How does the human body's respiratory system enable the rapid exchange of gases between oxygen and CO2?

The blood capillaries surrounding the alveoli of the lungs provide them with a rich supply of flowing blood. This means that the oxygen depleted blood returning from the body picks up oxygen from inside the alveoli, and the high concentration of CO2 inside this blood diffuses rapidly out of the blood stream into the alveoli. The mechanical act of breathing expels the CO2 from and inhales oxygen into the lungs- thus maintaining the concentration necessary for uptake into the blood. This act of ventilation ensures CO2 is removed swiftly from inside the lungs, meaning there is no build up and steep concentration gradients are maintained. The alveoli themselves are spherical and small in shape, so also increase the surface area of diffusion between the blood and the lungs enabling the rapid exchange of gases. Very thin alveolus walls mean the gases have a short diffusion distance to travel. The capillaries are all one cell thick which enables gases to exit and enter the blood stream quickly.