What is gas exchange in the blood, lungs and tissues? Features of gas exchange. What is gas exchange
Lungs- the most voluminous internal organ of our body. They are very similar in some ways to wood (this is what this department is called - bronchial tree), hung with fruit bubbles (). It is known that the lungs contain almost 700 million alveoli. And this is functionally justified - they are the ones who perform main role in air exchange. The walls of the alveoli are so elastic that they can stretch several times when inhaling. If we compare the surface area of the alveoli and the skin, it opens amazing fact: despite their apparent compactness, the alveoli are tens of times larger in area than the skin.
The lungs are the great workers of our body. They are in constant motion, sometimes contracting, sometimes stretching. This happens day and night against our wishes. However, this process cannot be called completely automatic. It's more of a semi-automatic one. We can deliberately hold our breath or force it. Breathing is one of the most necessary functions of the body. It would be worth recalling that air is a mixture of gases: oxygen (21%), nitrogen (about 78%), carbon dioxide (about 0.03%). In addition, it contains inert gases and water vapor.
From biology lessons, many probably remember the experiment with lime water. If you exhale through a straw into clear lime water, it will become cloudy. This is irrefutable evidence that the air after exhalation contains much more carbon dioxide: about 4%. The amount of oxygen, on the contrary, decreases and amounts to 14%.
What controls the lungs or breathing mechanism
The mechanism of gas exchange in the lungs is a very interesting process. The lungs themselves will not stretch or contract without muscle work. Pulmonary breathing involves the intercostal muscles and the diaphragm (a special flat muscle on the border of the thoracic and abdominal cavities). When the diaphragm contracts, the pressure in the lungs decreases, and air naturally rushes into the organ. Exhalation occurs passively: the elastic lungs themselves push the air out. Although sometimes the muscles can contract when exhaling. This happens with active breathing.
The whole process is under the control of the brain. The medulla oblongata has a special center for regulating breathing. It reacts to the presence of carbon dioxide in the blood. As soon as it becomes smaller, the center sends a signal to the diaphragm along the nerve pathways. The process of contraction occurs, and inhalation occurs. If the respiratory center is damaged, the patient's lungs are ventilated artificially.
How does gas exchange occur in the lungs?
The main task of the lungs is not just to transport air, but to carry out the process of gas exchange. The composition of the inhaled air changes in the lungs. And here the main role belongs to the circulatory system. What is the circulatory system of our body? It can be imagined as a large river with tributaries of small rivers into which streams flow. These are the capillary streams that permeate all the alveoli.
Oxygen entering the alveoli penetrates the walls of the capillaries. This happens because the blood and air contained in the alveoli have different pressures. Venous blood has lower pressure than alveolar air. Therefore, oxygen from the alveoli rushes into the capillaries. The pressure of carbon dioxide is less in the alveoli than in the blood. For this reason, from venous blood carbon dioxide is directed into the lumen of the alveoli.
There are in the blood special cells– red blood cells containing the protein hemoglobin. Oxygen attaches to hemoglobin and travels in this form throughout the body. Blood enriched with oxygen is called arterial.
The blood is then transported to the heart. The heart, another of our tireless workers, transports oxygen-enriched blood to tissue cells. And then through the “river streams” the blood along with oxygen is delivered to all the cells of the body. In cells, it gives off oxygen and takes in carbon dioxide, a waste product. And the reverse process begins: tissue capillaries - veins - heart - lungs. In the lungs, blood enriched with carbon dioxide (venous) returns to the alveoli and, together with the remaining air, is pushed out. Carbon dioxide, like oxygen, is transported by hemoglobin.
So, double gas exchange occurs in the alveoli. This whole process is carried out at lightning speed, thanks to the large surface area of the alveoli.
Non-respiratory lung functions
The importance of the lungs is determined not only by breathing. TO additional functions this body may include:
- mechanical protection: sterile air enters the alveoli;
- immune protection: the blood contains antibodies to various pathogenic factors;
- cleansing: blood removes gaseous toxic substances from the body;
- support of acid-base balance of blood;
- purification of blood from small blood clots.
But no matter how important they may seem, the main job of the lungs is breathing.
Instructions
Intercostal muscles and the diaphragm, a flat muscle located on the border of the abdominal and thoracic cavities, take part in pulmonary breathing. When the diaphragm contracts, the pressure in the lungs decreases, causing air to rush into them. Exhalation is done passively: the lungs independently push the air out. The breathing process is controlled by a part of the brain - the medulla oblongata. It houses the respiratory control center, which responds to the presence of carbon dioxide in the blood. As soon as its level rises, the center sends a signal to the diaphragm along the nerve pathways, it contracts, and inhalation occurs. In case of damage to the respiratory center, artificial ventilation is used.
The process of gas exchange takes place in the alveoli of the lungs - microscopic bubbles located at the ends of the bronchioles. They consist of squamous (respiratory) alveocytes, large alveocytes and chemoreceptors. Main role in in this case belongs to the circulatory system. Oxygen entering the alveoli of the lungs penetrates the walls of the capillaries. A similar process occurs due to the difference in the blood and air in the alveoli. The blood in the veins has less pressure, so oxygen rushes from the alveoli into the capillaries. Carbon dioxide in the alveoli has lower pressure, so it enters the lumen of the alveoli from the venous blood.
The blood contains red blood cells containing the protein hemoglobin. Oxygen molecules attach to hemoglobin. Oxygenated blood is called arterial blood and is transported to the heart. The heart drives it to tissue cells. In cells, the blood gives up oxygen and in return takes in carbon dioxide, which is also carried by hemoglobin. Then the reverse process occurs: blood flows from the tissue capillaries into the veins, into the heart and into the lungs. In the lungs, venous blood with carbon dioxide enters the alveoli, and carbon dioxide, along with air, is pushed out. Double gas exchange occurs in the alveoli with lightning speed.
The vital capacity of the lungs includes tidal volume, as well as inspiratory and expiratory reserve volumes. Tidal volume is the amount of air entering the lungs during 1 breath. If, after a calm inhalation, you take a strong inhalation, an additional amount of air will enter the lungs, which is called the inspiratory volume reserve. After a calm exhalation, you can exhale some more air (expiratory reserve volume). In general, the vital capacity of the lungs is the largest amount of air a person can exhale after taking a deep breath.
Gas exchange
To ensure vital activity between the body and environment Gas exchange must occur continuously. Aerobic organisms, as a result of diffusion, absorb oxygen (from the water in which it is dissolved or from the atmosphere) and release carbon dioxide. The respiratory surface on which gas exchange occurs must be:
Permeable to O 2 and CO 2 ;
Fine - diffusion is effective only over short distances;
Wet - these gases diffuse in solution;
Large - to maintain a sufficient rate of gas exchange.
The metabolic rate of plants is low and they require relatively little oxygen. Gas exchange occurs by diffusion of gases across the entire surface; in large plants, leaf stomata and cracks in the bark are used for these purposes. Cells containing chlorophyll can consume the oxygen they have just produced for respiration.
In unicellular animals, gas exchange occurs through cell membrane. The most primitive multicellular organisms - coelenterates, flatworms - also meet their oxygen needs by absorbing it into every cell in contact with the environment.
In more complex organisms it appears a large number of cells not in contact with the environment, and simple diffusion becomes ineffective. Requires special respiratory system, which will effectively absorb oxygen and release carbon dioxide. As a rule, this system is associated with the circulatory system, which provides oxygen delivery to tissues and cells. The solubility of oxygen in the blood is 0.2 ml per 100 ml of blood, but the presence of respiratory pigments can increase the efficiency of this process tens and hundreds of times. The best known respiratory pigment is hemoglobin.
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Some respiratory pigments |
Let's look at some of the most typical respiratory systems.
Air enters the body of insects through special openings - spiracles. They open into air cavities, from which special tubes extend - trachea. The trachea are reinforced with chitin and always remain open. In each segment of the body they branch into numerous small tubes - tracheoles, through which oxygen flows directly to the tissues; there is no need to transport it with blood. The tracheoles are filled with aqueous fluid through which oxygen and carbon dioxide diffuse. At active work muscle fluid is absorbed into the tissues, and oxygen goes directly to the cells already in gaseous state. The tracheal respiratory system is very effective, but the presence of a diffusion process in the respiratory chain limits the size of the insect (more precisely, its thickness).
Gas exchange in fish occurs with the help of special respiratory organs - gills. Each gill is supported by vertical cartilage - gill arch. In bony fishes, the gill arch consists of bone tissue. A series of horizontal folds extend from the septum lying above the gill arch - gill filaments, on each of which vertical secondary petals are formed. The free edges of the gill septa are elongated and act as folding valves. When the bottom of the oral cavity and pharynx drops, the pressure in them decreases, and water rushes into the gills through the mouth and squirts. The valve prevents water from entering the gills from the other side. Numerous capillaries piercing the gills are saturated with oxygen here and unite into gill arteries, which carry oxygen-rich blood from the gills. Note that the respiratory system of bony fish is more advanced than that of cartilaginous fish, since in bony fish the gills have a larger surface area, and the movement of blood towards the flow of water ensures a more efficient exchange of gases.
Amphibians obtain oxygen in three ways: through the skin, mouth and lungs. During cutaneous and oral respiration, the gas is absorbed by the moist epithelium lining the skin or oral cavity. The visible movements of the frog's throat are mouth breathing. The air entering the mouth can also enter the lungs through the larynx, trachea and bronchi. The frog's lungs are a pair of hollow sacs, the walls of which form numerous folds penetrated by blood capillaries. As a result of muscle contractions, inhalation and exhalation occur, the lungs are filled with air, oxygen from it enters the blood.
U higher forms In vertebrates, cutaneous respiration is absent; the lungs become the main respiratory organ. They have a much larger number of folds than the lungs of amphibians. Birds also have air sacs, thanks to which oxygen-rich air passes through the lungs both during inhalation and exhalation; this increases the efficiency of gas exchange.
In mammals, air enters through the nostrils; small hairs trap foreign particles, and the ciliated epithelium, which lines the nasal passages, humidifies the air, warms it, and also traps particles that managed to slip through the hairs. From the nose, air enters the pharynx and then into the larynx. The cartilaginous valve (epiglottis) protects the airways from food entering them. In the laryngeal cavity there are vocal cords; when exhaled air passes through the glottis, sound waves. As the tension of the ligaments changes, the pitch of the sound produced changes.
From the larynx, air enters the tube-shaped trachea. Its walls are covered with ciliated epithelium, which collects dust particles and microbes that enter the trachea. The walls of the trachea (as well as the larynx) are made of cartilage tissue, due to this it does not fall off when inhaling. At the lower end, the trachea branches into two bronchi. The bronchi divide into thinner bronchioles; in the smallest of them (diameter 1 mm or less) cartilage tissue absent. The bronchioles branch, in turn, into numerous alveolar ducts, ending in sacs lined with connective tissue - alveoli. There may be hundreds of millions of alveoli in the lungs of a mammal, total area their surface is such that they can cover an entire football field. The thickness of the alveolar wall is only 0.0001 mm. The outer side of the alveoli is covered with a dense network of blood capillaries. Absorbed by the moist epithelium, oxygen diffuses into the blood plasma and combines with hemoglobin there. Carbon dioxide diffuses in the opposite direction. The diameter of the capillaries is less than the diameter of the red blood cells; this ensures close contact of red blood cells with the surface of the alveoli.
The lungs are separated from the chest wall pleural cavity. It is impermeable to air; the pressure in it is 3–4 mm Hg. Art. lower than in the lungs, due to which the latter fill almost the entire chest. Ventilation of the lungs is carried out due to the simultaneous contraction of the diaphragm and external intercostal muscles. The volume of the chest increases, the pressure decreases, and air enters. During exhalation, the diaphragm and external muscles return to their previous position, and the internal intercostal muscles contract. The chest becomes smaller and air is pushed out of the lungs. At large physical activity exhalation becomes more active and requires additional energy expenditure.
When the air is insufficiently saturated with oxygen (for example, high in the mountains), hypoxia begins, manifested in malaise and a feeling of extreme fatigue. Over time, the respiratory system can adapt to a low oxygen content - in such cases the body is said to have acclimatized to new conditions.
Mammals capable of for a long time stay under water (whales, seals), when diving, they reflexively reduce their heart rate, their blood channels narrow, and only the most important organs for life are supplied with blood. The first breath after surfacing serves as a signal to increase the heart rate.
Gas exchange(in biology; hereinafter referred to as “G.”) is the exchange of gases between the body and external environment. Oxygen is continuously supplied to the body from the environment, which is consumed by all organs and tissues; The carbon dioxide formed in it and a small amount of other gaseous products are released from the body. G. is necessary for almost all organisms; without it, normal metabolism and energy, and therefore .
Gas exchange in humans occurs in the alveoli of the lungs and in the tissues of the body.
Rice. 1: Human respiratory system (hereinafter, click on the image to enlarge)
Oxygen entering the tissues of a living organism is used to oxidize products formed as a result of a long chain of chemical transformations of carbohydrates, fats, etc. In this case, CO 2, water, nitrogen compounds are formed and energy is released, which is used to maintain and perform work. The amount of CO 2 formed in the body and ultimately released from it depends not only on the amount of O 2 consumed, but also on what is predominantly oxidized: carbohydrates, fats or proteins. The ratio of CO 2 removed from the body to O 2 absorbed during the same time is called coefficient, which is approximately 0.7 for the oxidation of fats, 0.8 for the oxidation of proteins and 1.0 for the oxidation of carbohydrates. The amount of energy released per 1 liter of consumed O2 (caloric equivalent of oxygen) is 20.9 kJ (5 kcal) during the oxidation of carbohydrates and 19.7 kJ (4.7 kcal) during the oxidation of fats. Thus, from the consumption of O 2 per unit of time and from the respiratory coefficient, it is possible to calculate the amount of energy released in the body.
Rice. 2: Pulmonary respiration (gas exchange in the lungs): gas exchange between air and occurs by diffusion according to the difference in gas concentrations. IN There is no gas exchange in space. Venous turns into arterial.
Gas exchange (and therefore energy expenditure) in poikilothermic animals (cold-blooded animals) decreases with decreasing body temperature. The same dependence was found in homeothermic animals (warm-blooded) when thermoregulation is turned off (under conditions of natural or artificial hypothermia); with an increase in body temperature (at different temperatures), G. increases.
When the ambient temperature decreases, heat in warm-blooded animals (especially small ones) increases as a result of increased heat production. G. also increases after taking food, especially one rich in proteins (the so-called specific dynamic effect). G. reaches its greatest values during muscular activity. In humans, when working at moderate power, blood pressure increases; 3–6 minutes after it begins, it reaches a certain level and is then maintained at this level throughout the entire period of work. When operating at high power, G. continuously increases; soon after reaching the maximum for this person level (maximum aerobic work), work has to be stopped, because the body’s need for O 2 exceeds this level. In the first time after the end of work, an increased consumption of O 2 remains, which is used to cover the oxygen debt, i.e., for the oxidation of metabolic products formed during work. O2 consumption can increase from 200 - 300 ml/min at rest to 2000 - 3000 during work, and in well-trained athletes - up to 5000 ml/min. Accordingly, CO 2 release and energy consumption increase; At the same time, shifts in the respiratory coefficient occur, associated with changes in metabolism, acid-base balance and pulmonary ventilation.
Fig. 3: Gas exchange in lungs and tissues
Calculation of the total daily energy consumption of people of different professions and lifestyles, based on the definitions of gas, is important for rationing. Studies of gas changes during standard physical work are used in labor physiology and in the clinic to assess the functional state of systems involved in gas exchange.
The comparative constancy of gas exchange with significant changes in the partial pressure of O 2 in the environment, operational disruptions, etc. is ensured by the adaptive (compensatory) reactions of the systems involved in gas and regulated.
G. in humans and animals is usually studied under conditions of complete rest, with comfortable temperature environment (18 - 22 °C). The amounts of O2 consumed and energy released characterize the basal metabolism. To study G., methods based on the principle of an open or closed system are used. In the first case, the amount of exhaled air and its composition are determined (using chemical or physical gas analyzers), which makes it possible to calculate the amounts of O 2 consumed and CO 2 released. In the second case it happens in closed system(a sealed chamber or from a spirograph connected to the respiratory tract), in which the released CO 2 is absorbed, and the amount of O 2 consumed from the system is determined either by measuring an equal amount of O 2 automatically entering the system, or by reducing the volume of the system:
Rice. 4: Diagram of an apparatus for studying gas exchange: U - device for automatic oxygen supply; B - vessel with oxygen; K - camera; X - refrigerator; Ш - a vessel with alkali for capturing carbon dioxide; N - pump; CaCl 2 - a vessel with calcium chloride to absorb water vapor; T - thermometer; M - pressure gauge
, dealing with diseases of the respiratory system: trachea, bronchi, lungs and pleura - (comes from the Latin words: pulmono- (lungs) + logos (teaching)). You should contact him if you have symptoms:
- , especially with sputum;
- dyspnea;
- seizures;
- pain in chest, associated with .
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 gas exchange of blood with the environment. The outside of the organ is covered with pleura, consisting of two layers forming the pleural cavity of the lungs
The lungs are two voluminous, semi-cone-shaped organs that occupy most of the chest cavity. Each lung has a base that is supported by the diaphragm, the muscle that separates the chest and abdominal cavities; the upper parts of the lungs are round in shape. The lungs are divided into lobes by deep fissures. There are two slits in the right lung, and only one in the left.
The pulmonary acinus is a functional unit of the lungs, a tiny area of tissue ventilated by the terminal bronchiole, from which the respiratory bronchioles arise, which further form the alveolar canals or alveolar ducts. At the end of each alveolar canal are alveoli, microscopic elastic balls with thin walls filled with air; The alveoli make up the alveolar fascicle or sac where gas exchange occurs.
The thin walls of the alveoli consist of a single layer of cells surrounded by a layer of tissue that supports them and separates them from the alveoli. Along with the alveoli, a thin membrane also separates the blood capillaries that penetrate the lungs. The distance between the inner wall of the blood capillaries and the alveoli is 0.5 thousandths 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 “fuel”, thanks to which metabolism occurs 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 constantly need oxygen - for example, the nerves of the brain can hardly exist without oxygen even for several minutes.
Molecules of oxygen (02) and carbon dioxide (CO2) circulate through the blood, joining the hemoglobin of red blood cells, which transport them throughout the body. Once in the lungs, red blood cells give up carbon dioxide molecules and take away oxygen molecules through the process of diffusion: 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 diffusion process occurs again: oxygen passes from the blood into the cells, and carbon dioxide enters the blood from the cells. The blood then flows 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”.
