In this case, we need to know how vapour pressure at saturation varies with temperature. The alveolar ventilation equation is the most important quantitative relationship in pulmonary physiology. It is used to measure the volume of fresh air reaching the alveoli. The pulmonary circulation is the major flow of deoxygenated blood from the pulmonary artery that perfuses the lung, taking up O 2 and giving off CO 2 . Despite these rates, the pressure in the pulmonary circulation is very low.
Lungs are very compliant, largely due to the low surface tension of the liquid lining the lungs.
This decrease in surface tension is due to surfactant, a chemical composed of lipoprotein complexes that create very low surface tension on the liquid-air interface. Conversely, in aquatic animals, the primary stimulus to respiration is a lack of O 2 . In mammals there are both central and peripheral receptors that are responsible for controlling ventilation. Both aquatic and air breathing animals are capable of adjusting aspects of their respiratory physiology to cope with periods of hypoxia, hypercapnia, exercise and diving.