What kind of epithelium covers the respiratory tract? Organs of the respiratory system
Topic 22. RESPIRATORY SYSTEM
The respiratory system includes various organs that perform air-conducting and respiratory (gas exchange) functions: the nasal cavity, nasopharynx, larynx, trachea, extrapulmonary bronchi and lungs.
The main function of the respiratory system is external respiration, i.e., absorbing oxygen from the inhaled air and supplying it to the blood, as well as removing carbon dioxide from the body (gas exchange is carried out by the lungs, their acini). Internal, tissue respiration occurs in the form of oxidative processes in organ cells with the participation of blood. Along with this, the respiratory organs perform a number of other important non-gas exchange functions: thermoregulation and humidification of inhaled air, cleaning it from dust and microorganisms, depositing blood in a richly developed vascular system, participating in maintaining blood clotting due to the production of thromboplastin and its antagonist (heparin), participating in the synthesis of certain hormones and in water-salt, lipid metabolism, as well as in voice formation, smell and immunological defense.
Development
On the 22nd – 26th day of intrauterine development, a respiratory diverticulum—the rudiment of the respiratory organs—appears on the ventral wall of the foregut. It is separated from the foregut by two longitudinal esophagotracheal (tracheoesophageal) grooves, which protrude into the lumen of the foregut in the form of ridges. These ridges, coming together, merge, and the esophagotracheal septum is formed. As a result, the foregut is divided into a dorsal part (esophagus) and a ventral part (trachea and pulmonary buds). As it separates from the foregut, the respiratory diverticulum, lengthening in the caudal direction, forms a structure lying in the midline - the future trachea; it ends in two sac-like protrusions. These are pulmonary buds, the most distal parts of which constitute the respiratory rudiment. Thus, the epithelium lining the tracheal primordium and pulmonary buds is of endodermal origin. The mucous glands of the airways, which are derivatives of the epithelium, also develop from the endoderm. Cartilage cells, fibroblasts and SMCs are derived from the splanchic mesoderm surrounding the foregut. The right pulmonary kidney is divided into three, and the left - into two main bronchi, predetermining the presence of three lobes of the lung on the right and two on the left. Under the inductive influence of the surrounding mesoderm, branching continues, eventually forming the bronchial tree of the lungs. By the end of the 6th month there are 17 branches. Later, 6 more additional branchings occur, the branching process ends after birth. At birth, the lungs contain about 60 million primary alveoli, their number increases rapidly in the first 2 years of life. Then the growth rate slows down, and by 8–12 years the number of alveoli reaches approximately 375 million, which is equal to the number of alveoli in adults.
Stages of development. Differentiation of the lungs goes through the following stages - glandular, tubular and alveolar.
Glandular stage(5 – 15 weeks) is characterized by further branching of the airways (the lungs take on the appearance of a gland), the development of cartilage of the trachea and bronchi, and the appearance of bronchial arteries. The epithelium lining the respiratory rudiment consists of columnar cells. At the 10th week, goblet cells appear from the columnar epithelial cells of the airways. By the 15th week, the first capillaries of the future respiratory department are formed.
Tubular stage(16 – 25 weeks) is characterized by the appearance of respiratory and terminal bronchioles lined with cubic epithelium, as well as tubules (prototypes of alveolar sacs) and the growth of capillaries to them.
Alveolar(or terminal sac stage (26 – 40 weeks)) is characterized by massive transformation of tubules into sacs (primary alveoli), an increase in the number of alveolar sacs, differentiation of type I and II alveolocytes and the appearance of surfactant. By the end of the 7th month, a significant part of the cuboidal epithelial cells of the respiratory bronchioles differentiates into flat cells (type I alveolocytes), closely connected by blood and lymphatic capillaries, and gas exchange becomes possible. The remaining cells retain their cubic shape (type II alveolocytes) and begin to produce surfactant. During the last 2 months of prenatal and several years of postnatal life, the number of terminal saccules constantly increases. Mature alveoli are absent before birth.
Lung fluid
At birth, the lungs are filled with fluid, containing large quantities of chlorides, protein, some mucus coming from the bronchial glands, and surfactant.
After birth, pulmonary fluid is quickly resorbed by the blood and lymphatic capillaries, and a small amount is removed through the bronchi and trachea. The surfactant remains in the form of a thin film on the surface of the alveolar epithelium.
Developmental defects
Tracheoesophageal fistula occurs as a result of incomplete splitting of the primary intestine into the esophagus and trachea.
Principles of organization of the respiratory system
The lumen of the airways and alveoli of the lung - external environment. In the airways and on the surface of the alveoli there is a layer of epithelium. The epithelium of the airways carries out a protective function, which is performed, on the one hand, by the very fact of the presence of the layer, and on the other hand, due to the secretion of a protective material - mucus. It is produced by goblet cells present in the epithelium. In addition, under the epithelium there are glands that also secrete mucus; the excretory ducts of these glands open onto the surface of the epithelium.
The airways function as an air unification unit. The characteristics of external air (temperature, humidity, contamination by particles of different types, the presence of microorganisms) vary quite significantly. But the respiratory department must receive air that meets certain requirements. The function of bringing air to the required conditions is played by the airways.
Foreign particles are deposited in the mucous film located on the surface of the epithelium. Next, contaminated mucus is removed from the airways by constantly moving towards the exit of the respiratory system, followed by coughing. This constant movement of the mucous film is ensured by synchronous and wave-like oscillations of the cilia located on the surface of the epithelial cells directed towards the exit of the airways. In addition, the movement of mucus to the outlet prevents it from reaching the surface of the alveolar cells through which gases diffuse.
Conditioning the temperature and humidity of the inhaled air is carried out with the help of blood located in the vascular bed of the wall of the airways. This process occurs mainly in the initial sections, namely in the nasal passages.
The mucous membrane of the airways is involved in protective reactions. The epithelium of the mucous membrane contains Langerhans cells, while the layer proper contains a significant number of various immunocompetent cells (T- and B-lymphocytes, plasma cells that synthesize and secrete IgG, IgA, IgE, macrophages, dendritic cells).
Mast cells are very numerous in the layer of the mucous membrane. Mast cell histamine causes bronchospasm, vasodilation, hypersecretion of mucus from the glands and mucosal edema (as a result of vasodilation and increased permeability of the wall of postcapillary venules). In addition to histamine, mast cells, along with eosinophils and other cells, secrete a number of mediators, the action of which leads to inflammation of the mucous membrane, damage to the epithelium, reduction of the SMC and narrowing of the lumen of the airways. All of the above effects are characteristic of bronchial asthma.
Airways do not collapse. The lumen is constantly changing and adjusted depending on the situation. The collapse of the lumen of the airways prevents the presence in their wall of dense structures formed in the initial sections of bone, and then by cartilage tissue. Changes in the size of the lumen of the airways are ensured by the folds of the mucous membrane, the activity of smooth muscle cells and the structure of the wall.
Regulation of SMC tone. The tone of the SMCs of the airways is regulated by neurotransmitters, hormones, and arachidonic acid metabolites. The effect depends on the presence of the corresponding receptors in the SMC. SMCs of the airway walls have M-cholinergic receptors and histamine receptors. Neurotransmitters are secreted from the terminals of the nerve endings of the autonomic nervous system (for the vagus nerve - acetylcholine, for neurons of the sympathetic trunk - norepinephrine). Bronchoconstriction is caused by choline, substance P, neurokinin A, histamine, thromboxane TXA2, leukotrienes LTC4, LTD4, LTE4. Bronchodilation is caused by VIP, adrenaline, bradykinin, prostaglandin PGE2. Contraction of the SMC (vasoconstriction) is caused by adrenaline, leukotrienes, and angiotensin-II. Histamine, bradykinin, VIP, and prostaglandin PG have a relaxing effect on vascular SMCs.
The air entering the respiratory tract is subjected to chemical examination. It is carried out by the olfactory epithelium and chemoreceptors in the wall of the airways. Such chemoreceptors include sensitive endings and specialized chemosensitive cells of the mucous membrane.
Airways
The airways of the respiratory system include the nasal cavity, nasopharynx, larynx, trachea and bronchi. As air moves, it is purified, moistened, the temperature of inhaled air approaches body temperature, it receives gas, temperature and mechanical stimuli, as well as regulates the volume of inhaled air.
In addition, the larynx takes part in sound production.
Nasal cavity
It is divided into the vestibule and the nasal cavity itself, consisting of the respiratory and olfactory regions.
The vestibule is formed by a cavity, located under the cartilaginous part of the nose, covered with stratified squamous epithelium.
Under the epithelium in the connective tissue layer there are sebaceous glands and roots of bristle hair. Bristle hairs perform a very important function: they trap dust particles from the inhaled air in the nasal cavity.
The inner surface of the nasal cavity proper in the respiratory part is lined with a mucous membrane consisting of multirow prismatic ciliated epithelium and connective tissue lamina propria.
The epithelium consists of several types of cells: ciliated, microvillous, basal and goblet. Intercalary cells are located between the ciliated cells. Goblet cells are single-celled mucous glands that secrete their secretions onto the surface of the ciliated epithelium.
The lamina propria of the mucous membrane is formed by loose fibrous unformed connective tissue containing a large number of elastic fibers. It contains the terminal sections of the mucous glands, the excretory ducts of which open on the surface of the epithelium. The secretion of these glands, like the secretion of goblet cells, moisturizes the mucous membrane.
The mucous membrane of the nasal cavity is very well supplied with blood, which helps warm the inhaled air during the cold season.
Lymphatic vessels form a dense network. They are connected with the subarachnoid space and perivascular sheaths of various parts of the brain, as well as with the lymphatic vessels of the major salivary glands.
The mucous membrane of the nasal cavity has abundant innervation, numerous free and encapsulated nerve endings (mechano-, thermo- and angioreceptors). Sensory nerve fibers originate from the semilunar ganglion of the trigeminal nerve.
In the area of the superior turbinate, the mucous membrane is covered with a special olfactory epithelium containing receptor (olfactory) cells. The mucous membrane of the paranasal sinuses, including the frontal and maxillary sinuses, has the same structure as the mucous membrane of the respiratory part of the nasal cavity, with the only difference that their own connective tissue plate is much thinner.
Larynx
A complex organ in the structure of the air-bearing section of the respiratory system, which is involved not only in air conduction, but also in sound production. The larynx in its structure has three membranes - mucous, fibrocartilaginous and adventitial.
The mucous membrane of the human larynx, in addition to the vocal cords, is lined with multirow ciliated epithelium. The lamina propria of the mucous membrane, formed by loose fibrous unformed connective tissue, contains numerous elastic fibers that do not have a specific orientation.
In the deep layers of the mucous membrane, elastic fibers gradually pass into the perichondrium, and in the middle part of the larynx they penetrate between the striated muscles of the vocal cords.
In the middle part of the larynx there are folds of the mucous membrane, forming the so-called true and false vocal cords. The folds are covered by stratified squamous epithelium. Mixed glands lie in the mucous membrane. Due to the contraction of the striated muscles embedded in the thickness of the vocal folds, the size of the gap between them changes, which affects the pitch of the sound produced by the air passing through the larynx.
The fibrocartilaginous membrane consists of hyaline and elastic cartilage surrounded by dense fibrous connective tissue. This shell is a kind of framework for the larynx.
The adventitia consists of fibrous connective tissue.
The larynx is separated from the pharynx by the epiglottis, the basis of which is elastic cartilage. In the area of the epiglottis, the transition of the mucous membrane of the pharynx into the mucous membrane of the larynx occurs. On both surfaces of the epiglottis, the mucous membrane is covered with stratified squamous epithelium.
Trachea
This is the air-conducting organ of the respiratory system, which is a hollow tube consisting of the mucous membrane, submucosa, fibrocartilaginous and adventitial membranes.
The mucous membrane, with the help of a thin submucosa, is connected to the underlying dense parts of the trachea and, as a result, does not form folds. It is lined with multirow prismatic ciliated epithelium, in which ciliated, goblet, endocrine and basal cells are distinguished.
Ciliated cells of a prismatic shape flicker in the direction opposite to the inhaled air, most intensely at the optimal temperature (18 - 33 ° C) and in a slightly alkaline environment.
Goblet cells are single-celled endoepithelial glands that secrete a mucous secretion that moisturizes the epithelium and creates conditions for the adhesion of dust particles that enter with the air and are removed by coughing.
Mucus contains immunoglobulins, secreted by immunocompetent cells of the mucous membrane, which neutralize many microorganisms that enter the air.
Endocrine cells have a pyramidal shape, a rounded nucleus and secretory granules. They are found in both the trachea and bronchi. These cells secrete peptide hormones and biogenic amines (norepinephrine, serotonin, dopamine) and regulate the contraction of muscle cells of the airways.
Basal cells are cambial cells that have an oval or triangular shape.
The submucosa of the trachea consists of loose fibrous unformed connective tissue, without a sharp boundary, passing into the dense fibrous connective tissue of the perichondrium of open cartilaginous half-rings. In the submucosa there are mixed protein-mucosal glands, the excretory ducts of which, forming flask-shaped extensions on their way, open on the surface of the mucous membrane.
The fibrocartilaginous membrane of the trachea consists of 16–20 hyaline cartilaginous rings, not closed on the posterior wall of the trachea. The free ends of these cartilages are connected by bundles of smooth muscle cells that are attached to the outer surface of the cartilage. Thanks to this structure, the posterior surface of the trachea is soft and pliable. This property of the posterior wall of the trachea is of great importance: when swallowing, food lumps passing through the esophagus located directly behind the trachea do not encounter obstacles from its cartilaginous skeleton.
The adventitia of the trachea consists of loose, fibrous, unformed connective tissue that connects this organ to the adjacent parts of the mediastinum.
The blood vessels of the trachea, just like in the larynx, form several parallel plexuses in its mucous membrane, and under the epithelium - a dense capillary network. Lymphatic vessels also form plexuses, of which the superficial one is located directly under the network of blood capillaries.
The nerves approaching the trachea contain spinal (cerebrospinal) and autonomic fibers and form two plexuses, the branches of which end in its mucous membrane with nerve endings. The muscles of the posterior wall of the trachea are innervated from the ganglia of the autonomic nervous system.
Lungs
The lungs are paired organs that occupy most of the chest and constantly change their shape depending on the phase of breathing. The surface of the lung is covered with a serous membrane (visceral pleura).
Structure. The lung consists of branches of the bronchi, which are part of the airways (bronchial tree), and a system of pulmonary vesicles (alveoli), which act as the respiratory sections of the respiratory system.
The bronchial tree of the lung includes the main bronchi (right and left), which are divided into extrapulmonary lobar bronchi (large bronchi of the first order), and then into large zonal extrapulmonary (4 in each lung) bronchi (bronchi of the second order). Intrapulmonary segmental bronchi (10 in each lung) are divided into bronchi of the III – V orders (subsegmental), which are medium in diameter (2 – 5 mm). The middle bronchi are divided into small (1 - 2 mm in diameter) bronchi and terminal bronchioles. Behind them begin the respiratory sections of the lung, which perform a gas exchange function.
The structure of the bronchi (although not the same throughout the bronchial tree) has common features. The inner lining of the bronchi - the mucosa - is lined, like the trachea, with ciliated epithelium, the thickness of which gradually decreases due to a change in the shape of the cells from high prismatic to low cubic. Among the epithelial cells, in addition to ciliated, goblet, endocrine and basal, in the distal parts of the bronchial tree, secretory cells (Clara cells), bordered (brush) cells, and non-ciliated cells are found in humans and animals.
Secretory cells are characterized by a dome-shaped apex, devoid of cilia and microvilli and filled with secretory granules. They contain a rounded nucleus, a well-developed endoplasmic reticulum of the agranular type, and a lamellar complex. These cells produce enzymes that break down the surfactant that coats the respiratory tract.
Unciliated cells are found in bronchioles. They have a prismatic shape. Their apical end rises somewhat above the level of adjacent ciliated cells.
The apical part contains clusters of glycogen granules, mitochondria and secretion-like granules. Their function is not clear.
The border cells are distinguished by their ovoid shape and the presence of short and blunt microvilli on the apical surface. These cells are rare. They are believed to function as chemoreceptors.
The lamina propria of the bronchial mucosa is rich in longitudinally directed elastic fibers, which ensure stretching of the bronchi when inhaling and returning them to their original position when exhaling. The mucous membrane of the bronchi has longitudinal folds caused by the contraction of oblique bundles of smooth muscle cells that separate the mucous membrane from the submucous connective tissue base. The smaller the diameter of the bronchus, the relatively thicker the muscular plate of the mucosa is. Lymphatic follicles are found in the mucous membrane of the bronchi, especially large ones.
IN submucosal connective tissue the terminal sections of mixed mucous-protein glands lie. They are located in groups, especially in places that are devoid of cartilage, and the excretory ducts penetrate the mucous membrane and open on the surface of the epithelium. Their secretion moisturizes the mucous membrane and promotes adhesion and envelopment of dust and other particles, which are subsequently released outside. Mucus has bacteriostatic and bactericidal properties. There are no glands in small-caliber bronchi (1–2 mm in diameter).
As the caliber of the bronchus decreases, the fibrocartilaginous membrane is characterized by a gradual replacement of open cartilaginous rings in the main bronchi with cartilaginous plates (lobar, zonal, segmental, subsegmental bronchi) and islands of cartilaginous tissue (in medium-caliber bronchi). In the medium-caliber bronchi, hyaline cartilaginous tissue is replaced by elastic cartilaginous tissue. In small caliber bronchi there is no fibrocartilaginous membrane.
Outdoor adventitia built of fibrous connective tissue, which passes into the interlobular and interlobular connective tissue of the lung parenchyma. Among the connective tissue cells, tissue basophils are found that take part in the regulation of the composition of the intercellular substance and blood clotting.
The terminal (terminal) bronchioles have a diameter of about 0.5 mm. Their mucous membrane is lined with single-layer cuboidal ciliated epithelium, in which brush cells and secretory Clara cells are found. In the lamina propria of the mucous membrane of these bronchioles there are longitudinally running elastic fibers, between which separate bundles of smooth muscle cells lie. As a result, the bronchioles are easily distensible when inhaling and return to their original position when exhaling.
Respiratory Department. The structural and functional unit of the respiratory part of the lung is the acinus. It is a system of alveoli located in the wall of the respiratory bronchiole, alveolar ducts and sacs that carry out gas exchange between the blood and air of the alveoli. The acini begins with a respiratory bronchiole of the first order, which is dichotomously divided into respiratory bronchioles of the second and then third order. Alveoli open into the lumen of the bronchioles, which are therefore called alveolar. Each third-order respiratory bronchiole, in turn, is divided into alveolar ducts, and each alveolar duct ends in two alveolar sacs. At the mouth of the alveoli of the alveolar ducts there are small bundles of smooth muscle cells, which are visible in cross sections in the form of button-like thickenings. The acini are separated from each other by thin connective tissue layers; 12–18 acini form the pulmonary lobule. The respiratory bronchioles are lined with single-layer cuboidal epithelium. The muscle plate becomes thinner and breaks up into separate, circularly directed bundles of smooth muscle cells.
There are several dozen alveoli on the walls of the alveolar ducts and alveolar sacs. The total number of them in adults reaches an average of 300–400 million. The surface of all alveoli during maximum inhalation in an adult can reach 100 m2, and during exhalation it decreases by 2–2.5 times. Between the alveoli there are thin connective tissue septa through which blood capillaries pass.
Between the alveoli there are communications in the form of holes with a diameter of about 10 - 15 microns (alveolar pores).
The alveoli have the appearance of an open bubble. The inner surface is lined by two main types of cells: respiratory alveolar cells (type I alveolocytes) and large alveolar cells (type II alveolocytes). In addition, in animals there are type III cells in the alveoli - bordered.
Type I alveolocytes have an irregular, flattened, elongated shape. On the free surface of the cytoplasm of these cells there are very short cytoplasmic projections facing the cavity of the alveoli, which significantly increases the total area of contact of air with the surface of the epithelium. Small mitochondria and pinocytotic vesicles are found in their cytoplasm.
An important component of the airborne barrier is the alveolar surfactant complex. It plays an important role in preventing the collapse of the alveoli during exhalation, as well as in protecting them from the penetration of microorganisms from the inhaled air through the wall of the alveoli and the transudation of fluid from the capillaries of the interalveolar septa into the alveoli. Surfactant consists of two phases: membrane and liquid (hypophase). Biochemical analysis of the surfactant showed that it contains phospholipids, proteins and glycoproteins.
Alveolocytes of type II are somewhat larger in height than cells of type I, but their cytoplasmic processes, on the contrary, are short. In the cytoplasm, larger mitochondria, lamellar complex, osmiophilic bodies and endoplasmic reticulum are detected. These cells are also called secretory because of their ability to secrete lipoprotein substances.
Brush cells and macrophages containing trapped foreign particles and excess surfactant are also found in the alveolar wall. The cytoplasm of macrophages always contains a significant amount of lipid droplets and lysosomes. Lipid oxidation in macrophages is accompanied by the release of heat, which warms the inhaled air.
Surfactant
The total amount of surfactant in the lungs is extremely small. There is about 50 mm 3 of surfactant per 1 m2 of alveolar surface. The thickness of its film is 3% of the total thickness of the airborne barrier. Surfactant components enter type II alveolocytes from the blood.
Their synthesis and storage in the lamellar bodies of these cells is also possible. 85% of surfactant components are reused, and only a small amount is synthesized again. Removal of surfactant from the alveoli occurs in several ways: through the bronchial system, through the lymphatic system and with the help of alveolar macrophages. The main amount of surfactant is produced after the 32nd week of pregnancy, reaching its maximum amount by the 35th week. Before birth, excess surfactant is produced. After birth, this excess is removed by alveolar macrophages.
Neonatal respiratory distress syndrome develops in premature infants due to immaturity of type II alveolocytes. Due to the insufficient amount of surfactant secreted by these cells onto the surface of the alveoli, the latter are not straightened (atelectasis). As a result, respiratory failure develops. Due to alveolar atelectasis, gas exchange occurs through the epithelium of the alveolar ducts and respiratory bronchioles, which leads to their damage.
Compound. Pulmonary surfactant is an emulsion of phospholipids, proteins and carbohydrates, 80% are glycerophospholipids, 10% are cholesterol and 10% are proteins. The emulsion forms a monomolecular layer on the surface of the alveoli. The main surfactant component is dipalmitoylphosphatidylcholine, an unsaturated phospholipid that makes up more than 50% of surfactant phospholipids. The surfactant contains a number of unique proteins that promote the adsorption of dipalmitoylphosphatidylcholine at the interface of two phases. Among the surfactant proteins, SP-A and SP-D are distinguished. The SP-B, SP-C proteins and surfactant glycerophospholipids are responsible for reducing surface tension at the air-liquid interface, and the SP-A and SP-D proteins are involved in local immune reactions by mediating phagocytosis.
SP-A receptors are present in type II alveolocytes and macrophages.
Production regulation. The formation of surfactant components in the fetus is promoted by glucocorticosteroids, prolactin, thyroid hormones, estrogens, androgens, growth factors, insulin, cAMP. Glucocorticoids increase the synthesis of SP-A, SP-B and SP-C in the fetal lungs. In adults, surfactant production is regulated by acetylcholine and prostaglandins.
Surfactant is a component of the lung defense system. Surfactant prevents direct contact of alveolocytes with harmful particles and infectious agents entering the alveoli with inhaled air. The cyclic changes in surface tension that occur during inhalation and exhalation provide a breath-dependent clearance mechanism. Dust particles enveloped in surfactant are transported from the alveoli to the bronchial system, from which they are removed with mucus.
Surfactant regulates the number of macrophages migrating into the alveoli from the interalveolar septa, stimulating the activity of these cells. Bacteria that enter the alveoli with air are opsonized by surfactant, which facilitates their phagocytosis by alveolar macrophages.
Surfactant is present in bronchial secretions, coating ciliated cells, and has the same chemical composition as lung surfactant. Apparently, surfactant is necessary to stabilize the distal airways.
Immune protection
Macrophages
Macrophages make up 10–15% of all cells in the alveolar septa. There are many microfolds on the surface of macrophages. The cells form rather long cytoplasmic processes that allow macrophages to migrate through the interalveolar pores. While inside the alveoli, the macrophage, with the help of processes, can attach to the surface of the alveoli and capture particles. Alveolar macrophages secrete α1-antitrypsin, a glycoprotein from the family of serine proteases that protects alveolar elastin from: breakdown by leukocyte elastase. Mutation of the α1-antitrypsin gene leads to congenital pulmonary emphysema (damage to the elastic framework of the alveoli).
Migration routes. Cells loaded with phagocytosed material can migrate in different directions: up the sections of the acinus and into the bronchioles, where macrophages enter the mucous film, constantly shifting along the surface of the epithelium towards the exit from the airways; inside - into the internal environment of the body, i.e. into the interalveolar septa.
Function. Macrophages phagocytose microorganisms and dust particles entering the inhaled air, and have antimicrobial and anti-inflammatory activity mediated by oxygen radicals, proteases and cytokines. In lung macrophages, the antigen-presenting function is weakly expressed. Moreover, these cells produce factors that inhibit T-lymphocyte function, which reduces the immune response.
Antigen presenting cells
Dendritic cells and Langerhans cells belong to the mononuclear phagocyte system; they are the main antigen-presenting cells of the lung. Dendritic cells and Langerhans cells are numerous in the upper respiratory tract and trachea. As the caliber of the bronchi decreases, the number of these cells decreases. As antigen-presenting pulmonary Langerhans cells and dendritic cells, they express MHC class 1 molecules. These cells have receptors for the Fc fragment of IgG, the C3b fragment of the complement component, IL-2, and synthesize a number of cytokines, including IL-1, IL-6, tumor necrosis factor, stimulate T-lymphocytes, showing increased activity against the antigen that first appears in the body.
Dendritic cells
Dendritic cells are found in the pleura, interalveolar septa, peribronchial connective tissue, and in the lymphoid tissue of the bronchi. Dendritic cells, differentiating from monocytes, are quite mobile and can migrate in the intercellular substance of connective tissue. They appear in the lungs before birth. An important property of dendritic cells is their ability to stimulate the proliferation of lymphocytes. Dendritic cells have an elongated shape and numerous long processes, an irregular nucleus and an abundance of typical cellular organelles. There are no phagosomes because the cells have virtually no phagocytic activity.
Langerhans cells
Langerhans cells are present only in the epithelium of the airways and are absent in the alveolar epithelium. Langerhans cells differentiate from dendritic cells, and such differentiation is possible only in the presence of epithelial cells. Connecting with cytoplasmic processes penetrating between epithelial cells, Langerhans cells form a developed intraepithelial network. Langerhans cells are morphologically similar to dendritic cells. A characteristic feature of Langerhans cells is the presence in the cytoplasm of specific electron-dense granules that have a lamellar structure.
Metabolic lung function
In the lungs it metabolizes a number of biologically active substances.
Angiotensins. Activation is known only for angiotensin I, which is converted to angiotensin II. The conversion is catalyzed by angiotensin-converting enzyme localized in the endothelial cells of the alveolar capillaries.
Inactivation. Many biologically active substances are partially or completely inactivated in the lungs. Thus, bradykinin is inactivated by 80% (using angiotensin-converting enzyme). Serotonin is inactivated in the lungs, but not with the participation of enzymes, but by removal from the blood, part of the serotonin enters platelets. With the help of appropriate enzymes, prostaglandins PGE, PGE2, PGE2a and norepinephrine are inactivated in the lungs.
Pleura
The outside of the lungs is covered with pleura, called pulmonary (or visceral). The visceral pleura tightly fuses with the lungs, its elastic and collagen fibers pass into the interstitial tissue, so it is difficult to isolate the pleura without injuring the lungs. Smooth muscle cells are found in the visceral pleura. In the parietal pleura, which lines the outer wall of the pleural cavity, there are fewer elastic elements, and smooth muscle cells are rare.
Blood supply to the lung is carried out through two vascular systems. On the one hand, the lungs receive arterial blood from the systemic circulation through the bronchial arteries, and on the other, they receive venous blood for gas exchange from the pulmonary arteries, i.e., from the pulmonary circulation. The branches of the pulmonary artery, accompanying the bronchial tree, reach the base of the alveoli, where they form the capillary network of the alveoli. Through the alveolar capillaries, the diameter of which ranges from 5 to 7 microns, red blood cells pass in one row, which creates optimal conditions for gas exchange between the hemoglobin of red blood cells and the alveolar air. Alveolar capillaries collect into postcapillary venules, which merge to form the pulmonary veins.
The bronchial arteries arise directly from the aorta and supply the bronchi and pulmonary parenchyma with arterial blood. Penetrating the wall of the bronchi, they branch and form arterial plexuses in their submucosa and mucous membrane. In the mucous membrane of the bronchi, communication occurs between the vessels of the large and small circle by anastomosing the branches of the bronchial and pulmonary arteries.
The lymphatic system of the lung consists of superficial and deep networks of lymphatic capillaries and vessels. The superficial network is located in the visceral pleura. The deep network is located inside the pulmonary lobules, in the interlobular septa, lying around the blood vessels and bronchi of the lung.
Innervation carried out by sympathetic and parasympathetic nerves and a small number of fibers coming from the spinal nerves. Sympathetic nerves conduct impulses that cause dilatation of the bronchi and constriction of blood vessels, parasympathetic nerves conduct impulses that, on the contrary, cause constriction of the bronchi and dilation of blood vessels. The branches of these nerves form a nerve plexus in the connective tissue layers of the lung, located along the bronchial tree and blood vessels. In the nerve plexuses of the lung there are large and small ganglia, from which nerve branches arise that, in all likelihood, innervate the smooth muscle tissue of the bronchi. Nerve endings were identified along the alveolar ducts and alveoli.
From the book 100 Chinese healing exercises. Heal yourself! by Shin Soo From the book The Best for Health from Bragg to Bolotov. Large reference book of modern wellness author Andrey Mokhovoy From the book How to Stay Young and Live Long author Yuri Viktorovich Shcherbatykh From the book A Healthy Man in Your Home author Elena Yurievna Zigalova From the book Bath and sauna for health and beauty author Vera Andreevna Solovyova From the book Nordic Walking. Secrets of a famous trainer author Anastasia PoletaevaMucous membrane I
Mucous membrane (tunica mucosa)
the inner lining of hollow organs communicating with the external environment. Functional significance of S. o. diverse: it carries out a protective function, participates in absorption processes (), provides humidification and purification of the air entering the air (), etc. Histogenesis of S. o. is closely related to the development of relevant organs. S. o. consists of epithelium, native (connective tissue) and muscular plates ( rice.
). The latter is well expressed only in the organs of the digestive system and bronchi; in other organs it is absent () or represented by separate bundles of smooth muscles. Fabric composites S. o. develop from various embryonic rudiments: - from all three germ layers, blood and lymphatic vessels, and the lamina propria and muscle of the S. o. - from mesenchyme. Structure of S. o. depends entirely on the functional characteristics of a given organ or anatomical section. Where S. o. performs a protective function, it is represented by stratified squamous keratinizing epithelium (oral cavity, anal canal); S. o., ensuring the transport of substances from the environment or their removal, is a single-layer epithelium (, intestines); S. o. cleansing and warming the inhaled (, trachea, large and medium), - multi-row ciliated epithelium, etc. The lamina propria is separated from the epithelium by the basement membrane and consists of loose connective tissue containing blood and lymphatic vessels, nerve elements. , formed by one or several rows of smooth muscle cells, separates the S. o. from the submucosa. The latter consists of very loose connective tissue, which ensures the mobility of the lake. promotes the formation of folds of the lake, for example, in the gastrointestinal tract. Relief of S. o. varies depending on the functional characteristics of the organ. Surface of the S. o. can be smooth (oral cavity), form depressions (pits in the stomach, crypts in the intestines) or (in the small intestine). The mucous membrane contains its own glandular gland, represented by unicellular mucous glands that produce. Usually they are interspersed with other cells (goblet cells, endocrine cells), less often located in groups (Paneth cells of the intestine) or in the form of glandular fields (in the epithelium of the stomach and uterus). In his own record S. o. multicellular mucous glands are localized (simple, tubular, less often branched). The glands of the mucous membrane are exogenous; they, released onto the surface of the epithelium, moisturize it, protect it from, and adsorb foreign particles. The pathological processes developing in S. of the lake are varied. These can be inflammatory, mainly catarrhal, processes with an acute or chronic course. Violation of the integrity of the epithelium of S. o. leads to the formation of erosions and ulcers. S. o. are represented mainly by epithelial benign (papillomas, adenomas) and malignant () neoplasms. Less common are fibromas, lipomas, sarcomas and melanomas. In addition, in S. o. angiomas are observed in the digestive tract. In addition to the above forms of damage in S. o. Circulatory disorders in the form of venous stagnation and hemorrhages may be observed. During infections and intoxications, dystrophic changes in the mucous membrane occur. Rice. Schematic representation of the structure of the mucous membrane: I - epithelium; II - own plate; III - muscular plate; IV - submucosa; 1 - nerve trunk; 2 - nerve plexus; 3 - complex (alveolar-tubular) glands; 4 - simple tubular glands; 5 - venous vessel; 6 - lymphatic vessel; 7 - arterial vessel. the inner layer of the scene of the hollow organs of the digestive, respiratory and genitourinary systems, consisting of connective and smooth muscle tissue, lined with epithelium, the surface of which is covered with mucus produced by the o. mucous glands.
1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.
See what “Mucous membrane” is in other dictionaries:
Microscopic specimen of the middle part of the human esophagus (medium magnification) ... Wikipedia
MUCOSA, a layer of TISSUE (or EPITHELIA) lining the inner surface of the respiratory and digestive organs, the genitourinary tract and the excretory ducts of various glands. This membrane is constantly moistened by cells secreted by its glands... ... Scientific and technical encyclopedic dictionary
- (tunica mucosa), the membrane lining the coelomic. animals internal the surface is digestive. and breathe. organs, genitourinary system, paranasal cavities, middle ear, excretory ducts of glands. Thickness 0.5 4 mm. S. o. constantly moisturized... Biological encyclopedic dictionary
The mucous membrane, in humans and animals, lines the inner surface of the digestive and respiratory organs, the genitourinary tract, the nasal cavities, and the excretory ducts of the glands. Thickness 0.5-4 mm. Glands located in the mucous membrane secrete mucus... Modern encyclopedia
In humans and animals, it lines the internal surface of the digestive and respiratory organs, the genitourinary tract, the paranasal cavities, and the excretory ducts of the glands. Thickness 0.5-4 mm. The surface of the mucous membrane is covered with mucus secreted... ... Big Encyclopedic Dictionary
mucous membrane- - Biotechnology topics EN mucous membrane ... Technical Translator's Guide
Mucous membrane- MUCOSA, in humans and animals, lines the inner surface of the digestive and respiratory organs, genitourinary tract, nasal cavities, and excretory ducts of the glands. Thickness 0.5 – 4 mm. The glands located in the mucous membrane secrete... ... Illustrated Encyclopedic Dictionary
MUCOSA- Rice. 1. Diagram of organs lined with mucous membrane. Rice. 1. Diagram of organs lined with mucous membrane: 1 oral fissure; 2 nostrils; 3 palpebral fissure; 4 anal opening; 5 sex slit; 6 hole… … Veterinary encyclopedic dictionary
In humans and animals, it lines the inner surface of the digestive and respiratory organs, the genitourinary tract, the paranasal cavities, and the excretory ducts of the glands. Thickness 0.5-4 mm. The surface of the mucous membrane is covered with mucus secreted... ... encyclopedic Dictionary
mucous membrane- The stomach is the digestive cavity located between the esophagus and the intestines. The dimensions of a moderately distended stomach are 25 cm in length, 11 cm in width, 9 cm in diameter from front to back. The general shape of the stomach is the shape of a capital letter "J" with two... ... Universal additional practical explanatory dictionary by I. Mostitsky
A membrane 0.5-4 mm thick, lining the inner surface of the digestive and respiratory organs, the genitourinary system, the paranasal cavities, the middle ear, and the excretory ducts of the glands in animals and humans. The name "S. O." given in... ... Great Soviet Encyclopedia
Books
- Aesthetics in dentistry. An Integrative Approach, Claude R. Rufenacht. The purpose of this book, written by one of the founders of dental bioaesthetics, is to help practitioners develop a conscious understanding of aesthetic principles from the perspective of not only...
Respiratory system includes the lungs and airways. The airways include: the nasal cavity, pharynx, larynx, trachea and bronchi.
Development.
Connective tissue stroma, smooth muscle and cartilage tissue develop from mesenchyme; pleural mesothelium - from splanchnotome; epithelium of the larynx, trachea, bronchi and lungs - from the protrusion of the ventral wall of the foregut. The protrusion of the foregut appears in the 4th week of embryogenesis, then it is divided into right and left halves, from which epithelial tubular outgrowths of the bronchi begin. The connective tissue, smooth muscle and cartilaginous components of the wall of the trachea and bronchi are formed from the surrounding mesenchyme. By the 7th month, respiratory bronchioles and alveoli are formed. The epithelium of the alveoli has a cubic shape. The alveoli are in a collapsed state. When a newborn takes his first breath, the alveoli straighten, fill with air, and their epithelium takes on a flattened shape.
Nasal cavity(cavum nasi). Includes the vestibule of the nasal cavity (vestibulum cavi nasi) and the nasal cavity proper (cavum nasi propria). The mucous membrane of the vestibule of the nasal cavity is covered with stratified squamous keratinizing epithelium, which, as it moves away from the entrance to the nasal cavity, loses the stratum corneum. The lamina propria of the mucous membrane of the vestibule contains roots of bristle hair and sebaceous glands. The bristly hair traps dust particles and other foreign substances, purifying the inhaled air.
The nasal cavity itself lined with a mucous membrane consisting of 2 layers: 1) multirow epithelium and 2) lamina propria of the mucous membrane. Multirow epithelium includes ciliated, basal (undifferentiated), microvillous and goblet cells.
The lamina propria is represented by loose connective tissue, rich in multidirectional elastic fibers, in which there are end sections of the mucous glands, lymph nodes, the accumulations of which near the mouths of the auditory tubes form the tubal tonsils (tonsilla tubaria). Under the basement membrane there is a dense network of capillaries, the blood of which is involved in the thermoregulation of inhaled air (if the air is cold, it warms up, and if it is hot, it cools). The lamina propria contains a plexus of arteries and veins, the walls of which are rich in smooth muscle tissue. The venous plexus in the area of the inferior concha is represented by wide, thin-walled veins, when filled with blood, the mucous membrane swells, making breathing difficult. The lymphatic vessels of the nasal cavity are connected with the lymphatic vessels of the major salivary glands, the perivascular spaces of the brain and the subarachnoid space.
The olfactory epithelium is located in the area of the superior and - partially - middle nasal concha.
The frontal and maxillary sinuses, which are lined with the same mucous membrane as the nasal cavity, but thinner, open into the nasal cavity.
Innervation of the nasal cavity carried out by branches of the trigeminal nerve, the fibers of which end in mechano-, thermo- and vasoreceptors.
Pharynx (pharynx). The respiratory and digestive tracts cross at the pharynx. The wall of the pharynx consists of 4 membranes: 1) mucous membrane; 2) submucosa; 3) muscular; 4) adventitial. The pyutka is divided into 3 sections: oropharyngeal, nasopharyngeal and laryngopharyngeal.
Mucous membrane The oropharyngeal and laryngeal-pharyngeal sections are covered with multi-layered squamous non-keratinizing epithelium, the nasopharyngeal - multi-row. In the lamina propria of the mucous membrane, consisting of loose connective tissue, a layer of elastic fibers is well defined.
Submucosa consists of loose connective tissue in which the terminal sections of complex mucous glands are located.
Muscularis consists of inner longitudinal and outer circular layers of striated muscle tissue.
Adventitia represented by loose connective tissue.
Larynx (larinx). The larynx includes 3 membranes: 1) mucous membrane; 2) fibrocartilaginous; 3) adventitia.
Mucous membrane(tunica mucosa) consists of 2 layers: 1) epithelium and 2) lamina propria of the mucous membrane.
Epithelial lamina in The area of the vocal cords is represented by stratified squamous non-keratinizing epithelium, the rest of the mucous membrane is covered with multi-row epithelium, including the same cells as in the mucous membrane of the nasal cavity.
Own record The mucous membrane is represented by loose connective tissue, rich in multidirectional elastic fibers. In the lamina propria there is a cluster of lymph nodes that form the laryngeal tonsil (tonsilla laryngea) and the end sections of the protein-mucosal glands (glandulae mixtae seromucosae).
True and false vocal cords (plica vocalis Veritas et plica vocalis nonveritas) are folds of the mucous membrane. In the thickness of the true vocal cords there is an abundance of elastic fibers and there are striated muscle fibers, when contracted, the glottis narrows, and when relaxed, it expands. The false vocal cords contain only smooth myocytes.
Under the basement membrane there is a dense network of blood capillaries involved in the thermoregulation of inhaled air.
Fibrocartilaginous sheath consists of hyaline and elastic cartilage tissue and represents the skeleton of the larynx.
Adventitia represented by collagen connective tissue.
Epiglottis(epiglottis) separates the larynx from the pharynx; consists of elastic cartilage, covered with a mucous membrane, lined on the side of the pharynx and on the side of the larynx with stratified squamous non-keratinizing epithelium, the epiglottis fiction - closes the entrance to the larynx during swallowing.
Functions of the larynx: 1) air-conducting, 2) voice-forming and 3) participation in the thermoregulation of inhaled air.
Trachea. This is a tubular organ starting from the cricoid cartilage of the larynx and ending with the division into 2 main bronchi (bifurcation). The tracheal wall includes 4 membranes: 1) mucosa (tunica mucosa), 2) submucosa (tela submucosa), 3) fibrocartilaginous (tunica fibrocartilaginea) and 4) adventitia (tunica adventitia).
Mucous membrane represented by 2 layers:
1) multirow (pseudostratified) epithelium and 2) lamina propria of the mucous membrane.
Epithelial layer(stratum epithelialis) is represented by 5 types of cells: 1) ciliated (epitheliocytus ciliatus); 2) goblet-shaped (exocrinocytus caliciformis); 3) basal, or undifferentiated (epitheliocytus nondifferentiatus); 4) endocrine (endocrinocytus); 5) antigen-presenting.
Ciliated epithelial cells- the tallest, have a prismatic shape, with a narrow basal end adjacent to the basement membrane, at the wide apical end there are cilia (cilii) about 5 µm high. The cilia make oscillatory movements directed towards the exit from the trachea. As a result of vibrations of the cilia, mucus and dust particles and bacteria deposited on it are removed from the surface of the mucous membrane towards the exit from the trachea.
Vibrations of cilia are most active at a temperature of 18-33 °C. At higher or lower temperatures, the vibrations of the cilia weaken or stop altogether. High temperature occurs when smoking. During a puff, the temperature of the burning end of the cigarette rises to 600 °C. The smoke inhaled into the trachea has a temperature of about 50 °C. At this temperature, the cilia stick together and their movement stops. As a result of this, dust particles and bacteria deposited on the mucous membrane are not removed from the trachea, and the inflammatory process begins (tracheitis, tracheobronchitis). Chronic tracheobronchitis is a precancerous condition. According to American scientists, respiratory cancer occurs 15 times more often in smokers than in non-smokers.
Goblet exocrinocytes are similar in structure to goblet cells of the gastrointestinal tract, but differ from them in that their mucous secretion contains hyaluronic and sialic acids. As is known, all acids have a bactericidal effect.
The mucous secretion lining the tracheal mucosa contains immunoglobulin A (IgA). The protein component of this immunoglobulin is produced in plasma cells, the asecretory component - by epithelial cells. Thanks to immunoglobulin, an immune reaction occurs on the surface of the mucous membrane.
Nasal epithelial cells They have a conical shape, short length, a wide base lying on the basement membrane, their apical end does not extend to the surface of the epithelium. Function of these cells- regenerative.
Endocrine (pheochromic) cells contain a synthetic apparatus; their basal part contains secretory granules. These cells produce hormones: calcitonin, serotonin, dopamine, norepinephrine, bombesin, etc., which regulate the contraction of smooth muscles of the respiratory tract.
Antigen presenting cells (Langerhans cells) They have a branched shape, a lobed or oval nucleus, contain organelles of general importance, including lysosomes, and Birbeck granules, which look like a tennis racket. On the surface of cells there are receptors for EC fragments of immunoglobulin G (IgG) and C3 complement.
Antigen-presenting cells capture antigens that cause an allergic reaction, secrete a factor that causes necrosis of tumor cells, secrete cytokines, and stimulate the proliferation and differentiation of lymphocytes. Together with lymphocytes, these cells form the immune system of the respiratory tract.
Own record The mucous membrane is represented by loose connective tissue, rich in longitudinally directed elastic fibers. In the lamina propria there are lymph nodes, the excretory ducts of the tracheal glands pass through, single smooth myocytes are found, under the basement membrane there is a dense network of capillaries involved in the thermoregulation of inhaled air.
Submucosa consists of loose fibrous connective tissue. It contains the terminal sections of the fir-mucous tracheal glands.
Fibrocartilaginous sheath consists of connective (fibrous) tissue and 16-20 open rings on the posterior surface, consisting of hyaline cartilage. Smooth myocytes are attached to the ends of the semirings, forming the tracheal muscle, which, together with the connective tissue, forms the soft part of the tracheal wall to which the esophagus is adjacent. This has a beneficial effect on the passage of food through the esophagus.
Adventitia It is represented by loose fibrous connective tissue, the fibers of which pass into the surrounding tissue of the mediastinum.
Blood supply to the trachea is provided by the arterial and venous plexuses of the mucous membrane and a dense network of capillaries under the basement membrane, which is involved in the thermoregulation of inhaled air. In the lamina propria of the mucous membrane there is a plexus of lymphatic vessels.
Innervation of the trachea carried out by 2 nerve plexuses, including: 1) efferent sympathetic (adrenergic) and parasympathetic (cholinergic) nerve fibers; 2) afferent nerve fibers (dendrites of sensory neurons of the nerve ganglia) and 3) intramural nerve ganglia.
Functions of the trachea: air-conducting and thermoregulatory.
Lung. These are the bronchial tree and the respiratory section.
Bronchial tree(arbor bronchialis) refers to the airways of the lungs. It begins with the main bronchi (bronchus principalis) of large caliber (diameter - about 15 mm), extending from the trachea (tracheal bifurcation). From the main bronchi there are 2 extrapulmonary lobar bronchi of the 1st order of large caliber (diameter - about 12 mm). From these bronchi depart 4 extrapulmonary zonal bronchi of the 2nd order of large caliber (diameter 10-6 mm). From the bronchi of the 2nd order there are 10 intrapulmonary segmental bronchi of the 3rd order of medium caliber (diameter - about 5 mm). Subsegmental bronchi of the 4th order of medium caliber (diameter 4-3 mm) depart from them, which pass into subsegmental bronchi of the 5th order of medium caliber (diameter 3 mm). From the bronchi of the 5th order there are bronchi of small caliber (bronchus parvus), or small bronchi (diameter 2-1 mm). The small bronchi branch into terminal (end) bronchioles, the diameter of which is 1-0.5 mm. These bronchioles end the bronchial tree.
The structure of the wall of large and medium caliber bronchi. The wall of the bronchi of these calibers includes 4 membranes: 1) mucous membrane; 2) submucosa; 3) fibrocartilaginous; 4) adventitia.
Mucosa consists of 3 layers: 1) epithelial, 2) lamina propria and 3) muscular lamina.
Epithelial layer It is represented by multirow epithelium, including ciliated, goblet, basal and endocrine cells. As the bronchi decrease, the epithelium becomes thinner (the number of rows decreases), and the number of goblet cells decreases.
lamina propria of the mucous membrane It is represented by loose connective tissue, rich in longitudinally arranged elastic fibers. It contains single lymph nodes related to the immune defense system of the respiratory system. Under the basement membrane is a dense network of blood capillaries.
Muscular plate of the mucous membrane consists of circularly arranged myocytes, due to the contraction of which longitudinal folds of the mucous membrane are formed. As the diameter of the bronchi decreases, the relative thickness of the muscular plate increases.
Submucosa It is represented by loose connective tissue, in which the end sections of the protein-mucosal bronchial glands are located.
Fibrocartilaginous sheath consists of fibrous connective and cartilaginous tissue. In the main bronchi, cartilage tissue is represented by open hyaline rings, in large extrapulmonary lobar and zonal bronchi - by plates of hyaline cartilage, in intrapulmonary segmental and subsegmental bronchi of medium caliber - by plates (islands) of elastic cartilage.
Adventitia It is represented by loose connective tissue, the fibers of which extend into the interstitial (stromal) tissue of the lungs.
The structure of the wall of small caliber bronchi. The wall of the Ronchi of this caliber includes 2 membranes: 1) mucous and 2) adventitial.
Mucous membrane consists of 3 layers: 1) epithelial lamina, 2) lamina propria and 3) muscular lamina.
Ep thelial plate It is represented by double or single row ciliated epithelium, among the cells of which there are no goblet exocrinocytes.
Own record consists of loose connective tissue rich in elastic fibers.
Muscular plate is represented by a relatively thick layer of circularly located myocytes. Thanks to the muscular plate of the mucous membrane and the absence of a fibrocartilaginous membrane, the mucous membrane forms numerous deep longitudinal folds, which significantly narrows the lumen of the small bronchus.
Functional significance of the muscle plate of the mucous membrane of the small bronchi is that it participates in the regulation of air flow during inhalation and exhalation. During a spasm of the muscle plate, breathing becomes difficult, which is observed in bronchial asthma.
Terminal bronchioles.Wall of terminal bronchioles consists of 2 thinned membranes: 1) mucous and 2) adventitial.
Mucous membrane consists of 3 layers: 1) epithelial lamina, 2) lamina propria and 3) muscular lamina.
Epithelial plate It is represented by cubic ciliated epithelium, among the cells of which there are secretory Clara cells (cellula secretoria), bordered (epitheliocytus limbatus) and non-ciliated (epitheliocytus aciliatus) cells.
Secretory cells Clara their narrow base lies on the basement membrane, their wide apical part is dome-shaped, the nucleus is round in shape, the cytoplasm contains the Golgi complex, smooth ER, mitochondria and secretory granules.
Function of secretory cells- secrete lipoproteins and glycoproteins (surfactant components) and enzymes involved in the detoxification of toxins entering the respiratory tract.
Bordered (brush) the cells are barrel-shaped, i.e., a narrow base, a narrow apical part and a wide middle part. Their core has a round shape, in the cytoplasm there are organelles of general importance, on the apical surface there are microvilli that form a border.
Function of border cells- perceive odors (olfactory function).
Unciliated epithelial cells have a prismatic shape, somewhat elevated above the rest of the epithelial cells. Their cytoplasm contains the Golgi complex, mitochondria, EPS, inclusions of glycogen granules and secretory granules. Their function is unknown.
In his practice, an ENT doctor often has to deal with such a problem as mucus in the throat. There are quite a large number of patients whose main complaint is mucus. So where does it form and constantly bother your throat? Let's figure it out. The human upper respiratory tract is lined with mucous membrane. If you unfold the entire mucous membrane of the upper respiratory tract (pharynx, nasal cavity, paranasal sinuses) into one “carpet”, you will get a fairly decent area of about 25 sq.m. Such anatomy of the upper floor of the respiratory organs, such a large area of the mucous membrane, has an important biological meaning.
The fact is that we are forced to obtain oxygen from the air, and the air is not sterile; when breathing, a person inhales a huge number of microbes along with the air, so the respiratory organs, like no other human system, experience a colossal biological load. But when nature created us, it took all this into account, which is why the upper respiratory tract has such a structure as a perfect product of a long evolutionary process.
The main function of the mucous membrane lining the upper respiratory tract is protective; it is a complex multicomponent “filter”. If this “filter” works correctly, then the microbes that we constantly inhale do not bother us.
Causes of mucus in the throat
All problems begin when this complex multi-component defense system fails. The cause of such a failure is most often ARVI, but it can also be trauma, a sudden change in climate, weakening of a woman’s immunity during pregnancy, and a number of other reasons. Figuratively speaking, as a result of a breakdown, a “barrier” rises and microbes penetrate deeper into the mucous membrane and trigger a degenerative process in it.
In fact, the essence of all inflammatory ENT diseases, such as, is this degenerative process in the mucous membrane due to a weakening of the protective properties of the mucous membrane. One of the basis of these degenerative changes is impaired regeneration of the mucous membrane.
The fact is that all the tissues of our body are renewed throughout life, the upper layer of the skin is completely renewed within about five days, the upper layers of the mucous membrane of the respiratory organs are renewed in about a week. As a result of pathological mechanisms, against the background of a weakening of the protective properties of the mucous membrane, regeneration begins to proceed incorrectly and microerosions are formed on the mucous membrane, which are the “entry gate” for microbes, that is, the mucous membrane becomes like a “sieve”. Microbes again and again enter through this “sieve” into the mucous membrane, the degenerative process is supported, the protective properties become even more unusable, and the autonomic nerve endings, of which there are a huge number in the thickness of the mucous membrane, are also irritated, which leads to pathological impulses of the nerve endings of goblet cells.
In cases of illness, due to weakening of the protective properties, mucus continuously flows into the pharynx, accumulates in the throat, and the patient has to constantly cough up and spit.
Throughout the entire area of the mucous membrane there is a huge number of goblet cells; these are highly specialized cells, the main function of which is the production of mucus. Thanks to the presence of these cells, the mucosa is called mucosa, since a certain amount of mucus is necessary for its normal functioning. Due to pathological impulses of the autonomic nerve endings of goblet cells as a result of the degenerative process, they begin to malfunction and produce excessive mucus. This mucus continuously flows into the pharynx, accumulates in the throat, and the patient has to constantly cough up and spit, which causes indescribable discomfort.
Treatment of mucus in the throat
Despite the frequency of occurrence of such a problem as mucus in the throat, there are very few effective methods for treating this disease. Often, ENT doctors do not treat patients with mucus in the throat at all, they tell them that they are healthy and send them home. Often, after unsuccessful treatment, which also includes a huge number of antibiotics, such patients are referred to a psychiatrist. In very egregious cases, such patients are even operated on, which of course does not bring good results.
The catch is that in order for the treatment of mucus in the throat to be effective, it is necessary to influence all the important links in the pathogenesis of the degenerative process, namely, it is necessary to sanitize the entire area of the mucous membrane of the upper respiratory tract, restore it and stabilize local immunity. Unfortunately, this is not possible with the help of modern medications and surgical treatment.
With the help of the original treatment method that I use, I can achieve all this and get rid of such a seemingly unsolvable problem as mucus in the throat. The method is so effective that a decrease in mucus is already noted after one or two treatment sessions. The treatment is safe and has no side effects.
1. Concept of the respiratory system
2. Structure of the nasal cavity
3. Structure of the larynx
4. Structure of the trachea
5. Structure of the lungs
6. Structure of the bronchi
7. Blood supply to the lungs
1. The respiratory system consists of two parts: the airways and the respiratory section. The airways include the nasal cavity, nasopharynx, trachea, bronchial tree (extra- and intrapulmonary bronchi). The respiratory department includes respiratory bronchioles, alveolar ducts, and alveolar sacs. These structures unite to form the acini.
Source of development The main respiratory organ is the material of the ventral wall of the foregut, called the prechordal plate. At the 3rd week of embryogenesis, it forms a protrusion, which in the lower part is divided into two rudiments of the right and left lungs. There are 3 stages in lung development:
glandular stage, begins from the 5th week to the 4th month of embryogenesis. At this stage, the airway system and the bronchial tree are formed. At this time, the lung primordium resembles a tubular gland, since in the section, among the mesenchyme, numerous sections of large bronchi are visible, similar to the excretory ducts of the exocrine glands;
the canalicular stage (4-6 months of embryogenesis) is characterized by the completion of the formation of the bronchial tree and the formation of respiratory bronchioles. At the same time, capillaries are intensively formed, which grow into the mesenchyme surrounding the epithelium of the bronchial tubes;
alveolar stage and begins from the 6th month of intrauterine development and continues until the birth of the fetus. In this case, alveolar ducts and sacs are formed. Throughout embryogenesis, the alveoli are in a collapsed state.
Functions of the airways:
conducting air to the respiratory section;
air conditioning - warming, humidifying and cleaning;
barrier-protective;
secretory - the production of mucus, which contains secretory antibodies, lysozyme and other biologically active substances.
2. Nasal cavity
The nasal cavity consists of the vestibule and the respiratory part. Vestibule of the nose lined with a mucous membrane, which contains stratified squamous non-keratinizing epithelium and the lamina propria of the mucosa. Respiratory part lined with single-layer multirow ciliated epithelium. It consists of:
ciliated cells - have ciliated cilia that oscillate against the movement of inhaled air; with the help of these cilia, microorganisms and foreign bodies are removed from the nasal cavity;
goblet cells secrete mucins - mucus that glues foreign bodies and bacteria together and facilitates their removal;
microvilli cells are chemoreceptor cells;
basal cells play the role of cambial elements.
The lamina propria of the mucous membrane is formed by loose fibrous unformed connective tissue; it contains simple tubular protein-mucosal glands, vessels, nerves and nerve endings, as well as lymphoid follicles.
Mucous membrane lining the respiratory part of the nasal cavity has two areas, differing in structure from the rest of the mucosa:
the olfactory part, which is located on most of the roof of each nasal cavity, as well as in the superior turbinate and the upper third of the nasal septum.
The mucous membrane lining the olfactory areas forms the olfactory organ;
The mucous membrane in the area of the middle and inferior nasal concha differs from the rest of the nasal mucosa in that it contains thin-walled veins that resemble lacunae in the corpora cavernosa of the penis. Under normal conditions, the blood content in the lacunae is small, since they are in a partially collapsed state. When inflamed (rhinitis), the veins become filled with blood and narrow the nasal passages, making nasal breathing difficult. Olfactory organ
is a peripheral part of the olfactory analyzer. The olfactory epithelium contains
three types of cells:
olfactory cells are spindle-shaped and have two processes. The peripheral process has a thickening (olfactory club) with antennae - olfactory cilia, which run parallel to the surface of the epithelium and are in constant motion. In these processes, upon contact with an odorous substance, a nerve impulse is formed, which is transmitted along the central process to other neurons and further to the cortex. Olfactory cells are the only type of neurons that have a predecessor in the form of cambial cells in an adult individual. Thanks to the division and differentiation of basal cells, olfactory cells are renewed every month;
supporting cells are located in the form of a multirow epithelial layer and have numerous microvilli on the apical surface;
basal cells have a conical shape and lie on the basement membrane at some distance from each other. Basal cells are poorly differentiated and serve as a source for the formation of new olfactory and supporting cells. The first neuron is the olfactory cells, their axons form the olfactory nerves and end in the form of glomeruli in the olfactory bulbs on the dendrites of the so-called mitral cells. This is the second link of the olfactory pathway. The axons of mitral cells form the olfactory pathways in the brain. The third neurons are cells of the olfactory pathways, the processes of which end in the limbic region of the cerebral cortex.
Nasopharynx is a continuation of the respiratory part of the nasal cavity and has a structure similar to it: it is lined with multirow ciliated epithelium lying on the lamina propria. The lamina propria contains secretory sections of small protein-mucosal glands, and on the posterior surface there is an accumulation of lymphoid tissue (pharyngeal tonsil).
3. The wall of the larynx consists of mucous, fibrocartilaginous and adventitial membranes. The mucous membrane is represented by the epithelial and lamina propria. The epithelium is multirow ciliated, consists of the same cells as the epithelium of the nasal cavity. Vocal cords covered with stratified squamous non-keratinizing epithelium. The lamina propria is formed by loose fibrous unformed connective tissue and contains many elastic fibers. The fibrocartilaginous membrane plays the role of the frame of the larynx and consists of fibrous and cartilaginous parts. The fibrous part is dense fibrous connective tissue, the cartilaginous part is represented by hyaline and elastic cartilage.
Vocal cords(true and false) are formed by folds of the mucous membrane protruding into the lumen of the larynx. They are based on loose fibrous connective tissue. The true vocal cords contain several striated muscles and a bundle of elastic fibers. Muscle contraction changes the width of the glottis and the timbre of the voice. False vocal cords, lying above the true ones, do not contain skeletal muscles and are formed by loose fibrous connective tissue covered with stratified epithelium. In the mucous membrane of the larynx, in the lamina propria, there are simple mixed protein-mucous glands.
Functions of the larynx:
air conduction and conditioning;
participation in speech;
secretory function;
barrier-protective function.
4. The trachea is a layered organ, and consists of 4 membranes: mucous, submucosal, fibrocartilaginous and adventitial. Mucous membrane consists of multirow ciliated epithelium and lamina propria. The tracheal epithelium contains the following types of cells: ciliated, goblet, intercalary or basal, endocrine. Goblet cells and ciliated cells form the mucociliary (mucociliary) conveyor. Endocrine cells have a pyramidal shape; in the basal part they contain secretory granules with biologically active substances: serotonin, bombesin and others. Basal cells are poorly differentiated and serve as cambium. The lamina propria is formed by loose fibrous connective tissue and contains many elastic fibers, lymphatic follicles, and scattered smooth myocytes.
Submucosa formed by loose fibrous connective tissue in which complex protein-mucosal tracheal glands are located. Their secretion moisturizes the surface of the epithelium and contains secretory antibodies.
Fibrocartilaginous sheath consists of glial cartilaginous tissue, forming 20 half-rings, and dense fibrous connective tissue of the perichondrium. On the posterior surface of the trachea, the ends of cartilaginous half-rings are connected by bundles of smooth myocytes, which facilitates the passage of food through the esophagus lying behind the trachea. Adventitia formed by loose fibrous connective tissue. The trachea at the lower end is divided into 2 branches, forming the main bronchi, which are part of the roots of the lungs. The bronchial tree begins with the main bronchi. It is divided into extrapulmonary and intrapulmonary parts.
5. Basic functions of the lungs:
gas exchange;
thermoregulatory function;
participation in the regulation of acid-base balance;
regulation of blood coagulation - the lungs form large quantities of thromboplastin and heparin, which participate in the activity of the coagulant-antigoagulant blood system;
regulation of water-salt metabolism;
regulation of erythropoiesis by secretion of erythropoietin;
immunological function;
participation in lipid metabolism.
The lungs consist of two main parts: intrapulmonary bronchi (bronchial tree) and numerous acini that form the lung parenchyma.
Bronchial tree begins with the right and left main bronchi, which are divided into lobar bronchi - 3 on the right and 2 on the left. The lobar bronchi are divided into extrapulmonary zonal bronchi, which in turn form 10 intrapulmonary segmental bronchi. The latter are successively divided into subsegmental, interlobular, intralobular bronchi and terminal bronchi. There is a classification of bronchi according to their diameter. Based on this characteristic, bronchi are distinguished into large (15-20 mm), medium (2-5 mm), small (1-2 mm) caliber.
6. The wall of the bronchus consists of 4 membranes: mucous, submucosal, fibrocartilaginous and adventitial. These membranes undergo changes throughout the bronchial tree.
Inner, mucous membrane consists of three layers: multirow ciliated epithelium, lamina propria and muscular lamina. The epithelium contains the following types of cells:
secretory cells, cells secrete enzymes that destroy surfactant;
non-ciliated cells possibly perform a receptor function;
border cells, the main function of these cells is chemoreception;
ciliated;
goblet;
endocrine.
lamina propria of the mucous membrane consists of loose fibrous connective tissue rich in elastic fibers. Muscular plate of the mucous membrane formed by smooth muscle tissue. Submucosa represented by loose fibrous connective tissue. It contains the terminal sections of mixed mucous-protein glands. The secretion of the glands moisturizes the mucous membrane . Fibrocartilaginous sheath formed by cartilaginous and dense fibrous connective tissue. Adventitia represented by loose fibrous connective tissue.
Throughout the bronchial tree, the structure of these membranes changes. The wall of the main bronchus does not contain half rings, but closed cartilaginous rings. In the wall of large bronchi, cartilage forms several plates. Their number and size decrease as the diameter of the bronchus decreases. In the medium-caliber bronchi, hyaline cartilaginous tissue is replaced by elastic tissue. In small-caliber bronchi, cartilage is completely absent. The epithelium also changes. In large bronchi it is multirowed, then gradually becomes birowed, and in the terminal bronchioles it turns into a single row cubic. The number of goblet cells in the epithelium decreases. The thickness of the lamina propria decreases, while the thickness of the muscular lamina, on the contrary, increases. In the small-caliber bronchi, the glands disappear in the submucous membrane, otherwise the mucus would close the narrow lumen of the bronchus here. The thickness of the adventitial membrane decreases.
The airways end terminal bronchioles, having a diameter of up to 0.5 mm. Their wall is formed by the mucous membrane. The epithelium is single-layered cubic ciliated. It consists of ciliated, brush, borderless cells and Clara secretory cells. The lamina propria is formed by loose fibrous connective tissue, which passes into the interlobular loose fibrous connective tissue of the lung. The lamina propria contains bundles of smooth myocytes and longitudinal bundles of elastic fibers.
Respiratory section of the lungs
The structural and functional unit of the respiratory department is the acinus. Acinus is a system of hollow structures with alveoli in which gas exchange occurs.
The acinus begins with a respiratory or alveolar bronchiole of the 1st order, which is dichotomously sequentially divided into respiratory bronchioles of the 2nd and 3rd orders. Respiratory bronchioles contain a small number of alveoli; the rest of their wall is formed by a mucous membrane with cuboidal epithelium, thin submucosa and adventitia. Respiratory bronchioles of the 3rd order are dichotomously divided and form alveolar ducts with a large number of alveoli and correspondingly smaller areas lined with cuboidal epithelium. The alveolar ducts pass into the alveolar sacs, the walls of which are completely formed by alveoli in contact with each other, and there are no areas lined with cuboidal epithelium.
Alveolus- structural and functional unit of the acinus. It has the appearance of an open vesicle, lined from the inside with single-layer squamous epithelium. The number of alveoli is about 300 million, and their surface area is about 80 square meters. m. The alveoli are adjacent to each other, between them there are interalveolar walls, which contain thin layers of loose fibrous connective tissue with hemocapillaries, elastic, collagen and reticular fibers. Pores connecting them were found between the alveoli. These pores allow air to penetrate from one alveoli to another, and also ensure gas exchange in the alveolar sacs, whose own airways are closed as a result of the pathological process.
The alveolar epithelium consists of 3 types of alveolocytes:
type I alveolocytes or respiratory alveolocytes, gas exchange occurs through them, and they also participate in the formation of the aerohematic barrier, which includes the following structures - the endothelium of the hemocapillary, the basement membrane of the continuous type endothelium, the basement membrane of the alveolar epithelium (the two basement membranes are tightly adjacent to each other and are perceived as one); alveolocyte type I; surfactant layer lining the surface of the alveolar epithelium;
type II alveolocytes or large secretory alveolocytes, these cells produce surfactant - a substance of glycolipid-protein nature. Surfactant consists of two parts (phases) - the lower (hypophase). The hypophase smoothes out the surface irregularities of the alveolar epithelium; it is formed by tubules that form a lattice structure on the surface (apophase).
Apophase forms a phospholipid monolayer with the orientation of the hydrophobic parts of the molecules towards the alveolar cavity.
Surfactant performs a number of functions:
reduces the surface tension of the alveoli and prevents their collapse;
prevents the leakage of fluid from the vessels into the cavity of the alveoli and the development of pulmonary edema;
has bactericidal properties, as it contains secretory antibodies and lysozyme;
participates in the regulation of the functions of immunocompetent cells and alveolar macrophages.
Surfactant is constantly being exchanged. In the lungs there is a so-called surfactant-antisurfactant system. Surfactant is secreted by type II alveolocytes. And the old surfactant is destroyed by the secretion of the corresponding enzymes by the Clara secretory cells of the bronchi and bronchioles, type II alveolocytes themselves, as well as alveolar macrophages.
type III alveolocytes or alveolar macrophages that adhere to other cells.
They come from blood monocytes.
The function of alveolar macrophages is to participate in immune reactions and in the work of the surfactant-antisurfactant system (surfactant breakdown).
bronchial arteries depart from the aorta and carry out trophism of the lung. Their branches go along the bronchial tree up to the alveolar ducts. Here, capillaries that anastomose with each other extend from the arterioles to the alveoli. At the top of the alveoli, capillaries become venules.