Gas exchange in tissues and lungs how does it happen?

To provide cells, tissues and organs with oxygen in the human body, there is a respiratory system. It consists of the following organs: nasal cavity, nasopharynx, larynx, trachea, bronchi and lungs. In this article we will study their structure. And also consider gas exchange in tissues and lungs. Define the features of external respiration occurring between the body and the atmosphere, and internal, flowing directly on the cellular level.

Why do we breathe?

Most people will respond without hesitation: to get oxygen. But they do not know why we need it. Many respond simply: oxygen is needed to breathe. It turns out a vicious circle. To break it to us will help biochemistry, which studies the cellular metabolism.

The bright minds of mankind who study this science have long come to the conclusion that oxygen entering the tissues and organs oxidizes carbohydrates, fats and proteins. In this case, energetically poor compounds are formed: carbon dioxide, water, ammonia. But the main thing is that as a result of these reactions, ATP is synthesized - a universal energy substance used by the cell for its vital activity. It can be said that gas exchange in tissues and lungs will supply the body and its structures with oxygen necessary for oxidation.

Gas exchange mechanism

It implies the presence of at least two substances whose circulation in the body provides metabolic processes. In addition to the above oxygen, gas exchange in the lungs, blood and tissues occurs with another compound - carbon dioxide. It is formed in the reactions of dissimilation. Being a toxic exchange substance, it must be removed from the cytoplasm of cells. Let us consider this process in more detail.

Carbon dioxide diffuses through the cell membrane into the interstitial fluid. From it, he enters the blood capillaries - venules. Further, these vessels merge, forming the lower and upper hollow veins. They collect blood saturated with CO _2. And send it to the right atrium. With the reduction of its walls, a portion of venous blood enters the right ventricle. From here begins the pulmonary (small) circle of blood circulation. His task is to saturate the blood with oxygen. Venous in the lungs becomes arterial. A CO ₂ , in turn, comes out of the blood and is removed outside through the respiratory system. To understand how this happens, you first need to study the structure of the lungs. Gas exchange in the lungs and tissues is carried out in special structures - the alveoli and their capillaries.

Structure of the lungs

These are paired organs located in the thoracic cavity. The left lung consists of two lobes. The right is bigger in size. It has three parts. Through the gate of the lungs they contain two bronchi, which, branching, form a so-called tree. On its branches, air moves during inspiration and exhalation. On small, respiratory bronchioles there are bubbles - alveoli. They are collected in the acini. Those, in turn, form a pulmonary parenchyma. It is important that each respiratory vesicle is densely braided by the capillary network of small and large circles of circulation. Bringing branches of the pulmonary arteries, supplying venous blood from the right ventricle, transport carbon dioxide into the alveolus lumen. And the outgoing pulmonary venules take oxygen out of the alveolar air.

Arterial blood enters the left atrium through the pulmonary veins, and from it into the aorta. Her branches in the form of arteries are provided by the cells of the body necessary for internal breathing with oxygen. It is in the alveoli that the blood from the venous becomes arterial. Thus, gas exchange in tissues and lungs is directly carried out by circulation of blood through small and large circles of blood circulation. This is due to continuous contractions of the muscular walls of the cardiac chambers.

External breathing

It is also called ventilating the lungs. It is an exchange of air between the environment and the alveoli. Physiologically correct inhalation through the nose provides the body with a portion of air of such composition: about 21% O ₂ , 0.03% CO ₂ and 79% nitrogen. By airway, he enters the alveoli. They have their own portion of air. Its composition is as follows: 14.2% O ₂ , 5.2% CO ₂ , 80% N ₂ . Inhalation, as well as exhalation, is regulated in two ways: nerve and humoral (concentration of carbon dioxide). Thanks to the excitation of the respiratory center of the medulla oblongata, the nerve impulses are transmitted to the respiratory intercostal muscles and the diaphragm. The volume of the chest increases. Lungs, passively moving after contractions of the thoracic cavity, expand. The air pressure in them becomes below atmospheric pressure. Therefore, a portion of air from the upper respiratory tract enters the alveoli.

Exhalation follows the inspiration. It is accompanied by relaxation of the intercostal muscles and raising the arch of the diaphragm. This leads to a decrease in lung volume. The air pressure in them becomes higher than atmospheric pressure. And air with an excess of carbon dioxide rises to the bronchioles. Further, on the upper respiratory tract, it follows into the nasal cavity. The composition of the exhaled air is as follows: 16.3% O ₂ , 4% CO ₂ , 79 N ₂ . At this stage, external gas exchange takes place. Pulmonary gas exchange, carried out by the alveoli, provides cells with oxygen, necessary for internal breathing.

Cell respiration

It enters the system of catabolic reactions of metabolism and energy. These processes study both biochemistry, and anatomy, and human physiology. Gas exchange in the lungs and tissues is interrelated and impossible without each other. Thus, external breath supplies oxygen to the interstitial fluid and removes carbon dioxide from it. And the internal, carried out directly in the cell by its mitochondria, which provide oxidative phosphorylation and the synthesis of ATP molecules, uses oxygen for these processes.

The Krebs cycle

The cycle of tricarboxylic acids is the leading one in the respiration of the cell. It unites and coordinates the reactions of the oxygen-free stage of energy metabolism and processes involving transmembrane proteins. It also acts as a supplier of building cellular material (amino acids, simple sugars, higher carboxylic acids) formed in its intermediate reactions and used by the cell for growth and division. As we see, in this article gas exchange in tissues and lungs has been studied, and its biological role in the vital activity of the human body has been determined.