The lungs are not capable of inflating themselves, and will expand only when there is an increase in the volume of the thoracic cavity. In humans, as in the other mammals, this is achieved primarily through the … See more

The primary purpose of breathing is to refresh air in the alveoli so that gas exchange can take place in the blood. The equilibration of the partial pressures of the gases in the … See more

Inhaled air is by volume 78% nitrogen, 20.95% oxygen and small amounts of other gases including argon, carbon dioxide, neon, helium, and hydrogen.
The gas exhaled is 4% to 5% by volume of carbon dioxide, about a 100 fold increase over the inhaled … See more

Abnormal breathing patterns include Kussmaul breathing, Biot's respiration and Cheyne–Stokes respiration.
Other breathing disorders include shortness of breath (dyspnea), stridor, apnea, sleep apnea (most commonly obstructive sleep apnea See more

Upper airways
Ideally, air is breathed first out and secondly in through the nose. The nasal cavities (between the nostrils and the pharynx) are quite narrow, firstly by being divided in two by the nasal septum, and secondly by See more

The rate and depth of breathing is automatically controlled by the respiratory centers that receive information from the peripheral and central chemoreceptors. These See more

Breathing at altitude
Atmospheric pressure decreases with the height above sea level (altitude) and since the alveoli are open … See more