Lung

The lung (Latin pulmo, - onis m. ) Is a body organ that is used for breathing. Genuine lungs occur in many air-breathing vertebrates, with most land-dwelling vertebrates and some fish such as the lungfish. They arise as embryonic evagination of the foregut. The amphibians ( Amphibia ) have simple lungs. You are with them sack -shaped and smooth-walled or only weakly chambered. Much stronger they are chambered in reptiles ( reptiles). In birds, they are relatively small, but also much more complicated construction because of the additionally available air sacs.

The lungs of mammals are similar to those of reptiles. In humans, they consist of two lungs, which are divided into two left and right into three lobes. The mammalian lung has no muscles. Instead, the air is sucked by means of the diaphragm and the intercostal muscles. The chest expands, therefore the volume is greater and there is a negative pressure, which is balanced by the incoming air.

Etymology

The German word pulmonary comes over his Old High German form lunguna end of the Indo-European root * lengu̯h " slightly ( in motion and weight) " from, so it can be assumed from the original meaning as "the Light ". Linguists explain the designation with the already established long ago phenomenon that the lungs of a slaughtered animal as the sole organ on the water floats on top. The medical- Latin technical term pulmonary goes to an alternative spelling of the Greek word for lungs back: πλεύμων ( pleumon ), the standard language spelling πνεύμων ( Pneumon ) including the word " pneumonia ( pneumonia = ) " is based.

Mammalian lung

Both lungs of mammals, also referred to as the lung, are embedded in the movable chest (thorax). More or less deep cuts divide the lungs into lobes ( lobes ). The surface of the lung is covered by a smooth lining (tunica serosa ), the chest cavity as pleura ( pleura) is called. Between the pleura covering the lung and the pleura lining the chest cavity is a gap in which there is a negative pressure. It is of great importance for the breathing. With an injury of the thorax of this negative pressure can collapse, and the lung collapses (pneumothorax ).

Structure of the human lung

The human lungs than typical mammalian lungs, consist of a right lung ( right lung ) and left lung ( left lung ). Each lung is divided by furrows into so-called lobes. The right lung is divided into three, the left lung in only two lobes on. The lung lobes in turn be divided into lung segments. The designation is indicated here according to the allocation for supplying bronchial branch. 10 segments can be found in the right lung (pulmo dexter ). In the left wing (pulmo sinister), there are only 9 segments, since the 7th segment is missing. The left lung is slightly smaller than the right, as the heart takes some space on the left side. It consists of the right upper lobe of the apical, posterior and anterior upper lobe segment of the middle lobe (right only ) from the lateral and medial middle lobe segment ( segment 4.5 ), it follows the apical lower lobe segment ( 6 segment), and the four basal lower lobe segments to the right ( mediobasal, anterobasal, laterobasal, posterobasal ). On the left is the upper lobes of the segments 1 to 3, naming as in the right upper lobe, as well as from the two Lingulasegmenten ( 4.5 ) ( superior and inferior Lingulasegment ). It follows the apical lower lobe segment ( segment 6 ) and the three basal lower lobe segments: anterobasal, laterobasal, posterobasal (segments 8-10 ). The mediobasale segment is missing.

The lungs are in the chest cavity. Top towers over the lung apex by about 1-2 cm collarbone, below is the lung to the diaphragm, whose location is highly variable and mainly of the respiratory position and body position ( lying higher than the seats) depends. Roughly, one can say that the lung edges come to lie in the respiratory rest position on the ventral side at the level of the 6th rib, laterally equivalent to the 8th rib and on the dorsal side at the level of the 10th rib. This difference arises from the oblique line diaphragmatic approach.

The left lung is generally less because their resting heart for the most part. Because of this and due to the splitting of the trachea into the main bronchi, so that the left tracheal bronchus 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 greater than that between the trachea and the left main bronchus. This has consequences for the aspiration of foreign bodies: these come mostly in the right main bronchus. The lung volume of an adult human is on average 5 to 6 liters.

Feinbau

The tissue of the lung can be divided into an air-guiding part and a part in which the actual gas exchange takes place. The air-conducting bronchi end in blind-ending sacs, the alveoli (alveoli ). In this gas exchange takes place.

The whole of the air-conducting system is called bronchial ( bronchial tree ). From the inside out to find various layers. The epithelium ( surface tissue ) is still at the beginning, as in the trachea, from ciliated pseudostratified, columnar epithelium, but closer to the alveoli simplifies the structure, and in the bronchioles outweighs single- iso- or high- prismatic epithelium. In the underlying lamina propria there is smooth muscle, the proportion increases to the alveoli back. Furthermore, it includes a plurality of elastic fibers, and mucous and serous glands open their outputs into the bronchus and coat the mucosal surface with a protective film. Outermost is found in the large bronchi of hyaline cartilage, which ensures that the airways remain open. The smaller the diameter of the bronchi, the smaller is the proportion of cartilage until there are only small islands.

In the alveoli, the oxygenation of the blood takes place. It involves baggy extensions with a diameter of about 200 microns and an estimated adult humans of about 300 million. The surface formed by them is called respiratory surface. They consist of small alveolar cells or type I pneumocytes, which can be less than 0.1 micrometers thick and form the epithelium of the alveoli, and the great alveolar cells or type II pneumocytes, which produce surfactant. This reduces the surface tension and is used as Antiatelektasefaktor. Furthermore, there are still alveolar macrophages (scavenger cells ) derived from the blood and dust phagocytose (dust cells) or after bleeding hemosiderin, a breakdown product of the blood pigment hemoglobin, record (heart failure cells). Between air and blood, there is a three-layer partition, the blood- air barrier. It is formed from 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 microns thick.

Since the Interzellularkontakte the capillary endothelium of liquid are more permeable than that of the alveolar cells, in heart failure may leak fluid into the connective tissue and lead to interstitial edema ( pulmonary edema).

The connective tissue between the bronchi and alveoli containing the branchings of the pulmonary arteries and veins. The ramifications of the pulmonary artery carry blood to the alveoli. The lymphatic drainage is via the pulmonary lymph nodes ( Nll. pulmonary ) and then into the Tracheobronchiallymphknoten ( Nll. tracheobronchial ).

Ontogenetic development

The lung is the only organ whose functioning, while the fetus is still in the womb, is not essential for survival. Only after birth ( but then within seconds ) to take over its main function. Nevertheless, it comes before the birth of an important role: The lung produces up to 15 ml of amniotic fluid per kg body weight.

The development of the lung begins around day 30 with the formation of the lung bud from the ventral ( ventral ) part of the foregut. Like this is the epithelium, the lung and its air-conducting apparatus ( larynx, trachea, bronchi) lining, endodermal origin. In contrast, the muscle and cartilage tissue is derived from the mesoderm, which surrounds the intestinal tube.

The lung bud divides then into a right and a left branching ( the later main bronchus). Next, the right branching divides into three further bifurcations, the left in two. Each of these five other ramifications later forms a lobe of the lung ( lobe pulmonis ). From 5 to about 17 weeks later all of the air-conducting part of the lungs is applied, so the other branches of the bronchi to the terminal bronchioles. For now, this is lined by columnar epithelium only, from the 13th week of pregnancy, there are but first ciliated epithelial cells. Cells of the epithelium start to produce amniotic fluid.

In the 16th to 26th week be formed from the ends of the terminal bronchioles, the canaliculi, which shows the lung parenchyma. The latter is the function of the lung tissue, into the vonstattengeht after the birth of the gas exchange. A typical for the lung parenchyma cell type are type II pneumocytes that secrete surfactant. Some type II pneumocytes differentiate into type I pneumocytes, capillaries and penetrate into the developing lung parenchyma. The wall of the capillaries and the membrane of type I pneumocytes are the blood-air barrier later. The existence of the lung parenchyma and the formation of surfactant ( → lung maturation ) are important in order ' to ensure the ( approximately given from the 24th week ) Viability of the fetus outside the womb.

In the last trimester of pregnancy, the canaliculi form to further ramifications that ultimately end blindly as sacculi. All of these ramifications of Lungenperenchyms are lined with pneumocytes type I and type II. The walls of the sacs and some of the upstream bifurcations of double over to hemispherical alveoli. Like the previous operations this increases the area covered by parenchyma surface considerably. The walls of the alveoli include the above-mentioned blood-air barrier, the subsequent location of the gas exchange. A newborn child has far fewer alveoli than an adult. The formation of alveoli is completed only in childhood.

Physiology of respiration

Breathing starts with the inhalation ( inspiration ) usually with the intercostal muscles and the diaphragm. The diaphragm is the strongest muscle of inspiration, with its contraction, it flattens out and pushes the abdominal and pelvic viscera caudally ( tailbone down), thereby increasing the thoracic volume. In the chest breathing, the musculi external intercostals ( external intercostal muscles) contract. Here, the chest is raised and expanded, causing the lung, which, itself covered by the visceral pleura (or pulmonary ), via the pleural space ( Cavitas pleuralis ) is related to the parietal pleura of the chest in conjunction, is mitgedehnt. Characterized the pressure in the lungs is reduced. After major efforts, further auxiliary respiratory muscles may be called upon to facilitate respiration, such as the chest muscles. This make athletes after an intense race advantage by aufstützen with the poor, for example, on a wall: her arms are then fixed ( punctum fixed salary ), and thus tighten the chest muscles are not the arms to the chest, but conversely the chest to the poor, the ribs are raised, and the lungs fill with air. However, after the pressure-volume relationship ( Boyle's law ) must now at changes in pressure - if the nostrils and mouth are open and in communication with the outside world - the volume of isobaric (ie at the same pressure ) increase. The lung fills up, the inspiration is terminated.

In diaphragmatic breathing, the diaphragm lowers only by contraction ( the diaphragm is composed of muscle) and thus causes a stretching of the lung down.

The exhalation ( expiration) is usually passive vonstatten, because after the inspiration the lung along with rib cage is so far stretched that it elastic strain energy is stored (similar to a spring which is first stretched and then released), the "stale " the lungs air casts. If the expiration involving the expiratory respiratory muscles, then one speaks of forced expiration. In this case, the contraction of Mm. internal intercostals, but there may be various other accessory respiratory muscles come into play. A special role in connection with the forced expiration plays mainly the latissimus dorsi ( " cough muscle ").

Diseases

Obstructive lung diseases. In the chronic obstructive pulmonary disease ( COPD Abbr of Engl. Chronic obstructive pulmonary disease ) is a narrowing of the airways obstruct the airflow. This often leads to shortness of breath (dyspnea ). The most important risk factor is smoking, but also pollution, low birth weight and genetic factors are held responsible. Among the COPD includes chronic bronchitis and emphysema. A pulmonary emphysema can also develop from a hereditary metabolic disorder, the alpha -1 -antitrypsin deficiency.

Restrictive lung disease. In contrast, the flexibility of the lungs is restricted ( in the sense of reduction in lung mobility ) at the restrictive lung disease. This reduces lung volume and compliance, ie the elasticity relative to the pressure. These include sarcoidosis, pneumoconiosis ( black lung disease ) and other diseases that have a fibrosis of the lung tissue respectively, but also external influences such as deformities of the thorax ( kyphosis, scoliosis ).

Pulmonary edema. Denotes the pulmonary accumulation of fluid in the lungs. In this case, between Permeabilitätsödemen (ARDS, toxic pulmonary edema), in which the permeability of the capillaries is increased and hydrostatic pulmonary edema ( cardiac edema, Höhenödem ), wherein the pressure in the capillaries so much higher than the pressure in the alveoli, that the liquid from the capillaries also " pressed " is distinguished.

Atelectasis. When a lung atelectasis section has collapsed, and the alveoli contain no or very little air.

Tuberculosis. Tuberculosis, an infectious disease whose causative agent is Mycobacterium tuberculosis is transmitted by droplet infection and manifests itself first in the lungs. The radiograph show characteristic moth -eaten lesions, which brought in the disease also known as the " moth ".

Inflammation. Inflammation in the lungs are divided into pneumonia (lung inflammation ), in which the lung tissue affected, bronchitis as bronchitis and bronchiolitis, the inflammation of the small bronchi.

Neoplasms. Cancers of the lung are called lung cancer because they arise as malignant growths of abnormal cells of the bronchi or bronchioles. It is one of the most common human malignancies. According to the World Health Organisation different subtypes can be distinguished on the basis of histology: squamous cell carcinoma, adenocarcinoma, large cell carcinoma and small - and more rarely occurring types. In addition, can be found in the lungs through their filter function frequently metastases of other tumors.

Avian lung

Main article: Air bag ( bird)

In contrast to the mammalian lung, the lungs of birds are installed immobile into the chest cavity. They are dorsally a connective tissue membrane (septum horizontal ). The pleura is still created embryonic, but is back again. The avian lung is not lobed and performs during breathing any volume changes.

The air-conducting system splits at the fork of the windpipe (trachea ) into the two main bronchi. This is also the vocal organ of birds, the syrinx. From the main bronchi go four groups of secondary bronchi ( medioventrale, mediodorsal, and lateroventrale laterodorsale ). The further ramifications of the laterodorsal bronchi is called Neopulmo.

Of the secondary bronchi go parabronchi from (lung whistling). 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 among themselves mostly communicating tubes and the actual exchange tissue to the dense Blutkapillarnetze are formed. In contrast to mammals, there is not a blind -ending system, but an open tube system. After flowing through the lungs, the air enters the air bags, which provide as bellows for ventilation ( air flow ).