55) Stages of a breath. Gas exchange in lungs.

Breathing is the process that moves air in and out of the lungs, or oxygen through other respiratory organs such as gills. For organisms with lungs, breathing is also called ventilation, which includes both inhalation and exhalation. Breathing is one part of physiological respiration required to sustain life.

Gaseous Exchange in the Lungs--

The main function of the respiratory system is gaseous exchange. This refers to the process of Oxygen and Carbon Dioxide moving between the lungs and blood.

-Diffusion occurs when molecules move from an area of high concentration (of that molecule) to an area of low concentration.

-This occurs during gaseous exchange as the blood in the capillaries surrounding the alveoli has a lower oxygen concentration of Oxygen than the air in the alveoli which has just been inhaled.

-Both alveoli and capillaries have walls which are only one cell thick and allow gases to diffuse across them.

-The same happens with Carbon Dioxide (CO2). The blood in the surrounding capillaries has a higher concentration of CO2 than the inspired air due to it being a waste product of energy production. Therefore CO2 diffuses the other way, from the capillaries, into the alveoli where it can then be exhaled.

To demonstrate the use of Oxygen and Carbon Dioxide in respiration you can look at the amounts of both gases which we inhale and then exhale. The air we breathe contains approximately 21% Oxygen and 0.04% Carbon Dioxide. When we exhale there is approximately 17% Oxygen and 3% Carbon Dioxide. This shows a decrease in Oxygen levels (as it is used in producing energy) and an increase in Carbon Dioxide due to it being a waste product of energy production.

56) Surfactant, its importance.

Basis of surfactant is a double phospholipin layer similar of biological membranes. Surfactant continuously is updated owing to work of special cells alveolar epithelium, which allocate for a surface of an alveolus the smallest vesicles. In each of them the phospholipin layer densely packed, are opened on a surface of an alveolus. Due to surfactant diffusive way is slightly extended, that leads to decrease a concentration gradient on АCМ. However without surfactant breath in general would be impossible, as walls of an alveolus can stick with each other under action of the significant superficial tension inherent alveolar epitelium. Surfactant reduceses a superficial tension of alveolar walls.

57) Biomechanics of external breath.

Gas exchange between an alveolar gas mix and the atmospheric air, providing effective diffusion of oxygen and carbonic gas through a membrane, it is carried out owing to work of the device of ventilation, which consists of two formations: a thorax with respiratory muscles and lungs with respiratory ways. The thorax represents a rigid mobile case for lungs, hearts and the vessels, possessing elasticity. The thorax actively changes the volume by means of reduction of a diaphragm and other respiratory muscles. At reduction of a diaphragm its dome becomes flat and is displaced aside a belly cavity that leads to increase in volume of a thorax, and after it and lungs. According to Boyle's law ( P*V=const) the increase in volume of lungs is accompanied by pressure decline inside of them. It becomes below atmospheric and air is sucked in inside of lungs in alveoluses. So the breath is made.

At a breath air passes in a trachea and then on bronchial tubes reaches alveoluses. All respiratory ways in aggregate make the so-called branched out respiratory tube. The trachea has the least area of cross-section section (on the average 2,54 sm²) at the adult person). Total section of two main things (left and right) bronchial tubes more than this size. The total section of each subsequent generation of bronchial tubes becomes more in a direction to alveoluses.