Process of Respiration
Respiratory and Circulator System Gaseous exchange that is intake of oxygen and output of carbon dioxide, takes place at the respiratory surface since the surface is richly vascularised. The respiratory surface could be the general integument, a lung or a gill. Once the source of oxygen (atmospheric air or water containing dissolved oxygen) comes in contact along with the respiratory surface as a result of several ventilating mechanisms, exchange of gases, takes place, for example oxygen is absorbed into the blood and carbon dioxide from the blood is released into the environment. The exchange of gases occurs by simple diffusion, which is caused because of the partial pressure of the respiratory gases. Gases move from the medium with high partial pressure to the medium having low partial pressure. In the environment (air or water) the partial pressure of oxygen is relatively higher than in the blood. Hence, oxygen diffuses from the environment to the blood through the respiratory surface. Likewise the partial pressure of the carbon dioxide in the blood is higher than the immediate environment. Thus it diffuses outside from blood through the respiratory surface.