A specialized respiratory surface is thin, moist and highly vascular. It remains in contact with the environment outside the body and tissues inside the body. Diffusion of gases takes place from respiratory surface between the body and air from environment.
Functions of Nostrils hair: (i) The air passing through nostrils is filtered by the fine hairs that line the passage. So that the air going into the lungs is free from dust and other impurities.
Trachea is supported by c-shaped rings of cartilage which hold them in place when there is less air inside it. So, the walls of trachea do not collapse even when there is a little air.
The blood which brings O2 to tissues has lower concentration of carbon dioxide, but tissues have higher concentration of CO2. So, due to concentration difference, CO2 diffuses, from tissues into the blood of capillaries. From tissues blood is carried to lungs where CO2 diffuses into the air present due to difference in concentration. In lungs, air has much less concentration of carbon dioxide than the blood brought from tissues.
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