B3 - The Heart

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Mammals have a double circulatory system

The first system connects the heart to the lungs. Deoxygenated blood is pumped to the lungs to take in oxygen. The blood then returns to the heart

The second system connects the heart to the rest of the body. The oxygenated blood in the heart is pumped out to the body. It gives up its oxygen and then the deoxygenated blood returns to the heart to be pumped out to the lungs again

Not all animals have a double circulatory system, e.g. fish don't

There are advantages to mammals having a double circulatory system. Returning the blood to the heart after it's picked up oxygen at the lungs means it can be pumped out around the body at a much higher pressure. This increases the rate of blood flow to the tissues

The heart

The right atrium of the heart receives oxygenated blood from the body (through the vena cava)

The deoxygenated blood moves through to the right ventricle, which pumps it to the lungs (via the pulmonary artery)

The left atrium receives oxygenated blood from the lungs (through the pulmonary vein)

The oxygenated blood then moves through to the left ventricle, which pumps it out rounds the whole body (via the aorta)

The semilunar, tricuspid and bicuspid valves prevent the backflow of blood

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