, the blood flow slows down considerably (up to 0.5 mm / s). Such a low rate of blood flow through the capillaries allows you to give all the oxygen and nutrients to tissues, as well as take their life products. In the veins, as you approach the heart, the speed of blood flow increases.

What is blood pressure?

This term refers to the hydrodynamic blood pressure in arteries, veins, and capillaries. Blood pressure appears as a result of the exercise of his activity by the heart, which pumps blood into the vessels, and they resist. Its magnitude varies in different types of vessels. Arterial pressure increases with systole and decreases during diastole. The heart throws a portion of blood, which stretches the walls of the central arteries and aorta. This creates a high blood pressure: the maximum systolic values are equal to 120 mm Hg. St., And diastolic - 70 mm Hg. Art. During diastole, the stretched walls contract, thereby pushing the blood further through the arterioles and further. When blood flows through the capillaries, the blood pressure gradually decreases to 40 mm Hg. Art. And below. When the capillaries pass to the venules, the blood pressure is only 10 mm Hg. Art. This mechanism is caused by the friction of blood particles against the walls of the vessels, which gradually delays the flow of blood. In the veins, the drop in blood pressure continues. In hollow veins, it becomes even slightly below atmospheric. This difference between negative pressure in the hollow veins and high pressure in the pulmonary artery and aorta and ensures the continuous circulation of a person.

Blood pressure measurement

The determination of blood pressure can be done in two ways. The invasive method involves the insertion of a catheter connected to the measuring system into one of the arteries (more often the ray). This method allows you to continuously measure pressure and obtain high-precision results. A non-invasive method involves the use of mercury, semiautomatic, automatic or aneroid sphygmomanometers to measure blood pressure. Usually the pressure is measured on the arm, slightly above the elbow. The value obtained shows what the value of the pressure is in this artery, but not in the entire body. Nevertheless, this indicator allows to draw a conclusion about the magnitude of the blood pressure in the subject. The importance of blood circulation is enormous. Without a continuous movement of blood, a normal metabolism is impossible. Moreover, the life and functioning of the organism is impossible. Now you know how the blood from the arteries gets into the veins, and how the process of circulation takes place. We hope that our article has been useful to you.