To breathe is quite simply

The pulmonary circulation is the second entry into the body. (First entry is the digestive tract.) Here the blood absorbs oxygen directly from the air and is exempt from carbon dioxide. The blood is separated from the external environment, only the thin wall of the capillary. Through the lungs proceeds exactly the same blood as through a large circle, and then the speed of blood flow must be great. But skip the blood through the pulmonary capillaries under high pressure, as is done in a large circle, it is impossible: the capillaries will begin to let the blood directly into the pulmonary alveoli, will come pulmonary edema, and then life will be in danger. If hinder venous outflow from the lungs, and will succeed. Blood pressure in the right ventricle and the pulmonary artery so several times lower than in the left ventricle and the aorta. In a large circle, on the contrary, too low capillary pressure would not provide the nutrition of tissues, which require not only the exchange of gases, but in the plasma. Technologically, this problem is solved by shortening the path that the blood is in a small circle. There are, however, other challenges. The left and right half of the heart must pump blood under different pressures, but in exactly the same amount that otherwise would be a disaster, and very quickly: within seconds, at least minutes, all the blood percacets in one of the circles of blood circulation.
The balance between the flow in the lungs and the aorta is maintained by mechanoreceptors reflexes to increase pressure in the small circle (reflex Svigi - Larina) and on the increase of pressure in a large circle with receptors left heart, aorta, carotid sinus, carotid arteries.
In recent years, physiologists interested in the question of whether there are mechanoreceptors, directly measuring the speed of blood flow. Such measurement is possible in principle in two ways: by using a kind of hairs protruding into the lumen of the artery and curving in the direction of blood flow, respectively flow rate, and also due to the use of force acting on the vessel as a whole, because the blood tends to captivate the vascular wall behind him. Both options are investigated and, perhaps, bring information of the utmost importance. Why: a fundamentally new type of reception!
Either way, the balance between the two circles of blood circulation successfully supported. Probably, an important role in this difficult matter play capacitive vessels and blood depots, which are easily expandable and soften the sharp pressure drops.
Light perform two functions, serving as input for oxygen and release carbon dioxide and water vapor. Furthermore, this powerful receptor area. Polypropoline act breath perform intercostal muscles of the neck muscles and diaphragm (all striated, somatic), but control the frequency and depth of breathing is a matter of the respiratory center in the medulla. This centre works, guided chemoreceptor impulses emanating from the aortic and carotid pomozov and numerous tissue chemoreceptor regions, as well as special structures of the brain stem, a highly sensitive to excess carbon dioxide and hydrogen ions. The system is reliable.
The respiratory system is one of the main homeostatic of all systems of the body. Recall that the lung alveoli and the small bronchi not ventilated, filling their gas is carried out by the exchange of oxygen and carbon dioxide with ventilating bronchi by diffusion. Risking to bore the reader, again, at both entrances of the body - food and breath - is preliminary, rough homeontherange environment through which the body is in contact with the outside world. Because of this, in particular, on the walls of the pulmonary capillaries dust, not blows cold air, otherwise the blood, almost in contact with the atmosphere of the area of several square meters, could freeze, and that would do to the body temperature and think about it.