Pleural Membranes

To understand the relationship of pleura and lungs, imagine yourself pushing your fist into a partially inflated balloon. The part of the balloon wall adjacent to the skin of your fist is comparable to visceral pleura, the remainder of the balloon is comparable to parietal pleura. The air filled cavity between the two layers of balloon is analogous to the pleural cavity.
To view the the animation, press the begin button below, then press the next button (triangular button). To see the animation again, press the replay button (between the two triangular buttons).

Pulmonary Ventilation

Unlike in amphibians which use a force pump mechanism to force air into lungs, mammals use negative pressure ventilation, where increases in the lung volume decreases pressure in lungs leading to flow of air into the lungs.

Gas Exchange

The rate of gas exchange depends on:
1. Partial pressure of the gases
2. Solubility of the gases
3. Surface area
4. Diffusion distance
Partial Pressure
Partial pressure is the pressure exerted by and individual in a mixture of gases.
For example atmospheric pressure = 760 mm Hg
% of O₂ of in Atmosphere = 20.95%
P_O2 =20.95% of 760 mmHg = 159 mmHg
A gas always diffuses from the region of its higher partial pressure to the region of its partial pressure.

Gas	Atm.Air	Alveoli	Deoxygenated Blood	Oxygenated Blood	Tissues
O2	159	104	40	95	40
CO2	0.3	40	45	40	45

All units in mmHg.