Lungs

The right and left lungs are located in the thoracic cavity, each in its own half, in pleural sacks. Between the lungs are the organs of the mediastinum: the heart with the pericardium, the aorta and the upper hollow vein, the trachea with the main bronchi, the esophagus, the thymus, the lymph nodes, etc.

The shape and structure of the lungs. In shape, the lung resembles a cone with a flattened medial side and a rounded apex. The right lung has a length of about 25-27 cm, width - 12-14 cm. It is shorter than the left lung by approximately 2-3 cm and already 3-4 cm, which is associated with a higher location of the right dome of the diaphragm compared with the left one.

Light (pulmo) has apex (apex pulmonis), base (basis pulmonis) and 3 surfaces: diaphragmatic, rib and mediastinal. The diaphragmatic surface (facies diaphragmatis) corresponds to the base of the lung, it is concave, facing the diaphragm. The frontal surface (facies costalis) is convex, lying to the inner surface of the chest wall - to the ribs and intercostal spaces. The vertebral part (pars vertebralis) of this surface is rounded and bordered by the spine. The mediastinal (mediastinal) part (pars mediastinalis) of the lung is facing the mediastinum. The surfaces of the lung are separated by edges. The anterior margin of the lung (margo anterior) divides the costal and medial surfaces, the lower margin (margo inferior) separates the rib and medial surfaces from the diaphragm. At the anterior edge of the left lung is a depression - the heart incision (incisura cardiaca), bounded from below by the tongue of the left lung (lingula pulmonis sinistri).

Each lung with the help of deep cracks is divided into large parts - lobes. The right lung has 3 lobes: the upper lobus superior, the lobus medius and the lower lobus inferior. At the left lung allocate 2 shares - the top and bottom. The slit (fissura obliqua) is present in both lungs. This gap begins at the posterior edge of the lung, 6-7 cm below its apex (the level of the spinous process of the III thoracic vertebra), goes forward and downward towards the anterior edge of the organ at the level of the transition of the osseous part of the VI rib into its cartilage. Further, the slanting slit moves to the medial surface and is directed to the collar of the lung. The oblique crack in both lungs separates the upper part from the lower one. The right lung has a horizontal slit (fissura horizontalis pulmonis dextri). It begins on the costal surface approximately in the middle of the oblique slot, where it crosses the middle axillary line. Further, the horizontal slit goes first transversely to the anterior margin, then turns to the gates of the right lung (along the medial surface). The horizontal slit separates the middle part from the upper one. The average proportion of the right lung is visible only from the front and from the medial side. Between the lobes of each lung are located their inter-frontal surfaces (facies interlobares)

The medial surface of each lung has a depression - the gates of the lung (hillum pulmonis), through which the vessels, nerves and the main bronchus, forming the root of the lung (radix pulmonis) pass. At the gates of the right lung in the direction from top to bottom the main bronchus is located, below is the pulmonary artery, under which there are two pulmonary veins. In the gates of the left lung, there is a pulmonary artery at the top, beneath it is the main bronchus, below it - two pulmonary veins. The gate of the right lung is somewhat shorter and wider than that of the left one.

In the area of the gates, the right main bronchus (bronchus principalis dexter) is divided into 3 shared bronchi: the right upper lobe bronchus superior dexter, the middle lobe bronchus lobaris medius dexter, the lower lobe bronchus inferior dexter. When entering the upper lobe of the right lung, the upper lobar bronchus is located above the lobar artery (branch of the pulmonary artery), i.e. Is located epiarterially, and in other parts of the right and left lungs, the lobar bronchus passes under the lobar artery (gi rialno).

The left main bronchus (bronchus principalis sinister) in the light gate is divided into two equity bronchus: upper left lobar bronchi (bronchus lobaris superior sinister) and the lower left lobar bronchi (bronchus lobaris inferior sinister). The lobar bronchi give rise to smaller segmental (tertiary) bronchi that later divide dichotomically.

Segmental bronchus (bronchus segmentalis) enters the segment, which represents the lung segment, the base facing to its surface, the apex - to the root. Segmental bronchus and segmental artery are located in the center of the segment. On the border between adjacent segments, in the connective tissue, passes the segmental vein. Segmental bronchi are divided into subsegmental, then lobular.

Lobular bronchus (bronchus lobularis) is included in the lobule of the lung, the number of which in one lung is about 80 or more. Each lobule resembles a pyramid with a polygonal base of 5-15 mm in size. The length of the lobule reaches 20-25 mm. The top of each lobule faces the lung, and the base - to its surface, covered with pleura. Lobular bronchus, entering the lobule from the side of its apex, is divided into 12-20 terminal bronchioli terminates, the number of which in both lungs reaches 20 000. Terminal (terminal) bronchioles and bronchioli respiratory arteries formed by their branching ) do not already have cartilage in their walls.

The structure of the bronchi has common features throughout the bronchial tree (to the terminal bronchioles). The walls of the bronchi are formed by the mucosa with a submucosa, outside of which there are fibro-cartilaginous and adventitial membranes.

The mucous membrane of the bronchi is lined with ciliated epithelium. The thickness of the epithelial cover decreases with the decrease in the caliber of bronchi as a result of changes in the shape of cells from high prismatic to low cubic. In the walls of small caliber bronchi, the epithelium is two-row, then single-row. Among epithelial cells (in addition to ciliated) there are goblet, endocrine cells, basal cells (similar to the cells of the tracheal wall). In the distal parts of the bronchial tree, among the epithelial cells there are clara secretory cells that produce enzymes that break down the surfactant. The propria of the mucous membrane contains a significant amount of longitudinal elastic fibers. These fibers promote the stretching of the bronchi during inspiration and return to the initial position during exhalation. In the thickness of the plate of the mucous membrane there are lymphoid tissue (cells of the lymphoid series), vessels and nerves. The relative thickness of the muscular plate of the mucous membrane (in relation to the bronchial wall) increases from the large bronchi to the small ones. The presence of oblique and circular bundles of smooth muscle cells of the muscular plate contributes to the formation of longitudinal folds of the bronchial mucosa. These folds are present only in large bronchi (5-15 mm in diameter). In the submucosal base of the bronchi, in addition to blood vessels, nerves, lymphoid tissue, there are secretory sections of numerous muco-protein glands. Glands are absent only in bronchi of small caliber (diameter less than 2 mm).

Fibrous-cartilaginous shell as the diameter of the bronchi decreases, it changes its character. The main bronchi contain non-closed cartilaginous rings. In the walls of the lobar, segmental, subsegmental bronchi there are cartilaginous plates. Lobular bronchus with a diameter of 1 mm contains only individual small plates of cartilaginous tissue. Bronchi of a smaller caliber (bronchioles) do not have cartilaginous elements in their walls. The outer adventitia of the bronchi is constructed from the fibrous connective tissue that passes into the interlobar connective tissue of the lung parenchyma.

In the composition of the lungs, in addition to the bronchial tree (bronchus of different diameters), an alveolar tree is distinguished, which not only has an airway but also respiratory functions.

Alveolar tree, or pulmonary acinus, is a structural-functional unit of the lung. In each lung there are up to 150,000 acinus. Acinus is a system of branching of one terminal (terminal) bronchioles. Terminal bronchioles are divided into 11-16 respiratory (respiratory) bronchioles of the first order, which are dichotomously divided into respiratory bronchioles of the second order, and the latter - also dichotomously to respiratory bronchioles of the third order.

The length of one respiratory bronchiolis is 0.5-1 mm, the diameter is 0.15-0.5 mm. The name respiratory bronchioles was obtained due to the fact that on their thin walls (25-45 microns) there are single alveoli. Respiratory bronchioles are divided into alveolar ducts (ductuli alveolares), ending with alveolar pouches (sacculi alveolares). The diameter of alveolar courses and alveolar sacs in an adult is 200-600 microns (in children 150-400 microns). The length of alveolar courses and sacs is 0.7-1 m. Alveolar courses and sacs in their walls have protrusions - vesicles - alveoli of the lung (alveoli pulmonis). Alveolar course involves about 20 alveoli. The diameter of one alveolus is 200-300 microns, and its surface area is on average 1 mm ². The total number of alveoli in both lungs reaches 600-700 million. The total surface area of the alveoli ranges from 40 m ² when exhaled to 120 m ² when inhaled.

Acinus has a complex structure. The respiratory bronchioles are lined with a cubic epithelium, in which there are non-exfoliated epitheliocytes. The underlying layer of smooth myocytes is very thin, intermittent. Alveolar courses are lined with a flat epithelium. The entrance to each alveolus from the alveolar course is surrounded by thin beams of smooth myocytes. The alveoli are lined with cells of two types: respiratory (scaly) and large (granular) alveolocytes located on a solid basal membrane. In the alveolar epithelial lining there are also macrophagocytes. Respiratory alveolocytes - the main part in the structure of the walls of the alveoli. These cells have a thickness of 0.1-0.2 microns and a somewhat convex nucleus, as well as numerous micropinocytosis vesicles, ribosomes, and poorly developed other organelles. Through respiratory alveolocytes gas exchange takes place. Large alveolocytes are arranged in groups of 2-3 cells. These are large cells with a large rounded nucleus and well-developed organelles. The apical surface of large alveolocytes contains microvilli. Large alveolocytes are a source of recovery of cell lining of alveoli, they take an active part in the formation of surfactant.

Surfactant is a complex of substances of protein-carbohydrate-lipid nature. The surfactant is located on the inner surface of the alveoli and prevents the alveoli from collapsing and adhering during exhalation, maintaining the surface tension of the alveoli. The surfactant has bactericidal properties.

The air-blood (aerogematic) barrier formed by thin (90-95 nm) respiratory alveolocytes, the basement membrane of alveolocytes, which merges with the basement membrane of the blood capillaries, the thin (20-30 nm) layer of endotheliocytes through which gas exchange occurs, is very thin (0, 2-0.5 μm). The thickness of the total basal membrane is 90-100 nm. Capillaries form a thick hemocapillary network around the alveoli. Each capillary borders on one or more alveoli. Oxygen in the process of diffusion from the lumen of the alveoli passes through the blood barrier into the lumen of the blood capillary, CO ₂ - in the opposite direction. In addition to gas exchange, the lungs perform other functions. This regulation of acid-base equilibrium, the production of immunoglobulins by plasma cells, the release of immunoglobulins into the lumen of the airways,

Topography of the lungs (projection on the chest wall). The right and left lungs are located each in their own half of the thoracic cavity, and in many respects their topography is the same. However, there are differences regarding the location of the anterior margin of the lungs and their lower border due to the presence of a number of located organs (heart turned to the left, a higher right dome of the diaphragm). In this regard, skeleotopia of the right and left lungs is not the same. The tip of the right lung in front is 2 cm above the clavicle, 3-4 cm - over 1 rib. At the back of the tip of the right lung is projected at the level of the spinous process of the VII cervical vertebra. The front border of the right lung from the tip goes to the right sternoclavicular joint, then passes through the middle of the connection of the handle and the body of the sternum. The anterior edge of the right lung goes down behind the sternum (slightly to the left of the median line) to the level of the cartilage of the IV rib, tending to the lower border of the lung. The lower border of the right lung is along the middle clavic line at the level of the VI rib, along the anterior axillary line - at the level of the VII rib, the middle axillary - VIII, the back axillary - the IX rib, the scapula - X ribs, the near-vertebral line - at the level neck of the XI rib. At the level of the XI rib, the lower border of the right lung turns up and goes to the rear border, which rises to the head of the 2nd rib.

The tip of the left lung protrudes 2 cm above the clavicle. From the tip, the anterior border (edge) of the left lung goes to the left sternoclavicular joint, then behind the sternum to the level of the cartilage of the 4th rib. Further, the anterior border of the left lung is deflected to the left, directed along the lower edge of cartilage IV of the rib to the breast of another line, sharply turning down to the cartilage of the sixth rib, where it sharply moves to the left into the lower border of the lung. The lower border of the left lung passes about half a block lower than that of the right lung. On the near-vertebral line, the lower border of the left lung passes into its posterior border, which runs up along the spine. The back borders of the left and right lungs coincide.

Blood supply to the lungs

Blood vessels of the lungs are referred to a small and large circle of blood circulation.

Pulmonary vessels (a.et v. Pulmonales) constitute a small circle of blood circulation and perform mainly the gas exchange between blood and air, while the bronchial system (a.et v. Bronchiales) provides nourishment to the lungs and belongs to a large range of blood circulation.

Pulmonary arteries, departing from the pulmonary trunk, carry venous blood into the lungs. The pulmonary trunk is entirely located intrapericardially. Its length is 4-6 cm, its diameter is 3.5 cm. The right pulmonary artery in its direction and magnitude is, as it were, an extension of the pulmonary trunk, which is of practical importance in selective angiopulmonography, as well as in embolus swings.

The place of division of the pulmonary trunk is located below the tracheal bifurcation by 1.5-2 cm. Having entered through the root into the lungs, the pulmonary arteries are divided into lobar and segmental branches and repeat the branching of the bronchi, located next to them. Respiratory bronchioles are accompanied by arterioles. Pre-capillary arterioles are wider than those of a large circle and create little resistance to blood flow.

From the capillaries, the blood collects into postcapillaries, venules and veins, which, in contrast to the arteries, are located between the lobules. Intrasegmental branches of the pulmonary veins, not constant in caliber and length, flow into intersegmental veins, each of which collects blood from two adjacent segments. The veins combine into large trunks (two from each lung), flowing into the left atrium.

Bronchial arteries number from 2 to 4 start from the thoracic aorta, go to the roots of the lungs and, giving the branches of the pleura, branch together with the bronchi, reaching the level of bronchioles. Branches of bronchial arteries are located in the peribronchial connective tissue and bronchial adventitia. The smaller branches, forming the capillary network, reach their own plate of the mucous membrane of the bronchial wall. From the capillaries, blood passes into small veins, some of which flow into the pulmonary veins system, the other part (from the large bronchi) into the bronchial veins draining into the unpaired (semi-unpaired) vein. Between the branches of the pulmonary and bronchial arteries and veins there are anastomoses, the function of which is regulated by the closing arteries.

Innervation of the lungs and bronchi

According to modern concepts, the innervation of the lungs is due to the nerve branches separating from the vagus nerve, the nodes of the sympathetic trunk, bronchial and pulmonary branches, and also the diaphragmatic nerve forming the pulmonary plexus at the portal of the lungs, which divides into the front and back. The branches of the anterior and posterior plexuses form peribronchial and perivasal plexuses in the lungs, which enter the segments of the lung, performing afferent (sensory) and efferent (motor) innervation, and the influence of parasympathetic innervation on bronchi is more pronounced than sympathetic. Between the arch of the aorta, the bifurcation of the pulmonary trunk and the trachea is a reflexogenic zone - a deep extracardiac neural plexus. Here, in the advent of the bifurcation of the pulmonary trunk, there is a permanent nerve ganglion, and in front - a superficial extracardiac neural plexus.

The nerves form plexuses at the collar of the lungs, anastomosing with the interweaving of the trachea and heart. The presence of connections of the nerves of the lungs and the heart partly explains the reflex stopping of the heart during manipulations in the region of the lung root.

Nerve stems that form a plexus in the gates of the lungs are sent by small branches that form on the walls of large bronchi and pulmonary vessels a finely mottled nerve plexus continuing along the walls of the bronchi to the smallest parts of the bronchial tree. The bonds that form between the nerve branches form the peribronchial nerve plexus, the individual branches of which penetrate into the thickness of the bronchial wall, forming the intrabronchial plexus. In the course of their occurrence, small accumulations of nerve cells occur.

The walls of the vessels of the lungs are the place of origin of afferent impulses that exert a regulatory influence on respiration and circulation.

Afferent fibers start from "irritation receptors" in the mucous membrane of the larynx, trachea and bronchi and from receptors that perceive stretching in the walls of the alveoli. "Receptors of irritation", involved in the implementation of a cough reflex, are found between cells in the cover epithelium of the respiratory tract. A significant part of the afferent fibers in the vagus nerve is directed to the sensitive cells of the gnathing ganglion, the other part to the stellate ganglion, to the lower cervical and upper thoracic, and sometimes to the caudal spinal ganglions.

Efferent vagal fibers begin primarily from the cells of the dorsal nuclei in the medulla oblongata. In the nerve plexuses of the bronchi they are replaced by short postganglionic fibers, which impart an impulse to the muscles and glands of the trachea, bronchi and bronchioles, and also to the vessels. Vagal innervation refers to cholinergic innervation and causes a contraction of the smooth muscles of the respiratory tract, gland secretion and vasodilation.

Efferent sympathetic fibers begin in the spinal cord at a level from I-II to V-VI of the thoracic segment. Fibers innervating the larynx and the upper part of the trachea are switched to postganglionic fibers in the upper cervical sympathetic node. Fibers carrying impulses to the caudal part of the trachea, bronchi, bronchioles, switch in the upper thoracic ganglia of the border sympathetic trunk. They are directed into the pulmonary plexus and are adrenergic. Irritation of the sympathetic nerve causes relaxation of the musculature of the bronchi and bronchioles, inhibition of gland secretion and narrowing of the vessels.

The innervation of the lungs is controlled by the hypothalamus and the cerebral cortex, which ensures the integration of respiration and the functions of other organs, as well as double (automatic and voluntary) regulation of respiration.

Lymphatic vasculature of the lungs

Lymphatic vessels of the lungs are divided into superficial and deep. The superficial form a coarse and shallow network in the thickness of the pleura, anastomosing with the deep vessels located in the connective tissue layers between the lobes, subsegments, segments, and also in the walls of the bronchi. The deep lymphatic network of the lung consists of capillaries, the thinnest vessels located around the alveoli, respiratory and terminal bronchi, and also the lymph vessels accompanying the bronchi and large blood vessels. The alveoli are devoid of lymphatic capillaries. The beginning of the lymphatic system is the lymphatic capillaries in the interalveolar spaces. Out-of-body networks form outflowing lymphatic collectors, which accompany the bronchi and go to the collar of the lung.

On the way outflow of lymph to the roots of the lung is several groups of bronchopulmonary lymph nodes. They are located along the way and mainly in places of branching of the bronchi. Near the main bronchi and trachea, the lower tracheobronchial, upper right and left tracheobronchial, right and left tracheal (paratracheal) lymph nodes are distinguished.

According to modern ideas, bifurcation lymph nodes are the main regional nodes for the lower lobes of both lungs. The majority of bifurcation nodes (in 52.8% of cases) is located under the right main bronchus. In this regard, it is advisable to puncture bifurcation nodes through the inner wall of the right main bronchus, retreating 5-6 mm from the carina, since almost always the bifurcation lymph node is located 2/3 of its size under the right bronchus, and 1/3 - directly under the carina.

Outflow of lymph to the left tracheobronchial lymph nodes is carried out from the left bronchopulmonary (root) and bifurcation nodes, from the left lung and trachea, esophagus. In most cases, outflow of lymph from these nodes is directed directly into the thoracic duct, in 1/3 of cases - to the upper right tracheobronchial lymph nodes, and then to the thoracic duct.

[1], [2], [3], [4], [5]