Circulatory System Function

The function of the circulatory system is to transport blood around the body. It consists of the heart and blood vessels.


The main organ of the circulatory system is the Human Heart. The other main parts of the circulatory system include the Arteries, Arterioles, Capillaries, Venules, Veins, and Blood. The lungs also play a major part in the pulmonary circulation system.

circulatory system structure

The function of the circulatory system

The function of the circulatory system is to transport blood around the body. Blood itself also carries numerous other substances that the body requires to function:

  • Oxygen is carried by a protein called haemoglobin and found inside red blood cells
  • White blood cells fight disease and infection
  • Platelets are essential for clotting the blood following an injury, preventing blood loss
  • Waste products, such as Carbon Dioxide away from muscles and organs to the lungs

Systemic & pulmonary circulation

There are three circulatory system processes occurring simultaneously within the body. Firstly, systemic circulation carries blood around the body. Pulmonary circulation carries blood to the lungs. Coronary circulation provides the heart with its own blood supply.

Systemic circulation

At the start of the blood circulatory cycle, the heart pumps oxygenated blood out of the left ventricle, through the Aorta (the largest artery in the body).

The aorta divides into smaller arteries, then arterioles. Then finally microscopic capillaries are found deep within muscles and organs. Here Oxygen (and other nutrients) pass through the thin capillary walls, into the tissues where it is used to produce the energy for muscles to contract.

A waste product of energy production (metabolism) is Carbon dioxide (CO2). Carbon dioxide also passes across the walls of the capillaries, into the blood. Blood continues back towards the heart, through venules, into veins, and eventually back to the right atrium of the heart.

Pulmonary circulation

Once blood returns to the heart it is pumped from the right ventricle through the Pulmonary arteries to the lungs. Here the waste carbon dioxide is expelled and more Oxygen collected. The Pulmonary vein then carries oxygenated blood back to the left atrium of the heart. The cycle then starts again.

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