The human lungs are the organ that provides the breathing process. But they are not the only ones involved in it. This error is inherent in many. Breathing is provided by: nostrils, oral cavity, larynx, trachea, chest muscles and others. The task of the lungs themselves is to supply blood, namely red blood cells (red blood cells) in it, with oxygen, ensuring its transition from the inhaled air to the cells.
Brief anatomy of the lungs
The lungs are located in the chest and fill most of it. The lungs are a complex structure of the plexus of the blood, air, lymph and nerve pathways. Between the lungs and other organs (stomach, spleen, liver, etc.) is the diaphragm that separates them.
It should be noted that the right and left lungs are anatomically different. The main difference is the number of shares. If the right has three (lower, upper and middle), then the left has only two (lower and upper). The left lung is also longer than the right.
Inside the lungs are the bronchi. They are divided into segments that are clearly separated from each other. There are 18 such segments in the lungs: 10 in the right and 8 in the left, respectively. Further, the bronchi branch into lobes. In total there are about 1600 - 800 for each lung.
The bronchial lobes are divided into alveolar passages (from 1 to 4 pieces), at the end of which are the alveolar sacs from which the alveoli open. All this together is called the collective name the airways, which consist of a bronchial tree and an alveolar tree.
Below we will consider the features of the blood supply to the lung system.
Arteries, veins, vessels and capillaries of the lungs
The diameter of the pulmonary artery and branches (arterioles) extending from it is more than 1 mm. They have an elastic structure, due to which the pulsation of blood is mitigated in case of heart systoles, when blood is ejected by the right ventricle into the pulmonary trunk. Arterioles and capillaries are closely intertwined with the alveoli, thereby forming the lung parenchyma. The number of such plexuses determines the level of blood supply to the lungs during ventilation.
The capillaries of a large circle of circulation are 7–8 micrometers in diameter. At the same time, there are 2 types of capillaries in the lungs. Wide, the diameter of which ranges from 20 to 40 micrometers, and narrow - with a diameter of 6 to 12 micrometers. The area of capillaries inside the human lungs is 35–40 square meters. The very transition of oxygen into the blood occurs through the thin walls (or membranes) of the alveoli and capillaries, which work as a single functional whole.
Oxygen deficiency
The main function of the vessels of the pulmonary circulation is gas exchange in the lungs. Whereas the bronchial vessels provide nutrition to the tissues of the lungs themselves. The network of venous bronchial vessels penetrates both the large circle system (right atrium and unpaired vein) and the small circle system (left atrium and pulmonary veins). Therefore, according to the large circle system, 70% of the blood passing through the bronchial arteries does not reach the right ventricle of the heart, and penetrates into the pulmonary vein through capillary and venous anastomoses.
The described property is responsible for the formation of the so-called physiological lack of oxygen in the blood of a large circle. Mixing bronchial venous blood with arterial blood of the pulmonary veins reduces the amount of oxygen compared to what it was in the pulmonary capillaries. Although this feature has almost no effect on the daily life of a person, it can play a role in various diseases (embolism, mitral stenosis), leading to serious respiratory failure. For violation of the blood supply to the lobe of the lung, the following are characteristic: hypoxia, cyanosis of the skin, fainting, rapid breathing, etc.
Blood volume in the lungs
As mentioned above, the main function of the lungs is to ensure the transfer of oxygen from air to the blood. Pulmonary ventilation and blood flow are 2 parameters that determine the oxygen saturation (oxygenation) of blood in the lungs. The ratio of ventilation and blood flow among themselves also matters.
The amount of blood that passes through the lungs per minute is approximately the same as the IOC (minute circulation of blood) in the large circle system. At rest, the value of this treatment is 5–6 liters.
The pulmonary vessels are characterized by greater extensibility, since their walls are thinner than in similar vessels, for example, in the muscles. Thus, they perform the role of a kind of blood storage, increasing in diameter under load and transferring large volumes of blood.
Blood pressure
One of the features of the blood supply to the lungs is that low pressure remains in the small circle. The pressure in the pulmonary artery averages from 15 to 25 millimeters of mercury, in the pulmonary veins - from 5 to 8 mm Hg. Art. In other words, the movement of blood in a small circle is determined by the pressure difference and ranges from 9 to 15 mm RT. Art. And this is much less pressure inside a large circle of blood circulation.
It should be noted that during exercise, which leads to a significant increase in blood flow in a small circle, there is no increase in pressure due to the elasticity of the vessels. The same physiological feature prevents pulmonary edema.
Uneven blood supply to the lungs
Low pressure in a small circle causes uneven blood saturation of the lungs from their upper part to the base. In the vertical state of a person, there is a difference between the blood supply to the upper and lower lobes, in favor of reduction. This is due to the fact that the movement of blood from the level of the heart to the upper lobes of the lungs is complicated by hydrostatic forces, which depend on the height of the blood column at the levels between the heart and the apex of the lungs. At the same time, hydrostatic forces, on the contrary, contribute to the movement of blood down. This heterogeneity of blood movement divides the lungs into three conditional parts (upper, middle and lower lobe), which are called West zones (first, second and third, respectively).
Nervous regulation
Blood supply and innervation of the lungs are connected and work as a single system. Providing vessels with nerves occurs on two sides: afferent and efferent. Or also called vagal and sympathetic. The afferent side of the innervation occurs due to the vagus nerves. That is, nerve fibers associated with sensitive cells of the nodular ganglion. The efferent is provided by the cervical and upper pectoral nerves.
The blood supply to the lungs and the anatomy of this process are complex, and consist of many organs, including the nervous system. It has the greatest effect on a large circle of blood circulation. Thus, stimulation of nerves by stimulation by electricity in a small circle leads to an increase in pressure by only 10-15%. In other words, it is immaterial.
Large vessels of the lungs (especially the pulmonary artery) have an extremely high reaction. An increase in pressure in the pulmonary vessels slows down the rhythm of the heartbeat, decreases blood pressure, fills the spleen with blood, and relaxes smooth muscles.
Humoral regulation
Catecholamine and acetylcholine in the regulation of a large circle are of greater importance than small ones. The introduction of the same doses of catecholamine into the vessels of different organs shows that in a small circle a smaller narrowing of the lumen of the blood vessels is caused (vasoconstriction). An increase in the amount of acetylcholine in the blood leads to a moderate increase in the volume of pulmonary vessels.
Humoral regulation of blood supply in the lungs and pulmonary vessels is carried out using drugs containing substances such as: serotonin, histamine, angiotensin-II, prostaglandin-F. Their introduction into the blood leads to a narrowing of the pulmonary vessels in the pulmonary circulation and increased pressure in the pulmonary artery.