The human lungs are an organ that provides the process of respiration. But they are not the only ones involved in it. This delusion is common to many. Breathing is provided by: nostrils, oral cavity, larynx, trachea, chest muscles and others. The task of the lungs themselves is to supply the blood, namely the erythrocytes (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 plexus of blood, air, lymphatic and nerve tracts. Between the lungs and other organs (stomach, spleen, liver, etc.) there is a 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 one has three (lower, upper andmiddle), then the left has only two (lower and upper). Also, the left lung is longer than the right one.
Inside the lungs are the bronchi. They are divided into segments that are clearly separated from each other. In total, there are 18 such segments in the lungs: 10 in the right and 8 in the left, respectively. In the future, the bronchi branch into lobes. There are approximately 1600 of them in total - 800 for each lung.
The bronchial lobes are divided into alveolar passages (from 1 to 4 pieces), at the end of which there are alveolar sacs, from which the alveoli open. All this together is called the collective name of the airways, which consist of the bronchial tree and the alveolar tree.
The features of the blood supply to the lung system will be discussed below.
Arteries, veins, vessels and capillaries of the lungs
The diameter of the pulmonary artery and its branches (arterioles) is more than 1 mm. They have an elastic structure, due to which the blood pulsation softens during heart systoles, when blood is ejected from 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 large circulation capillaries are 7–8 micrometers in diameter. At the same time, there are 2 types of capillaries in the lungs. Wide, the diameter of which is in the range from 20 to 40 micrometers, and narrow - with a diameter of 6 to 12 micrometers. Squarecapillaries 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 unit.
Oxygen voltage 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 into the system of a large circle (right atrium and azygos vein) and into the system of a small circle (left atrium and pulmonary veins). Therefore, according to the great circle system, 70% of the blood passing through the bronchial arteries does not reach the right ventricle of the heart, and enters 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. The mixing of bronchial venous blood with the arterial blood of the pulmonary veins lowers the amount of oxygen compared to what it was in the pulmonary capillaries. Although this feature has almost no effect on a person's daily life, it can play a role in various diseases (embolism, mitral stenosis), leading to serious respiratory failure. For impaired blood supply to the lobe of the lung, hypoxia, cyanosis of the skin, fainting, rapid breathing, etc. are characteristic.
Lung blood volume
As stated above, the main function of the lungs is to carryoxygen from the 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 between ventilation and blood flow is also important.
The amount of blood that passes per minute through the lungs, about the same as the IOC (minute circulation of blood) in the system of the great circle. At rest, the magnitude of this circulation is 5–6 liters.
Pulmonary vessels are characterized by greater extensibility, since their walls are thinner than those of similar vessels, for example, in muscles. Thus, they act as a kind of blood storage, increasing in diameter under load and carrying 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 the small circle is determined by the pressure difference and ranges from 9 to 15 mm Hg. Art. And this is significantly less pressure inside the systemic circulation.
It should be noted that during physical activity, which leads to a significant increase in blood flow in the small circle, there is no increase in pressure due to the elasticity of the vessels. The same physiological feature prevents pulmonary edema.
Irregular blood supply to the lungs
Low pressure in the pulmonary circulation causes uneven saturation of the lungs with blood from theirtop to base. In the vertical state of a person, there is a difference between the blood supply of the upper lobes and the lower ones, in favor of a decrease. 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, depending 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 flow divides the lungs into three conditional parts (upper, middle and lower lobe), which are called West zones (first, second and third, respectively).
Nervous regulation
The blood supply and innervation of the lungs are connected and work as a single system. The provision of vessels with nerves occurs from two sides: afferent and efferent. Or also called vagal and sympathetic. The afferent side of innervation occurs due to the vagus nerves. That is, the nerve fibers associated with the sensitive cells of the nodular ganglion. The efferent is provided by the cervical and upper thoracic nerve nodes.
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 the systemic circulation. So, excitation of nerves by stimulation with electricity in a small circle leads to an increase in pressure by only 10-15%. In other words, not essential.
The large vessels of the lungs (especially the pulmonary artery) are highly responsive. Increased pressure in the lungsblood vessels leads to a slowing of the heart rate, a decrease in blood pressure, filling the spleen with blood, relaxation of smooth muscles.
Humoral regulation
Catecholamine and acetylcholine in the regulation of the large circle are more important than the small. The introduction of the same doses of catecholamine into the vessels of different organs shows that less narrowing of the lumen of the blood vessels (vasoconstriction) is caused in the small circle. 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 with the help of 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 an increase in pressure in the pulmonary artery.
