1: Trachea
2: pulmonary vein
3: pulmonary artery
4: Headed alveolar
5: Alveole
6 7: Bronchioles
8: Primary Bronche
9: Bronche secondary
10: Bronche tertiary
11: Larynx

The lung is an organ invagine to exchange vital gases, including oxygen and carbon dioxide. Oxygen is necessary for the metabolism of the body, and carbon dioxide must be evacuated. In addition, it participates in other functions, such as the regulation of metabolism acid and a role blood filtration eliminating small clots.

Human Anatomy
The man has two lungs, left and right chest two bodies, separated from one another by the mediastinum, médialement. They are laid on the diaphragm and protected by the ribcage forward, out and back, except at their summit because they exceed the upper edge of the first coast.

The right lung has three lobes (upper, middle and lower), the left divided into two lobes (upper and lower). Left, the party lingulaire lobe upper lobe is the right way. The lobes are separated by scissures, two on the right (large or "oblique", and the small or "horizontal") and left (oblique).

The lungs are broken down by movements chest during inspiration and expiration, which is a respiratory cycle. At the same time, the cells receive blood pumped by the heart right. At rest, 4 liters of air and 5 litres of blood through the lungs per minute. In an effort, these amounts may vary significantly (up to 160 litres of air and 30 litres of blood per minute). These contributions allow the cells to perform their role of gas exchange, through thin membranes that separate cells of the blood capillaries.

The air passes through the nose (the usual way at rest) or by mouth, through the pharynx and larynx, which constitute the upper airways. He then reached the level of the trachea, which is divided into two strains bronchess (at T5, the hull), to divide many times to train terminal bronchioles. Until this level, there is no socket, hence its name conductive part. Then s'embranchent the respiratory bronchioles, starting point of the game breathing. It contains the alveoli, which may take place gas exchange.

In addition to their role as conduction of air, the upper airway provide air conditioning. They allow warm air to a temperature of 37 ° C (body temperature) and to ensure water saturation. Moreover, the air undergoes a filtering, in effect all along the respiratory tract are willing cells secreting mucous glands and hair cells. This can create a layer of mucus lining the tracks, and thus set particulate matter (dust, bacteria, ...) through the so-called channels. The movement of cilia (hair cells) moves the mucus in the direction of the pharynx to its elimination in the digestive tract (one speaks of escalateur mucociliaire). This is an important mechanism of lung defence against external aggressions. Besides, there are macrophages, which by their action of phagocytosis, complete this defensive system.

It is in the alveoli, small bags ended the respiratory tract, lung sacs called vesicles or lung, which occur gas exchange. They are upholstered wall of a very fine (up to 0.2 μ m, for comparison, the diameter of red blood cells is 7 μ m) containing the hair. The total area for the exchanges is about 200 square metres, the size of a tennis court. This allows the cells to ensure their role, which is to transmit oxygen to the blood and remove carbon dioxide.

At this level, we find the pneumocytes type 2, which secrete the surfactant. The presence of the latter is essential, insofar as it helps reduce the surface tension by allowing a distended lung easier. For comparison, its role is the same as the soap is added to water to form soap bubbles.

The movement of the air for pulmonary ventilation
Dependent primarily on the contraction of muscles that causes respiratory a pressure gradient leading to the air inside the lungs. The inspiration is therefore described as active, contraction of the diaphragm, which increases the vertical diameter of the ribcage and external intercostal muscles, which increases the diameter antéropostérieur, will decrease the pressure inside the lungs and therefore an air inlet.

The expiration is a natural phenomenon liabilities resulting from forces reminder elastic when the muscles relax who are returning to the ribcage volume beginning of inspiration and therefore hunting air from the lungs. It may nevertheless make a forced exhalation, which is active. It involves the abdominal muscles and internal intercostal muscles.

The trade and transport of gas
The external respiration, pulmonary, allows the transformation of blood désoxygéné which comes from the heart oxygenated blood, who will return to be redistributed throughout the body. Exchanges between the alveoli and blood are a function of differences in partial pressures, a gas disseminate high pressure to low pressure under the law of Fick. The partial pressure of the alveoli of 100 mmHg for oxygen and 40 mmHg for carbon dioxide respectively when it is 40 mmHg and 46 mmHg in the capillary, the oxygen goes to the blood cells and carbon dioxide is the reverse path. The time of contact between the blood cells and is 0.75 seconds, but third time only enough to achieve the balance. The heart-lung system is called small circulation.

The regulation of breathing
Breathing takes place so unconscious and rhythmic through activity of certain neurons in the brain stem. Its regulation depends crucially on the partial pressure of carbon dioxide in the blood, which is captured by two types of chémorécepteurs located on the outskirts or in the central nervous system. The first lie in the grip of the aorta and the bifurcation of the carotid, the latter lie on the ventral side of the medulla. All changes in carbon dioxide in the blood lead to a response from the pace and depth of ventilation. The modulations of respiratory activities may also be due to other stimuli, such as during the emotions (fear, excitement ...)

The lung Vertebrate takes its origin in embryological an outgrowth of the esophagus, the swimbladder and is therefore composed of endoderm (doubled secondarily of mesoderm for vasculature). The lungs of birds is very amended forming a series of tubes between two air sacs where air circulates in one direction (unlike the other lungs where the air because of movements back and forth during a cycle inspiration / expiration). There are also "lungs" in invertebrates that are not counterparts in the lungs of vertebrates, they are trained by intussusception of the ectoderm. They are among Chelicerates (spider, scorpion), land crabs (Gecarcinidae, Grapsidae,…) and among gastropods Pulmonés (snail) where the cavity palleale who plays the role of lung, communicating with the outside by a small hole called pneumostome. Broadly speaking, lungs breathing to allow a mid air while avoiding dehydration.

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