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Circulatory system

Transport system of the body made up of the heart, the blood vessels and the blood. Also known as the cardiovascular system.

Blood vessels



Very small blood vessel with walls made of a single layer of epithelial cells. Exchange of materials, such as nutrients, oxygen and carbon dioxide, takes place between the blood and the cells of the body across the capillary walls.


The spreading out of the particles of a gas or any substance in solution down a concentration gradient


Blood vessel(s) which carries blood away from the heart


A list of often difficult or specialised words with their definitions.




Blood vessel which carries blood to the heart


The poisonous waste compound produced when excess amino acids are broken down in your liver

What is the circulatory system?

The circulatory system is the transport system of your body. It delivers food and oxygen to your cells and removes the waste products such as carbon dioxide and urea. It is made up of blood (the transport medium), the blood vessels which act as the pipes and the heart which pumps the blood around the body.


The circulatory system

Your cells need a constant supply of food and oxygen to provide the energy needed for all of the reactions of the body. At the same time the cells are constantly making waste products which are poisonous if they are allowed to build up.

Food is absorbed from the digestive system and oxygen is picked up in the lungs to be carried in the blood around the body. The food molecules and oxygen move into the cells from the blood by diffusion.

Waste products also move from the cells into the blood by diffusion. They are removed from the body in the lungs or by the kidneys.

The blood is carried around the body in a system of blood vessels which vary in size and structure. The main types of vessels are the arteries, veins and capillaries.

To transport substances the blood must be moved around the circulatory system and this is the function of the heart. Your heart is a muscular pump which starts beating long before you are born and continues to beat throughout your life around 70 times every minute.

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