The conditions necessary for effective gaseous exchange

In order for effective gaseous exchange to take place certain functions need to be fulfilled. During inspiration a number of things happen. The diaphragm contracts along with intercostal muscles to make room in the thoracic cavity for the lungs to expand. Air can then be drawn down the respiratory tract into the lungs. Upper respiratory infections such as the common cold or flu can inhibit inspiration by narrowing the respiratory tract.

Air that has passed through the upper respiratory tract has been humidified. This so that when it reaches the lungs it is easily dissolved in water before being diffused in to the blood stream.


Within the lungs themselves the conditions have to be in a constant state of balance. Gas exchange happens by diffusion, high concentrations of carbon dioxide in the blood diffuse into the alveoli where concentrations are lower. Oxygen concentrations are high in the alveoli and low in the blood.

Another important factor for gas exchange is pulmonary surfactant. This is produced by cells within the alveoli and consists of a mixture of lipids and proteins that reduces surface tension of the thin liquid film that lines each alveolus. (Sherwood 2007). The tension of this liquid is such that without the surfactant each alveolus would collapse in on itself.

In order for effective gaseous to take place effectively the entire respiratory tract needs to be functioning correctly and be free from infection. Any number of infections can cause this delicate system to function below optimum capacity.

References:

Sherwood L (2007), 'Human Physiology', From Cells to Systems
Thomson, Brooks/Cole