Respiratory system of the person parameters of breath. The structure of the human respiratory system. The biological significance of respiration

Breath - a set of physiological processes constantly occurring in a living organism, as a result of which it absorbs oxygen from the environment and releases carbon dioxide and water. Respiration provides gas exchange in the body, which is a necessary link in the metabolism. Respiration is based on the processes of oxidation of organic substances - carbohydrates, fats and proteins, as a result of which energy is released that ensures the vital activity of the body.

Inhaled air through airways (nasal cavity, larynx, trachea, bronchi) reaches the pulmonary vesicles (alveoli), through the walls of which, richly braided with blood capillaries, gas exchange occurs between air and blood.

In humans (and vertebrates), the breathing process consists of three interrelated stages:

• external respiration,
• transport of gases by the blood and
• tissue respiration.

Essence external respiration It consists in the exchange of gases between the external environment and the blood, which occurs in special respiratory organs - in the lungs. Oxygen enters the blood from the external environment, and carbon dioxide is released from the blood (only 1-2% of the total gas exchange is provided by the surface of the body, that is, through the skin).
The change of air in the lungs is achieved by rhythmic respiratory movements of the chest, carried out by special muscles, due to which an alternate increase and decrease in the volume of the chest cavity is obtained. In humans, the chest cavity during inhalation increases in three directions: anterior-posterior and lateral - due to the raising and rotation of the ribs, and vertically - due to the lowering of the abdominal barrier (diaphragms).

Depending on the direction in which the chest volume mainly increases, there are:

• chest,
• abdominal and
• mixed types of breathing.

When breathing, the lungs passively follow the chest walls, expanding when inhaling and contracting when exhaling.
The total surface area of ​​the lung alveoli in humans is on average 90 m 2 . A person (adult) at rest does. 16-18 respiratory cycles (i.e., inhalations and exhalations) in 1 min.
With each breath, about 500 ml of air enters the lungs, which is called respiratory. With a maximum breath, a person can inhale about 1500 more ml of the so-called. additional air . If, after a calm exhalation, an additional intensified exhalation is made, then another 1500 ml of the so-called. reserve air .
Breathing, supplementary and reserve air add up lung capacity.
However, even after the most intense exhalation, 1000-1500 ml of residual air still remains in the lungs.

Minute breathing volume or ventilation of the lungs, varies depending on the body's need for oxygen and in an adult at rest is 5-9 liters of air per 1 minute.
During physical work, when the body's need for oxygen sharply increases, ventilation of the lungs increases to 60-80 liters per minute, and in trained athletes even up to 120 liters per minute. With aging, the body's metabolism decreases, and size also decreases; lung ventilation. With an increase in body temperature, the respiratory rate increases slightly and in some diseases reaches 30-40 per 1 minute; while the depth of breathing decreases.

Respiration is regulated by the respiratory center in the medulla oblongata of the central nervous system. In humans, in addition, the cerebral cortex plays an important role in the regulation of breathing.

Gasooben occurs in the alveoli of the lungs. To get into the alveoli of the lungs, the air during breathing passes through the so-called respiratory tract: it first penetrates into nasal cavity, further into throat, which is a common path for air and for food entering it from the oral cavity: then the air moves through the purely respiratory system - larynx, respiratory throat, bronchi. Bronchi, gradually branching, reaches microscopic bronchioles, from which air enters pulmonary alveoli.

tissue respiration - a complex physiological process, manifested in the consumption of oxygen by cells and tissues of the body and in the formation of carbon dioxide by them. Tissue respiration is based on redox processes accompanied by the release of energy. Due to this energy, all vital processes are carried out - continuous renewal, growth and development of tissues, secretion of glands, muscle contraction, etc.

NOSE AND NOSE CAVITY - the initial part of the respiratory tract and the organ of smell.
Nose built from paired nasal bones and nasal cartilages, giving it an external shape.
nasal cavity It is located in the center of the facial skeleton and represents a bone canal lined with mucous membrane, which runs from the holes (nostrils) to the choanae, connecting it with the nasopharynx.
The nasal septum divides the nasal cavity into right and left halves.
Characteristic of the nasal cavity are adnexal sinuses - cavities in adjacent bones (maxillary, frontal, ethmoid), which communicate with the nasal cavity through holes and channels.

The mucous membrane lining the nasal canal consists of ciliated epithelium; its hairs have constant oscillatory movements in the direction of the entrance to the nose, which blocks access to the respiratory tract for small coal, dust, and other particles inhaled with air. The air entering the nasal cavity is warmed in it due to the abundance of blood vessels in the mucous membrane of the nasal cavity and the warmed air of the paranasal sinuses. This protects the respiratory tract from direct exposure to low external temperatures. Forced breathing through the mouth (eg, deviated septum, nasal polyps) raises the possibility of respiratory infections.

PHARYNX - part of the digestive and respiratory tube, located between the nasal and oral cavities at the top and the larynx and esophagus at the bottom.
The pharynx is a tube, the basis of which is the muscular layer. The pharynx is lined with a mucous membrane, and on the outside it is covered with a connective tissue layer. The pharynx lies in front of the cervical spine down from the skull to the 6th cervical vertebra.
The uppermost part of the pharynx - the nasopharynx - lies behind the nasal cavity, which opens into it with choanae; this is the way for air inhaled through the nose to enter the pharynx.

During the act of swallowing, the airways are isolated: the soft palate (palatine curtain) rises and, pressing against the back wall of the pharynx, separates the nasopharynx from the middle part of the pharynx. Special muscles pull the pharynx up and forward; due to this, the larynx is also pulled up, and the root of the tongue presses down on the epiglottis, which thus closes the entrance to the larynx, preventing food from entering the respiratory tract.

LARYNX - the beginning of the windpipe (trachea), including a voice box. The larynx is located on the neck.
The structure of the larynx is similar to the device of wind so-called reed musical instruments: in the larynx there is a narrowed place - the glottis, into which the air pushed out of the lungs vibrates the vocal cords, which play the same role as the tongue plays in the instrument.

The larynx is located at the level of the 3rd-6th cervical vertebrae, bordering behind the esophagus and communicating with the pharynx through an opening called the entrance to the larynx. Below the larynx passes into the windpipe.
The base of the larynx forms an annular-shaped cricoid cartilage, which connects below with trachea. On the cricoid cartilage, movably connected to it by a joint, is the largest cartilage of the larynx - the thyroid cartilage, consisting of two plates, which, connecting in front at an angle, form a protrusion on the neck that is clearly visible in men - Adam's apple.

On the cricoid cartilage, also connected to it by joints, there are symmetrically located 2 arytenoid cartilages, each bearing a small santorini cartilage at its apex. Between each of them and the inner corner of the thyroid cartilage are stretched 2 true vocal cords that limit the glottis.
The length of the vocal cords in men is 20-24mm, in women - 18-20mm. Short ligaments give a higher voice than long ligaments.
When breathing, the vocal cords diverge, and the glottis takes the form of a triangle with its apex forward.

RESPIRATORY THROAT (Trachea) - the airway following the larynx through which air passes to the lungs.
The windpipe begins at the level of the 6th cervical vertebra and is a tube consisting of 18-20 incomplete cartilaginous rings, closed behind by smooth muscle fibers, as a result of which its back wall is soft and flattened. This allows the esophagus lying behind it to expand during the passage of the food bolus through it when swallowing. Having passed into the chest cavity, the windpipe is divided at the level of the 4th thoracic vertebra into 2 bronchi going to the right and left lungs.

BRONCHI The branches of the windpipe (trachea) through which air enters and leaves the lungs during breathing.
The trachea in the chest cavity is divided into right and left primary bronchi, which enter the right and left lungs, respectively: successively dividing into smaller and smaller secondary bronchi. They form the bronchial tree, which forms the dense base of the lung. The diameter of the primary bronchi is 1.5-2 cm.
The smallest bronchi bronchioles, have microscopic dimensions and represent the final sections of the airways, at the ends of which the respiratory tissue of the lung itself is located, formed alveoli.

The walls of the bronchi are formed by cartilaginous rings and smooth muscles. Cartilaginous rings cause the obstinacy of the bronchi, their non-falling and unhindered movement of air during breathing. The inner surface of the bronchi (as well as other parts of the respiratory tract) is lined with a mucous membrane with ciliated epithelium: epithelial cells are provided with cilia.

LUNGS represent a paired organ. They are enclosed in the chest and are located on the sides of the heart.
Each lung has the shape of a cone, the wide base of which is turned down to the thoracic obstruction. (aperture), the outer surface - to the ribs that form the outer wall of the chest, the inner surface covers the heart shirt with the heart enclosed in it. The apex of the lung protrudes above the clavicle. The average size of an adult lung is: the height of the right lung is 17.5 cm, the left one is 20 cm, the width at the base of the right lung is 10 cm, the left one is 7 cm. The lungs have a fluffy texture, because they are filled with air. From the inner surface, the bronchus, vessels and nerves enter the gates of the lung.

The bronchus conducts air into the lungs through the nasal (oral) cavity, into the larynx and trachea. In the lungs, the bronchus gradually divides into smaller secondary, tertiary, etc. bronchi, making up, as it were, the cartilaginous skeleton of the lung; the final branching of the bronchi is the conducting bronchiole; she aims at the alveolar passages, the walls of which are dotted with pulmonary vesicles - alveoli.

The pulmonary arteries carry carbon dioxide-rich venous blood from the heart to the lungs. The pulmonary arteries divide parallel to the bronchi and eventually break up into capillaries, covering the alveoli with their network. Back from the alveoli, the capillaries gradually gather into veins, which leave the lungs in the form of pulmonary veins, which enter the left half of the heart and carry oxygenated arterial blood.

Gas exchange between the external environment and the body occurs in the alveoli.
Air containing oxygen enters the cavity of the alveoli, and blood flows to the walls of the alveoli. When air enters the alveoli, they expand and, conversely, collapse when air leaves the lung.
Thanks to the thinnest wall of the alveoli, gas exchange easily occurs here - oxygen enters the blood from the inhaled air and carbon dioxide is released into it from the blood; blood is purified, it becomes arterial and is carried further through the heart to the tissues and organs of the body, in which it gives off oxygen and takes in carbon dioxide.

Each lung is covered with a sheath - pleura, passing from the lungs to the chest wall; thus, the lung is enclosed in a closed pleural sac formed by the parietal pleura. Between the pulmonary and parietal pleura there is a narrow gap containing a small amount of fluid. With respiratory movements of the chest, the pleural cavity (together with the chest) expands, and the descending diaphragm lengthens its upper-lower size. Due to the fact that the gap between the sheets of the pleura is airless, the expansion of the chest causes negative pressure in the pleural cavity, stretches the lung tissue, which thus sucks in through the airways (mouth - trachea - bronchi) atmospheric air entering the alveoli.

Expansion of the chest during inhalation is active and is performed with the help of respiratory muscles (intercostal, scalariform, abdominal); its fall during exhalation occurs passively and with the assistance of the elastic forces of the tissue of the lung itself. The pleura provides sliding of the lung in the chest cavity during respiratory movements.

Falsely overestimate the importance of oxygen for the human body. A child still in the womb will not be able to fully develop with a lack of this substance, which enters through the maternal circulatory system. And when the baby is born, it lets out a cry, making the first respiratory movements that do not stop throughout life.

Oxygen hunger is not regulated by consciousness in any way. With a lack of nutrients or fluids, we feel thirsty or need food, but hardly anyone felt the body's need for oxygen. Regular breathing occurs at the cellular level, since no living cell is able to function without oxygen. And so that this process is not interrupted, the respiratory system is provided in the body.

Human respiratory system: general information

The respiratory, or respiratory, system is a complex of organs, thanks to which oxygen is delivered from the environment to the circulatory system and the subsequent removal of exhaust gases back into the atmosphere. In addition, it is involved in heat transfer, smell, the formation of voice sounds, the synthesis of hormonal substances and metabolic processes. However, it is gas exchange that is of greatest interest, since it is the most significant for maintaining life.

At the slightest pathology of the respiratory system, the functionality of gas exchange decreases, which can lead to the activation of compensatory mechanisms or oxygen starvation. To assess the functions of the respiratory system, it is customary to use the following concepts:

• The vital capacity of the lungs, or VC, is the maximum possible volume of atmospheric air that enters in one breath. In adults, it varies between 3.5-7 liters, depending on the degree of training and the level of physical development.
• Tidal volume, or DO, is an indicator that characterizes the average statistical intake of air per breath in calm and comfortable conditions. The norm for adults is 500-600 ml.
• The inspiratory reserve volume, or ROVd, is the maximum amount of atmospheric air that enters under calm conditions in one breath; is about 1.5–2.5 liters.
• The expiratory reserve volume, or ROV, is the maximum volume of air that leaves the body at the time of a calm exhalation; the norm is approximately 1.0–1.5 liters.
• Respiratory rate - the number of respiratory cycles (inhalation-exhalation) per minute. The norm depends on age and degree of load.

Each of these indicators has a certain significance in pulmonology, since any deviation from the normal numbers indicates the presence of a pathology that requires appropriate treatment.

The structure and function of the respiratory system

The respiratory system provides the body with a sufficient supply of oxygen, participates in gas exchange and the elimination of toxic compounds (in particular carbon dioxide). Entering the airways, the air is warmed, partially purified, and then transported directly to the lungs - the main human organ in breathing. Here the main processes of gas exchange between the tissues of the alveoli and the blood capillaries take place.

Red blood cells contain hemoglobin, an iron-based complex protein that can attach oxygen molecules and carbon dioxide compounds to itself. Entering the capillaries of the lung tissue, the blood is saturated with oxygen, capturing it with the help of hemoglobin. Then red blood cells carry oxygen to other organs and tissues. There, the incoming oxygen is gradually released, and its place is taken by carbon dioxide - the end product of respiration, which at high concentrations can cause poisoning and intoxication, even death. After that, red blood cells, deprived of oxygen, are sent back to the lungs, where carbon dioxide is removed and the blood is re-oxygenated. Thus, the cycle of the human respiratory system closes.

Regulation of the breathing process

The ratio of the concentration of oxygen and carbon dioxide is more or less constant and is regulated at an unconscious level. In calm conditions, the supply of oxygen is carried out in the optimal mode for a particular age and body, however, under stress - during physical training, with sudden severe stress - the level of carbon dioxide rises. In this case, the nervous system sends a signal to the respiratory center, which stimulates the mechanisms of inhalation and exhalation, increasing the level of oxygen supply and compensating for the excess of carbon dioxide. If this process is interrupted for some reason, the lack of oxygen quickly leads to disorientation, dizziness, loss of consciousness, and then to irreversible brain damage and clinical death. That is why the work of the respiratory system in the body is considered one of the dominant ones.

Each breath is carried out due to a certain group of respiratory muscles that coordinate the movements of the lung tissue, since it itself is passive and cannot change shape. Under standard conditions, this process is ensured by the diaphragm and intercostal muscles, however, with deep functional breathing, the muscular frame of the cervical, thoracic and abdominal muscles are also involved. As a rule, during each breath in an adult, the diaphragm drops by 3–4 cm, which allows an increase in the total volume of the chest by 1–1.2 liters. At the same time, the intercostal muscles, contracting, raise the costal arches, which further increases the total volume of the lungs and, accordingly, lowers the pressure in the alveoli. It is because of the difference in pressure that air is forced into the lungs, and inspiration occurs.

Exhalation, unlike inhalation, does not require the work of the muscular system. Relaxing, the muscles again compress the volume of the lungs, and the air, as it were, is “squeezed out” from the alveoli back through the airways. These processes occur quite quickly: newborns breathe on average 1 time per second, adults - 16-18 times per minute. Normally, this time is enough for high-quality gas exchange and removal of carbon dioxide.

Organs of the human respiratory system

The human respiratory system can be conditionally divided into the respiratory tract (transportation of incoming oxygen) and the main paired organ - the lungs (gas exchange). The airways at the intersection with the esophagus are classified into upper and lower airways. The upper ones include openings and cavities through which air enters the body: nose, mouth, nasal, oral cavities and pharynx. To the lower - the paths along which the air masses go directly to the lungs, that is, the larynx and trachea. Let's look at the function of each of these organs.

upper respiratory tract

1. Nasal cavity

The nasal cavity is the link between the environment and the human respiratory system. Through the nostrils, air enters the nasal passages, lined with small villi that filter out dust particles. The inner surface of the nasal cavity is distinguished by a rich vascular-capillary network and a large number of mucous glands. Mucus acts as a kind of barrier for pathogenic microorganisms, preventing their rapid reproduction and destroying the microbial flora.

The nasal cavity itself is divided by the ethmoid bone into 2 halves, each of which, in turn, is divided into several more passages by means of bone plates. The paranasal sinuses open here - maxillary, frontal and others. They also belong to the respiratory system, since they significantly increase the functional volume of the nasal cavity and contain, albeit a small, but still quite significant amount of mucous glands.

The mucous membrane of the nasal cavity is formed by ciliated epithelial cells that perform a protective function. Alternately moving, cellular cilia form peculiar waves that keep the nasal passages clean, removing harmful substances and particles. Mucous membranes can vary significantly in volume depending on the general condition of the body. Normally, the lumens of numerous capillaries are rather narrow, so nothing prevents full nasal breathing. However, at the slightest inflammatory process, for example, during a cold or flu, mucus synthesis increases several times, and the volume of the circulatory network increases, which leads to swelling and difficulty breathing. Thus, a runny nose occurs - another mechanism that protects the respiratory tract from further infection.

The main functions of the nasal cavity include:

• filtration from dust particles and pathogenic microflora,
• warming the incoming air
• humidification of air flows, which is especially important in arid climates and during the heating season,
• protection of the respiratory system during colds.

2. Oral cavity

The oral cavity is a secondary respiratory opening and is not so anatomically thought out for supplying the body with oxygen. However, it can easily perform this function if nasal breathing is difficult for any reason, for example, with a nose injury or a runny nose. The path that air passes through the oral cavity is much shorter, and the opening itself is larger in diameter compared to the nostrils, so the inspiratory reserve volume through the mouth is usually larger than through the nose. However, this is where the benefits of mouth breathing end. On the mucous membrane of the mouth there are neither cilia nor mucous glands that produce mucus, which means that the filtration function in this case completely loses its significance. In addition, the short air flow path makes it easier for air to enter the lungs, so it simply does not have time to warm up to a comfortable temperature. Because of these features, nasal breathing is more preferable, and oral breathing is intended for exceptional cases or as compensatory mechanisms when air cannot enter through the nose.

3. Throat

The pharynx is the connecting area between the nasal and oral cavities and the larynx. It is conditionally divided into 3 parts: nasopharynx, oropharynx and laryngopharynx. Each of these parts is in turn involved in the transport of air during nasal breathing, gradually bringing it to a comfortable temperature. Once in the laryngopharynx, the inhaled air is redirected to the larynx through the epiglottis, which acts as a kind of valve between the esophagus and the respiratory system. During breathing, the epiglottis, adjacent to the thyroid cartilage, blocks the esophagus, providing air only to the lungs, and during swallowing, on the contrary, it blocks the larynx, protecting against foreign bodies entering the respiratory organs and subsequent suffocation.

lower respiratory tract

1. Larynx

The larynx is located in the anterior cervical region and is the upper part of the respiratory tube. Anatomically, it consists of cartilaginous rings - thyroid, cricoid and two arytenoid. The thyroid cartilage forms an Adam's apple, or Adam's apple, especially pronounced in the stronger sex. The laryngeal cartilages are interconnected by means of connective tissue, which, on the one hand, provides the necessary mobility, and on the other hand, limits the mobility of the larynx in a strictly defined range. The vocal apparatus, represented by the vocal cords and muscles, is also located in this area. Thanks to their coordinated work, wave-like sounds are formed in a person, which are then transformed into speech. The inner surface of the larynx is lined with ciliated epithelial cells, and the vocal cords are lined with squamous epithelium, devoid of mucous glands. Therefore, the main moisturizing of the ligamentous apparatus is provided due to the outflow of mucus from their overlying organs of the respiratory system.

2. Trachea

The trachea is a tube 11–13 cm long, reinforced in front with dense hyaline half rings. The posterior wall of the trachea adjoins the esophagus, so there is no cartilage tissue there. Otherwise, it would impede the passage of food. The main function of the trachea is the passage of air through the cervical region further into the bronchi. In addition, the ciliary epithelium lining the inner surface of the breathing tube produces mucus, which provides additional air filtration from dust particles and other pollutants.

Lungs

The lungs are the main organ for air exchange. Paired formations, unequal in size and shape, are located in the chest cavity, bounded by costal arches and the diaphragm. Outside, each lung is covered with a serous pleura, which consists of two layers and forms an airtight cavity. Inside, it is filled with a small amount of serous fluid, which acts as a shock absorber and greatly facilitates respiratory movements. The mediastinum is located between the right and left lungs. In this relatively small space, the trachea, thoracic lymphatic duct, esophagus, heart and large vessels extending from it adjoin.

Each lung contains bronchial-vascular bundles formed by primary bronchi, nerves and arteries. It is here that the branching of the bronchial tree begins, around the branches of which numerous lymph nodes and vessels are located. The exit of blood vessels from the lung tissue is carried out through 2 veins extending from each lung. Once in the lungs, the bronchi begin to branch depending on the number of lobes: in the right - three bronchial branches, and in the left - two. With each branch, their lumen gradually narrows down to half a millimeter in the smallest bronchioles, of which there are about 25 million in an adult.

However, the path of air does not end at the bronchioles: from here it enters even narrower and more branched alveolar passages, which lead the air to the alveoli - the so-called "destination". It is here that the processes of gas exchange take place through the adjoining walls of the lung sacs and the capillary network. The epithelial walls lining the inner surface of the alveoli produce a surface-active surfactant that prevents them from collapsing. Before birth, a child in the womb does not receive oxygen through the lungs, so the alveoli are in a collapsed state, but during the first breath and cry they straighten out. It depends on the full formation of surfactant, which normally appears in the fetus in the seventh month of intrauterine life. In this state, the alveoli remain throughout life. Even with the most intense exhalation, some of the oxygen will certainly remain inside, so the lungs do not collapse.

Conclusion

Anatomically and physiologically, the human respiratory system is a well-coordinated mechanism that maintains the vital activity of the body. Providing every cell of the human body with the most important substance - oxygen - is the basis of life, the most significant process, without which no person can do. Regular inhalation of polluted air, low level of ecology, smog and dust of city streets have a negative impact on the functions of the respiratory organs, not to mention smoking, which annually kills millions of people around the world. Therefore, carefully monitoring the state of health, it is necessary to take care not only of your own body, but also of the environment, so that in a few years a breath of clean, fresh air will not be the ultimate dream, but the daily norm of life!

The cells of the human body require a constant supply of oxygen to stay alive. The respiratory system provides oxygen to the body's cells while removing carbon dioxide, waste products that can be deadly if accumulated. There are 3 main parts of the respiratory system: the airways, the lungs, and the respiratory muscles. The airways, which include the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles, carry air into and out of the lungs. Lungs… [Read below]

• Upper paths
• lower paths

[Beginning at the top] … act as functional units of the respiratory system, allowing oxygen into the body and removing carbon dioxide from the body. Finally, the breathing muscles, including the diaphragm and intercostal muscles, work together to move air in and out of the lungs during breathing.

The nose and nasal cavity form the main external opening for the respiratory system and the first section of the airway, the body's airways, through which air moves. The nose is a structure of cartilage, bones, muscles, and skin that supports and protects the front of the nasal cavity. The nasal cavity is a hollow space inside the nose and skull, which is covered with hairs and mucous membranes. The function of the nasal cavity is to warm, humidify and filter the air entering the body before it reaches the lungs. The hairs and mucus that line the nasal cavity help trap dust, mold, pollen and other environmental pollutants before they can reach the inside of the body. Air leaving the body through the nose returns moisture and heat to the nasal cavity before it is released into the environment.

Mouth

The mouth, also known as the oral cavity, is the secondary external airway opening. Most normal breathing occurs through the nasal cavity, but the oral cavity can be used to supplement or replace the functions of the nasal cavity when needed. Since the path of air entering the body from the mouth is shorter than the path for air entering the body from the nose, the mouth does not warm or humidify the air entering the lungs. The mouth also lacks hair and sticky mucus to filter the air. One of the advantages of mouth breathing is that the shorter distance and larger diameter allows more air to enter the body quickly.

Pharynx
The pharynx, also known as the throat, is a muscular funnel that extends from the posterior end of the nasal cavity to the upper end of the esophagus and larynx. The pharynx is divided into 3 regions: nasopharynx, oropharynx, and hypopharynx. The nasopharynx is the highest region of the pharynx, located at the back of the nasal cavity. Inhaled air from the nasal cavity passes into the nasopharynx and descends through the oropharynx, located at the back of the mouth. Air is inhaled through the mouth and enters the throat. Then, the inhaled air descends into the hypopharynx, where it will be redirected to the orifice of the larynx by the epiglottis. The epiglottis is a flap of elastic cartilage that acts as a switch between the trachea and the esophagus. Since the larynx is also used to swallow food, the epiglottis ensures that air passes into the trachea, closing the opening to the esophagus. During the swallowing process, the epiglottis moves to cover the trachea in order for food to enter the esophagus and prevent choking.
Larynx
The larynx, also known as the vocal cords, is a short section of the airway that connects the hypopharynx and trachea. The larynx is located in front of the neck, slightly inferior to the hyoid bone and superior to the trachea. Several cartilaginous structures make up the larynx. The epiglottis is one of the cartilaginous pieces in the larynx and serves as the lid of the larynx when swallowing. Inferior to the epiglottis is the thyroid cartilage, often referred to as the Adam's apple, and is most often enlarged and visible in adult males. The thyroid cartilage keeps the anterior end of the larynx open and protects the vocal cords. Below the thyroid cartilage is the annular cricoid cartilage, which holds the larynx open and supports its posterior end. In addition to cartilage, the larynx contains special structures known as vocal folds that allow the body to produce the sounds of speech and singing. The vocal cords are folds of mucous membrane that vibrate to create vocal sounds. The tension and vibration of the vocal folds can be changed to change the pitch of the vibrations that they produce.

Trachea

The trachea, or windpipe, is a 12-cm tube made of C-shaped hyaline cartilage rings, with multi-row ciliated columnar epithelium. The trachea connects the larynx to the bronchi and allows air to pass through the neck into the chest. The rings of cartilage that make up the trachea allow it to remain open to air at all times. The open end of the cartilage rings, facing posteriorly to the esophagus, allows the esophagus to expand in the space occupied by the trachea to allow the mass of food to move through the esophagus.

The main function of the trachea is to provide a clear airway for air to enter and exit the lungs. In addition, the epithelium lining the trachea produces mucus, which has accumulated dust and other contaminants and prevents it from entering the lungs. Cilia on the surface of the epithelial cells move the mucus directly to the pharynx, where it can be swallowed and digested in the gastrointestinal tract.

Bronchi and bronchioles
At the lower end of the trachea, the airways split into left and right branches, known as the primary bronchi. The left and right bronchi go to each lung, followed by smaller outgoing bronchi - secondary. Secondary bronchi carry air to the lobes of the lungs - 2 in the left lung and 3 in the right lung. The secondary bronchi in turn divide into many smaller tertiary bronchi within each lobe. The tertiary bronchi break up into many small bronchioles that spread over the entire surface of the lungs. Each bronchiole further splits into many smaller branches less than a millimeter in diameter, called terminal bronchioles. Finally, millions of tiny terminal bronchioles carry air into the alveoli of the lungs.

As it splits into treelike branches of the bronchi and bronchioles in the airways, the structure of the walls of the airways begins to change. The primary bronchi contain many C-shaped cartilage rings that hold the airways firmly open and give the bronchi a flattened circle or D shape. Where the bronchi branch into secondary and tertiary bronchi, the cartilage becomes more widely spaced and covered with smoother muscle containing the protein elastin. Bronchioles differ from the structure of the bronchi in that they do not contain any cartilage at all. The presence of smooth and elastic muscles allows the smaller bronchi and bronchioles to be more flexible and plastic.

The main function of the bronchi and bronchioles is to carry air from the trachea to the lungs. The smooth muscle tissue in their walls helps regulate the flow of air into the lungs. When large volumes of air are required by the body, such as during exercise, smooth muscle relaxes to dilate the bronchi and bronchioles. Dilated airways provide less resistance to airflow and allow more air to pass in and out of the lungs. Smooth muscle fibers are able to contract during rest to prevent hyperventilation. The bronchi and bronchioles also use the mucus and cilia of their epithelial lining to trap and move dust and other contaminants out of the lungs.

Lungs

The lungs are a pair of large, friable organs located in the chest on the side of the heart and superior to the diaphragm. Each lung is surrounded by a pleural membrane that provides room for expansion and also serves to create a negative pressure relative to atmospheric pressure. Negative pressure allows the lungs to passively fill with air while they relax. The left and right lungs are slightly different in size and shape due to the heart being on the left side of the body. Thus, the left lung is slightly smaller than the right and consists of 2 lobes, while the right lung has 3 lobes.

The inside of the lungs is made up of spongy tissue containing many capillaries and about 30 million tiny sacs known as alveoli. Alveoli are cup-shaped structures located at the terminal end of the bronchioles and surrounded by capillaries. The alveoli are lined with a thin layer of squamous epithelium, which allows air to enter the alveoli and exchange its gases as the blood passes through the capillaries.

Breathing muscles

A set of muscles surrounding the lungs that are able to suck in air for inhalation or exhale it from the lungs. The main respiratory muscle in the human body is the diaphragm, a thin sheet of skeletal muscle. When the diaphragm contracts, it moves down a few centimeters into the abdominal cavity, increasing the space inside the chest cavity and allowing air to pass into the lungs. Relaxation of the diaphragm allows air to flow back into the lungs during exhalation.

Between the ribs are many intercostal muscles that help the diaphragm with the expansion and contraction of the lungs. These muscles are divided into two groups: internal intercostal and external intercostal muscles. The internals are a deeply located set of muscles that depress the ribs to compress the chest cavity and the lungs to expel air from the lungs. The external intercostal muscles are on the surface and function to elevate the ribs, allowing for expansion of the chest cavity and causing air to escape from the lungs.

Pulmonary ventilation

Pulmonary ventilation is the process of moving air in and out of the lungs to facilitate gas exchange. The respiratory system uses a negative pressure system and muscle contraction to achieve pulmonary ventilation. The negative pressure system of the respiratory system involves the creation of a negative pressure gradient between the alveoli and the external atmosphere. The membrane seals the lungs and keeps the pressure slightly lower than in the atmosphere when the lungs are at rest. This leads to passive filling of the lungs at rest. To fill the lungs with air, the pressure in them rises until it matches atmospheric pressure. At this stage, even more air can be inhaled by the contraction of the diaphragm and external intercostal muscles, which increase the volume of the chest and again reduce the pressure in the lungs below that in the atmosphere.
In order to exhale air, the diaphragm and external intercostal muscles relax, while the internal intercostal muscles contract to decrease the volume of the chest and increase pressure within the chest cavity. The pressure gradient at this time is restored, which leads to the exhalation of air until the pressure inside the lungs and outside the body become equal. At this stage, the elasticity property of the lungs causes them to return back to their resting volume, restoring the negative pressure gradient present during inhalation.

external respiration

External respiration - the exchange of gases between the air filling the alveoli and the blood in the capillaries and surrounding the walls of the alveoli. Air entering the lungs from the atmosphere has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than blood has in capillaries. The difference in partial pressures encourages gases to diffuse passively along their high to low pressure gradients through the simple squamous epithelium of the lining of the alveoli. The end result of external respiration is the movement of oxygen from the air into the blood and the movement of carbon dioxide from the blood into the air. Oxygen becomes possible to be transported to the tissues of the body, while carbon dioxide is released into the atmosphere during exhalation.

internal breathing

This is the exchange of gases between the blood in the capillaries and the tissues of the body. Capillary blood has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than the tissues through which it passes. The difference in partial pressures leads to the diffusion of gases along their pressure gradients from high to low pressure through the capillary endothelium. The end result of internal respiration is the diffusion of oxygen into tissues and the diffusion of carbon dioxide into the blood.

Gas transportation
The 2 main respiratory gases, oxygen and carbon dioxide, are transported throughout the body with the help of blood. Blood plasma has the ability to transport dissolved oxygen and carbon dioxide, but most of the gases carried in the blood exist to transport molecules. Hemoglobin is an important transport molecule found in red blood cells, which contain almost 99% of the oxygen in the blood. Hemoglobin can also carry small amounts of carbon dioxide from the tissues back to the lungs. However, the vast majority of carbon dioxide is present in plasma as the bicarbonate ion. When the partial pressure of carbon dioxide is high in tissues, the enzyme carbonic anhydrase catalyzes the reaction between carbon dioxide and water to form carbonic acid. Carbon dioxide then dissociates into hydrogen ions and bicarbonate ions. When the partial pressure of carbon dioxide is low in the lungs, reverse reactions occur and carbon dioxide is released into the lungs to be expelled.

Homeostatic breath control

Under normal resting conditions, the body maintains a calm breathing rate and depth - normal breathing. Normal breathing is maintained until there is an increased demand for oxygen from the body. And the production of carbon dioxide is increased due to the greater load. Autonomic chemoreceptors in the body are able to control the partial pressure of oxygen and CO2 in the blood and send signals to the respiratory center of the brainstem. The respiratory center then regulates the rate and depth of breathing to bring the blood back to its normal gas partial pressure level.

human respiratory system- a set of organs and tissues that provide in the human body the exchange of gases between the blood and the environment.

Function of the respiratory system:

intake of oxygen into the body;

excretion of carbon dioxide from the body;

excretion of gaseous products of metabolism from the body;

thermoregulation;

synthetic: some biologically active substances are synthesized in the tissues of the lungs: heparin, lipids, etc.;

hematopoietic: mast cells and basophils mature in the lungs;

deposition: the capillaries of the lungs can accumulate a large amount of blood;

suction: ether, chloroform, nicotine and many other substances are easily absorbed from the surface of the lungs.

The respiratory system consists of the lungs and airways.

Pulmonary contractions are carried out with the help of the intercostal muscles and the diaphragm.

Respiratory tract: nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles.

The lungs are made up of pulmonary vesicles - alveoli.

Rice. Respiratory system

Airways

nasal cavity

The nasal and pharyngeal cavities are the upper respiratory tract. The nose is formed by a system of cartilage, thanks to which the nasal passages are always open. At the very beginning of the nasal passages there are small hairs that trap large dust particles of inhaled air.

The nasal cavity is lined from the inside with a mucous membrane penetrated by blood vessels. It contains a large number of mucous glands (150 glands/cm2 of mucous membrane). Mucus prevents the growth of microbes. A large number of phagocytes, which destroy the microbial flora, come out of the blood capillaries to the surface of the mucous membrane.

In addition, the mucous membrane can vary significantly in its volume. When the walls of its vessels contract, it contracts, the nasal passages expand, and the person breathes easily and freely.

The mucous membrane of the upper respiratory tract is formed by ciliated epithelium. The movement of the cilia of an individual cell and the entire epithelial layer is strictly coordinated: each previous cilium in the phases of its movement is ahead of the next by a certain period of time, therefore the surface of the epithelium is undulatingly mobile - “flickers”. The movement of the cilia helps keep the airways clear by removing harmful substances.

Rice. 1. Ciliated epithelium of the respiratory system

The olfactory organs are located in the upper part of the nasal cavity.

Function of the nasal passages:

filtration of microorganisms;

dust filtration;

humidification and warming of the inhaled air;

mucus washes away everything filtered into the gastrointestinal tract.

The cavity is divided by the ethmoid bone into two halves. Bone plates divide both halves into narrow, interconnected passages.

Open into the nasal cavity sinuses air bones: maxillary, frontal, etc. These sinuses are called paranasal sinuses. They are lined with a thin mucous membrane containing a small amount of mucous glands. All these partitions and shells, as well as numerous adnexal cavities of the cranial bones, sharply increase the volume and surface of the walls of the nasal cavity.

Paranasal sinuses

Paranasal sinuses (paranasal sinuses)- air cavities in the bones of the skull that communicate with the nasal cavity.

In humans, there are four groups of paranasal sinuses:

maxillary (maxillary) sinus - a paired sinus located in the upper jaw;

frontal sinus - a paired sinus located in the frontal bone;

ethmoid labyrinth - a paired sinus formed by cells of the ethmoid bone;

sphenoid (main) - a paired sinus located in the body of the sphenoid (main) bone.

Rice. 2. Paranasal sinuses: 1 - frontal sinuses; 2 - cells of the lattice labyrinth; 3 - sphenoid sinus; 4 - maxillary (maxillary) sinuses.

The significance of the paranasal sinuses is still not known exactly.

Possible functions of the paranasal sinuses:

reduction in the mass of the anterior facial bones of the skull;

mechanical protection of the head organs during impacts (depreciation);

thermal insulation of the roots of teeth, eyeballs, etc. from temperature fluctuations in the nasal cavity during breathing;

humidification and warming of the inhaled air, due to the slow air flow in the sinuses;

perform the function of a baroreceptor organ (an additional sense organ).

Maxillary sinus (maxillary sinus)- a pair of paranasal sinuses, occupying almost the entire body of the maxillary bone. From the inside, the sinus is lined with a thin mucous membrane of ciliated epithelium. There are very few glandular (goblet) cells, vessels and nerves in the sinus mucosa.

The maxillary sinus communicates with the nasal cavity through openings on the inner surface of the maxillary bone. Normally, the sinus is filled with air.

The lower part of the pharynx passes into two tubes: the respiratory (in front) and the esophagus (behind). Thus, the pharynx is a common department for the digestive and respiratory systems.

Larynx

The upper part of the respiratory tube is the larynx, located in front of the neck. Most of the larynx is also lined with a mucous membrane of ciliated (ciliary) epithelium.

The larynx consists of movably interconnected cartilages: cricoid, thyroid (forms Adam's apple, or Adam's apple) and two arytenoid cartilages.

Epiglottis covers the entrance to the larynx at the time of swallowing food. The anterior end of the epiglottis is connected to the thyroid cartilage.

Rice. Larynx

The cartilages of the larynx are interconnected by joints, and the spaces between the cartilages are covered with connective tissue membranes.

When pronouncing a sound, the vocal cords come together until they touch. With a current of compressed air from the lungs, pressing on them from below, they move apart for a moment, after which, due to their elasticity, they close again until the pressure of air opens them again.

The vibrations of the vocal cords that arise in this way give the sound of the voice. The pitch of the sound is regulated by the tension of the vocal cords. The shades of the voice depend both on the length and thickness of the vocal cords, and on the structure of the oral cavity and nasal cavity, which play the role of resonators.

The thyroid gland is attached to the outside of the larynx.

Anteriorly, the larynx is protected by the anterior muscles of the neck.

Trachea and bronchi

The trachea is a breathing tube about 12 cm long.

It is made up of 16-20 cartilaginous semirings that do not close behind; half rings prevent the trachea from collapsing during exhalation.

The back of the trachea and the spaces between the cartilaginous half-rings are covered with a connective tissue membrane. Behind the trachea lies the esophagus, the wall of which, during the passage of the food bolus, protrudes slightly into its lumen.

Rice. Cross section of the trachea: 1 - ciliated epithelium; 2 - own layer of the mucous membrane; 3 - cartilaginous half ring; 4 - connective tissue membrane

At the level of IV-V thoracic vertebrae, the trachea is divided into two large primary bronchus going to the right and left lungs. This place of division is called a bifurcation (branching).

The aortic arch bends through the left bronchus, and the right bronchus bends around the unpaired vein going from behind to the front. In the words of old anatomists, "the arch of the aorta sits astride the left bronchus, and the unpaired vein - on the right."

Cartilaginous rings located in the walls of the trachea and bronchi make these tubes elastic and non-collapsing, so that air passes through them easily and unhindered. The inner surface of the entire respiratory tract (trachea, bronchi and parts of the bronchioles) is covered with a mucous membrane of multi-row ciliated epithelium.

The device of the respiratory tract provides warming, moistening and purification of the air coming with inhalation. Dust particles move upward with ciliated epithelium and are removed outside with coughing and sneezing. Microbes are rendered harmless by mucosal lymphocytes.

Lungs

The lungs (right and left) are located in the chest cavity under the protection of the chest.

Pleura

Lungs covered pleura.

Pleura- thin, smooth and moist, rich in elastic fibers, the serous membrane that covers each of the lungs.

Distinguish pulmonary pleura, tightly fused with lung tissue, and parietal pleura lining the inside of the chest wall.

At the roots of the lungs, the pulmonary pleura passes into the parietal. Thus, a hermetically closed pleural cavity is formed around each lung, representing a narrow gap between the pulmonary and parietal pleura. The pleural cavity is filled with a small amount of serous fluid, which acts as a lubricant that facilitates the respiratory movements of the lungs.

Rice. Pleura

Mediastinum

The mediastinum is the space between the right and left pleural sacs. It is bounded in front by the sternum with costal cartilages, and in the back by the spine.

In the mediastinum is the heart with large vessels, trachea, esophagus, thymus gland, nerves of the diaphragm and thoracic lymphatic duct.

bronchial tree

The right lung is divided by deep furrows into three lobes, and the left into two. The left lung, on the side facing the midline, has a recess with which it is adjacent to the heart.

Thick bundles consisting of the primary bronchus, pulmonary artery and nerves enter each lung from the inside, and two pulmonary veins and lymphatic vessels exit each. All these bronchial-vascular bundles, taken together, form lung root. A large number of bronchial lymph nodes are located around the pulmonary roots.

Entering the lungs, the left bronchus is divided into two, and the right - into three branches according to the number of pulmonary lobes. In the lungs, the bronchi form the so-called bronchial tree. With each new "branch", the diameter of the bronchi decreases until they become completely microscopic bronchioles with a diameter of 0.5 mm. In the soft walls of the bronchioles there are smooth muscle fibers and no cartilaginous semirings. There are up to 25 million such bronchioles.

Rice. bronchial tree

Bronchioles pass into branched alveolar ducts, which end in lung sacs, the walls of which are strewn with swellings - pulmonary alveoli. The walls of the alveoli are permeated with a network of capillaries: gas exchange occurs in them.

The alveolar ducts and alveoli are entwined with many elastic connective tissue and elastic fibers, which also form the basis of the smallest bronchi and bronchioles, due to which the lung tissue easily stretches during inhalation and collapses again during exhalation.

Alveoli

Alveoli are formed by a network of the finest elastic fibers. The inner surface of the alveoli is lined with a single layer of squamous epithelium. The walls of the epithelium produce surfactant- a surfactant that lines the inside of the alveoli and prevents them from collapsing.

Under the epithelium of the pulmonary vesicles lies a dense network of capillaries, into which the terminal branches of the pulmonary artery break. Through the adjoining walls of the alveoli and capillaries, gas exchange occurs during respiration. Once in the blood, oxygen binds to hemoglobin and spreads throughout the body, supplying cells and tissues.

Rice. Alveoli

Rice. Gas exchange in the alveoli

Before birth, the fetus does not breathe through the lungs and the pulmonary vesicles are in a collapsed state; after birth, with the first breath, the alveoli swell and remain straightened for life, retaining a certain amount of air even with the deepest exhalation.

Gas exchange area

The completeness of gas exchange is ensured by the huge surface through which it occurs. Each pulmonary vesicle is an elastic sac 0.25 mm in size. The number of pulmonary vesicles in both lungs reaches 350 million. If we imagine that all pulmonary alveoli are stretched and form one bubble with a smooth surface, then the diameter of this bubble will be 6 m, its capacity will be more than 50 m3, and the inner surface will be 113 m2 and, thus Thus, it will be approximately 56 times larger than the entire skin surface of the human body.

The trachea and bronchi do not participate in respiratory gas exchange, but are only airways.

Physiology of respiration

All life processes proceed with the obligatory participation of oxygen, that is, they are aerobic. Particularly sensitive to oxygen deficiency is the central nervous system and, above all, cortical neurons, which die earlier than others in oxygen-free conditions. As you know, the period of clinical death should not exceed five minutes. Otherwise, irreversible processes develop in the neurons of the cerebral cortex.

Breath- the physiological process of gas exchange in the lungs and tissues.

The whole breathing process can be divided into three main stages:

pulmonary (external) breathing: gas exchange in the capillaries of the pulmonary vesicles;

transport of gases by blood;

cellular (tissue) respiration: gas exchange in cells (enzymatic oxidation of nutrients in mitochondria).

Rice. Lung and tissue respiration

Red blood cells contain hemoglobin, a complex iron-containing protein. This protein is able to attach oxygen and carbon dioxide to itself.

Passing through the capillaries of the lungs, hemoglobin attaches 4 oxygen atoms to itself, turning into oxyhemoglobin. Red blood cells transport oxygen from the lungs to the tissues of the body. In the tissues, oxygen is released (oxyhemoglobin is converted to hemoglobin) and carbon dioxide is added (hemoglobin is converted to carbohemoglobin). The red blood cells then transport carbon dioxide to the lungs for removal from the body.

Rice. Transport function of hemoglobin

The hemoglobin molecule forms a stable compound with carbon monoxide II (carbon monoxide). Carbon monoxide poisoning leads to the death of the body due to oxygen deficiency.

Mechanism of inhalation and exhalation

inhale- is an active act, as it is carried out with the help of specialized respiratory muscles.

The respiratory muscles include the intercostal muscles and the diaphragm. Deep inhalation uses the muscles of the neck, chest and abs.

The lungs themselves do not have muscles. They are unable to expand and contract on their own. The lungs only follow the ribcage, which expands thanks to the diaphragm and intercostal muscles.

The diaphragm during inspiration drops by 3-4 cm, as a result of which the volume of the chest increases by 1000-1200 ml. In addition, the diaphragm pushes the lower ribs to the periphery, which also leads to an increase in the capacity of the chest. Moreover, the stronger the contraction of the diaphragm, the more the volume of the chest cavity increases.

The intercostal muscles, contracting, raise the ribs, which also causes an increase in the volume of the chest.

The lungs, following the stretching of the chest, stretch themselves, and the pressure in them drops. As a result, a difference is created between the pressure of atmospheric air and the pressure in the lungs, air rushes into them - inspiration occurs.

Exhalation, unlike inhalation, is a passive act, since muscles do not take part in its implementation. When the intercostal muscles relax, the ribs descend under the action of gravity; the diaphragm, relaxing, rises, taking its usual position - the volume of the chest cavity decreases - the lungs contract. There is an exhalation.

The lungs are located in a hermetically sealed cavity formed by the pulmonary and parietal pleura. In the pleural cavity, the pressure is below atmospheric ("negative"). Due to the negative pressure, the pulmonary pleura is tightly pressed against the parietal one.

A decrease in pressure in the pleural space is the main reason for the increase in lung volume during inspiration, that is, it is the force that stretches the lungs. So, during an increase in the volume of the chest, the pressure in the interpleural formation decreases and, due to the pressure difference, air actively enters the lungs and increases their volume.

During exhalation, the pressure in the pleural cavity increases, and, due to the pressure difference, the air comes out, the lungs collapse.

chest breathing carried out mainly by the external intercostal muscles.

abdominal breathing carried out by the diaphragm.

In men, the abdominal type of breathing is noted, and in women - chest. However, regardless of this, both men and women breathe rhythmically. From the first hour of life, the rhythm of breathing is not disturbed, only its frequency changes.

A newborn baby breathes 60 times per minute, in an adult, the respiratory rate at rest is about 16 - 18. However, during physical exertion, emotional arousal or with an increase in body temperature, the respiratory rate can increase significantly.

Vital capacity of the lungs

Vital capacity of the lungs (VC) is the maximum amount of air that can enter and exit the lungs during maximum inhalation and exhalation.

The vital capacity of the lungs is determined by the device spirometer.

In an adult healthy person, VC varies from 3500 to 7000 ml and depends on gender and on indicators of physical development: for example, chest volume.

ZhEL consists of several volumes:

Tidal volume (TO)- this is the amount of air that enters and exits the lungs during quiet breathing (500-600 ml).

Inspiratory reserve volume (IRV)) is the maximum amount of air that can enter the lungs after a quiet breath (1500 - 2500 ml).

Expiratory reserve volume (ERV)- this is the maximum amount of air that can be removed from the lungs after a quiet exhalation (1000 - 1500 ml).

Breathing regulation

Respiration is regulated by nervous and humoral mechanisms, which are reduced to ensuring the rhythmic activity of the respiratory system (inhalation, exhalation) and adaptive respiratory reflexes, that is, a change in the frequency and depth of respiratory movements that occur under changing environmental conditions or the internal environment of the body.

The leading respiratory center, as established by N. A. Mislavsky in 1885, is the respiratory center located in the medulla oblongata.

Respiratory centers are found in the hypothalamus. They take part in the organization of more complex adaptive respiratory reflexes, which are necessary when the conditions of the organism's existence change. In addition, the respiratory centers are also located in the cerebral cortex, carrying out the highest forms of adaptive processes. The presence of respiratory centers in the cerebral cortex is proved by the formation of conditioned respiratory reflexes, changes in the frequency and depth of respiratory movements that occur during various emotional states, as well as voluntary changes in breathing.

The autonomic nervous system innervates the walls of the bronchi. Their smooth muscles are supplied with centrifugal fibers of the vagus and sympathetic nerves. The vagus nerves cause contraction of the bronchial muscles and constriction of the bronchi, while the sympathetic nerves relax the bronchial muscles and dilate the bronchi.

Humoral regulation: inhalation is carried out reflexively in response to an increase in the concentration of carbon dioxide in the blood.

Breathing called a set of physiological and physico-chemical processes that ensure the consumption of oxygen by the body, the formation and removal of carbon dioxide, and the production of energy used for life due to the aerobic oxidation of organic substances.

Breathing is carried out respiratory system, represented by the respiratory tract, lungs, respiratory muscles, controlling the functions of nervous structures, as well as blood and the cardiovascular system that transport oxygen and carbon dioxide.

Airways subdivided into upper (nasal cavities, nasopharynx, oropharynx) and lower (larynx, trachea, extra- and intrapulmonary bronchi).

To maintain the vital activity of an adult, the respiratory system must deliver about 250-280 ml of oxygen per minute to the body under conditions of relative rest and remove approximately the same amount of carbon dioxide from the body.

Through the respiratory system, the body is constantly in contact with atmospheric air - the external environment, which may contain microorganisms, viruses, harmful substances of a chemical nature. All of them are able to enter the lungs by airborne droplets, penetrate the air-blood barrier into the human body and cause the development of many diseases. Some of them are rapidly spreading - epidemic (influenza, acute respiratory viral infections, tuberculosis, etc.).

Rice. Diagram of the respiratory tract

A great threat to human health is the pollution of atmospheric air with chemicals of technogenic origin (harmful industries, vehicles).

Knowledge of these ways of influencing human health contributes to the adoption of legislative, anti-epidemic and other measures to protect against the action of harmful atmospheric factors and prevent its pollution. This is possible if medical workers carry out extensive explanatory work among the population, including the development of a number of simple rules of conduct. Among them are the prevention of environmental pollution, the observance of elementary rules of behavior during infections, which must be instilled from early childhood.

A number of problems in the physiology of respiration are associated with specific types of human activity: space and high-altitude flights, staying in the mountains, scuba diving, using pressure chambers, staying in an atmosphere containing toxic substances and an excessive amount of dust particles.

Respiratory functions

One of the most important functions of the respiratory tract is to ensure that air from the atmosphere enters the alveoli and is removed from the lungs. The air in the respiratory tract is conditioned, undergoing purification, warming and humidification.

Air purification. From dust particles, the air is especially actively cleansed in the upper respiratory tract. Up to 90% of dust particles contained in the inhaled air settle on their mucous membrane. The smaller the particle, the more likely it is to enter the lower respiratory tract. So, bronchioles can reach particles with a diameter of 3-10 microns, and alveoli - 1-3 microns. Removal of settled dust particles is carried out due to the flow of mucus in the respiratory tract. The mucus covering the epithelium is formed from the secretion of goblet cells and mucus-forming glands of the respiratory tract, as well as fluid filtered from the interstitium and blood capillaries of the walls of the bronchi and lungs.

The thickness of the mucus layer is 5-7 microns. Its movement is created due to the beating (3-14 movements per second) of the cilia of the ciliated epithelium, which covers all the airways with the exception of the epiglottis and true vocal cords. The effectiveness of the cilia is achieved only with their synchronous beating. This wave-like movement will create a current of mucus in the direction from the bronchi to the larynx. From the nasal cavities, mucus moves towards the nasal openings, and from the nasopharynx - towards the pharynx. In a healthy person, about 100 ml of mucus is formed per day in the lower respiratory tract (part of it is absorbed by epithelial cells) and 100-500 ml in the upper respiratory tract. With synchronous beating of cilia, the speed of mucus movement in the trachea can reach 20 mm / min, and in small bronchi and bronchioles it is 0.5-1.0 mm / min. Particles weighing up to 12 mg can be transported with a layer of mucus. The mechanism for expelling mucus from the respiratory tract is sometimes called mucociliary escalator(from lat. mucus- slime, ciliare- eyelash).

The volume of mucus expelled (clearance) depends on the rate of its formation, the viscosity and efficiency of the cilia. The beating of the cilia of the ciliated epithelium occurs only with sufficient formation of ATP in it and depends on the temperature and pH of the environment, humidity and ionization of the inhaled air. Many factors can limit mucus clearance.

So. with a congenital disease - cystic fibrosis, caused by a mutation of a gene that controls the synthesis and structure of a protein involved in the transport of mineral ions through the cell membranes of the secretory epithelium, an increase in the viscosity of mucus and the difficulty of its evacuation from the respiratory tract by cilia develop. Fibroblasts in the lungs of patients with cystic fibrosis produce ciliary factor, which disrupts the functioning of the cilia of the epithelium. This leads to impaired ventilation of the lungs, damage and infection of the bronchi. Similar changes in secretion can occur in the gastrointestinal tract, pancreas. Children with cystic fibrosis need constant intensive medical care. Violation of the processes of beating cilia, damage to the epithelium of the respiratory tract and lungs, followed by the development of a number of other adverse changes in the broncho-pulmonary system, is observed under the influence of smoking.

Air warming. This process occurs due to the contact of the inhaled air with the warm surface of the respiratory tract. The efficiency of warming is such that even when a person inhales frosty atmospheric air, it heats up when it enters the alveoli to a temperature of about 37 ° C. The air removed from the lungs gives up to 30% of its heat to the mucous membranes of the upper respiratory tract.

Air humidification. Passing through the respiratory tract and alveoli, the air is 100% saturated with water vapor. As a result, the pressure of water vapor in the alveolar air is about 47 mm Hg. Art.

Due to the mixing of atmospheric and exhaled air, which has a different content of oxygen and carbon dioxide, a “buffer space” is created in the respiratory tract between the atmosphere and the gas exchange surface of the lungs. It contributes to maintaining the relative constancy of the composition of the alveolar air, which differs from the atmospheric one by a lower content of oxygen and a higher content of carbon dioxide.

The airways are reflexogenic zones of numerous reflexes that play a role in the self-regulation of breathing: the Hering-Breuer reflex, protective reflexes of sneezing, coughing, the "diver" reflex, and also affecting the work of many internal organs (heart, blood vessels, intestines). The mechanisms of a number of these reflections will be considered below.

The respiratory tract is involved in the generation of sounds and giving them a certain color. Sound is produced when air passes through the glottis, causing the vocal cords to vibrate. For vibration to occur, there must be an air pressure gradient between the outer and inner sides of the vocal cords. Under natural conditions, such a gradient is created during exhalation, when the vocal cords close when talking or singing, and the subglottic air pressure, due to the action of factors that ensure exhalation, becomes greater than atmospheric pressure. Under the influence of this pressure, the vocal cords move for a moment, a gap is formed between them, through which about 2 ml of air breaks through, then the cords close again and the process repeats again, i.e. the vocal cords vibrate, generating sound waves. These waves create the tonal basis for the formation of the sounds of singing and speech.

The use of breath to form speech and singing are called respectively speech and singing breath. The presence and normal position of the teeth are a necessary condition for the correct and clear pronunciation of speech sounds. Otherwise, fuzziness, lisp, and sometimes the impossibility of pronouncing individual sounds appear. Speech and singing breathing constitute a separate subject of research.

About 500 ml of water evaporates through the respiratory tract and lungs per day and thus they participate in the regulation of the water-salt balance and body temperature. The evaporation of 1 g of water consumes 0.58 kcal of heat and this is one of the ways in which the respiratory system participates in heat transfer mechanisms. Under conditions of rest, due to evaporation through the respiratory tract, up to 25% of water and about 15% of the produced heat are excreted from the body per day.

The protective function of the respiratory tract is realized through a combination of air conditioning mechanisms, the implementation of protective reflex reactions and the presence of an epithelial lining covered with mucus. Mucus and ciliated epithelium with secretory, neuroendocrine, receptor, and lymphoid cells included in its layer create the morphofunctional basis of the airway barrier of the respiratory tract. This barrier, due to the presence of lysozyme, interferon, some immunoglobulins and leukocyte antibodies in the mucus, is part of the local immune system of the respiratory system.

The length of the trachea is 9-11 cm, the inner diameter is 15-22 mm. The trachea branches into two main bronchi. The right one is wider (12-22 mm) and shorter than the left one, and departs from the trachea at a large angle (from 15 to 40°). The bronchi branch, as a rule, dichotomously, and their diameter gradually decreases, while the total lumen increases. As a result of the 16th branching of the bronchi, terminal bronchioles are formed, the diameter of which is 0.5-0.6 mm. The following are the structures that form the morphofunctional gas exchange unit of the lung - acinus. The capacity of the airways to the level of the acini is 140-260 ml.

The walls of the small bronchi and bronchioles contain smooth myocytes, which are located in them circularly. The lumen of this part of the respiratory tract and the air flow rate depend on the degree of tonic contraction of myocytes. The regulation of the air flow rate through the respiratory tract is carried out mainly in their lower sections, where the lumen of the tracts can change actively. Myocyte tone is controlled by neurotransmitters of the autonomic nervous system, leukotrienes, prostaglandins, cytokines, and other signaling molecules.

Airway and lung receptors

An important role in the regulation of respiration is played by receptors, which are especially abundantly supplied to the upper respiratory tract and lungs. In the mucous membrane of the upper nasal passages between the epithelial and supporting cells are located olfactory receptors. They are sensitive nerve cells with mobile cilia that provide the reception of odorous substances. Thanks to these receptors and the olfactory system, the body is able to perceive the smells of substances contained in the environment, the presence of nutrients, harmful agents. Exposure to some odorous substances causes a reflex change in airway patency and, in particular, in people with obstructive bronchitis, can cause an asthmatic attack.

The remaining receptors of the respiratory tract and lungs are divided into three groups:

• stretching;
• irritant;
• juxtaalveolar.

stretch receptors located in the muscular layer of the respiratory tract. An adequate irritant for them is the stretching of muscle fibers, due to changes in intrapleural pressure and pressure in the airway lumen. The most important function of these receptors is to control the degree of stretching of the lungs. Thanks to them, the functional respiratory control system controls the intensity of lung ventilation.

There is also a number of experimental data on the presence in the lungs of receptors for the decline, which are activated with a strong decrease in lung volume.

Irritant receptors possess the properties of mechano- and chemoreceptors. They are located in the mucous membrane of the respiratory tract and are activated by the action of an intense air stream during inhalation or exhalation, the action of large dust particles, the accumulation of purulent discharge, mucus, and food particles entering the respiratory tract. These receptors are also sensitive to the action of irritating gases (ammonia, sulfur vapors) and other chemicals.

Juxtaalveolar receptors located in the ingerstitial space of the pulmonary alveoli near the walls of the blood capillaries. An adequate irritant for them is an increase in blood filling of the lungs and an increase in the volume of intercellular fluid (they are activated, in particular, with pulmonary edema). Irritation of these receptors reflexively causes the occurrence of frequent shallow breathing.

Reflex reactions from respiratory tract receptors

When stretch receptors and irritant receptors are activated, numerous reflex reactions occur that provide self-regulation of breathing, protective reflexes and reflexes that affect the functions of internal organs. Such a division of these reflexes is very arbitrary, since the same stimulus, depending on its strength, can either provide regulation of the change in the phases of the calm breathing cycle, or cause a defensive reaction. The afferent and efferent pathways of these reflexes run in the trunks of the olfactory, trigeminal, facial, glossopharyngeal, vagus, and sympathetic nerves, and most of the reflex arcs are closed in the structures of the respiratory center of the medulla oblongata with the nuclei of the above nerves connected.

Reflexes of self-regulation of breathing provide regulation of the depth and frequency of breathing, as well as the lumen of the airways. Among them are Hering-Breuer reflexes. Inspiratory inhibitory Hering-Breuer reflex It is manifested by the fact that when the lungs are stretched during a deep breath or when air is blown in by artificial respiration apparatus, the inhalation is reflexively inhibited and the exhalation is stimulated. With a strong stretching of the lungs, this reflex acquires a protective role, protecting the lungs from overstretching. The second of this series of reflexes - expiratory-relief reflex - manifests itself in conditions when air enters the respiratory tract under pressure during exhalation (for example, with artificial respiration). In response to such an impact, exhalation is reflexively prolonged and the appearance of inspiration is inhibited. reflex to lung collapse occurs with the deepest exhalation or with chest injuries accompanied by pneumothorax. It is manifested by frequent shallow breathing, preventing further collapse of the lungs. Allocate also paradoxical head reflex manifested by the fact that with intensive blowing of air into the lungs for a short time (0.1-0.2 s), inhalation can be activated, followed by exhalation.

Among the reflexes that regulate the lumen of the airways and the force of contraction of the respiratory muscles, there are upper airway pressure reflex, which is manifested by muscle contraction that expands these airways and prevents them from closing. In response to a decrease in pressure in the nasal passages and pharynx, the muscles of the wings of the nose, the geniolingual and other muscles that shift the tongue ventrally anteriorly contract reflexively. This reflex promotes inhalation by reducing resistance and increasing upper airway patency for air.

A decrease in air pressure in the lumen of the pharynx also reflexively causes a decrease in the force of contraction of the diaphragm. This pharyngeal diaphragmatic reflex prevents a further decrease in pressure in the pharynx, adhesion of its walls and the development of apnea.

Glottis closure reflex occurs in response to irritation of the mechanoreceptors of the pharynx, larynx and root of the tongue. This closes the vocal and epiglottal cords and prevents the inhalation of food, liquids and irritating gases. In unconscious or anesthetized patients, the reflex closure of the glottis is impaired and vomit and pharyngeal contents may enter the trachea and cause aspiration pneumonia.

Rhinobronchial reflexes occur when irritant receptors of the nasal passages and nasopharynx are irritated and are manifested by a narrowing of the lumen of the lower respiratory tract. In people prone to spasms of the smooth muscle fibers of the trachea and bronchi, irritation of irritant receptors in the nose and even some odors can provoke the development of an asthma attack.

The classic protective reflexes of the respiratory system also include cough, sneeze and diving reflexes. cough reflex caused by irritation of irritant receptors of the pharynx and underlying airways, especially the area of ​​the tracheal bifurcation. When it is implemented, a short breath first occurs, then the closing of the vocal cords, contraction of the expiratory muscles, and an increase in the subglottic air pressure. Then the vocal cords instantly relax and the air stream passes through the airways, glottis and open mouth into the atmosphere at a high linear speed. At the same time, excess mucus, purulent contents, some products of inflammation, or accidentally ingested food and other particles are expelled from the respiratory tract. A productive, "wet" cough helps clear the bronchi and performs a drainage function. To more effectively cleanse the respiratory tract, doctors prescribe special drugs that stimulate the production of liquid discharge. sneeze reflex occurs when the receptors of the nasal passages are irritated and develops like a cough reflex, except that the expulsion of air occurs through the nasal passages. At the same time, tear formation increases, the lacrimal fluid enters the nasal cavity through the lacrimal-nasal canal and moisturizes its walls. All this contributes to the cleansing of the nasopharynx and nasal passages. diver's reflex caused by the ingress of fluid into the nasal passages and is manifested by a short-term cessation of respiratory movements, preventing the passage of fluid into the underlying respiratory tract.

When working with patients, resuscitators, maxillofacial surgeons, otolaryngologists, dentists and other specialists need to take into account the features of the described reflex reactions that occur in response to irritation of the receptors of the oral cavity, pharynx and upper respiratory tract.