Breathing is a combination of processes that ensure the continuous supply of oxygen to the tissues, its use in oxidative reactions, and the removal of carbon dioxide and partially water from the body.
Breathing consists of the following main stages: external breathing, which provides gas exchange between the lungs and the external environment; gas exchange between alveolar air and venous blood flowing to the lungs; blood transport of gases; gas exchange between arterial blood and tissues; tissue respiration.
External breathing is a rhythmic process, the frequency of which in a healthy adult is 16 to 20 cycles per minute. Each breathing cycle consists of inhalation and exhalation. Inhalation and exhalation are caused by changes in the volume of the chest while reducing and relaxing the respiratory muscles. As the volume of the chest increases, the pressure in the pleural cavity decreases, and air enters the lungs. When you exhale, the chest volume decreases, the pressure in the lungs exceeds atmospheric, and the air comes out of the lungs.
If you attach a rubber cuff filled with air and connected through a Marey capsule with a light lever, you can register respiratory movements of the chest. This method is called pneumography.Go
The alternation of inhalation and exhalation occurs due to the automatic rhythmic activity of the respiratory center. Under the respiratory center understand the totality of nerve cells that regulate the rhythmic process of external respiration and adaptation of respiration to changing environmental conditions. The constituent components of the respiratory center are located in the medulla oblongata, the pons (pons) and the midbrain. The activity of the lower parts of the respiratory center is controlled by the hypothalamic structures and the cortex of the cerebral hemispheres. The respiratory center includes inspiratory (“inspiratory center”) and expiratory neurons (“expiratory center”).
The main factor influencing the excitation of the "center of the breath" is carbon dioxide . During inhalation, the alveoli of the lungs are stretched, which leads to irritation of the mechanoreceptors in the alveoli. From them to the respiratory center through the vagus nerve afferent stimuli flow. With a gradual increase in inhalation, the frequency of afferent impulses becomes more and more. Under the influence of an excessively high frequency of afferent impulsation, the "center of inhalation" is inhibited and exhalation occurs.
The alveolar air (see. Vital capacity of the lungs) carries out gas exchange with venous blood flowing to the lungs, being like an internal gaseous medium of the body. The composition of the alveolar air is distinguished by constancy, changing little during normal breathing. With quiet breathing, 350 cm 3 of air enters the alveoli with each breath of an adult, and the alveolar air is renewed only by 1/10 of its volume (ventilation coefficient).
Minute ventilation of the lungs - the amount of air passing through the lungs for 1 min. The magnitude of the minute ventilation of the lungs increases dramatically with physical and emotional stress, which is explained by the increased oxidative processes in the tissues under these conditions.
Oxygen entering from the alveolar air into the blood (see Gas exchange ) is bound to the hemoglobin of the erythrocytes and is delivered to the tissues. In tissue capillaries, oxygen is cleaved from oxyhemoglobin and goes into tissues, where it is included in oxidative processes (see Biological oxidation). The carbon dioxide produced in the tissues enters the blood and enters the red blood cells . Then a portion of the carbon dioxide is combined with hemoglobin and delivered to the lungs. With the participation of the enzyme carbonic anhydrase, most of the carbon dioxide in the erythrocytes is converted into bicarbonates, which are converted into plasma and transported to the lungs. In the pulmonary capillaries, bicarbonates break down with carbonic anhydrase and carbon dioxide is released. Carbon dioxide is cleaved from hemoglobin. Carbon dioxide enters the alveolar air and is removed with exhaled air into the external environment.
There are chest, abdominal and mixed types of breathing. The types of breathing are developed and changed under the diverse influences of the external and internal environment, especially under the influence of labor and sports exercises.