The lungs ( Latin pulmo ) are a pair of organs for breathing ; it serves the purpose of creating a large surface for gas exchange between air and blood . Real lungs are found in many air-breathing vertebrates , such as most land-dwelling vertebrates and some fish such as fish . B. the lungfish . Humans have two lungs ( Pulmo dexter for the right lung and Pulmo sinister for the left), which in German are also known as lungs or halves of the lungs. The left one is divided into two and the right one into three lobes. The gas exchange takes place at the level of the alveoli , as the end structures ramified airways with the air tube are connected.
Fresh air is brought up to the blood-air barrier by inhaling and exhaling ; this is not an achievement of the lungs themselves (the mammalian lung has no muscles), but of the diaphragm and the intercostal muscles . The pleural space , the fluid film of which transmits forces via adhesion and cohesion , mediates the movable positioning of the lungs in the chest; since they tend to contract as it expands, there is a negative pressure in the pleural space.
The lungs arise in the embryo as protuberances in the foregut (see gill intestine ) and initially resemble glands. The amphibians have simple lungs; they are sack-shaped and smooth-walled or only weakly chambered. They are much more chambered in reptiles . In birds , they are relatively small, but also much more complex because of the additional air sacs . The lungs of mammals are similar to those of reptiles.
The German word lung comes from the Old High German form lunguna from the Indo-European root * lengu̯h "light (in movement and weight)", so that the original meaning as "the light one" can be assumed. Linguists explain the name with the long-established phenomenon that the lungs of a slaughtered animal are the only organ floating on top of the water. The medical Latin term pulmo goes back to an alternative spelling of the Greek word for lung: ancient Greek πλεύμων (pleumon) , whose standard spelling πνεύμων (pneumon) u. a. the word "pneumonia" (= pneumonia) is based on.
The lungs of the mammals
Both lungs of mammals, also known as the lungs, are movably embedded in the chest cavity ( thorax ). More or less deep incisions divide the lungs into lobes ( lobi ). The surface of the lungs is covered by a smooth lining ( tunica serosa ), which in the chest cavity is known as the pleura and is divided into the pleura (pulmonary pleura) and the pleura (thoracic pleura). Between the pleural membrane of the lungs and the pleural lining of the chest cavity is the pleural space, a space filled with a little fluid and in which there is negative pressure.
Structure of the human lungs
The human lungs, as typical mammalian lungs, consist of a right lung (right lung) and a left lung (left lung). Each lung is divided into so-called lobes by furrows . The right lung is divided into three (upper lobe or ventrocranial lobe, middle lobe or lobe medius and lower lobe or lobe dorsocaudalis), the left lung into only two lobes (upper lobe and lower lobe). The lobes of the lungs, in turn, are divided into lung segments. The designation is based on the allocation to the bronchial branch supplying it. 10 segments are found in the right lung (pulmonary dexter). In the left wing (Pulmo sinister) there are only 9 segments because the 7th segment is missing. The left lung is slightly smaller than the right because the heart takes up some space on the left side. The right upper lobe of the lung consists of the apical, the posterior and the anterior upper lobe segment and the middle lobe (right only) consists of the lateral and medial middle lobe segment (segments 4 and 5). This is followed by the apical lower lobe segment (6th segment) and the four basal lower lobe segments on the right (mediobasal, anterobasal, laterobasal, posterobasal). On the left side, the upper lobe consists of segments 1 to 3, named as in the right upper lobe, and the two lingula segments (4, 5) (superior and inferior lingula segment). This is followed by the apical lower lobe segment (6th segment) and the three basal lower lobe segments: anterobasal, laterobasal and posterobasal (segments 8 to 10). The mediobasal segment is missing.
The lungs lie in the chest cavity . At the top, the tip of the lungs protrudes about 1–2 cm above the collarbone , at the bottom the lungs lie on the diaphragm , the position of which is very variable and primarily depends on the breathing position and the body position (higher when lying down than when sitting). Roughly, one can say that when breathing is at rest, the edges of the lungs come to lie on the abdomen at the level of the 6th rib, on the side at the level of the 8th rib and on the back at the level of the 10th rib. This difference results from the oblique line of the diaphragm.
The left lung is generally smaller because most of the heart rests on it. As a result, and due to the division of the trachea into the main bronchi, so that the left trachea-bronchial angle is smaller than the right, the right lung is usually better ventilated. The angle enclosed by the trachea and the right main bronchus is larger than that between the trachea and the left main bronchus. This has consequences for the aspiration of foreign bodies: These mostly end up in the right main bronchus. The average lung volume of an adult person is 5 to 6 liters.
The tissue of the lungs can be divided into an air-carrying part and a part in which the actual gas exchange takes place. The air-conducting bronchi end in blind-ended sacs, the alveoli (alveoli). The gas exchange takes place in these.
The entirety of the air-conducting system is called the bronchial system (bronchial tree). From the inside out there are different layers. The epithelium (covering tissue) initially consists of multi-row, highly prismatic ciliated epithelium , as in the trachea, but closer to the alveoli the structure is simplified, and single-layer iso- or highly prismatic ciliated epithelium predominates in the bronchioles. In the lamina propria below there are smooth muscles , the proportion of which increases towards the alveoli. It also contains a large number of elastic fibers as well as mucosal and serous glands, the outlets of which open into the bronchus and which cover the surface of the mucous membrane with a protective film. On the very outside, in the large bronchi, there is hyaline cartilage , which ensures that the airways remain open. The smaller the diameter of the bronchi, the smaller the proportion of cartilage mass until there are only small islands.
The oxygenation of the blood and the release of CO 2 take place in the alveoli. These approximately 300 million bag-like extensions (in adults) have a diameter of approx. 200 μm. The area they form is called the respiratory area . The alveoli consist of the small alveolar cells or pneumocytes type I , which can be less than 0.1 micrometers thick and form the epithelium of the alveoli, and the large alveolar cells or pneumocytes type II , which produce surfactant . The anti- atelectasis factor reduces the surface tension against collapse. There are also alveolar macrophages (scavenger cells) that originate from the blood and phagocytize dust ( dust cells) or, after bleeding , absorb hemosiderin , a breakdown product of the blood pigment hemoglobin ( heart defect cells ).
There is a three-layer dividing wall between the air and blood, the blood-air barrier . It is formed by the epithelium of the alveoli, the epithelial and endothelial basement membrane and the endothelium of the capillaries and is between 0.1 and 1.5 μm thick.
Since the intercellular contacts of the capillary endothelium are more permeable to fluid than those of the alveolar cells, fluid can leak into the connective tissue when the heart is weak and lead to interstitial edema ( pulmonary edema ).
The connective tissue between the bronchi and alveoli contains the branches of the pulmonary arteries and veins . The branches of the pulmonary artery carry the blood to the alveoli. The lymphatic drainage is via the pulmonary lymph nodes ( lymph nodes. Pulmonary ) and then into the Tracheobronchiallymphknoten ( Nll. Tracheobronchiales ).
The blood supply to the wall of the alveoli takes place via the capillaries of the pulmonary circulation ( Vasa publica, 'public vessels'). The rest of the tissue, i.e. the area surrounding the bronchi and the connective tissue septa, supply bronchial vessels ( rami bronchiales, vasa privata, 'own vessels') from the body's circulation . The rami bronchiales for the left lung (usually two) arise directly from the thoracic aorta. The bronchial branches of the right lung arise from a trunk of the third or fourth posterior intercostal artery . Both vascular systems often form anastomoses in the periphery .
Most bronchial veins flow into the pulmonary veins , while the bronchial veins near the hilum on the right into the azygos vein and the hemiazygos vein on the left . Blood that reaches the pulmonary veins from the bronchial arteries, together with blood from coronary vessels that flow into the left heart (Vv. Cardiacae minimae), creates a small, physiological right-left shunt . Together with functional short circuits in the pulmonary circulation (blood flow to non-ventilated parts of the lung), this explains the lower oxygen partial pressure in the arteries of the body circulation compared to the alveoli.
The lungs are the only organs whose functionality is not necessary for survival while the fetus is still in the uterus . Only after birth (but then within seconds) does it take on its main function. Nevertheless, it has an important role to play before birth: the lungs produce up to 15 ml of amniotic fluid per kg of body weight every day .
The development of the lungs begins around the 30th day with the formation of the lung bud from the ventral (stomach-side) part of the foregut . As with this, the epithelium that lines the lungs and their air-conducting apparatus ( larynx , trachea , bronchi ) is of endodermal origin. In contrast, the muscle and cartilage tissue originate from the mesoderm that surrounds the intestinal tube.
The lung bud then divides further into a right and a left branch (the later main bronchi). The right branch further divides into three further branches, the left into two. Each of these five further branches later forms a lobe of the lung ( lobus pulmonis ). From the 5th to around the 17th week, the entire air-conducting part of the lungs is applied, i.e. the other branches of the bronchi up to the terminal bronchioles . For the time being, this is only lined with highly prismatic epithelium , but the first ciliated epithelial cells are found from the 13th week of pregnancy . Cells of the epithelium begin to produce amniotic fluid.
In the 16th to the 26th week the canaliculi , from which the lung parenchyma emerges, form from the ends of the terminal bronchioles . The latter is the functional tissue of the lungs in which gas exchange takes place after birth. Type II pneumocytes , which secrete surfactant, are a typical type of cell in the lung parenchyma . Some type II pneumocytes differentiate into type I pneumocytes , and capillaries invade the resulting lung parenchyma. The wall of the capillaries and the membrane of type I pneumocytes later form the blood-air barrier when surfactant (→ lung maturation ) is formed from the 28th week of pregnancy .
In the last trimester of pregnancy , the canaliculi transform into further branches, which ultimately end blindly as sacculi . All of these branches of the lung parenchyma are lined with type I and type II pneumocytes. The walls of the sacculi and some of the upstream branches turn out to form hemispherical alveoli . Like the previous processes, this significantly increases the surface area covered by parenchyma. Disturbances in this development can lead to lung malformation . A newborn has far fewer alveoli than an adult. The formation of the alveoli is only completed in childhood.
The lungs contain amniotic fluid until shortly after birth; then the muscular system on the ribs and diaphragm increases the volume of the chest and, as a result of the greater air pressure outside, air flows into the bronchi and penetrates the alveoli. The surfactant reduces the surface tension of the water and thus prevents the newborn's respiratory distress syndrome . The existing fluid is more likely to be absorbed and carried away in the blood than expelled or coughed up. A first scream confirms the inflation of the newborn's lungs. The bypass cycles are closing.
Physiology of inhalation and exhalation
When you inhale ( inspiration ), breathing usually begins with the intercostal muscles or the diaphragm . The diaphragm is the strongest inspiratory muscle; when it contracts, it flattens and pushes the abdominal and pelvic viscera caudally (towards the coccyx), which increases the thoracic volume. When breathing in the chest , the intercostales externi (external intercostal muscles ) contract. The chest is raised and widened, whereby the lungs, which are covered by the visceral pleura (or pulmonalis ), are connected to the parietal pleura of the chest via the pleural space ( cavitas pleuralis ) . This reduces the pressure in the lungs. After greater exertion, additional breathing muscles can be used to facilitate breathing , e.g. B. the small and large pectoral muscles . Athletes take advantage of this after an intense race by leaning their arms against a wall, for example: their arms are then fixed (punctum fixum), and thus the chest muscles do not pull the arms towards the chest, but vice versa the arms, the ribs are raised, and the lungs are filled with air. According to the pressure-volume relationship ( Boyle-Mariotte's law ), however, when the pressure changes - provided the nostrils or mouth are open and connected to the outside world - the volume must increase isobarically (i.e. at the same pressure). The lungs fill up, inspiration is over.
With diaphragmatic breathing , the diaphragm only lowers through contraction (the diaphragm consists of muscles) and thus causes the lungs to expand downwards.
The exhalation ( expiration ) is usually passive vonstatten, because after the inspiration the lung, including chest is expanded to fulfill in elastic strain energy stored (similar to a spring, which is first stretched and then released), "stale" of the lungs, the Expelling air. If the expiration takes place with the involvement of the expiratory auxiliary muscles, one speaks of forced expiration . Initially the Mm contract. intercostales interni, but various other auxiliary respiratory muscles can also come into play. The latissimus dorsi muscle ("cough muscle") plays a special role in connection with forced expiration .
Pulmonary embolism . In pulmonary embolism , an embolus clogs one of the supplying blood vessels (vein), thereby preventing a section of the lung from being supplied with blood. This disease can be compared to a heart attack.
Obstructive pulmonary disease . In the case of chronic obstructive pulmonary diseases (from English Chronic obstructive pulmonary disease , COPD) a narrowing of the airways restrict air flow. This often leads to shortness of breath ( dyspnoea ). The most important risk factor is smoking, but environmental pollution, a low birth weight and genetic factors are also blamed for this. COPD includes chronic bronchitis and emphysema . Pulmonary emphysema can also develop from a hereditary metabolic disorder, alpha-1-antitrypsin deficiency .
Restrictive lung disease . In contrast, with restrictive lung diseases, the flexibility of the lungs is restricted (in the sense of: restriction of lung mobility). This reduces the lung volume and compliance , i.e. the flexibility relative to the pressure. These include sarcoid , pneumoconiosis ( pneumoconiosis ) and other diseases that result in fibrosis of the lung tissue, but also external influences such as deformities of the chest ( kyphosis , scoliosis ).
Pulmonary edema . Pulmonary edema is the accumulation of fluid in the lung tissue. A distinction is made between permeability edema ( ARDS , toxic pulmonary edema), in which the permeability of the capillaries is increased, and hydrostatic pulmonary edema (cardiac edema, altitude edema), in which the pressure in the capillaries exceeds the pressure in the alveoli so much that the fluid escapes is “pressed” out of the capillaries.
Atelectasis . In atelectasis , a segment of the lung has collapsed and the alveoli contain little or no air.
Pneumothorax . If the pleural space gains connection to the air from inside or outside, the negative pressure in the pleural space collapses and the corresponding lung collapses. In contrast to a completely missing lung, a pneumothorax means a functional right-left shunt, since blood from the circulatory system returns to the circulatory system via the affected lung without significant oxygenation, so that full saturation cannot be achieved.
Tuberculosis . Tuberculosis , an infectious disease caused by Mycobacterium tuberculosis , is transmitted by droplet infection and first manifests itself in the lungs. The x-ray shows characteristic moth-eaten lesions, which earned the disease the nickname "the moths".
Inflammation . Inflammations in the lungs are divided into pneumonia ( inflammation of the lungs ), in which the lung tissue is affected, bronchitis as an inflammation of the bronchi and bronchiolitis , the inflammation of the small bronchi.
Neoplasms . Lung cancers are known as bronchial carcinoma because they develop as malignant neoplasms of degenerate cells in the bronchi or bronchioles. It is one of the most common malignant diseases in humans. According to the World Health Organization , different subtypes are differentiated on the basis of histology : squamous cell carcinoma , adenocarcinoma , small and large cell carcinoma and other, rarely occurring types. In addition, due to their filter function, metastases from other tumors are often found in the lungs .
If breathing stops , the lungs can be ventilated - pulsing - by filling them with low-dose excess air pressure via the bronchi, which in an emergency or under anesthesia serves to sustain life.
In contrast to the mammalian lung, the bird's lungs are immobile in the chest cavity . They lie dorsal to a connective tissue membrane ( horizontal septum ). The pleura is created embryonically , but forms back again. The bird lungs are not lobed and do not change their volume while breathing , but are ventilated through air sacs.
At the bifurcation of the windpipe ( trachea ), the air-conducting system divides into the two trunk bronchi . This is also where the birds' vocal organ, the syrinx, is located . Four groups of secondary bronchi (medioventral, mediodorsal, lateroventral and laterodorsal) go from the trunk bronchi . The further branches of the laterodorsal bronchi are called neopulmo .
Parabronchia (lung pipes) emanate from the secondary bronchi. They are 0.5–2 mm thick. In its wall there are small funnel-shaped openings that lead into the air capillaries ( pneumocapillares ). The air capillaries form a network of tubes that communicate with one another and are the actual exchange tissue around which dense blood capillary networks are formed. In contrast to mammals , it is not a blind ending system, but an open tube system. After flowing through the lungs, the air enters the air sacs, which, like bellows, provide ventilation (the air flow).
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- List of all Wikipedia articles whose title begins with lung
- List of all Wikipedia articles whose title contains lungs
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