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. We define the features of external respiration, which occurs between the body and the atmosphere, and internal, proceeding directly at the cellular level.
What are we breathing for?
Most people, without hesitation, will answer: to get oxygen. But they don’t know why we need him. Many answer simply: oxygen is needed to breathe. It turns out some kind of vicious circle. To break it, biochemistry that studies cellular metabolism will help us.
The bright minds of humanity studying this science have long concluded that the oxygen entering the tissues and organs oxidizes carbohydrates, fats and proteins. In this case, energy-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 energetic substance used by a cell for its vital functions. We can say that gas exchange in tissues and lungs will precisely supply the body and its structures with the 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 dissimilation reactions. Being a toxic substance of metabolism, it must be removed from the cytoplasm of cells. Consider this process in more detail.
Carbon dioxide by diffusion penetrates through the cell membrane into the interstitial fluid. From it, he enters the capillaries of blood - venules. Further, these vessels merge, forming the lower and upper vena cava. They collect blood saturated with CO 2. And they direct her into 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. Its task is to saturate the blood with oxygen. Venous in the lungs becomes arterial. And CO 2 , in turn, leaves the bloodstream and is expelled through the respiratory system. To understand how this happens, you must first study the structure of the lungs. Gas exchange in the lungs and tissues is carried out in special structures - alveoli and their capillaries.
Lung structure
These are paired organs located in the chest cavity. The left lung consists of two lobes. The right one is larger. It has three shares. Through the gate of the lungs, two bronchi enter them, which, branching, form the so-called tree. On its branches, air moves during inhalation and exhalation. On the small, respiratory bronchioles are bubbles - alveoli. They are collected in acini. Those, in turn, form a pulmonary parenchyma. It is important that each respiratory vesicle is densely braided by the capillary network of the small and large circles of blood circulation. The bringing branches of the pulmonary arteries, supplying venous blood from the right ventricle, transport carbon dioxide into the lumen of the alveoli. And the efferent pulmonary venules take oxygen from the alveolar air.
Arterial blood flows through the pulmonary veins into the left atrium, and from it into the aorta. Its branching in the form of arteries provides the body cells with oxygen necessary for internal respiration. It is in the alveoli that the blood from the venous becomes arterial. Thus, gas exchange in the tissues and lungs is directly carried out by blood circulation in the small and large circles of blood circulation. This happens due to continuous contractions of the muscle walls of the heart chambers.
External respiration
It is also called lung ventilation. It is an exchange of air between the environment and the alveoli. A physiologically correct breath through the nose provides the body with a portion of air of this composition: about 21% O 2 , 0.03% CO 2 and 79% nitrogen. Through the airways, it 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: nervous and humoral (concentration of carbon dioxide). Due to the excitation of the respiratory center of the medulla oblongata, 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 chest cavity, expand. The air pressure in them becomes lower than atmospheric. Therefore, a portion of the air from the upper respiratory tract enters the alveoli.
Exhalation is carried out after inhalation. It is accompanied by relaxation of the intercostal muscles and the lifting of the diaphragm. This leads to a decrease in lung volume. The air pressure in them becomes higher than atmospheric. And air with an excess of carbon dioxide rises into the bronchioles. Further, along 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 occurs. Pulmonary gas exchange by the alveoli provides the cells with the oxygen necessary for internal respiration.
Cell respiration
Included in the system of catabolic metabolic and energy reactions. These processes are studied by both biochemistry and anatomy, and human physiology. Gas exchange in the lungs and tissues is interconnected and impossible without each other. Thus, external respiration supplies oxygen to the interstitial fluid and removes carbon dioxide from it. And the internal, carried out directly in the cell by its organelles - mitochondria, which provide oxidative phospholation and synthesis of ATP molecules, uses oxygen for these processes.
Krebs cycle
The tricarboxylic acid cycle is leading in the respiration of cells. It combines and harmonizes the reactions of the oxygen-free phase of energy metabolism and processes involving transmembrane proteins. He 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 you can see, in this article, gas exchange in the tissues and lungs was studied, and its biological role in the life of the human body was determined.