Gas Exchange and Partial Pressure

Study Notes

The movement of oxygen and carbon dioxide across thin membranes in the lungs (alveoli) and tissues.
In the lungs, oxygen from inhaled air diffuses from the alveoli (high oxygen concentration) into the capillaries (low oxygen concentration).
Carbon dioxide travels from the blood (high concentration) to the alveoli (low concentration) to be exhaled.
In tissues, oxygen from the blood diffuses into cells, where it is used for cellular respiration.
Waste product carbon dioxide diffuses from cells into the blood.

The pressure exerted by each gas in a mixture, for example, oxygen in the air.
This pressure is the driving force behind the movement of gases, as they move from areas of higher partial pressure to areas of lower partial pressure.
In the lungs, the high partial pressure of oxygen in the alveoli pushes oxygen into the blood.
In tissues, the higher partial pressure of oxygen in the blood drives oxygen into cells, while carbon dioxide moves from cells into the blood.

This process involves the contraction of the diaphragm, which moves down, increasing the volume of the chest cavity.
The intercostal muscles (between ribs) also contract expanding the ribcage outward.
These actions lower the pressure in the lungs, pulling air in from the higher pressure outside.
Air flows from high pressure (outside) to low pressure (inside) through the nose/mouth, trachea, bronchi, bronchioles, and alveoli.

Involves the relaxation of the diaphragm, which moves up, decreasing the volume of the chest cavity.
The intercostal muscles also relax, causing the ribcage to move inwards.
These actions increase the pressure in the lungs, pushing air out through the alveoli, bronchioles, bronchi, trachea, and nose/mouth.

Birds: Air sacs allow continuous airflow through the lungs, providing a high level of oxygen needed for flight.
Fish: Gills with counter-current exchange maximize oxygen absorption from water.
Insects: Spiracles and tracheae allow direct oxygen delivery to cells.