The basis of the wall of large bronchi, for example, lobar and segmental, is made up of cartilaginous rings - this dense base does not allow the wall to contract and keeps the lumen of the bronchi always open, which ensures free movement of air both during inhalation and exhalation. As the diameter of the bronchus decreases, the amount of cartilage tissue decreases, and smooth muscle tissue appears. In the small bronchi already more muscle tissue, in the terminal bronchioles, cartilage tissue is completely absent and the basis of their wall is smooth muscle tissue, therefore, a spasm is possible at the level of bronchioles, which happens during an attack bronchial asthma. In the respiratory bronchi, in the alveolar ducts, and sacs, the wall is formed by a single layer of squamous epithelial cells. The wall of the alveoli is also formed by a layer of squamous epithelium, the cells of which are called pneumocytes.
Trachea
Right main bronchus Left main bronchus
Lobar bronchi of the 2nd order.
Segmental bronchi of the 3rd order.
Lobular bronchi of the 23rd order.
terminal bronchioles.
Respiratory bronchioles.
Alveolar passages.
Alveolar sacs.
Alveoli.
The structure of the lungs.
The lungs are paired parenchymal organs located in chest cavity. They are cone shaped. On the lung, the apex is isolated (1.5-2 cm above the clavicle) and the base is isolated, which lies on the diaphragm. The lung has three surfaces: external or costal; lower - diaphragmatic; mediastinal-mediastyle or medial.
Gates are located on the medial surface.
Draw a conclusion about the features of the vascular bed of the lungs:
All structures located in the area of the gates of the lungs form the root of the lung. Inflammation of these structures is assessed as hilar pneumonia, in contrast to focal pneumonia, when the walls of the alveoli become inflamed.
Each lung is divided into sections called lobes. The right lung is divided into three lobes and the left into two. The lobes are separated from each other by deep furrows. In the furrows there are partitions from connective tissue.
Make a schematic drawing. "External structure of the lung".
The shares are divided into segments. Each lung has ten segments. The segments are divided into lobules, of which there are about a thousand in each lung. Both segments and lobules are separated from each other by connective tissue. The connective tissue of the lungs that forms the partitions between the lobes, segments and lobules are called interstitial and interstitial lung tissue . Inflammation of this tissue is also regarded as interstitial pneumonia.
The outside of the lung is covered with a serous membrane called pleura. Like all serous membranes, it consists of two sheets: the inner visceral, which is tightly adjacent to the lung tissue, and the outer parietal (parietal), which is adjacent to the inner surface of the lungs. A closed space between leaves is pleural cavity, it is filled with a small amount of serous fluid. Inflammation of the pleura is called pleurisy. With pleurisy in the cavity is formed a large number of serous or purulent fluid, the fluid compresses the lung and it is turned off from breathing. Help with such a pathology can be provided by performing a pleural puncture (puncture). Violation of the integrity of the pleura and entry into the pleural cavity of atmospheric air pneumothorax. The entry of blood into the pleural cavity is called hemothorax.
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 a 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 clara cells they lie on the basement membrane with a narrow base, their wide apical part is dome-shaped, the nucleus is round, 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.
Kamchatye (brush) the cells are barrel-shaped, i.e., a narrow base, a narrow apical part, and a wide middle part. Their nucleus has a round shape, in the cytoplasm - organelles general meaning, on the apical surface there are microvilli that form a border.
^ Function of the limbic cells - perceive smells (olfactory function).
Unciliated epitheliocytes have a prismatic shape, slightly rise above the rest of the epitheliocytes. Their cytoplasm contains the Golgi complex, mitochondria, ER, inclusions of glycogen granules, and secretory granules. Their function is unknown.
Respiratory section of the lungs
Pulmonary acinus is the structural and functional unit of the lungs. Respiratory begins with acinus part of a lung. It is a branching of the respiratory bronchiole of the 1st order. How does this bronchiole branch? The respiratory bronchiole of the 1st order is divided into 2 respiratory bronchioles of the 2nd order, each of which branches into 2 bronchioles of the 3rd order, from which 2 alveolar passages (ductus alveolaris) depart, each alveolar passage ends with 2 alveolar sacs (sacculus alveolaris ). The walls of the respiratory bronchioles, alveolar ducts and alveolar sacs contain alveoli(alveolus).
Thus, the branches of the respiratory bronchiole of the 1st order and all the alveoli that make up their composition are the pulmonary acinus.
Acini are separated from each other by layers of loose connective tissue. 12-18 acini form a lung lobule, which is also separated from other lobules by a layer of loose connective tissue.
^ Wall of respiratory bronchioles (bronchiolus respiratorius) is thinned and includes 2 weakly expressed membranes: 1) mucous and 2) adventitial.
mucous membrane respiratory bronchioles is lined with a single-layer cubic non-ciliated epithelium, in which ciliated epitheliocytes are sometimes found, there are secretory Clara cells.
The lamina propria is thinned, the muscular lamina is represented by separate circularly arranged bundles of smooth myocytes.
^ adventitial sheath respiratory bronchioles, represented by loose connective tissue, is also thinned, its fibers pass into the interalveolar connective tissue.
There are separate alveoli in the wall of the respiratory bronchioles. The wall of the alveolar ducts and alveolar sacs consists of alveoli.
Alveoli are open bubbles with a diameter of 120-140 microns, opening into the lumen of the respiratory bronchioles, alveolar ducts and alveolar sacs. Between the alveoli there are connective tissue septa 2-8 microns thick, which contain: a plexus of elastic fibers, a network of thin collagen fibers, fibroblasts, tissue basophils and antigen-presenting cells, which were mentioned when talking about the tracheal epithelium. Capillaries with a diameter of 5-7 microns pass through the partitions, occupying about 75% of the area of the alveoli. The alveoli communicate with each other with the help of Kuhn's alveolar pores with a diameter of 10-15 microns.
^ Wall of alveoli It is lined with alveolocytes (pneumocytes) lying on a basement membrane reinforced with a framework consisting of thin collagen and reticular fibers. Alveolocytes of the alveoli are represented by 2 main types: respiratory (type I alveolocytes) and secretory (type II alveolocytes). In the wall of the alveoli and on their surface there are alveolar macrophages (macrophagocytus alveolaris).
^ Respiratory alveolocytes (alveolocytus respiratorius) have a flattened shape, small mitochondria and pinocytic vesicles are present in their cytoplasm, and there are short outgrowths (microvilli) on the apical surface. The thickness of the nucleated part of the respiratory alveolocytes is 5-6 microns, the non-nuclear part is 0.2 microns. Opposite the non-nuclear part of the alveolocytes lies the non-nuclear part of the endotheliocytes, the thickness of which is also about 0.2 microns. Therefore, the partition between the air of the alveoli and the lumen of the capillaries, which forms an air-blood barrier, is about 0.5 microns. The composition of the air-blood barrier includes: the nuclear-free part of the respiratory alveolocytes, the basement membrane of the alveoli, the interalveolar connective tissue, the basement membrane of the capillary and the endothelium.
^ Function of respiratory alveolocytes - gas exchange between the air of the alveoli and the hemoglobin of erythrocytes (respiratory function).
secretory alveolocytes, or type II alveolocytes, or large alveolocytes (alveolocytus magnus), make up only 5% of total number cells that line the inner surface of the alveolar wall. They have a cubic or oval shape, microvilli extend from their cytolemma. The cytoplasm contains: the Golgi complex, EPS, ribosomes, mitochondria, multivesicular bodies, cytophospholiposomes (lamellar osmiophilic bodies), which are markers of type II alveolocytes.
^ Function of secretory alveolocytes - secrete components of the surfactant alveolar complex, i.e. phospholipids and proteins.
Surfactant alveolar complex covers the inner surface of alveolocytes and includes 3 components: 1) membrane, similar in structure to cell membranes and including phospholipids and proteins synthesized by secretory alveolocytes; 2) hypophase (liquid component), consisting of lipoproteins and glycoproteins secreted by secretory Clara cells; 3) reserve surfactant.
^ Functional value surfactant alveolar complex:
1) prevents the inner surface of the walls of the alveoli from sticking together during exhalation (if the alveoli stick together, the next breath would be impossible and death would occur in 4-5 minutes);
2) prevents the penetration of microorganisms from the alveoli into the surrounding connective (interstitial) tissue;
3) prevents the flow (transudation) of fluid from the interstitial tissue into the alveoli.
^ Alveolar macrophages have a process shape, an oval nucleus and a well-developed lysosomal apparatus, located in the wall of the alveoli or on them outer surface, can migrate from the alveoli to the interstitial tissue. Their cytoplasm contains lipid inclusions, during the oxidation of which the inhaled air warms up, its temperature should correspond to body temperature.
^
Macrophage function
- protective, they phagocytize microorganisms, dust particles, cell fragments and surfactant; participate in the metabolism of lipids, release thermal energy.
^
Blood supply to the lungs.
The lungs include the pulmonary and bronchial arteries. Venous blood flows through the pulmonary artery. This artery branches along the bronchi. Having reached the alveoli, its branches are divided into capillaries with a diameter of 5-7 microns, intertwining the alveoli. Each capillary will simultaneously run to two alveoli. The fact that the erythrocytes in the capillaries go in one row, and that the capillaries pass between the two alveoli, in contact with them, promotes gas exchange between the air of the alveoli and the hemoglobin of the erythrocytes.
Having given carbon dioxide and enriched with oxygen, blood from the interalveolar capillaries enters the pulmonary vein system, which flows into the left atrium.
The bronchial arteries are branches of the aorta; they also branch out along the bronchi and provide oxygen to their wall and lung tissues. In the wall of the bronchi, the branches of these arteries form plexuses in the submucosa and the lamina propria. The arterioles of these plexuses branch into capillaries that form a dense network under the basement membrane. The capillaries drain into venules that carry venous blood into small veins flowing into the anterior and posterior bronchial veins. At the level of small-caliber bronchi between the arterioles of the bronchial artery system and the venules of the pulmonary vein system, ABA are formed, through which part of the arterial blood returns to the heart.
^ The lymphatic system It is represented by superficial and deep plexuses of lymphatic capillaries and vessels. Superficial plexus is localized in the visceral pleura, deep - in the connective tissue around the acini, lobules, along the bronchi and blood vessels. In the wall of the bronchi there are 2 lymphatic plexuses: in the submucosa and in the lamina propria of the mucous membrane.
innervation provided by nerve plexuses located in the layers of connective tissue along the blood vessels and bronchi. The structure of the plexuses includes intramural nerve ganglia, efferent (sympathetic and parasympathetic) and afferent nerve fibers. Efferent sympathetic fibers are axons of efferent neurons of the sympathetic ganglia, ending with motor effectors on the myocytes of the bronchi and blood vessels and secretory effectors on the bronchial glands.
Parasympathetic efferent fibers are axons of motor neurons (type I Dogel cells) of intramural ganglia, to which impulses come from fibers vagus nerve. Efferent parasympathetic fibers also terminate in motor and secretory effector endings.
When the sympathetic fibers are stimulated, the vessels constrict, the bronchi expand, and breathing becomes easier. When the parasympathetic fibers are excited, on the contrary, the vessels expand, the bronchi narrow, breathing becomes difficult.
Afferent nerve fibers are the dendrites of the sensory neurons of the nerve ganglia. They terminate in receptors in the bronchial wall and lung parenchyma.
Age changes of the respiratory system are characterized by an increase in the number of alveoli and elastic fibers from infancy to youth. In old age, the number of alveoli in the lungs decreases, the elastic fibers of the alveolar skeleton are destroyed, the connective tissue stroma grows, in which collagen fibers predominate. As a result of these changes, the elasticity of the lungs decreases, their expansion (emphysema) occurs due to insufficient collapse of the alveoli during exhalation. At the same time, salts are deposited in the bronchi of large caliber, resulting in a restriction of respiratory excursions and a decrease in gas exchange.
Pleura, covering the lung is called visceral; lining the wall of the chest cavity - parietal. The basis of the visceral and parietal pleura is connective tissue lined with mesothelium from the side pleural cavity. The visceral pleura differs in that its connective tissue base is more smooth muscle cells and elastic fibers. The fibers of the visceral pleura penetrate into the interstitial tissue of the lung.
Depending on the excursions of the lungs, the mesothelium of the pleura changes its shape: when inhaling it flattens, when exhaling it acquires a cubic shape.
^ Functions of the respiratory system: respiratory and non-respiratory.
In the process of respiratory function, gas exchange is carried out between the hemoglobin of erythrocytes and the air of the alveoli.
Non-respiratory functions include:
1) thermoregulatory, that is, warming the inhaled air if it is cold, and cooling if it is hot, since the temperature of the air entering the alveoli must correspond to body temperature;
2) humidification of the inhaled air;
3) purification of inhaled air from dust particles, bacteria and other harmful components;
4) immune protection;
5) participation in lipid metabolism and water-salt metabolism (with exhaled air in the form of steam, up to 500 ml of water is removed daily);
6) participation in the maintenance of the blood coagulation system due to tissue basophils of the lungs;
7) hormonal (secretion of calcitonin, bombesin, norepinephrine, dopamine, serotonin);
8) inactivation of serotonin with the help of monoamine oxidase contained in macrophages and mast cells of the lungs, and bradycardin;
9) synthesis of lysozyme, interferon and pyrogen by lung macrophages;
10) destruction of small blood clots and tumor cells in the vessels of the lungs;
11) deposition of blood in the vessels of the pulmonary circulatory system;
13) olfactory;
14) participation in the excretion of certain volatile substances (acetone, ammonia, alcohol vapors) from the body.
LECTURE 25
^ LEATHER AND ITS DERIVATIVES
Leather(cutis) consists of the skin itself (corium) and the epidermis covering the surface of the skin (epidermis), which is a stratified squamous keratinized epithelium. Beneath the dermis proper is the subcutaneous fat, or hypodermis (hipoderma).
Sources of development. The main cells of the epidermis - keratinocytes and skin appendages (nails, hair, sebaceous, sweat and mammary glands) develop from the skin ectoderm; melanocytes and Merkel cells of the epidermis - from the neural crest; intraepidermal macrophages - from monocytes. The connective tissue basis of the skin develops from the dermatomes of the mesodermal somites.
The thickest epidermis(600 microns) covers the palmar surface of the hands and soles of the feet, and the thinnest (170 microns) lines the dermis of the face and head.
The structure of the epidermis of the palmar surface of the hands and soles of the feet. In this epidermis, cells form approximately 50 layers, but all of them can be grouped into 5 main ones:
1) basal (stratum basale);
2) prickly (stratum spinosum);
3) granular (stratum granulosum),
4) brilliant (stratum lucidum);
5) horny (stratum corneum).
On the rest of the skin there is no shiny layer.
^ Basal layer includes 4 differenton cells: a) keratinocytes, b) melanocytes, c) Merkel cells, d) intraepidermal macrophages.
Keratinocytes make up more than 85% of all cells of this layer, lie on the basement membrane, have a prismatic shape, connect to each other and other epithelial cells with the help of desmosomes, and with the basement membrane with the help of hemidesmosomes.
The cytoplasm of keratinocytes of the basal layer stains basophilically; the oval, chromatin-rich nucleus is located in the basal part of the cell. In the cytoplasm there are organelles of general importance. On the granular ER, keratin protein molecules are synthesized, from which filaments are polymerized. In the cytoplasm are melanin pigment granules captured by phagocytosis.
Among the keratinocytes of the basal layer, there are stem cells that are in the G 0 period. However, they can leave this period, enter into cell cycle and undergo mitotic division. The daughter cells formed as a result of division also continue to divide and undergo differentiation. Due to the division of keratinocytes, a complete renewal of epidermal cells takes place within 3-4 weeks. Therefore, the basal layer is called the germ layer. As differentiation proceeds, basal keratinocytes shift into the spinous layer.
^ Functions of keratinocytes: regenerative, synthesis of keratin, synthesis of thymosin and thymopoietin, stimulating proliferation and antigen-independent differentiation of T-lymphocytes (substitution of thymus function).
melanocytes they are not connected by desmosomes with other cells and the basement membrane, they have a process shape, weakly stained cytoplasm, which contains: a synthetic apparatus, melanin pigment granules, and tyrosinase and DOPA oxidase enzymes involved in the synthesis of this pigment. The pigment is released from cells by exocytosis. Melanocytes are large in size, so their processes penetrate into the spinous layer. The total number of melanocytes does not exceed 10% of all cells in the basal layer.
^ Merkel cells shorter but wider than keratinocytes, contain irregular shape nucleus, weakly stained cytoplasm, which contains secretory granules containing bombesin, VIP, enkephalin. Merkel cells are approached by nerve fibers that come into contact with them through the Merkel discs.
^ Functions of Merkel cells:
1) endocrine (secretion of bombesin, VIP, enkephalin);
2) participation in the regeneration of the epidermis;
3) participation in the regulation of the tone and permeability of the blood vessels of the dermis with the help of VIP and by emulating the release of histamine from mast cells;
4) perceive irritation, so their greatest number is in the most sensitive parts of the skin (tip of the nose, fingers).
^ Intraepidermal macrophages (Langerhans cells) - the largest, have a process shape. Their processes are deeply embedded in the spiny layer. The nucleus most often has a lobed shape. Of the common organelles, lysosomes are best developed, containing the enzyme cholesterol sulfatase, etc. The cytoplasm contains Birbeck granules that look like a tennis racket. These macrophages have the ability to migrate to the dermis and regional lymph nodes.
^ Functions of intraepidermal macrophages:
1) produce IL-1, which stimulates the proliferation and differentiation of lymphocytes;
2) perceive antigens and present them to lymphocytes of the epidermis and regional lymph nodes(participate in immune reactions);
3) secrete prostaglandins, kalons, epithelial growth factor, the enzyme cholesterol sulfatase, which breaks down the intercellular cement of the surface part of the stratum corneum of the epidermis;
4) are the centers of epidermal proliferative units (EPU), regulating the proliferation and keratinization of keratinocytes with the help of epithelial growth factor, kalons and cholesterol sulfatase.
^ Epidermal proliferative units have the appearance of columns, starting from the basal layer and ending on the surface of the stratum corneum of the epidermis, at the base of which are intraepidermal macrophages.
^ Spiny layer It is represented by irregularly shaped keratinocytes, located in 5-10 rows, and intraepidermal macrophages. The nuclei of cells adjacent to the basal layer are round, and closer to the granular layer, they are oval. Outgrowths extend from the cell bodies - spikes in which there are microfibrils. The spikes of one cell are in contact with the spikes of another cell. Between the spikes of the cells are desmosomes.
^ Functions of the cells of the spinous layer: the synthesis of keratin continues, the polymerization of keratin tonofilaments, from which bundles are formed - tonofibrils. Keratinosomes are formed in the cells, which are lamellar (lamellar) bodies containing lipid substances: cholesterol sulfates and ceramides. Taken together, the basal and spiny layers form the epidermal growth layer. With further differentiation, the cells of the spinous layer are shifted to the next, granular layer.
^ Granular layer It is represented by oval or slightly wrinkled cells arranged in 3-4 rows. Cell nuclei are pycnotized. In the keratinocytes of this layer, the synthesis of keratin continues, the synthesis of filaggrin, keratolaminin, and involucrin begins. Keratin tonofibrils are packaged with filaggrin into keratohyalin granules, in which filaggrin plays the role of an amorphous matrix. Keratolaminin and involucrin are adjacent to the cell cytolemma, providing its high strength and resistance to the effects of keratinosome and lysosome enzymes, which are activated under the influence of intraepidermal macrophages.
By this time, the nucleus and organelles begin to disintegrate. As a result of their decay, proteins, lipids, polysaccharides and amino acids are formed, which, joining the bundles of tonofibrils packed with filaggrin, take part in the formation of keratohyalin granules. These granules are diffusely scattered throughout the cytoplasm. The formation of keratohyalin granules is the 1st stage of keratinization.
In keratinocytes of the granular layer, the formation of keratinosomes containing lipids (cholesterol sulfate and ceramides) and enzymes continues.
Keratinosomes enter the intercellular space by exocytosis, where a cementing substance is formed from them, gluing the cells of the granular and shiny layers and the stratum corneum of the stratum corneum. Thanks to the cementing agent, a waterproof layer of the epidermis is formed, which prevents dehydration of the skin and at the same time is a barrier that protects the skin from the penetration of bacteria, chemical substances and other harmful ingredients.
The number of desmosomes between the cells of the granular layer decreases. With further differentiation, the cells of the granular layer are shifted to the next, shiny layer.
^ Shiny layer It is represented by flattened cells, the nucleus and organelles of which are completely destroyed. There are no desmosomes between the cells and they are interconnected by means of a cementing substance. Keratohyalin granules coalesce into a solid mass called eleidin. The formation of eleidin is the next, 2nd stage of keratinization. Eleidin does not stain with dyes, but refracts light well. Therefore, on preparations stained with hematoxylin-eosin, this layer is presented in the form of a shiny strip. As further differentiation (keratinization, keratinization) occurs, the cells of the zona pellucida flatten even more and move to the next, stratum corneum.
^ stratum corneum consists of 14-coal scales covered with a cytolemma reinforced with the protein keratolaminin. Inward from the thickened cytolemma, there are longitudinally located bundles of keratin microfibrils, devoid of filaggrin, which is cleaved to the amino acids that make up keratin. The keratinized structures of the horny scales are soft keratin. In the center of the scale, instead of the core, there is an air bubble.
The cementitious substance that connects the most superficial scales of the stratum corneum is destroyed by the lipolytic enzyme cholesterol sulfatase secreted by intraepidermal macrophages. Therefore, the scales are exposed desquamation (peeling).
The stratum corneum on the palmar surface reaches a thickness of 600 microns. This layer has a high density, low thermal conductivity and impermeability to water, bacteria and toxins.
^ The process of keratinization (keratinization) lasts 3-4 weeks. It involves keratin filaments and fibrils, keratinosomes, desmosomes, cementum, intraepidermal macrophages (Langerhans cells), which secrete:
1) epithelial growth factor, which stimulates the division of keratinocytes;
2) kalons that inhibit the division of keratinocytes;
3) cholesterol sulfatase, which breaks down the lipids of the cementing substance, resulting in desquamation of the surface scales.
The intensity of keratinization increases with mechanical action on the skin, with a lack of vitamin A or an excess of cortisol (a hormone of the adrenal cortex).
Terminal bronchioles (TB) have almost the same structure as the preterminal bronchioles, however, they are smaller in diameter and their walls are thinner (Fig. 1). The terminal bronchiole divides into two or three respiratory bronchioles (RB), in the final segments of which alveoli appear (A). Each respiratory bronchiole divides into two or three alveolar ducts (ACh), which together form the pulmonary acinus (LA). Many alveoli open into alveolar ducts.
The mucous membrane of the bronchioles consists of a single layer of cuboidal epithelium (E) and a very thin lamina propria. In the initial department respiratory bronchioles the smooth muscle fibers (B) of the muscular coat (MO) are separated from each other, so that the muscular coat no longer looks like a single layer. The number of smooth muscle bundles sharply decreases towards the branching point respiratory bronchioles on the alveolar passages, ultimately remaining only in the form of smooth muscle rings (K) between the alveoli of the respiratory bronchioles and around the alveolar openings along the alveolar passages. Smooth muscle rings are located in the pineal thickenings on the free edges of the alveolar septa (AL).
Contraction of the smooth muscles of the alveoli and airways can cause severe asthmatic symptoms.
On fig. 1 also shows the anastomosis sites of the pulmonary artery (LA) system with the system of bronchial artery (BA) branches. Both systems are located in the adventitia (AO) of the bronchioles. A branch of the pulmonary artery gives rise to smaller vessels, which then form an extensive capillary network (CAP) around the alveoli of the respiratory bronchioles and alveolar ducts. The terminal branches of the bronchial artery (shown by the arrow) flow into this network.
Epithelium (E) of preterminal bronchioles(Fig. 2) is represented by epithelial cells from low prismatic to cubic shape with ciliated cells (RC) and Clara cells (CC) located on the basement membrane (BM). Towards the terminal segment of the respiratory bronchiole, the epithelium becomes flattened due to the appearance of the first alveoli.
Ciliated cells make up the bulk of the cells. They have an elliptical nucleus with a small nucleolus, a Golgi complex, few cisterns of the granular endoplasmic reticulum, lysosomes, large mitochondria, and a few residual bodies. At the apical end, ciliated cells bear several microvilli and kinocilia (K), whose vibrations are directed towards the intrapulmonary bronchi.
Clara cells (CC) are ciliated cells with a convex apical pole, an elongated nucleus, many large mitochondria, a well-developed Golgi complex, and subnuclear ergastoplasm containing many free ribosomes. In the supranuclear cytoplasm there is a small number of tubules, and a granular endoplasmic reticulum surrounded by electron-dense granules (G), which originated from the Golgi complex and smooth endoplasmic tubules. Secretory granules contain a mixture of glycosaminoglycans and cholesterol, which, when released onto the epithelial surface, probably form a protective layer.
Rice. 3. corresponds to the place of the beginning of the alveolar course, indicated by a white arrow in fig. 1. In terminal and respiratory bronchioles the epithelium gradually becomes cuboidal, the number of ciliated cells (RC) decreases and the number of Clara cells (CC) increases. AT primary departments passages or alveoli of the respiratory bronchioles, the epithelium becomes a single-layer flat, formed by extremely flat type I alveolar cells (AC I) and cuboidal type II alveolar cells (AC II). The capillary network (CAP) is located directly under this epithelial layer.
A group of smooth muscle cells (MC) protruding beyond the cut plane forms a muscle ring around the origin
Page 63 of 70
The bronchiole, entering the lobule, gives rise to numerous branches, which, like a tree, diverge to all parts of the lobule. Due to the fact that the bronchioles, as well as the intralobular ducts of the glands, lie inside the parenchyma of the lobules, they are attached on all sides to an elastic tissue similar to a sponge containing air spaces in which gas exchange occurs (Fig. 23 - 15). Therefore, when inhaling, they do not tend to fall off; moreover, while they experience stretching around their entire circumference due to stretching of the elastic fibers of the surrounding spongy tissue.
Rice. 23 - 13. Scheme of the structure of the lung lobule, the base directed to the pleura.
For clarity, the dimensions of the bronchioles and airways, as well as blood and lymphatic vessels, are enlarged. To make it easier to follow the course of the blood and lymphatic vessels, the first ones are not shown on the right, and the second ones on the left.
1 - apex, 2 - bronchiole, 3 - air, 4 - pulmonary vein, 5 - interalveolar septum, 6 - respiratory bronchiole, 7 - pleura, 8 - alveoli, 9 - alveolar passage, 10 - lymphatic vessel, 11 - pulmonary artery.
Therefore, in order for the lumen of the bronchioles to remain open, there is no need for cartilaginous rings or plates located in their wall. They differ from the bronchi also in that there are no glands in their walls. Indeed, they are located so close to the areas where gas exchange takes place that if a secret secreted by the glands got into them, it could be sucked into these areas. In addition, the epithelial lining of the bronchioles is thinner than that of the bronchi. In larger branches, cylindrical ciliated cells predominate, but cells without cilia are also scattered between them (Fig. 23 - 14). These taller cells are sometimes referred to as Clara cells. A feature of these cells is the abundance of mitochondria (in some species), and between the nucleus and the surface through which secretion is secreted, there is a very well-developed smooth endoplasmic reticulum. These cells are characterized by high metabolic activity. However, the function of their serous secretion has not yet been precisely established. AT terminal branches bronchioles there are tall cubic cells without cilia. Thus, the walls of bronchioles (Fig. 23 - 12) consist of epithelium, which lies on a thin elastic lamina propria, and this membrane, in turn, is surrounded by a muscular membrane, which was previously described in relation to the bronchi. Muscle tissue is located on the connective tissue, which performs a supporting function (Fig. 23 - 12).
Orders of the bronchioles. After the bronchiole, called the preterminal, enters the lobule, it gives off branches known as terminal bronchioles, the number of which varies depending on the size of the lobule. There are usually 3 to 7 terminal bronchioles.
Bronchioles of the next order, arising from the terminal ones, are called respiratory bronchioles (Fig. 23 - 13 and 23 - 15). They were named so because as these bronchioles branch and continue into lung parenchyma an increasing number of thin, air-containing protrusions appear in their walls. These small vesicles are surrounded by capillary networks that form thin plexuses, which will be described later. Between the blood in the capillaries of the wall of these protrusions, and the air inside them, gas exchange occurs.
Rice. 23-14. Electron micrograph showing mucosal cells of a small bronchiole from a 6000 mouse lung (courtesy of A. Collet).
Among the ciliated epithelial cells (1) is the Clara cell without cilia (2). Note numerous mitochondria and a well-developed smooth endoplasmic reticulum, especially under the apical surface. Asterisks mark the basement membrane of the epithelium. In the underlying lamina propria of the mucosa lie smooth muscle cells (3) and connective tissue fibroblasts (4). Top left - lumen of the bronchiole.
Since gas exchange is carried out in the protrusions of the walls of these bronchioles, the latter were called respiratory bronchioles. The free ends of the respiratory bronchioles expand somewhat and open into the so-called alveolar passages.
RESPIRATORY SECTION - ALVEOLAR MOVEMENTS,
Alveolar sacs and alveoli
Before we begin a discussion of the alveolar ducts into which the respiratory bronchioles open, it is useful to emphasize that the bronchi and bronchioles are tubes that have their own walls, and their main function is to conduct air to and from the respiratory section of the lobules. The terms that we will now use to describe how air is conducted to all parts of the respiratory lobule (alveolar ducts, alveolar sacs and alveoli) do not refer to structures that have their own wall, but to spaces of various orders and shapes that are located in elastic tissue similar to a sponge and containing numerous capillary networks (Fig. 23 - 13 and 23 - 15). 
Rice. 23 - 15. Micrograph of a lung of a small child (low magnification).
The respiratory bronchiole (1) has entered the longitudinal section, and it can be seen how it opens in two alveolar passages (2). Asterisks indicate alveolar sacs. The latter, in turn, open into rounded air spaces called alveoli.
The alveolar ducts, alveolar sacs and alveoli contain air that is constantly being renewed. This air is in close contact with the capillaries in the walls of the spongy tissue that divide this section of the lung into spaces, and since air and blood are separated only by thin tissue films through which diffusion easily occurs, an effective functional device is created that ensures the removal of carbon dioxide and uptake of oxygen as blood moves through the capillary networks of that part of the lung.
Alveolar ducts, alveolar sacs and alveoli. The spaces where the respiratory bronchioles open directly take the form of long branching "corridors", along which there are numerous " open doors» two main sizes. Corridors are called alveolar passages (Fig. 23 - 15). Larger open doors communicate with rotunda-like spaces called alveolar sacs, which are marked in Fig. 23 - 15 stars. The peripheral zone of each rotunda-shaped sac is divided by spur-shaped partitions extending inward into a number of cells that open into the central part of the sac. The cells are alveoli. It is estimated that in the lungs of an adult there are about 300 million alveoli, forming a total surface of the order of 70-80 m2, with which the air contained in them comes into contact.
Before starting the description histological structure walls separating some air spaces from others, we will briefly describe the structural units of the respiratory department, which are smaller than the lobules, they are important for understanding some pathological processes in the lungs.
Structural units within the lobule. As already noted, the bronchi branch, eventually forming bronchioles, which are part of the structural units of the lung, called lobules. However, there is no general agreement on how to name the structural units that include the branches resulting from the subsequent division of the bronchiole into a lobule. An exception in this regard is the unit of the lung, to which the terminal bronchiole fits, this unit is now often called the acinus. Millard considers the acinus to be the most practical structural unit to deal with in pathology. There are no standard names for more distal units, but Barrie suggests that they should be named according to the "tubules" that go with them. Thus, the structural unit to which the respiratory bronchiole fits can be called the respiratory bronchiolar unit, and the structural unit served by the alveolar passage (ductus) can be called the ductal unit.
Wall structure respiratory tract(mostly by von Hayek)
The walls of the trachea and bronchi consist of three main layers: the mucous membrane, the submucosa and the fibrocartilaginous layer, which also includes smooth muscles.
The mucous membrane is formed by a pseudostratified ciliated epithelium. The superficial layer mainly consists of ciliary cells. Among them are scattered goblet cells that secrete mucus. For the most part, goblet cells are surrounded by ciliary cells and their number decreases with a decrease in the caliber of the bronchi. Under the surface layer of cells in the large bronchi, there are 2-3 more rows of cuboidal intermediate cells, the number of which gradually decreases towards the periphery, so that only a number of ciliary cells with single goblet cells remain in the bronchioles. The mucous membrane is delimited from the outside by a basal membrane formed by bundles of intertwining fibers. Above the spur of the tracheal bifurcation and often in the region of the underlying bifurcations, the ciliated epithelium is replaced by a stratified squamous epithelium.
There are intercellular gaps in the mucosa, which may contain lymphocytes, leukocytes, mast cells, and also, especially near the bifurcation, round, slightly stained cells, which may be sensitive receptors. The mucous membrane is often arranged in longitudinal folds, the thickness of which probably depends in part on the tone of the bronchial muscles.
The submucosal layer is thicker under the folds of the mucous membrane, and in the trachea and large bronchi - in the area rear wall, between the ends of the cartilage rings. In the submucosal layer, the capillary network is located directly in the basement membrane, while the pre- and post-capillary vessels lie in deeper layers, between the elastic fibers. The bundles of elastic fibers are located mainly longitudinally, along the folds of the mucous membrane, in thin layers penetrating into it, although they are also associated with the mucous membrane, cartilage and with circular elastic fibers of the fibrocartilaginous layer. In the bronchioles, elastic fibers penetrate outward and connect with the elastic tissue of the alveoli.
Mucous glands are found all over from the trachea to the smallest bronchi and are especially numerous in the bronchi of medium caliber. In large bronchi, they are located in the submucosal layer between the mucosa and cartilage, often penetrating outward through cracks in the cartilage. Often they lie extramuscularly, and their ducts perforate the muscles and can even penetrate through the fibrous layers into the peribronchial connective tissue. The mucous glands are usually sausage-shaped with a duct opening at one end and running perpendicular to the long axis of the bronchus, emptying on the surface of its mucous membrane. The size of the glands is very variable, with the largest of them reaching 1 mm in length. The epithelium of the mucous glands is ciliated with a variable number of goblet cells. Outward from the muscular layer of the bronchi, the ducts can become ampulloidal, they can be surrounded by lymphoid tissue. Some cells of the mucous glands appear granular and presumably secrete serous fluid, although Florey et al. on the basis of histochemical studies, this phenomenon is considered deceptive and it is believed that in most cases these cells probably secrete mucus.
In the trachea and large bronchi downwards, up to 4-5 subdivisions of segmental bronchi, the cartilages have a semicircular shape, sometimes a horseshoe shape, being open at the back. This posterior "membranous" part of the bronchus is formed from the outside by a fibrous plate running in the longitudinal direction between the cartilages and connecting their ends.
The bifurcations of the bronchi and trachea are marked by cartilaginous spurs, the edge of which is concave in relation to the trachea. In the smaller bronchi, the cartilage breaks into uneven plates, which are increasingly rare along the descending branches. bronchial tree until they disappear completely at the level of the bronchioles.
In the trachea, smooth muscles connect the ends of the cartilages, being medially from the fibrous plate. When the muscles contract, the ends of the cartilages converge, resulting in invagination of the posterior mucosa into the lumen of the trachea. As the bronchial branches descend, the muscles spread more anteriorly along the inner surface of the cartilage until they take the form of a ring. In those bronchi in which the cartilages are no longer arranged circularly, the bronchial muscles have a more longitudinal direction and the appearance of a spiral, therefore, when they contract, the lumen narrows and the bronchi shorten. In the smaller bronchi, the muscles are separated from the cartilage by a loose vascular layer with numerous branches of the bronchial artery, veins, and lymphatic vessels. In the bronchioles, the muscles tend to sink into the surrounding lung tissue. In relation to the thickness of the bronchial wall, the most developed muscle layer is located in the bronchioles. The extramuscular venous network ends at the level of the bronchioles, where the fibrous layer and the mucosa merge.
The bronchi are surrounded by peribronchial tissue, which consists mainly of loose connective tissue that does not interfere with the movement of the bronchi, which passes into the perivascular tissue of the pulmonary arteries and large veins. It contains bronchial arteries and veins, nerves, lymphatic vessels, lymphoid and adipose tissue. Dust is often deposited in the peribronchial tissue, especially in the region of the bronchial outlet angles, where the lymphoid tissue is surrounded by macrophages that have absorbed the dust. Bronchioles contain neither cartilage nor mucous glands. They are formed by a single layer of ciliated epithelium with single goblet cells. The terminal bronchiole is the most distant and has a complete epithelial lining. The respiratory bronchiole is partly formed by the alveoli that open into it.
