Lung

Human anatomy

The Homme has two lungs, left and right, two thoracic , separate bodies one of the other by the Médiastin, médialement. They are posed on the diaphragm and protected by the Rib cage ahead, outwards and behind, except on the level of their top, because they exceed the higher edge of the first coast.

The right lung is divided into three lobes (superior, means and inferior), left divided it into two lobes (superior and inferior). On the left, the lingulate part of the higher lobe corresponds to the lobe average right. The lobes are separated by fissures, two on the right (the large one or " oblique" , and the small one or " horizontale") and one on the left (the oblique).

Each lobe of the lungs is divided into pulmonary segments:

Arterial pulmonary vascularization is double: the pulmonary and bronchial system. The pulmonary arteries bring the venous blood of the ventricle right for oxygenation, their course following the bronchi. The bronchial arteries come from the aorta or the arteries intercostales and bring blood oxygenated to the bronchial wall to the level of final bronchioles.

The lungs are connected to the coasts of the rib cage by two membranes called plèvres. The inspiration and the expiry are under the control of the intercostaux muscles and the diaphragm which deform the rib cage and thus the lungs via the play of the plèvres.

Physiology

The lungs are ventilated by the thoracic movements at the time of the inspiration and the expiry, which constitute a respiratory cycle. At the same time, the cells receive blood pumped by the right heart. At rest, 4 liters of air and 5 liters of blood cross the lungs per minute. At the time of an effort, these quantities can vary in an important way (up to 160 liters of air and 30 liters of blood per minute). These contributions make it possible the cells to fulfill their role of gaseous exchange, through fine membranes which separate the cells from the blood capillaries.

Air routes

The air passes by the nose (the usual way at rest) or by the mouth, to cross the Pharynx and the Larynx, which constitute the higher air routes. He manages then to the level of the trachea which is divided into two bronchi stocks (on the level of T5, of the hull), to subdivide many times, until forming final bronchioles. Up to this level, there is no cell, from where its name of conducting part. Then connect up the respiratory bronchioles, starting point of the respiratory part. This one contains the cells, where the gaseous exchange can take place.

In addition to their role of conduction of the air, the higher air routes ensure the air conditioning. They thus make it possible to heat the air until the temperature of 37°C (body temperature) and to ensure water saturation of it. Moreover the air a filtering undergoes, indeed all along the respiratory tracts are laid out of the cells secreting of mucus, glands and the ciliées cells. This makes it possible to create a layer of mucus papering the ways, and thus to fix the particles (dust, bacteria,…) crossing to them known as ways. The movement of the lashes (of the ciliées cells) moves this mucus in direction of the pharynx allowing its elimination in the digestive tract (one speaks about escalator mucociliaire). This constitutes an important mechanism of defense of the lungs against the external aggressions. Moreover, one finds Macrophage S, which, by their action of Phagocytose, supplement this defense system.

Cells

It is in the cells, small bags finishing the respiratory tracts, called pulmonary bags or pulmonary blisters , that the gaseous exchange occurs. They are papered of a very fine wall (up to 0,2 μm ; for comparison, the diameter of the red globules is of 7 μm) containing the capillaries. The entire surface intended for the exchanges is approximately 200 m ², that is to say the size of a tennis court. This makes it possible the cells to ensure their role, who is to transmit oxygen to blood and to extract carbon dioxide from it.

On this level, one finds the Pneumocyte S of the type 2, which secrete the surfactant . The presence of this last is essential, insofar as it makes it possible to decrease the surface Tension by thus allowing an easier pulmonary distension. For comparison, its role is the same one as the soap which one adds to water in order to form of the soap bubbles.

Movements of the air during pulmonary ventilation

Depend primarily on the contraction of the respiratory muscles which causes a gradient of Pression involving the air inside the lungs. Inspiration is thus qualified of active, contraction of Diaphragm, which increases the vertical diameter of the rib cage and the external intercostaux muscles, which increases the diameter anteroposterior, involves a pressure decrease inside the lungs and thus an air intake. The natural expiry is a passive phenomenon, resulting from elastic forces of recall when the muscles are slackened which make return the rib cage to its volume of beginning of inspiration and thus displaces air of the lungs. One can nevertheless carry out a forced expiry, which is active. It utilizes the abdominal muscles and the internal intercostaux muscles.

Exchanges and the transport of gases

The Breathing external, pulmonary, allows the transformation of the deoxygenized blood which comes from the heart in oxygenated blood, which will go back there to be redistributed with the whole of the body. The exchanges between the cells and blood are function of the differences of the partial pressures, a gas will diffuse pressure raised towards the low pressure according to the Loi of Fick. The pressure partial of the cells being of 100 mmHg for the Dioxygène and of 40 mmHg for the Carbon dioxide when respectively it is of 40 mmHg and 46 mmHg in the capillary, the dioxygene goes from the cells to blood and carbon dioxide makes the opposite way. The time of contact between blood and the cells is of 0,75 second, but a third of time only is enough to reach balances. The system artificial heart-lung is called small circulation.

Regulation of breathing

Breathing proceeds in an unconscious and rhythmic way thanks to the activity of some Neurons of the cerebral Tronc. Its regulation depends primarily on the pressure partial of carbon dioxide in blood, this one being collected by two types of Chémorécepteur S located in periphery or in the central nervous system. The first are in the stick of the Aorte and at the junction of the carotids, the seconds are located on the ventral face of the medulla. All modifications of the content carbon dioxide in blood involve an answer of the rate/rhythm and depth of ventilation. Modulations of the respiratory activities can also be due to other stimulations, such as for example during the emotions (fear, excitation…)

Zoology

See also: Respiratory system (bird), Respiratory system of the birds

The lung of the Vertébré S takes its embryologic origin in an outgrowth of the esophagus and is thus made of Endoderme (doubled secondarily Mésoderme for vascularization). The lung of the Birds is very modified forming a series of tubes between two air bags where the air circulates in only one direction (contrary to the other lungs where the air makes back and forth passes during a cycle inspiration/expiry). There exist also “lungs” at the Invertébré S which are not homologous with the lungs of Vertébré S, since they are formed by invagination of the Ectoderme. One finds them at the Chélicérate S (Araignée, scorpion) and at the Gastéropode S Pulmonés (snail) where it is the cavity palléale which plays the part of lung, communicating with outside by a small opening called pneumostome. Generally, the lungs allow a breathing in air medium while avoiding dehydration.

See too

Internal bonds

Lung cancer

External bonds

pulmonary and thoracic Anatomy

Fiu-vro: Täü Simple: Lung Zh-min-nan: Hì (khì-koan)

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