Lungs

The Russian name of the lungs is due to the fact that when cutting animal carcasses, the insides of the animal are placed in a container with water, the lungs stay on the water, and the other organs sink ^[1] . Names in other Slavic languages ​​are continued pluťe / pľuťe ( Polish. płuca , Czech plíce ), which is formed from the same Proto-Indo-European root * pleu- "swim", which Latin. pulmo et al. πνεύμων . The internal form of the word here is almost the same as that of the Russian word, “that which floats on water” ^{[2] [3]} .

Many medical and biological terms associated with the lungs are derived from the Latin root pulmo- (for example, pulmonology - a discipline studying lung diseases) or from Greek πνεύμω- (for example, pneumonia - pneumonia).

In fish with light, the latter are an additional organ of respiration and function along with the organs of water respiration - the gills .

In reptiles and birds, lungs are placed in the thoracic region of the general body cavity, and in mammals, they occupy most of the specific thoracic cavity , which is limited to the chest and separated from the abdominal cavity by a thoracic obstruction . The lungs are paired organs: the surface of the lung is outside covered with a visceral pleura — the serous membrane , which in mammals and in humans also lines the inside of the chest cavity and the front (in humans) upper surface of the abdominal barrier (parietal pleura). The lungs constantly change their shape ( excursion of the lungs ) depending on the phase of breathing (inhalation or exhalation).

In the structure of light terrestrial vertebrates, one can observe all transitions from sacciform smooth-walled lungs (in permanently amphibian amphibians, polyperans) to light ones, whose walls have a complex cellular and spongy structure due to the presence in the lungs of numerous outgrowths and vesicles formed by them - the alveoli , which increase the respiratory surface of the lungs. most mammals). Thus, the lung of vertebrates includes the main bronchi (right and left), which are dichotomously divided into smaller bronchi. As the bronchi dividing, their diameter decreases: the small bronchi pass into the terminal (or terminal) bronchioles , after which the respiratory department of the lung begins, which performs the gas exchange function. The alveoli (pulmonary vesicles) are separated by thin connective tissue septa, in which, among other things, pass through the blood capillaries. The alveoli communicate with each other through tiny holes - the alveolar pores . Due to this interposition of the walls of the alveoli and capillaries, the barrier between blood and air is extremely thin and does not exceed 0.5 microns. It prevents the alveoli from collapsing on the exhale, and also protects them from the penetration of microorganisms from the inhaled air and the release of fluid from the blood capillaries of the interalveolar septa, a special substance - surfactant , which covers the alveoli from the inside. Surfactant contains phospholipids , proteins and glycoproteins ^[4] .

Some invertebrates have organs, also called lungs, which are not homologous lungs of vertebrates, but are formed by invagination from the ectoderm . Many primitive invertebrates are characterized by diffusion of respiratory gases across the entire surface of the body.

In pulmonary snails, the mantle cavity has become a lung, and the opening through which the cavity of the latter communicates with the external environment can be closed; a dense vascular plexus is developed on the arch of the mantle cavity. Pulmonary snail gills are found only as an exception. Thus, the majority of freshwater forms breathe atmospheric air, and therefore snails must occasionally rise to the surface of the water, gathering a supply of air into their pulmonary cavity.

Many arachnids for atmospheric gas exchange are used paired organs, the so-called light-books ^[5] . Their structure resembles a book, where the pages are sheets of tissue filled with hemolymph (a liquid that plays the role of blood in arthropods), this structure is embedded in the lung sac ( atrium ), which communicates with the external atmosphere through the respiratory opening ( stigma , or spiracle ) on the lower front of the abdomen, sometimes also on the posterior segments of the cephalothorax . The gaps between the sheets are filled with air, oxygen and carbon dioxide diffuse between the hemolymph and air through the surface of the sheets. In most species, respiration of the lungs is not required for respiration, gas exchange occurs passively. Lung bags are characteristic of spiders (usually having one pair of these organs, along with trachea) and scorpions (up to four pairs of lung bags, trachea are absent). At the same time, many arachnid lungs are absent (they breathe with the help of trachea and / or through the surface of the body), which served to divide the whole arachnid class into two groups: those with lungs (such units as spiders , scorpions , teliphons , frins , schizomidas ) and not having (these include mites , false scorpions , palpigrads , ricinulea , haymakers , phalanxes ). This organ has existed in almost unchanged form since the Devonian period; it is found in fossil arachnids in the “ Rainia features ” in Scotland, dating back 410 million years ago ^[6] . It is assumed that spider-shaped lung sacs formed from extremities invaginating into the body cavity. At the same time, there are gills-books in the chelicea that are homologous to light-books ( en: Book gills ).

Respiratory organs in amphibians are represented by:

• lungs (special organs of air breathing);
• skin and mucous lining of the oropharyngeal cavity (additional respiratory organs);
• gills (in some aquatic inhabitants and in tadpoles ).

Most species (except for lung-free salamanders and Barbourula kalimantanensis frogs ) have light, not very large, in the form of thin-walled bags, braided by a dense network of blood vessels. Each lung opens with an independent hole in the laryngeal-tracheal cavity (in which the vocal cords are located, opening with a slit in the oropharyngeal cavity). Due to the change in the volume of the oropharyngeal cavity, air enters the oropharyngeal cavity through the nostrils while lowering its bottom. When the bottom rises, the air is pushed into the lungs. In toads adapted to dwell in a more arid environment, the skin is keratinized, and breathing is predominantly light.

For reptiles (or reptiles ), breathing of the suction type is characteristic by expanding and narrowing the chest with the help of the intercostal and abdominal muscles. Trapped through the larynx air enters the trachea - a long breathing tube, which at the end is divided into the bronchi leading to the lungs. By analogy with amphibians, lungs of reptiles have a bag-like structure, although their internal structure is much more complicated. The inner walls of the lung sacs have a folded cellular structure, which significantly increases the respiratory surface. Some snakes have a tracheal lung .

Since the body of representatives of this class of vertebrates is covered with scales, skin respiration is not present in reptiles (except for soft-bodied turtles and sea ​​snakes ), the lungs are the only respiratory organ.

The lungs of the representatives of the class of birds are arranged in such a way that the air passes through them. When inhaling, only 25% of the outside air remains directly in the lungs, and 75% passes through them and enters special air bags . When you exhale, the air from the air sacs again goes through the lungs, but already outside, forming the so-called double breath. Thus, the blood circulating in the vessels of the lungs is constantly saturated with oxygen both during inspiration and expiration ^[7] . At rest, the bird breathing is carried out by expanding and compressing the chest. When flying, when moving wings need a solid support, the chest of birds remains almost motionless and the passage of air through the lungs is determined by the expansion and contraction of air sacs ^[8] . The faster the flapping flight, the more intense the breathing. When the wings rise, they stretch, and the air is sucked into the lungs and into the air bags. When wings are lowered, exhalation occurs and air passes from the bags from the lungs ^[8] .

Thus, the respiratory system of birds is characterized by signs of adaptation to flight, during which the body needs enhanced gas exchange . This system of organs in birds is considered one of the most difficult among all groups of animals ^[9] . A long trachea leaves the pharynx and divides into two bronchi in the chest cavity. At the site of the trachea bifurcation there is an extension - the lower larynx, in which the vocal cords are located; its walls have bone rings. The lower larynx is a vocal apparatus and is most strongly developed in birds singing and making loud sounds. Lungs of birds are small in size, less elastic and grow to the ribs and the spinal column ^[10] . They are characterized by a tubular structure and a very dense capillary network. 5 pairs of air sacs are connected with the lungs - thin-walled, easily stretchable outgrowths of the ventral branches of the large bronchi, located among the internal organs, between the muscles and in the cavities of the wing tubular bones. These bags play a large role in the process of breathing birds during flight ^[8] . Along with the respiratory function, the air sacs have additional functions: they facilitate the body weight of the bird and, adjacent to large groups of muscles, participate in thermoregulation (dissipation of excess heat) ^[10] .

Lungs in most mammals consist of lobes, the number of which in the right lung (up to 6 lobes) is always greater than in the left one (up to 3 lobes). The skeleton (base) of the lungs is the bronchi. In the lungs of mammals, the main bronchus (extending from the respiratory throat) is divided into secondary bronchi, which, in turn, break up into smaller and smaller bronchi of the 3rd and 4th order, turning into respiratory bronchioles; these bronchioles end in t. alveolar bronchioles with their final extensions - alveoli . The bronchioles with their branches form lobules of the lungs, separated from each other by interlayers of connective tissue; thanks to this, the lungs of mammals are like a bunch of grapes.

Human lungs are paired respiratory organs. The lungs are located in the chest cavity , in the left and right half of it, limiting the mediastinal organocomplex ( heart , etc.) to the sides. They have the shape of a semi- cone , the base of which lies on the diaphragm , and the tip protrudes 1-3 cm above the collarbone to the shoulder girdle. The lungs have a convex rib surface (sometimes there are fingerprints on the ribs on the ribs ), a concave diaphragmatic and mediastinal (mediastinal) surface facing the mediastinal organs. All the organs located in the middle between the lungs (heart, aorta and a number of other blood vessels, the trachea and the main bronchi, the esophagus , the thymus , nerves, lymph nodes and ducts) make up the mediastinum . On the mediastinal surface of both lungs there is a groove - the gate of the lungs. These include the bronchi, the pulmonary artery and two pulmonary veins. The pulmonary artery branches parallel to the branching of the bronchi. On the mediastinal surface of the left lung there is a sufficiently deep heart impression, and on the anterior margin is a heart tenderloin. The main part of the heart is located right here - to the left of the median line.

The right lung consists of 3, and the left of 2 lobes. The skeleton of the lung form a tree-branching bronchi. Each lung is covered with a serous membrane - a pulmonary pleura and lies in the pleural sac. The internal surface of the chest cavity is covered with a parietal pleura. Outside, each pleura has a layer of glandular cells (mesotheliocytes) that secrete serous pleural fluid into the pleural cavity (narrow slit-like space between the leaves of the pleura).

Each lobe of the lungs consists of segments - parenchyma areas, resembling an irregular truncated cone facing the lung root, each of which is ventilated with a segmental bronchus and a corresponding branch of the pulmonary artery . The bronchus and artery occupy the center of the segment, and the veins through which blood flows out of the segment are located in the connective tissue septa between the adjacent segments. In the right lung there are usually 10 segments (3 in the upper lobe, 2 in the middle and 5 in the lower), in the left lung - 8 segments (4 in the upper and lower lobes) ^[11] .

The lung tissue inside the segment consists of pyramidal lobules (lobules) 25 mm long and 15 mm wide , the base of which faces the surface. The bronchus enters the apex of the lobule, which by gradual division forms in it 18-20 terminal bronchioles . Each of the latter ends with a structural and functional element of the lungs - an acini . The acinus consists of 20-50 respiratory bronchioles dividing into alveolar passages; the walls of those and other densely littered with alveoli. Each alveolar course passes into the end sections - 2 alveolar sacs.

The alveoli are hemispherical protrusions and consist of connective tissue and elastic fibers, lined with the thinnest alveolar epithelium and braided by a thick network of blood capillaries. In the alveoli, gas exchange occurs between the blood and atmospheric air. At the same time, oxygen and carbon dioxide pass through the process of diffusion from the erythrocyte to the alveoli, overcoming the total diffusion barrier from the epithelium of the alveoli, the basement membrane and the blood capillary wall, with a total thickness of up to 0.5 μm , in 0.3 s ^[12] . The diameter of the alveoli is from 150 microns in an infant to 280 microns in an adult and 300-350 microns in the elderly. The number of alveoli in an adult is 600–700 million, and in a newborn infant it is from 30 to 100 million. The total area of ​​the inner surface of the alveoli varies between expiration and inhalation from 40 m² to 120 m² (for comparison, the area of ​​a person’s skin is 1.5— 2.3 m² ).

Thus, the air is delivered to the alveoli through a tree-like structure - the tracheobronchial tree, starting from the trachea and further branching out into the main bronchi, lobar bronchi, segmental bronchi, interlobular, lobular, intralobular bronchi, terminal bronchioles. After the terminal bronchioles, air enters the respiratory departments of the lung.

The average height of the right lung in men is 27.1 cm , in women it is 21.6 cm , while that of the left lung is 29.8 and 23 cm, respectively. According to one data, the average mass of one normal lung was 374 ± 14 g, and the maximum mass - 470 g ^[13] . According to other measurements made by a larger number of people, the average mass of the male right lung was 455 g, female - 401 g, average mass of the male left lung - 402 g, female - 342 g ^[14] . The total capacity ranges from 1290 to 4080 ml and averages 2680 ml ^[15] .

In children, the lung tissue is pale pink. In adults, the lung tissue gradually darkens due to inhaled particles of coal and dust , which are deposited in the connective tissue basis of the lungs.

The lungs are abundantly supplied with sensitive, autonomic nerves and lymphatic vessels.

Pulmonary ventilation

When you inhale, the pressure in the lungs is lower than atmospheric, and when you exhale, it is higher, which allows air to move into the lungs from the atmosphere and back.

Normal quiet breathing is associated with the activity of the muscles of the diaphragm and external intercostal muscles , if the breath is intense, some other (auxiliary) muscles of the trunk and neck, such as the latissimus dorsi , trapezius muscles , sternocleidomastoid muscles, and others are connected. When you inhale, the diaphragm goes down, the ribs rise, the distance between them increases. A normal quiet exhalation occurs to a large extent passively, while the internal intercostal muscles and some abdominal muscles are actively working. Intensive exhalation occurs actively, with the participation of the rectus abdominis , the iliophis and other. When you exhale, the diaphragm rises, the ribs move down, the distance between them decreases ^[16] .

There are several types of breathing:

• rib or chest breathing;
• abdominal or diaphragmatic breathing;
• mixed

Back breathing

In the places of joining the ribs to the spine there are pairs of muscles that are attached at one end to the rib, and the other - to the vertebra. The muscles that are attached to the dorsal side of the body are called the external intercostal muscles . They are located right under the skin. With their reduction, the ribs are moved apart, pushing and raising the walls of the chest cavity. The muscles that are located on the ventral side are called the internal intercostal muscles . When they contract, the walls of the chest cavity shift, reducing the volume of the lungs. They are used in forced (active) exhalation, since normal exhalation occurs passively, due to the elastic traction of the lung tissue.

Abdominal breathing

Abdominal or diaphragmatic breathing is performed, in particular, with the help of the diaphragm. The diaphragm has a dome shape in a relaxed state. With contraction of the muscles of the diaphragm, the dome becomes flat, with the result that the volume of the chest cavity increases and the volume of the abdominal cavity decreases. When muscles relax, the diaphragm assumes its initial position due to its elasticity, pressure drop and pressure of the organs in the abdominal cavity.

Lung capacity

The total capacity of the lungs is 5000 ml , the vital capacity (with the maximum inhalation and exhalation) is 3000–5000 ml or more ^[17] ; regular inhalation and exhalation is about 400-500 ml (the so-called breathing capacity ). Maximum deep breath is about 2000 ml of air. The maximum expiration is also about 2000 ml . After a maximum expiration of the lungs air remains in an amount of about 1500 ml , called the residual volume of the lungs . After a quiet exhalation, approximately 3000 ml remains in the lungs. This air volume is called the functional residual capacity (FOY) of the lungs. Due to the functional residual capacity of the lungs in the alveolar air, a relatively constant ratio of oxygen to carbon dioxide is maintained, as FOY is several times larger than the respiratory volume. Only about ² ⁄ ₃ tidal volume reaches the alveoli; This value is called the volume of alveolar ventilation . The diagnostic procedure for measuring the volume of the lungs ( spirometry ) is performed using a special instrument, a spirometer , through which air exhaled by man is passed.

Breath

Breathing is regulated in the centers of inhalation and exhalation. Some receptive fields are located in the region of the respiratory center on the border between the medulla oblongata and the posterior brain . Рецепторы, с помощью которых происходит регуляция дыхания, располагаются на кровеносных сосудах ( хеморецепторы , реагирующие на концентрацию диоксида углерода и, в меньшей степени, кислорода), на стенках бронхов ( барорецепторы , реагирующие на давление в бронхах). Некоторые рецептивные поля находятся в каротидном синусе (место расхождения внешних и внутренних сонных артерий).

Также симпатическая и парасимпатическая системы могут изменять просвет бронхов.

Второстепенные функции лёгких

Кроме своей основной функции — газообмена между атмосферой и кровью — лёгкие выполняют в организме человека (и млекопитающих) ряд других функций:

• Изменяют pH крови, облегчая изменения в парциальном давлении углекислого газа
• Преобразуют ангиотензин I в ангиотензин II под действием ангиотензинпревращающего фермента .
• Служат для амортизации сердца , предохраняя его от ударов.
• Выделяют иммуноглобулин -А и антимикробные соединения в бронхиальный секрет, защищая организм от респираторных инфекций ^[18] . Слизь бронхов содержит гликопротеины с антимикробным действием, такие, как муцин , лактоферрин ^[19] , лизоцим , лактопероксидаза ^{[20] [21]} .
• Мерцательный эпителий бронхов является важной системой защиты от инфекций, передающихся воздушно-капельным путём. Частицы пыли и бактерии во вдыхаемом воздухе попадают в слизистый слой, присутствующий на поверхности слизистой оболочки дыхательных путей, и перемещаются вверх к глотке мерцательным движением ресничек, покрывающих эпителий.
• Обеспечение воздушного потока для создания звуков голоса.
• Лёгкие служат резервуаром крови в организме. Объём крови в лёгких составляет около 450 миллилитров, в среднем около 9 процентов от общего объёма крови всей системы кровообращения. Это количество легко может изменяться в два раза в ту или другую сторону от нормального объёма. Потеря крови из большого круга кровообращения при кровотечении может быть частично компенсирована выбросом крови из лёгких в кровеносную систему ^[22] .
• Терморегуляция за счёт испарения воды с поверхности альвеол в выдыхаемый воздух (более важна для животных, лишённых потовых желёз, чем для человека).

Заболевания

Органы дыхания поражаются актиномикозом , аспергиллёзом , гриппом , кандидамикозом , ОРЗ , туберкулёзом , сифилисом и другими инфекциями . При СПИДе может развиться пневмоцистоз .

Паразитарные болезни , поражающие лёгкие, — акариаз лёгочный , альвеококкоз , аскаридоз , метастронгилёз , парагонимоз , стронгилоидоз , томинксоз , тропическая лёгочная эозинофилия , шистозомоз , эхинококкоз и др.

Из другой патологии встречаются различные пороки развития лёгких (агенезия, аплазия, гипоплазия, врождённая локализованная эмфизема лёгкого и т. д.), свищи, пневмопатии, онкологические заболевания ( рак лёгкого , кисты ), наследственно обусловленные заболевания (например, муковисцидоз ) и т. д. Повреждение сосудов грудной стенки может обусловить гемоторакс , а повреждение лёгочной ткани — пневмоторакс .

К заболеваниям лёгких предрасполагает курение , отравление выхлопными газами, работа на вредном производстве ( пневмокониозы ).

См. также: бронхиальная астма , бронхит , лёгочное сердце , пневмония .

Органогенез и развитие

Лёгкие человека закладываются на третьей неделе внутриутробного развития . На четвёртую неделю возникают две бронхолёгочные почки, которые разовьются соответственно в бронхи и лёгкие. Бронхиальное дерево формируется от пятой недели до четвёртого месяца. На четвёртом-пятом месяце закладываются дыхательные бронхиолы , появляются первые альвеолы и формируются ацинусы . К моменту рождения количество долей, сегментов , долек соответствует количеству этих образований у взрослого человека.

Однако развитие лёгких продолжается и после рождения. В течение первого года жизни бронхиальное дерево увеличивается в полтора-два раза. Следующий период интенсивного роста соответствует половому созреванию . Появление новых разветвлений альвеолярных протоков заканчивается в период от 7 до 9 лет, альвеол — от 15 до 25 лет. Объём лёгких к 20 годам превышает объём лёгких у новорождённого в 20 раз. После 50 лет начинается постепенная возрастная инволюция лёгких, которая усиливается в возрасте свыше 70 лет.

• Лабиринтовый орган — функциональный аналог лёгкого
• Плавательный пузырь — орган рыб, гомологичный лёгким

• История исследований; актуально на начало XX века. Лёгкие // Энциклопедический словарь Брокгауза и Ефрона : в 86 т. (82 т. и 4 доп.). - SPb. , 1890-1907.
• Пятин В. Ф. Глава 8. Дыхание // Физиология человека / В. М. Покровский, Г. Ф.Коротько. — М. : Медицина, 1998. — Т. 1. — С. 401—442. — 448 с. - 10 000 copies — ISBN 5-225-009-603 .
• Шмальгаузен И. И. , Основы сравнительной анатомии позвоночных животных, 4 изд., М., 1947.
• Руководство по клинической физиологии дыхания , под ред. Л. Л. Шика и Н. Н. Канаева, Л., 1980.