The circulatory system is a system that uses blood to:
• transport nutrients and hormones
• transports the cells that fight diseases
• transport oxygen and waste products such as carbon dioxide
• stabilize the body temperature by transporting heat
• maintain a constant pH creating a constant stable environment within the body.
An average adult contains approximately 5 litres of blood, which is a blend of plasma, red blood cells, white blood cells, and platelets.
The main organs of the human circulatory (cardiovascular) system are the heart and the blood vessels. Oxygen poor (deoxygenated) blood is pumped from the right side of the heart through the pulmonary arteries to the lungs. Here, oxygen bonds with haemoglobin in the red blood cells which makes the blood turn bright red.
This oxygen rich (oxygenated) blood then goes to the left side of the heart where it is pumped through the bodies network of 100,000 km of arteries, arterioles, capillaries and veins.
The blood delivers oxygen to the bodies tissues through the capillaries and in return picks up carbon dioxide which is mainly dissolved in the blood plasma.
This deoxgenated blood is then returned to the heart where the cycle begins again. This cycle takes around 1 minute to complete.
The digestive system works with the circulatory system to provide the nutrients to the body. So you shouldn’t eat close to freediving otherwise all your blood will go to your stomach and not your lungs and muscles which is where you need it!

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