Double Circulation

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Types of Circulatory Systems

All animals have circulatory systems to transport substances around their bodies. These systems are made of blood vessels, a pump (the heart) and valves to stop blood moving in the wrong direction.

Open circulatory systems

In open circulatory systems, the organism's blood is free to flow throughout the body cavity.
Open circulatory systems are found in insects.

Closed circulatory systems

In closed circulatory systems, blood is restricted to flowing through blood vessels and a pump (the heart) is required to get blood to all parts of the body.
Closed circulatory systems are found in fish and mammals.
- Fish have single closed circulatory systems.
- Mammals have double closed circulatory systems.

Single closed circulatory systems

Fish have what is known as a single circulatory system because blood only travels through the heart once in every circuit around the body.

Double closed circulatory systems

Mammals have a double circulatory system, where blood travels through the heart twice per circuit.
- Double circulatory systems get oxygenated blood to tissues (like muscles) that need it faster than single circulatory systems.
- The concentration gradient between the blood and cells is also better maintained in double circulatory systems, so substances are exchanged between the blood and body cells faster.

The Double Circulatory System

Complex multicellular organisms require a specialised system for transporting nutrients throughout their bodies and removing waste products.

Heart

The heart is the centre of the circulatory system.
Mammals have a double circulatory system. This means blood flows through the heart twice in one circuit.
- Deoxygenated blood is pumped to the lungs.
- Oxygenated blood is pumped around the body.

Coronary arteries

The heart is a muscle that is constantly contracting and relaxing.
The heart muscle needs a constant supply of oxygen for respiration.
The coronary arteries supply blood to the heart.

Pulmonary artery and vein

Deoxygenated blood is pumped out of the heart to the lungs via the pulmonary artery.
Oxygen diffuses into the deoxygenated blood in the lungs and the blood becomes oxygenated.
Oxygenated blood flows into the heart from the lungs via the pulmonary vein.

Aorta and vena cava

Oxygenated blood is pumped out of the heart around the body via the aorta.
Blood in the aorta is very high pressure to ensure the blood can be pumped to all the tissues in the body.
Oxygen dissociates from the blood at respiring cells in the body and the blood becomes deoxygenated.
Deoxygenated blood flows into the heart from the body via the vena cava.

Renal artery and vein

Oxygenated blood flows out of the aorta to the kidneys.
Oxygenated blood enters the kidneys through the renal artery.
Oxygen diffuses out of the blood to be used in the kidney cells and the blood becomes deoxygenated.
Deoxygenated blood flows out of the kidneys via the renal vein.