The mechanism of breathing.

When volume is increased pressure is decreased.
Air rushes into areas of lower pressure.
So increasing volume in the lungs brings air in:

Breathing in (inspiration)
Diaphragm contracts: flattens- increasing volume.
Intercostal  muscles contract: pulling up and out- increasing volume.

When volume is decreased it increases pressure.
Air rushes to areas of lower pressure.
So if volume is decreased in the lungs air will rush out:

Breathing out (Expiration)
Diaphragm relaxes: becoming a dome shape and pushing up- decreasing volume.
Intercostal muscles relax: pushing the ribcage down and in- decreasing volume.

Pulmonary ventilation as the product of tidal volume and ventilation rate.

Tidal volume is the amount of air breathed in. Measured in decemeters cubed.

Ventilation rate is the number of breaths taken in one minute. Measured in minutes to the power of -1.

If you times these two things together you get a measure of pulmonary ventilation in dm3min-1.

The exchange of gases in the lungs.

Oxygen diffuses from the alveoli- where it is in high concentration- into the capillaries- where it is in low concentration.

Carbon dioxide diffuses from the capillaries- high conc.- into the alveoli- low conc..

The essential features of the alveolar epithelium as a surface over which gas exchange takes place.

Epithelila cells make up the walls of alveoli.

The alveoli are surrounded by capillaries, this means there is a constant flow of blood that takes oxygen away from the area of diffusion, and the lungs bring a constant supply of oxygen to be diffused on the other side; the opposite is true for CO2- this keeps a big difference in concentration gradient to speed up diffusion.

Both alveoli and capillaries have very thin walls making the diffusion distance short (so diffusion happens more quickly.)

Because there are so many alveoli there is a very large total surface area fro gasses to diffuse through (quicker diffusion.)

There is mucus lining the alveoli which helps gasses to diffuse across.

The gross structure of the human gas exchange system limited to the alveoli, bronchioles, bronchi, trachea and lungs.

Once air is breathed in through the mouth or nose it travels down the trachea. The trachea splits into two- one going into the left lung and one going into the right lung- these pipes are called bronchi. Each bronchus will then divide further into many bronchioles: each ending in a sac called an alveoli.

The trachea and bronchi have walls of muscle that are supported by cartilage. The cartilage is in partial rings so that the tubes can be moved in any direction. Cilia on the walls move mucus out of the breathing system and into the stomach.

wikibooks