What Is Gas Exchange?
Gas exchange refers to the gas exchange between the alveoli and blood, and between blood and tissue. It is a physical diffusion process, and the gas diffuses from the high partial pressure side to the low side. The partial pressure of oxygen in the inhaled air is higher than the partial pressure of oxygen in the blood, so oxygen enters the blood from the alveoli and then into the tissues. The partial pressure of carbon dioxide in the tissue is higher than the partial pressure of carbon dioxide in the blood, so carbon dioxide is discharged into the blood from the tissue and then into the alveoli.
- Chinese name
- Gas exchange
- Foreign name
- Gas exchange
- Also called
- Breathe
- Belong to
- Material exchange
- the way
- Gas diffusion
- Gas exchange refers to the gas exchange between the alveoli and blood, and between blood and tissue. It is a physical diffusion process, and the gas diffuses from the high partial pressure side to the low side. The partial pressure of oxygen in the inhaled air is higher than the partial pressure of oxygen in the blood, so oxygen enters the blood from the alveoli and then into the tissues. The partial pressure of carbon dioxide in the tissue is higher than the partial pressure of carbon dioxide in the blood, so carbon dioxide is discharged into the blood from the tissue and then into the alveoli.
Gas exchange anatomy:
- 1. Gas exchange:
- Gas exchange refers to the process of exchanging inhaled oxygen and exhaled carbon dioxide in the body. The physiological process of breathing is to inhale oxygen from the outside air and at the same time expel carbon dioxide from the body. The gas exchange between oxygen and carbon dioxide between the alveoli and the capillaries of the lung is called external breathing or pulmonary breathing. After oxygen enters the blood, it reaches various tissues in the body for gas exchange. Oxygen is released for use by the cells. Carbon dioxide, a metabolite of the cells, is carried away by the blood. The gas exchange in the tissue is called inner breathing or tissue breathing. Internal and external breathing cooperates to complete the entire breathing process. In the resting state, 1/20 of the alveolar area participates in gas exchange, and the other alveoli serve as reserves. The quietness of the ventilation / blood flow ratio is about 0.8, which is an indicator of lung gas exchange efficiency. When the ventilation / blood ratio is equal to 0.8, it indicates that the venous blood in the alveoli can be fully arterialized. When the ventilation / blood ratio is greater than 0.8, it indicates that the ventilation is normal, and the pulmonary capillary blood flow is reduced, and the gas entering the alveoli and the blood is not sufficiently exchanged, resulting in an increase in dead volume. The result is alveolar ventilation cut back. When the ventilation / blood flow ratio is less than 0.8, in addition to the physiological shunts that occur under physiological conditions, the ratio can be low. In clinical practice, it is common to see a decrease in ventilation or an increase in blood flow, resulting in a hypoxic state in the body.
- 2. Alveoli:
- The alveoli are about 0.2 mm in diameter and are thin film-shaped. There is a rich capillary network between the alveoli and the alveoli.
- There are a large number of alveolar macrophages in and between the alveoli, which can capture and swallow dust and bacteria leaking from the two lines of defense of the nose and trachea. The bacteria are digested and the dust is discharged with mucus. However, if you smoke for a long time or work in a dusty place, the performance of alveolar macrophages will be reduced, so that smoke and dust are deposited in the lungs, which will seriously affect lung function for a long time. When dissected, the lungs of a long-term smoker are black.
- There is a thin layer of breathing membrane between the alveoli and the blood of the capillaries. This membrane only allows oxygen and carbon dioxide to pass freely, and other things cannot pass.
- The concentration of oxygen in the inhaled gas is higher than that in the blood, so the oxygen diffuses into the capillaries through the respiratory membrane, combines with the hemoglobin in the red blood cells, and is transported to all parts of the body through the arteries. The concentration of carbon dioxide in the venous blood entering the capillaries is high, so the carbon dioxide enters the alveoli through the respiratory membrane and is expelled from the body with the exhalation.
- There are hundreds of millions of alveoli in a human lung. The total area of the alveoli after full deployment is 100 square meters, so it has a very strong exchange capacity. During calm breathing, only about 5% of the alveolar area is ventilated or ventilated. The remaining alveoli are trapped, so the lung reserves are large.
The function of gas exchange:
- Gas exchange refers to the exchange of oxygen and carbon dioxide between the alveoli and blood and between blood and tissue. Gas molecules are always in constant motion, and molecular motion creates pressure. The more gas molecules, the greater the pressure generated by their movement. Gas molecules always move from high pressure to low pressure. This phenomenon is called diffusion or diffusion in physics. Gas exchange is carried out by diffusion. The direction and speed of gas diffusion in the human body depends on the partial pressure difference of the two gases in the cell membrane, so the differential pressure of gas is the driving force for gas exchange. Gas partial pressure refers to the pressure of a certain gas in two or more mixed gases. The partial pressures of oxygen and carbon dioxide in the alveoli, blood, and tissue are different (see table). Due to the partial pressure difference between them, there is a motive force for gas exchange.
- Gas exchange between alveoli and blood is also called pulmonary ventilation. The partial pressure of oxygen in the alveoli (102 mmHg) is higher than the partial pressure of venous blood (40 mmHg), so oxygen diffuses from the alveoli to the venous blood. The partial pressure of carbon dioxide in the alveoli (40 mmHg) is lower than that of venous blood (46 mmHg), so when blood flows through the alveoli, the carbon dioxide in the blood diffuses into the alveoli. In this way, after pulmonary ventilation, the venous blood containing more carbon dioxide and less oxygen becomes arterial blood containing more oxygen and less carbon dioxide. Due to the continuous breathing exercise, the gas components in the alveoli remain relatively stable, that is, the partial pressure of oxygen is high, and the partial pressure of carbon dioxide is low, thereby ensuring continuous lung ventilation.
- Gas exchange between blood and tissue is also called tissue ventilation. Because tissue cells continuously use oxygen and produce carbon dioxide during metabolism, their oxygen partial pressure is low (30 mm Hg) and carbon dioxide partial pressure is high (50 mm Hg). Oxygen diffuses from the blood to the tissue, while carbon dioxide diffuses from the tissue to the blood, resulting in arterial blood becoming venous blood. Because the metabolic process of tissue cells continuously consumes oxygen and generates carbon dioxide, the partial pressure of oxygen in the tissue is always lower than that of arterial blood, and the partial pressure of carbon dioxide is always higher than that of arterial blood, so that tissue ventilation can be continued. .
- The amount of gas exchange is mainly related to the gas partial pressure difference. The larger the partial pressure difference, the larger the gas exchange amount. It is also related to the number of open alveoli and capillaries. The larger the number of open, the larger the area for gas exchange, and the larger the amount of gas exchange.