Gas exchange in the lung
Gas exchange between blood and alveolar air (external respiration) is associated with the structure of the lungs. The number of alveoli in humans approximately 700 million. For pulmonary respiration is important respiratory surface, or the surface of the alveoli, which comes in men to 130 m2, and in women – to 103.5 m2.
Respiratory alveolar surface is relatively larger in children than in adults (for 1 kg body weight). The amount of blood flowing through the lungs in a time unit, also in children is relatively larger than that of adults. In view of the abundant capillary pulmonary blood contact surface with the alveolar air at children is also relatively higher than that of adults. This provides an increased gas exchange needed to enhance the metabolism of the growing organism.
The thickness of the alveolar epithelial layer of 0.004 mm. Through this epithelium, and the capillary walls adjacent to the alveoli, and gas exchange takes place.
The exchange of gases between the alveolar air and venous blood is accomplished thanks to the difference in partial pressures of O2 (8246 Pa) and CO2 (931). This pressure differential is sufficient for the diffusion of gases on the surface of contact with the venous blood alveolar air.
Determining the diffusion rate showed that even when the differential pressure 4655 Pa at 02 per minute through a 1 cm3 6.7 cm3 passes alveoli, and through the entire surface of human alveolar – 6000 cm3 O2. This is fully guaranteed by the need for O2 during the most intensive work, equal 5000-6000 cm3. Since at rest for 1 minute in the average person consumes 300 cm3 O2, the diffusion of O2 at rest sufficient differential pressure of several hundred Pascals.
CO2 diffuses into the alveoli through about 25 times faster, and therefore it is sufficient pressure difference of 3.99 Pa to allow diffusion 250 cm3 of CO2 exhaled that person in 1 minute at rest.
Thus, the gas exchange in the lungs is due to the diffusion of gases through the alveoli. The assumption that the pulmonary epithelium absorbs O2 was not confirmed.
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