Describe and explain how the mammalian respiratory system is adapted for efficient gas exchange.

The mammalian respiratory system is adapted for efficient gas exchange by increasing the rate of diffusion through targeted manipulations of Fick's law. These manipulations are centred around maximising surface area, minimising the length of the diffusion pathway and maintaining a concentration gradient. Mammalian lungs maximise surface area through the presence of large amounts of alveoli, this means there are more sites for gas exchange to occur, thereby increasing the rate of diffusion. Diffusion is the net passive movement of particles from a region of high concentration to a region of low concentration, thus a steep concentration gradient must be maintained to allow efficient gas exchange. In the lungs this is achieved through ventilation and the presence of a rich network of capillaries surrounding the alveoli. Ventilation allows the removal of waste CO2 and introduces fresh O2. While the rich blood capillary network supplies CO2 to the exchange sites from the body and removes diffused oxygen. These mechanisms ensure a large concentration gradient is maintained increasing the rate of gas exchange. Finally, a short diffusion pathway is brought about by separating the alveoli and the capillary network with a one cell thick endothelium, this means the gases have to diffuse across a shorter distance and increases the rate of gas exchange. Mammalian respiratory systems combine these adaptions to maximise the efficiency of gas exchange.