B-vascularization:
There are two blood circulation in the lungs: the first is provided by the bronchial vessels (arteries and veins, bronchial) and provide the organ of oxygen and substances necessary for its operation. The second, consisting of veins and pulmonary arteries serves the function of gas exchange.

C-The pleura
The pleura consists of two sheets, one attached to the lungs, the visceral and the other adjacent to the chest wall, the parietal. The pleural space is imbued with a thin layer of liquid, which by capillary action, holds the two layers joined together, and provides a sliding sheets against one another without friction excessive. The pleural cavity is a “virtual”, but becomes really in certain pathologies, such as pneumothorax (presence of air between the two layers, causing their uncoupling and retraction lung), hemothorax (even principle), pleurisy.
The pleura can grow the lung during the expansion of the chest, thus causing a depression which results in the incoming air into the lungs is inspiration. This mechanism of variation of pressure in the socket which allows gas exchange.

D-The respiratory muscles
To achieve the inspiration, the respiratory muscles must oppose the elastic resistance of lungs, tending naturally to retract on itself and the friction of two layers of the pleura. For this, several muscles are involved: the diaphragm, scalene and intercostal and, to a lesser extent, sternocleidomastoid mastoid:

• Like all fluids, air flows from areas of high pressure to low pressure areas. The respiratory muscles act together on the coast. They have a special, double obliquity (hat down and forward reverse).
• The diaphragm, large muscle dome separates the abdominal cavity of the chest cavity, innervated by the phrenic nerves (C 3 C 4 C 5). The contraction causes a decrease in its curvature, up to 10cm.
• The external intercostal muscles, they are innervated by the intercostal nerves, from D1 to D12.
• The scalene, sternocleidomastoid mastoid, trapezius and paravertebral them, can be contracted at a rate significant ventilatory.

The expiration, it is naturally passive part of the natural elasticity of the lungs. Forced expiration will involve the abdominal muscles (by raising the diaphragm), the external intercostal.

II-Physiology:

A – Volumes usual
There are several types of respiratory volumes, highly dependent on age, size and sex of the subject:
The tidal volume, VC, firstly, is the volume inhaled normally and naturally in a quiet breathing at rest.
The inspiratory reserve volume, IRV is the volume available during a forced inspiration, as well as the expiratory reserve volume, ERV, obviously is the volume expired during a forced expiration. It thus determines the vital capacity (VC) of an individual as the sum of its current volume, added an inspiration and forced expiration: one obtains the formula
CV = VRI + VC + ERV
At the end of forced expiration, there remains an air volume expellable by the individual, this is called the residual volume RV determining the functional residual capacity RV + ERV.

B – Control of breathing
To adapt to changing circumstances, whether they be internal during physical exertion, for example, or external, when changes in the composition or pressure of the atmosphere, ventilation suits by situations, witnessed a complex neural activity can interpret all necessary information.

a – the nerve centers:
The nerve centers located in the hemispheres (the central nervous system) are responsible for modifications volunteers in activities developed, but are absolutely not sensitive to changes in blood composition and different metabolic requirements. It has also been demonstrated by sections of the central nervous system, the basic ventilation system was not affected as the pons and the medulla remained intact.

In 1890, L. FREDERICQ was the first to demonstrate that the nervous breathing are directly sensitive to the composition of the blood passing through them: He has therefore made the experience of traffic cephalic cross two dogs.
In this experiment, represented by the diagram above, Fredericq irrigated head of the first dog with the blood of the second body, and vice versa. He then strangled the first dog breath closed, and found that it is the second dog hyperventilates increasing, while the former will leave quietly suffocate the body.
This experience has highlighted the sensitivity of nerve centers respiratory blood composition, while the rest of the body did not respond and left stifle.
We now know that this is the content of O 2 / CO 2 and pH of blood stimulant activity of respiratory centers, through chemo and baroreceptors (usually located on the junction of the butt aorta).
Similarly, a significant decrease in the partial pressure of O 2 (Pa O2), determine an increase in breathing rate. Here, the pH and Pa CO2 did not change, the decrease in Pa O2 is the only stimulus.

Reflexes modifying the respiratory rate:
In addition to the cerebral hemispheres, which voluntarily alter this rate, there are different reactions that can alter significantly the respiratory rate.
The cough reflex: There are many nerve endings located on the epithelial cells of mucous larynx, the bronchi, which are stimulated by inhalants, dust, gases, irritants, foreign bodies … Their stimulation triggers the cough reflex by laryngeal and bronchial constriction.
Similarly, stimulation of myelinated fibers in the epithelium of the bronchi and bronchioles results in hyperventilation, bronchoconstriction, and a contraction of the larynx.
The propriorecepteurs placed at the limb muscles causes an increase of respiration during stimulation, to increase the intake of oxygen before the changes of partial pressures of O2 CO2 does it charge.
Baroreceptor blood pressure causes hypo ventilation in cases of hypertension and conversely.
Other stimuli:

• Stimulus hormones: adrenaline in large quantities shows hyperventilation. It would act by stimulating chemoreceptors arterial
• Stimulus temperature: a temperature increase from 37 to 39 degrees Triple naturally ventilation, hypocapnia resulting mask by reducing it by half. This stimulus is seen, but its mechanism is still unknown.

C – Physiology of pulmonary respiration
In adult humans, there are about 23 divisions between the trachea and air sacs. The first 16 have a role in conduction and there goes on no gas exchange. The 3 following these few cells, but especially beyond the 20th Division that will form the respiratory bronchioles. The exchange surface of cells is particularly extensive, there were 3 500 000 000 cells for an area of 80-90 m 2.
The cell wall has a striated by the blood capillaries in contact. This wall is very thin, about 0.3 mu.m and contains pores allowing gas flow between them. There are also elastic fibers, giving the lung’s skeleton, phagocytic cells and epithelial cells secrete surfactant. There are two blood systems, the pulmonary and bronchial system, one for oxygenation and the other in the vasculature.
The gas exchange there are so passive, pressure gradient, according to the law of Henry. At inspiration, the pressure O 2 atmosphere is higher than that of blood, it causes its dissolution, while at the end is the partial pressure of blood CO 2 which is lower than atmospheric.
The airways provide a variety of roles, in addition to the conduction of gas: The adjusting temperature and humidity of inspired air that reaches those of the body at cellular as well as purification and filtration the latter, thanks to hair cells, mucus and cough.