1. Double Circulation

2. Where it is found?
In mammals, birds and amphibians. Other creatures have single cycle circulation. Everything with lungs has double circulation.

3. The Difference
Double Circulation has two different circuits - one for oxygenated blood and the other for de-oxygenated blood
Single Circulation has only one circuit - the heart has only one chamber and 2 pumps

4. How Single Cycle Circulation and Double Circulation Works 1
For example fish have Single circulation. The cycle is very simple – heart gills body heart
Whereas in a human it goes
Heart body heart lungs heart

5. Fish Heart The heart of a fish looks like this –
As can you can see it is just one
chamber with no valves

6. Disadvantages of Double Circulation
Double circulation is much more efficient than single. In a fish blood pressure goes down as is passes through capillaries in gills so its slower and takes longer for oxygen and nutrients to get around the body. This is ok for a fish but not a human!

7. Advantages of Double Circulation
In humans the blood pressure can be increased after it has left the lungs. It is faster. Humans are more active than fish and need to produce more energy and heat.