What is the respiratory system responsible for? Structure and functions of the human respiratory system

General characteristics of the respiratory system

The most important indicator of human vitality can be called breath. A person can live without water and food for some time, but life is impossible without air. Breathing is the link between a person and the environment. If air flow is obstructed, then respiratory organs The human body and the heart begin to work at an increased rate to provide the necessary amount of oxygen for breathing. The respiratory and respiratory system in humans is capable of adapt to environmental conditions.

Scientists have established an interesting fact. The air that enters respiratory system person, conditionally forms two streams, one of which passes into the left side of the nose and penetrates left lung, the second stream penetrates the right side of the nose and supplies right lung.

Studies have also shown that in the artery of the human brain, the air received is also divided into two streams. Process breathing must be correct, which is important for normal life. Therefore, it is necessary to know about the structure of the human respiratory system and respiratory organs.

Breathe-helping machine person includes trachea, lungs, bronchi, lymphatic, and vascular system. They also include the nervous system and respiratory muscles, pleura. The human respiratory system includes the upper and lower respiratory tract. Upper respiratory tract: nose, pharynx, oral cavity. Lower respiratory tract: trachea, larynx and bronchi.

The airways are necessary for the entry and exit of air from the lungs. The most important organ of the entire respiratory system is lungs, between which the heart is located.

Respiratory system

Lungs- main respiratory organs. They are shaped like a cone. The lungs are located in the chest area, located on either side of the heart. The main function of the lungs is gas exchange, which occurs with the help of the alveoli. Blood enters the lungs from the veins thanks to the pulmonary arteries. Air penetrates through the respiratory tract, enriching the respiratory organs with the necessary oxygen. Cells need oxygen in order for the process to take place. regeneration, and the nutrients needed by the body were supplied from the blood. Covering the lungs is the pleura, consisting of two lobes separated by a cavity (pleural cavity).

The lungs include the bronchial tree, which is formed by bifurcation trachea. The bronchi, in turn, are divided into thinner ones, thus forming segmental bronchi. Bronchial tree ends in very small bags. These sacs are many interconnected alveoli. Alveoli provide gas exchange in respiratory system. The bronchi are covered by epithelium, which in its structure resembles cilia. The cilia remove mucus to the pharyngeal area. Promotion is facilitated by coughing. The bronchi have a mucous membrane.

Trachea is a tube connecting the larynx and bronchi. The trachea is approximately 12-15 see The trachea, unlike the lungs, is an unpaired organ. The main function of the trachea is to carry air into and out of the lungs. The trachea is located between the sixth vertebra of the neck and the fifth vertebra of the thoracic region. At the end trachea bifurcates into two bronchi. The bifurcation of the trachea is called bifurcation. At the beginning of the trachea, the thyroid gland adjoins it. At the back of the trachea is the esophagus. The trachea is covered by a mucous membrane, which is the basis, and it is also covered by muscle-cartilaginous tissue with a fibrous structure. The trachea consists of 18-20 rings of cartilage tissue that make the trachea flexible.

Larynx- a respiratory organ connecting the trachea and pharynx. The voice box is located in the larynx. The larynx is located in the area 4-6 vertebrae of the neck and is attached to the hyoid bone with the help of ligaments. The beginning of the larynx is in the pharynx, and the end is a bifurcation into two tracheas. The thyroid, cricoid, and epiglottic cartilages make up the larynx. These are large unpaired cartilages. It is also formed by small paired cartilages: cornicular, wedge-shaped, arytenoid. The connection between the joints is provided by ligaments and joints. Between the cartilages there are membranes that also serve as a connection.

Pharynx is a tube that originates in the nasal cavity. The digestive and respiratory tracts intersect in the pharynx. The pharynx can be called the link between the nasal cavity and the oral cavity, and the pharynx also connects the larynx and esophagus. The pharynx is located between the base of the skull and 5-7 vertebrae of the neck. The nasal cavity is the initial section of the respiratory system. Consists of the external nose and nasal passages. The function of the nasal cavity is to filter the air, as well as cleanse and humidify it. Oral cavity- This is the second way air enters the human respiratory system. The oral cavity has two sections: posterior and anterior. The anterior section is also called the vestibule of the mouth.

(ANATOMY)

The respiratory system combines organs that perform pneumatic (oral cavity, nasopharynx, larynx, trachea, bronchi) and respiratory or gas exchange (lungs) functions.

The main function of the respiratory organs is to ensure gas exchange between air and blood by diffusion of oxygen and carbon dioxide through the walls of the pulmonary alveoli into the blood capillaries. In addition, the respiratory organs are involved in sound production, smell detection, the production of certain hormone-like substances, lipid and water-salt metabolism, and maintaining the body's immunity.

In the airways, the inhaled air is cleansed, moistened, warmed, as well as the perception of smell, temperature and mechanical stimuli.

A characteristic feature of the structure of the respiratory tract is the presence of a cartilaginous base in their walls, as a result of which they do not collapse. The inner surface of the respiratory tract is covered with a mucous membrane, which is lined with ciliated epithelium and contains a significant number of glands that secrete mucus. The cilia of epithelial cells, moving against the wind, remove foreign bodies along with mucus.

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. Breathing ensures gas exchange in the body, which is a necessary part of metabolism. Respiration is based on the oxidation processes of organic substances - carbohydrates, fats and proteins, as a result of which energy is released that ensures the vital functions of the body.

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

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

external respiration,
transfer of gases in the blood and
tissue respiration.

Essence external respiration consists in the exchange of gases between the external environment and the blood, which occurs in special respiratory organs - 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, i.e., through the skin).
The change of air in the lungs is achieved by rhythmic respiratory movements of the chest, carried out by special muscles, resulting in an alternate increase and decrease in the volume of the chest cavity. In humans, when inhaling, the chest cavity increases in three directions: anterior-posterior and lateral - due to the elevation and rotation of the ribs, and vertically - due to the lowering of the thoraco-abdominal barrier (diaphragm).

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

chest,
abdominal and
mixed types of breathing.

When breathing, the lungs passively follow the chest walls, expanding with inhalation and collapsing with exhalation.
The total surface area of the pulmonary alveoli in humans is on average 90 m2. A person (adult) does this at rest. 16-18 respiratory cycles (i.e. inhalations and exhalations) in 1 minute.
With each breath, approximately 500 ml of air enters the lungs, which is called respiratory. At maximum inhalation, a person can inhale about 1500 ml more of the so-called. additional air . If, after a calm exhalation, you make an additional forced exhalation, then another 1500 ml of the so-called. reserve air .
Breathing, supplementary and reserve air add up vital 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, fluctuates depending on the body’s need for oxygen and amounts to 5-9 liters of air per minute in an adult at rest.
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. As the body ages, metabolism decreases and size decreases; ventilation of the lungs. As body temperature rises, the respiratory rate increases slightly and in some diseases reaches 30-40 per minute; at the same time, the depth of breathing decreases.

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

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

Tissue respiration - a complex physiological process manifested in the consumption of oxygen by the cells and tissues of the body and 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 life processes are carried out - continuous renewal, growth and development of tissues, secretion of glands, muscle contraction, etc.

NOSE AND NASAL CAVITY – the initial part of the respiratory tract and the organ of smell.
Nose constructed from paired nasal bones and nasal cartilage, giving it its external shape.
Nasal cavity located in the center of the facial skeleton and represents a bone canal lined with mucous membrane, running from the openings (nostrils) to the choanae, connecting it to the nasopharynx.
The nasal septum divides the nasal cavity into right and left halves.
Characteristic of the nasal cavity are the adnexa sinuses – cavities in adjacent bones (maxillary, frontal, ethmoid), which communicate with the nasal cavity through holes and canals.

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 the 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 external low temperatures. Forced breathing through the mouth (for example, with a deviated nasal septum, with nasal polyps) causes the possibility of respiratory tract infection.

PHARYNX - part of the digestive and respiratory tube located between the nasal and oral cavities above and the larynx and esophagus below.
The pharynx is a tube, the basis of which is the muscle layer. The pharynx is lined with a mucous membrane, and the outside 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 by the choanae; This is the path for air inhaled through the nose to enter the pharynx.

During the act of swallowing, the airways are isolated: the soft palate (velum) 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 upward and anteriorly; thanks to this, the larynx is pulled upward, and the root of the tongue presses the epiglottis, which thus closes the entrance to the larynx, preventing food from entering the respiratory tract.

LARYNX – beginning of the windpipe (trachea), including the voice apparatus. The larynx is located in the neck.
The structure of the larynx is similar to the structure of the 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 the esophagus posteriorly and communicating with the pharynx through an opening called the laryngeal inlet. At the bottom, the larynx becomes the windpipe.
The base of the larynx forms a ring-shaped cricoid cartilage, which connects below with trachea. On the cricoid cartilage, movably connecting to it with a joint, is located the largest cartilage of the larynx - the thyroid cartilage, consisting of two plates that connect in front at an angle, forming 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 2 arytenoid cartilages located symmetrically, each bearing at its apex a small Santorini cartilage. Between each of them and the inner angle of the thyroid cartilage there is tension 2 true vocal cords , limiting the glottis.
The length of the vocal cords in men is 20-24mm, in women – 18-20mm. Short chords give a higher voice than long ones.
When breathing, the vocal cords diverge, and the glottis takes the shape of a triangle, with its apex facing forward.

Windpipe (Trachea) - next to the larynx is the respiratory tract 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 at the back by smooth muscle fibers, as a result of which its posterior wall is soft and flattened. This allows the underlying esophagus to expand as bolus food passes through it during swallowing. Having passed into the chest cavity, the windpipe divides at the level of the 4th thoracic vertebra into 2 bronchi, going to the right and left lungs.

BRONCHI - branches of the windpipe (trachea), through which air enters and exhales from the lungs when 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 basis 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 actual respiratory tissue of the lung is located, formed alveoli.

The walls of the bronchi are formed by cartilaginous rings and smooth muscles. Cartilaginous rings determine the inflexibility of the bronchi, their non-collapse and the 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 equipped with cilia.

LUNGS represent a paired organ. They are enclosed in the chest and located on the sides of the heart.
Each lung has the shape of a cone, the wide base of which faces downwards towards the thoraco-abdominal barrier. (diaphragm), 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 collarbone. The average dimensions of an adult's lung are: 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 lung is 7 cm. The lungs have a fluffy consistency because they are filled with air. From the inner surface, the hilum of the lung contains the bronchus, vessels and nerves.

The bronchus carries air into the lungs, entering through the nasal (oral) cavity, into the larynx and trachea. In the lungs, the bronchus gradually divides into smaller secondary, tertiary, etc. bronchi, forming, as it were, the cartilaginous skeleton of the lung; the final branching of the bronchi is the conducting bronchiole; she aims at the alveolar ducts, 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 ultimately break up into capillaries, covering the alveoli with their network. Back from the alveoli, the capillaries gradually collect into veins, which leave the lungs in the form of pulmonary veins, entering the left side of the heart and carrying oxygenated arterial blood.

Gas exchange between the external environment and the body occurs in the alveoli.
Oxygen-containing air enters the cavity of the alveoli, and blood flows to the walls of the alveoli. When air enters the alveoli, they stretch and, conversely, collapse when air leaves the lung.
Thanks to the thinnest wall of the alveoli, gas exchange easily occurs here - the entry of oxygen into the blood from the inhaled air and the release of carbon dioxide from the blood into it; The blood is cleansed, it becomes arterial and spreads further through the heart to the tissues and organs of the body, where it releases oxygen and receives carbon dioxide.

Each lung is covered with a membrane - pleura, passing from the lungs to the walls of the chest; Thus, the lung is enclosed in a closed pleural sac formed by the parietal layer of the pleura. Between the pulmonary and parietal layers of the 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 layers of the pleura is airless, the expansion of the chest causes negative pressure in the pleural cavity, stretches the lung tissue, which thus sucks through the airways (mouth - trachea - bronchi) atmospheric air entering the alveoli.

Expansion of the chest during inhalation is active and is accomplished with the help of respiratory muscles (intercostal, scalene, abdominal); its collapse during exhalation occurs passively and with the assistance of the elastic forces of the tissue of the lung itself. The pleura allows the lung to slide into the chest cavity during breathing movements.

The human respiratory system is a set of organs necessary for proper breathing and gas exchange. It includes the upper and lower respiratory tracts, between which there is a conventional boundary. The respiratory system functions 24 hours a day, increasing its activity during physical activity, physical or emotional stress.

The purpose of the organs included in the upper respiratory tract

The upper respiratory tract includes several important organs:

Nose, nasal cavity.
Throat.
Larynx.

The upper section of the respiratory system is the first to take part in the processing of inhaled air flows. It is here that the initial purification and warming of the incoming air is carried out. Then there is a further transition to the lower paths to participate in important processes.

Nose and nasal cavity

The human nose consists of a bone that forms its back, lateral wings and a tip, which is based on flexible septal cartilage. The nasal cavity is represented by an air canal that communicates with the external environment through the nostrils, and is connected at the back to the nasopharynx. This section consists of bone and cartilaginous tissue, separated from the oral cavity by the hard and soft palate. The inside of the nasal cavity is covered with mucous membrane.

Proper functioning of the nose is ensured by:

purification of inhaled air from foreign inclusions;
neutralization of pathogenic microorganisms (this occurs due to the presence of a special substance in nasal mucus - lysozyme);
humidification and warming of the air flow.

In addition to breathing, this section of the upper respiratory tract performs the olfactory function and is responsible for the perception of various aromas. This process occurs due to the presence of a special olfactory epithelium.

An important function of the nasal cavity is its supporting role in the process of voice resonance.

Nasal breathing ensures disinfection and warming of the air. In the process of mouth breathing, such processes are absent, which, in turn, leads to the development of bronchopulmonary pathologies (mainly in children).

Functions of the pharynx

The pharynx is the back of the throat into which the nasal cavity passes. It looks like a funnel-shaped tube 12-14 cm long. The pharynx is formed by 2 types of tissue - muscle and fibrous. It also has a mucous membrane on the inside.

The pharynx consists of 3 sections:

Nasopharynx.
Oropharynx.
Laryngopharynx.

The function of the nasopharynx is to provide movement of air that is inhaled through the nose. This section communicates with the ear canals. It contains adenoids, consisting of lymphoid tissue, which take part in filtering the air from harmful particles and maintaining immunity.

The oropharynx serves as a pathway for air to pass through when breathing through the mouth. This section of the upper respiratory tract is also intended for food intake. The oropharynx contains tonsils, which, together with the adenoids, support the protective function of the body.

Food masses pass through the laryngopharynx and enter the esophagus and stomach. This part of the pharynx begins in the area of 4-5 vertebrae, and gradually passes into the esophagus.

What is the significance of the larynx?

The larynx is an organ of the upper respiratory tract involved in the processes of breathing and voice formation. It is designed like a short pipe and occupies a position opposite the 4-6 cervical vertebrae.

The anterior part of the larynx is formed by the hyoid muscles. In the upper region is the hyoid bone. On the side, the larynx borders the thyroid gland. The skeleton of this organ consists of unpaired and paired cartilages connected by joints, ligaments and muscles.

The human larynx is divided into 3 sections:

The upper one, called the vestibule. This area stretches from the vestibular folds to the epiglottis. Within its boundaries there are folds of the mucous membrane, between them there is a vestibular fissure.
The middle (interventricular section), the narrowest part of which, the glottis, consists of intercartilaginous and membranous tissue.
Lower (subglottic), occupying the area under the glottis. Expanding, this section passes into the trachea.

The larynx consists of several membranes - mucous, fibrocartilaginous and connective tissue, connecting it with other cervical structures.

This body is endowed with 3 main functions:

respiratory - by contracting and expanding, the glottis promotes the correct direction of inhaled air;
protective - the mucous membrane of the larynx includes nerve endings that cause a protective cough if food enters the wrong way;
voicing – timbre and other characteristics of the voice are determined by the individual anatomical structure and the condition of the vocal cords.

The larynx is considered an important organ responsible for the production of speech.

Some disorders in the functioning of the larynx can pose a threat to human health and even life. Such phenomena include laryngospasm - a sharp contraction of the muscles of this organ, leading to complete closure of the glottis and the development of inspiratory dyspnea.

The principle of the structure and operation of the lower respiratory tract

The lower respiratory tract includes the trachea, bronchi and lungs. These organs form the final section of the respiratory system, serve to transport air and carry out gas exchange.

Trachea

The trachea (windpipe) is an important part of the lower respiratory tract, connecting the larynx to the bronchi. This organ is formed by arcuate tracheal cartilages, the number of which in different people ranges from 16 to 20 pieces. The length of the trachea also varies, and can reach 9-15 cm. The place where this organ begins is at the level of the 6th cervical vertebra, near the cricoid cartilage.

The windpipe includes glands, the secretion of which is necessary to destroy harmful microorganisms. In the lower part of the trachea, in the area of the 5th vertebra of the sternum, it is divided into 2 bronchi.

The structure of the trachea contains 4 different layers:

The mucous membrane is in the form of multilayer ciliated epithelium lying on the basement membrane. It consists of stem cells, goblet cells that secrete a small amount of mucus, as well as cellular structures that produce norepinephrine and serotonin.
The submucosal layer has the appearance of loose connective tissue. It contains many small vessels and nerve fibers responsible for blood supply and regulation.
The cartilaginous part, which contains hyaline cartilages, connected to each other by means of annular ligaments. Behind them is a membrane connected to the esophagus (due to its presence, the respiratory process is not disturbed by the passage of food).
The adventitia is a thin connective tissue that covers the outside of the tube.

The main function of the trachea is to conduct air flow to both lungs. The windpipe also plays a protective role - if foreign small structures get into it along with the air, they become enveloped in mucus. Then, with the help of cilia, foreign bodies are pushed into the larynx area and enter the pharynx.

The larynx partially warms the inhaled air and also participates in the process of voice formation (by pushing air currents to the vocal cords).

How the bronchi work

The bronchi are a continuation of the trachea. The right bronchus is considered the main one. It is positioned more vertically and is larger in size and thicker than the left one. The structure of this organ consists of arcuate cartilages.

The area where the main bronchi enter the lungs is called the “hilum”. Next, they branch into smaller structures - bronchioles (in turn, they pass into alveoli - tiny spherical sacs surrounded by vessels). All “branches” of the bronchi, having different diameters, are combined under the term “bronchial tree”.

The walls of the bronchi consist of several layers:

external (adventitia), including connective tissue;
fibrocartilaginous;
submucosal, which is based on loose fibrous tissue.

The inner layer is mucous and includes muscles and columnar epithelium.

The bronchi perform essential functions in the body:

Deliver air masses to the lungs.
They clean, moisturize and warm the air inhaled by a person.
Supports the functioning of the immune system.

This organ largely ensures the formation of the cough reflex, thanks to which small foreign bodies, dust and harmful microbes are removed from the body.

The final organ of the respiratory system is the lungs

A distinctive feature of the structure of the lungs is the paired principle. Each lung includes several lobes, the number of which is unequal (3 in the right and 2 in the left). In addition, they have different shapes and sizes. Thus, the right lung is wider and shorter, while the left, closely adjacent to the heart, is narrower and elongated.

The paired organ completes the respiratory system and is densely penetrated by the “branches” of the bronchial tree. Vital gas exchange processes take place in the alveoli of the lungs. Their essence is the processing of oxygen entering during inhalation into carbon dioxide, which is released into the external environment with exhalation.

In addition to providing breathing, the lungs perform other important functions in the body:

maintain acid-base balance within acceptable limits;
take part in the removal of alcohol vapors, various toxins, ethers;
participate in the elimination of excess liquid, evaporate up to 0.5 liters of water per day;
help complete blood clotting (coagulation);
are involved in the functioning of the immune system.

Doctors state that with age, the functionality of the upper and lower respiratory tract is limited. The gradual aging of the body leads to a decrease in the level of ventilation of the lungs and a decrease in the depth of breathing. The shape of the chest and the degree of its mobility also change.

To avoid early weakening of the respiratory system and prolong its full functions as much as possible, it is recommended to give up smoking, alcohol abuse, a sedentary lifestyle, and carry out timely, high-quality treatment of infectious and viral diseases that affect the upper and lower respiratory tract.

The respiratory system performs the function of gas exchange, but also takes part in such important processes as thermoregulation, air humidification, water-salt exchange and many others. The respiratory organs are represented by the nasal cavity, nasopharynx, oropharynx, larynx, trachea, bronchi, and lungs.

Nasal cavity

It is divided by the cartilaginous septum into two halves - right and left. On the septum there are three nasal conchae, which form the nasal passages: upper, middle and lower. The walls of the nasal cavity are lined with mucous membrane with ciliated epithelium. The cilia of the epithelium, moving sharply and quickly in the direction of the nostrils and smoothly and slowly in the direction of the lungs, trap and remove dust and microorganisms that have settled on the mucus membrane.

The mucous membrane of the nasal cavity is abundantly supplied with blood vessels. The blood flowing through them warms or cools the inhaled air. The glands of the mucous membrane secrete mucus, which moisturizes the walls of the nasal cavity and reduces the activity of bacteria coming from the air. On the surface of the mucous membrane there are always leukocytes that destroy a large number of bacteria. In the mucous membrane of the upper part of the nasal cavity there are the endings of nerve cells that form the organ of smell.

The nasal cavity communicates with cavities located in the bones of the skull: the maxillary, frontal and sphenoid sinuses.

Thus, the air entering the lungs through the nasal cavity is cleaned, warmed and disinfected. This does not happen to it if it enters the body through the oral cavity. From the nasal cavity through the choanae, air enters the nasopharynx, from it into the oropharynx, and then into the larynx.

It is located on the front side of the neck and from the outside its part is visible as an elevation called the Adam's apple. The larynx is not only an air-bearing organ, but also an organ for the formation of voice and sound speech. It is compared to a musical apparatus that combines elements of wind and string instruments. From above, the entrance to the larynx is covered by the epiglottis, which prevents food from entering it.

The walls of the larynx consist of cartilage and are covered on the inside with a mucous membrane with ciliated epithelium, which is absent on the vocal cords and part of the epiglottis. The cartilages of the larynx are represented in the lower section by the cricoid cartilage, in front and on the sides by the thyroid cartilage, on the top by the epiglottis, and in the back by three pairs of small ones. They are semi-movably connected to each other. Muscles and vocal cords are attached to them. The latter consist of flexible, elastic fibers that run parallel to each other.

Between the vocal cords of the right and left halves there is a glottis, the lumen of which varies depending on the degree of tension of the ligaments. It is caused by contractions of special muscles, which are also called vocal muscles. Their rhythmic contractions are accompanied by contractions of the vocal cords. As a result, the stream of air leaving the lungs acquires an oscillatory character. Sounds and voices appear. The shades of the voice depend on the resonators, the role of which is played by the cavities of the respiratory tract, as well as the pharynx and oral cavity.

Anatomy of the trachea

The lower part of the larynx passes into the trachea. The trachea is located in front of the esophagus and is a continuation of the larynx. The length of the trachea is 9-11 cm, diameter is 15-18 mm. At the level of the fifth thoracic vertebra it is divided into two bronchi: right and left.

The tracheal wall consists of 16-20 incomplete cartilaginous rings that prevent narrowing of the lumen, connected by ligaments. They extend 2/3 of a circle. The posterior wall of the trachea is membranous, contains smooth (non-striated) muscle fibers and is adjacent to the esophagus.

Bronchi

From the trachea, air enters the two bronchi. Their walls also consist of cartilaginous half-rings (6-12 pieces). They prevent the walls of the bronchi from collapsing. Together with blood vessels and nerves, the bronchi enter the lungs, where they branch to form the bronchial tree of the lung.

The inside of the trachea and bronchi are lined with mucous membrane. The thinnest bronchi are called bronchioles. They end in alveolar ducts, on the walls of which there are pulmonary vesicles, or alveoli. The diameter of the alveoli is 0.2-0.3 mm.

The alveolar wall consists of one layer of squamous epithelium and a thin layer of elastic fibers. The alveoli are covered with a dense network of blood capillaries in which gas exchange occurs. They form the respiratory part of the lung, and the bronchi form the airway section.

In the lungs of an adult there are about 300-400 million alveoli, their surface is 100-150 m2, i.e. the total respiratory surface of the lungs is 50-75 times greater than the entire surface of the human body.

Lung structure

The lungs are a paired organ. The left and right lungs occupy almost the entire chest cavity. The right lung is larger in volume than the left and consists of three lobes, the left - of two lobes. On the inner surface of the lungs are the hilum of the lungs, through which the bronchi, nerves, pulmonary arteries, pulmonary veins and lymphatic vessels pass.

On the outside, the lungs are covered with a connective tissue membrane - the pleura, which consists of two layers: the inner layer is fused with the air-bearing tissue of the lung, and the outer layer is fused with the walls of the chest cavity. Between the leaves there is a space - the pleural cavity. The contacting surfaces of the inner and outer layers of the pleura are smooth and constantly moistened. Therefore, normally, their friction is not felt during breathing movements. In the pleural cavity the pressure is 6-9 mm Hg. Art. below atmospheric. The smooth, slippery surface of the pleura and the reduced pressure in its cavities favor the movements of the lungs during the acts of inhalation and exhalation.

The main function of the lungs is gas exchange between the external environment and the body.