Question

Describe the flow of air through the respiratory system in mammals. (From where it enters all the way to gas exchange)

Answer 1

The main organ in mammals respiration is the lungs. The lungs are actively ventilated via a suction-pump mechanism of inhalation and exhalation. Breathing is dependent upon the rib muscles and the diaphragm, a structure shaped like a dome-shaped floor just beneath the lungs. 

Inhalation happens when the rib cage opens up and the diaphragm flattens and moves downward. The lungs expand into the larger space, causing the air pressure inside to decrease. The drop in air pressure inside the lung makes the outside air rush in. 

Exhalation is the opposite process. The diaphragm and the rib muscles relax to their neutral state, causing the lungs to contract. The squashing of the lungs increases their air pressure and forces the air to flow out.