B3 - Double Circulatory Systems

In a double circulatory system, there are two systems (no surprise there). The first connects the heart to the lungs, and the second connects the heart to the rest of the body.

In the first system...

• deoxygenated blood is pumped to the lungs to take in oxygen in the red blood cells.
• the blood then returns to the heart.

In the second system...

• oxygenated blood is pumped from the heart and to the rest of the body
• it gives up the oxygen it is holding, before returning to the heart.

Double circulatory systems are found in mammals, e.g. humans. Single circulatory systems are found in organisms like fish. Having a double circulatory system is more efficient though; it means that blood can be pumped at a much higher pressure, and more oxygen is delivered to the cells at a faster rate.