Gas exchange system.

alveoli surface:

• has a large surface area.
• small distance between source and destination.
• high conc gradient.

ventilation:

• movement of air over the gas exchange surface.
• air always flows from high pressure to low.

pulmonary veniltation:

• volume of air ventilating each min.
• tidal volume is the normal volume breathed in each breath.
• can increase so that oxygen can diffuse from air to blood faster and carbon dioxide from blood to air faster.