Two spongy organs located inside the chest cavity communicate with the external environment through the respiratory tract and are responsible for a vital function for the whole organism, performing blood gas exchange with the environment. Outside, the organ is covered with a pleura, consisting of two sheets forming the pleural cavity of the lungs.
Lungs - two volumetric organs of a semi-conical shape, occupying most of the chest cavity. Each lung has a base supported by the diaphragm, the muscle that separates the chest and abdominal cavities; the upper parts of the lungs are rounded. The lungs are divided into lobes by deep slits. There are two slits in the right lung, and only one in the left.
The pulmonary acinus is the functional unit of the lungs, a tiny piece of tissue ventilated by the terminal bronchiole, from which the respiratory bronchioles extend, further forming the alveolar canals or alveolar ducts. At the end of each alveolar canal are alveoli, microscopic, thin-walled, elastic balls filled with air; alveoli make up the alveolar bundle or sac, where gas exchange takes place.
The thin walls of the alveoli are composed of a single layer of cells surrounded by a layer of tissue that supports them and separates them from the alveoli. Together with the alveoli, the blood capillaries penetrating the lungs are also separated by a thin membrane. The distance between the inner wall of the blood capillaries and the alveoli is 0.5 thousandth of a millimeter.
The human body needs constant gas exchange with the environment: on the one hand, the body needs oxygen to maintain cellular activity - it is used as a "fuel" due to which metabolism is carried out in cells; on the other hand, the body needs to get rid of carbon dioxide - the result of cellular metabolism, since its accumulation can cause intoxication. The cells of the body need oxygen constantly - for example, the nerves of the brain can hardly exist without oxygen for even a few minutes.
Molecules of oxygen (02) and carbon dioxide (CO2) circulate through the blood, joining the hemoglobin of red blood cells, which carry them throughout the body. Once in the lungs, red blood cells give off carbon dioxide molecules and carry away oxygen molecules through a diffusion process: oxygen attaches to hemoglobin, and carbon dioxide enters the capillaries inside the alveoli, and the person exhales it.
Blood enriched with oxygen, leaving the lungs, goes to the heart, which throws it into the aorta, after which it reaches the capillaries of various tissues through the arteries. There, the process of diffusion again takes place: oxygen passes from the blood into the cells, and carbon dioxide enters the blood from the cells. Then the blood goes back to the lungs to be enriched with oxygen. Detailed information on the physical and physiological characteristics of gas exchange can be found in the article: "Gas exchange and gas transport".
Every cell in the body needs oxygen. It is carried throughout the body by red blood cells. erythrocytes.
Since oxygen cannot enter the bloodstream directly through the skin, the function of supplying this gas to the body is performed by the lungs. They take in oxygen from the air and transfer it to the bloodstream.
Where are the lungs located?
The lungs are located on either side of the heart and fill the chest. Each lung of an adult weighs a little over 400 g. The right lung is slightly heavier than the left, since the latter has to share space in the chest with the heart.
Lungs protected chest. Between its ribs are small muscles involved in the breathing process.
Under the lungs is diaphragm- a dome-shaped muscle formation that separates the chest from the abdominal cavity and is also involved in breathing.
What are the lungs made of?
Both lungs consist of lobes: three in the right and two in the left. The tissue of this organ is a mass of thin tubes bronchioles, which end in tiny air sacs - alveoli.
There are about 300 million alveoli in the human lungs, and their total area is comparable to the size of a tennis court. The alveoli have very thin walls that wrap around the smallest blood vessels in the body. capillaries.
How does breathing happen?
Before birth, the baby receives oxygen directly from its mother's blood, so its lungs are filled with fluid and do not work. At the moment of birth, the baby takes the first breath, and from that moment his lungs work without rest.
The respiratory center of the brain constantly receives signals about how much oxygen the body needs at any given moment.
For example, if a person is sleeping, he needs much less oxygen than when he is running after a bus.
The brain sends messages along the nerves to the respiratory muscles, which help regulate the amount of air that enters the lungs.
As soon as this signal is received, the diaphragm expands, and the muscles stretch the chest out and up. This allows you to maximize the volume that the lungs can take in the chest.
When exhaling, the diaphragm and intercostal muscles relax, reducing the volume of the chest. This pushes air out of the lungs.
What happens during inhalation?
During each breath, air is drawn into the nose or mouth and travels down through the larynx into trachea. This "windpipe" is a tube about 10-15 cm long, which is divided into two tubes - bronchi. Through them, air enters the right and left lungs.
The bronchi branch into 15-25 thousand tiny bronchioles, which end in alveoli.
How does oxygen get into the blood?
Through the thin walls of the alveoli, oxygen enters the blood vessels. Here it is picked up by "transport" - hemoglobin found in erythrocytes. At the same time, in the opposite direction - into the alveoli - carbon dioxide enters from the blood, which is removed from the body during exhalation.
Oxygenated blood is sent from the lungs to the left side of the heart, where it is distributed through the arteries throughout the body. As soon as the oxygen from the blood is used up, the blood flows through the veins to the right side of the heart and from there back to the lungs.
What else do the lungs do?
Every day, the lungs of an adult pump about ten thousand liters of air.
With each breath, they receive not only oxygen, but also dust, microbes and other foreign objects. Therefore, the lungs also perform the function of physical and chemical defense against unwanted objects from the air.
Tiny villi are located on the walls of the bronchi, which trap dust and germs. In the walls of the airways, special cells produce mucus that helps clean and lubricate these villi. Contaminated mucus is excreted through the bronchi to the outside and coughed up.
What prevents the lungs from working?
The normal work of the lungs is often interfered with by their owner himself. If he smokes, moves little, is overweight and rarely goes out in nature, lung function is impaired. how to keep your lungs healthy for years to come.
The most important
The lungs are perfectly adapted to perform a complex respiratory function and protect the body from harmful substances and microorganisms.
However, this well-oiled mechanism is easily damaged if a person smokes or does not treat a respiratory tract infection.
Once again, it must be emphasized that the constant rate of diffusion of both oxygen and carbon dioxide through the air-blood barrier is determined by a fairly stable composition of the alveolar gas during inhalation and exhalation.
Lung capillaries
The functions of gas exchange in the lungs and the saturation of blood with oxygen are carried out with the participation of the vessels of the pulmonary circulation. The walls of the branches of the pulmonary artery are thinner than the walls of the same caliber of the arteries of the systemic circulation. The vascular system of the lungs is very malleable and can be easily stretched. A relatively large volume of blood (6 liters / min) from the right ventricle enters the pulmonary artery system, and the pressure in the small circle is low - 15-20 mm Hg. Art., because the vascular resistance is about 10 times less than in the vessels of the systemic circulation. The network of alveolar capillaries is not comparable with the organization of the capillary beds of other organs. Distinctive features of the capillary bed of the lungs are 1) the small size of the capillary segments, 2) their abundant interconnection, which forms a looped network, 3) the high density of individual capillary segments per unit area of the alveolar surface, 4) low blood flow velocity. The capillary network in the walls of the alveoli is so dense that some physiologists consider it to be a continuous layer of moving blood. The surface area of the capillary network is close to the surface area of the alveoli (80 m 2), it contains about 200 ml of blood. The diameter of the alveolar blood capillaries ranges from 8.3 - 9.9 microns, and the diameter of erythrocytes is 7.4 microns. Thus, erythrocytes adhere tightly to the walls of the capillaries. These features of the blood supply to the lungs create conditions for rapid and efficient gas exchange, as a result of which the gas composition of the alveolar air and arterial blood is balanced. Look again at Table 2 and note that the arterial oxygen tension becomes 100 and that of carbon dioxide becomes 40 mmHg. Art.
Transport of oxygen in the blood
Most of the oxygen in the body of mammals is carried in the blood in the form of a chemical compound with hemoglobin. Freely dissolved oxygen in the blood is only 0.3%. The oxygenation reaction, the conversion of deoxyhemoglobin to oxyhemoglobin, occurring in the erythrocytes of the capillaries of the lungs, can be written as follows:
Hb + 4O 2 ⇄ Hb(O 2 ) 4
This reaction proceeds very quickly - the half-saturation time of hemoglobin with oxygen is about 3 milliseconds. Hemoglobin has two amazing properties that make it an ideal oxygen carrier. The first is the ability to attach oxygen, and the second is to give it away. Turns out The ability of hemoglobin to attach and release oxygen depends on the oxygen tension in the blood. Let's try to graphically depict the dependence of the amount of oxygenated hemoglobin on the oxygen tension in the blood, and then we will be able to find out: in which cases hemoglobin attaches oxygen, and in which it gives it away. Hemoglobin and oxyhemoglobin absorb light rays differently, so their concentration can be determined by spectrometric methods.
A graph that reflects the ability of hemoglobin to attach and release oxygen is called the "Oxyhemoglobin Dissociation Curve". The abscissa on this graph shows the amount of oxyhemoglobin as a percentage of total hemoglobin in the blood, the ordinate shows the oxygen tension in the blood in mm Hg. Art.
Figure 9A. Normal oxyhemoglobin dissociation curve
Consider the graph in accordance with the stages of oxygen transport: the highest point corresponds to the oxygen tension that is observed in the blood of the pulmonary capillaries - 100 mm Hg. (the same as in the alveolar air). It can be seen from the graph that at such a voltage, all hemoglobin passes into the form of oxyhemoglobin - it is completely saturated with oxygen. Let's try to calculate how much oxygen binds hemoglobin. One mole of hemoglobin can bind 4 moles O 2 , and 1 gram Hb binds 1.39 ml O 2 ideally, but in practice 1.34 ml. With a concentration of hemoglobin in the blood, for example, 140 g / liter, the amount of bound oxygen will be 140 × 1.34 = 189.6 ml / liter of blood. The amount of oxygen that hemoglobin can bind when it is completely saturated is called the oxygen capacity of the blood (KEK). In our case, KEC = 189.6 ml.
Let us pay attention to an important feature of hemoglobin - when the oxygen tension in the blood decreases to 60 mm Hg, saturation practically does not change - almost all hemoglobin is present in the form of oxyhemoglobin. This feature allows you to bind the maximum possible amount of oxygen while reducing its content in the environment (for example, at an altitude of up to 3000 meters).
The dissociation curve has an s-shaped character, which is associated with the peculiarities of the interaction of oxygen with hemoglobin. A hemoglobin molecule binds 4 oxygen molecules in stages. Binding of the first molecule dramatically increases the binding capacity, so do the second and third molecules. This effect is called the cooperative action of oxygen.
Arterial blood enters the systemic circulation and is delivered to the tissues. Oxygen tension in tissues, as can be seen from Table 2, ranges from 0 to 20 mm Hg. Art., a small amount of physically dissolved oxygen diffuses into the tissues, its tension in the blood decreases. The decrease in oxygen tension is accompanied by the dissociation of oxyhemoglobin and the release of oxygen. The oxygen released from the compound passes into a physically dissolved form and can diffuse into the tissues along the voltage gradient. At the venous end of the capillary, the oxygen tension is 40 mm Hg, which corresponds to approximately 73% hemoglobin saturation. The steep part of the dissociation curve corresponds to the usual oxygen tension for body tissues - 35 mm Hg and below.
Thus, the hemoglobin dissociation curve reflects the ability of hemoglobin to attach oxygen if the oxygen tension in the blood is high, and give it away when the oxygen tension decreases.
The transition of oxygen in tissues is carried out by diffusion, and is described by Fick's law, therefore, it depends on the oxygen stress gradient.
You can find out how much oxygen is extracted by the tissue. To do this, you need to determine the amount of oxygen in the arterial blood and in the venous blood flowing from a certain area. In arterial blood, as we were able to calculate (KEK) contains 180-200 ml. oxygen. Venous blood at rest contains about 120 ml. oxygen. Let's try to calculate the oxygen utilization factor: 180 ml. - 120 ml. \u003d 60 ml is the amount of oxygen extracted by the tissues, 60 ml / 180 100 \u003d 33%. Therefore, the oxygen utilization factor is 33% (normally 25 to 40%). As can be seen from these data, not all oxygen is utilized by the tissues. Normally, about 1000 ml is delivered to the tissues within one minute. oxygen. If we consider the utilization factor, it becomes clear that tissues are recovered from 250 to 400 ml. oxygen per minute, the rest of the oxygen returns to the heart as part of the venous blood. With heavy muscular work, the utilization factor rises to 50 - 60%.
However, the amount of oxygen that tissues receive depends not only on the utilization factor. When conditions change in the internal environment and in those tissues where oxygen diffusion occurs, the properties of hemoglobin may change. The change in the properties of hemoglobin is reflected in the graph and is called "curve shift". We note an important point on the curve - the half-saturation point of hemoglobin with oxygen is observed at an oxygen voltage of 27 mm Hg. Art., at this voltage, 50% of hemoglobin is in the form of oxyhemoglobin, 50% in the form of deoxyhemoglobin, therefore 50% of the bound oxygen is free (about 100 ml / l). If the concentration of carbon dioxide, hydrogen ions, temperature increases in the tissue, then curve shifts to the right. In this case, the half-saturation point will move to higher values of oxygen tension - already at a voltage of 40 mm Hg. Art. 50% oxygen will be released (Figure 9B). Intensely working tissue, hemoglobin will release oxygen more easily. The change in the properties of hemoglobin is due to the following reasons: acidification environment as a result of an increase in the concentration of carbon dioxide acts in two ways: 1) an increase in the concentration of hydrogen ions contributes to the release of oxygen by oxyhemoglobin because hydrogen ions bind more easily to deoxyhemoglobin, 2) direct binding of carbon dioxide to the protein part of the hemoglobin molecule reduces its affinity for oxygen; an increase in the concentration of 2,3-diphosphoglycerate, which appears during anaerobic glycolysis and is also integrated into the protein part of the hemoglobin molecule and reduces its affinity for oxygen.
A shift of the curve to the left is observed, for example, in the fetus, when a large amount of fetal hemoglobin is determined in the blood.
Figure 9 B. Influence of changing the parameters of the internal environment
Answer from No_name_No_face[guru]
Rice. Scheme of the human respiratory system: a - general plan of the structure; b - the structure of the alveoli; 1 - nasal cavity; 2 - epiglottis; 3 - pharynx; 4 - larynx; 5 - trachea; b - bronchus; 7 - alveoli; 8 - left lung (in section); 9 - diaphragm; 10 - the area occupied by the heart; 11 - right lung (outer surface); 12 - pleural cavity; 13 - bronchiole; 14 - alveolar passages; 15 - capillaries.
Bronchioles are the last elements of the airways. The ends of the bronchioles form extensions - alveolar passages, on the walls of which there are protrusions in the form of hemispheres (0.2-0.3 mm in diameter) - pulmonary vesicles, or alveoli. The walls of the alveoli are formed by a single-layer epithelium lying on an elastic membrane, due to which they are easily extensible. The adhesion of their walls from the inside during exhalation is prevented by a surfactant, which includes phospholipids. The walls of the alveoli are braided with a dense network of blood capillaries. The total thickness of the walls of the alveoli and the capillary is 0.4 µm. Due to such a small thickness of gas exchange surfaces, oxygen from the alveolar air easily penetrates into the blood, and carbon dioxide from the blood into the alveoli. In an adult, the total number of alveoli reaches 300 million, and their total surface is approximately 100 m2.
The lungs are paired spongy organs formed by bronchi, bronchioles and alveoli. They are located in the chest cavity and are separated from each other by the heart and large blood vessels. Each lung is conical in shape. Its wide base faces the lower wall of the chest cavity - the diaphragm, and the narrow top protrudes above the clavicle. On the inner surface of the lungs are the gates of the lungs - the place of entry into the lungs of the bronchi, nerves and blood vessels. The right lung is divided by deep fissures into three lobes, and the left into two.
Gas exchange in the lungs and tissues. Gas exchange in the lungs occurs due to the diffusion of gases through the thin epithelial walls of the alveoli and capillaries. The oxygen content in the alveolar air is much higher than in the venous blood of the capillaries, and there is less carbon dioxide. As a result, the partial pressure of oxygen in the alveolar air is 100-110 mm Hg. Art. , and in the pulmonary capillaries - 40 mm Hg. Art. The partial pressure of carbon dioxide, on the contrary, is higher in venous blood (46 mm Hg) than in alveolar air (40 mm Hg). Due to the difference in the partial pressure of gases, the oxygen of the alveolar air will diffuse into the slowly flowing blood of the capillaries of the alveoli, and carbon dioxide will diffuse in the opposite direction. The oxygen molecules that enter the blood interact with the hemoglobin of erythrocytes and are transferred to the tissues in the form of the formed oxyhemoglobin.
Thus, the driving force of gas exchange is the difference in the content and, as a consequence, the partial pressure of gases in tissue cells and capillaries.
Answer from User deleted[guru]
Oxygen comes in. There are many capillaries in the lungs that are saturated with it and carry it through the blood
Answer from On[guru]
The lungs are a spongy porous body, and their tissue is highly elastic. They are covered with a thin but strong sack, known as the pleura, one wall of which is in close contact with the lung, the other with the inner wall of the chest. The player releases a liquid from itself, which allows the inner surface of the walls to easily slide over each other during the act of breathing.
The blood flow is distributed among millions of microscopic lung cells. Moreover, fresh air and oxygen comes into contact with polluted blood through the thin walls of the hairy blood vessels of the lungs, the walls of which are strong enough to hold blood within their boundaries, and at the same time thin enough to allow oxygen to pass through.
When oxygen comes into contact with the blood, a combustion process takes place; the blood takes in oxygen and is liberated from carbon dioxide formed from the putrefactive material that it has collected from all parts of the body. Purified and enriched with oxygen, the blood is sent back to the heart, becoming again red and rich in life-giving qualities and properties. Having reached the left atrium, it enters the left ventricle, from where it then again spreads through the arteries, bringing life with it to all parts of the body.
Answer from 3 answers[guru]
Hey! Here is a selection of topics with answers to your question: how does air enter the blood from the lungs?
That's right, it breathes air (mostly a mixture of nitrogen and oxygen) and inhales this mixture. But oxygen
Oxygen is a vital element in our body. It provides life to every cell in the body. In atmospheric air, its concentration is 21%, but with normal lung function, this amount is enough for the full functioning of our body. In diseases of the lungs, heart or central nervous system, when the respiratory function is reduced, special devices can be used that increase its percentage in the inhaled air up to 95%, for example, the Invacare PerfectO2 oxygen concentrator.
Functions of oxygen in the body
Oxygen enters our body with inhaled air and immediately goes to the alveoli of the lungs - their smallest structures in which gas exchange occurs. Alveoli have a thin wall, on one side of which there are capillaries - small blood vessels, and on the other side they communicate with the inhaled air. Through the wall of the alveoli, oxygen diffuses into the lumen of the capillaries, where it penetrates into the erythrocytes and binds in them with an unstable bond with iron in the composition of hemoglobin. Further, with the blood flow, red blood cells carry it throughout the body to cells and tissues.
Outside of the capillaries, tissue fluid flows, where the partial pressure of oxygen is always lower than in the circulatory system. Due to this difference, oxygen from erythrocytes easily penetrates through the capillary wall into an environment with a lower concentration. From the tissue fluid, it enters the cells, where it is included in a chain of chemical reactions.
These chemical reactions take place in special cell organelles - mitochondria. They are an essential component of any cell responsible for its life. In mitochondria, the main chemical reaction for cell life takes place - energy is extracted from molecules of carbohydrates, proteins, fats and converted into ATP (adenosine triphosphoric acid), which is a universal source of energy for all other cell structures. In the course of a chain of reactions, hydrogen electrons are released from the molecules, which are captured by oxygen entering the cell. If the body lacks oxygen, then the entire circuit is interrupted, ATP production stops and the cells starve.
This is its main, but not the only function in the body. It is known that oxygen is a strong oxidizing agent. This property is used by liver cells to neutralize many xenobiotics in the body, as well as to inactivate steroid hormones, bile acids and cholesterol. Oxygen is part of the microsomal liver enzymes. These enzymes oxidize molecules, increasing their ability to dissolve in biological fluids and penetrate cell membranes. Due to this, xenobiotics and oxidation products of their own proteins and lipids easily leave the body, excreted by the kidneys and intestines.
In addition, oxygen is used in the body for plastic purposes. The oxygen molecule consists of two atoms, one of which, as a result of a chain of complex reactions involving cytochromes, goes into the oxidized substance, and the other goes to the construction of a water molecule.
For the implementation of the above processes, it is necessary that the percentage of saturation of hemoglobin with oxygen (saturation) be maintained at the level of 96 - 97%. For this purpose, it is used