The circulatory system
Your body is made up of billions of cells and most of them are a long way from a direct source of food or Oxygen.
A transport system is absolutely vital to supply the needs of your body cells and remove waste material produced.
This is the job of the blood circulation system. It has three elements - the pipes (Blood vessels), the pump (Heart) and the medium (Blood)
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You actually have a double circulation system. One carries blood from your heart to the lungs and back again, to exchange Oxygen and CO2 with the air. The other carries blood all around the rest of your body and back again
This double circulatory system is very important in warm blooded, active animals like ourselves. It makes our circulatory system very efficient. Fully oxygenated blood returns to the heart from the lungs, and then can be sent off to different parts of the body.
This means that more areas of your body can receive fully oxygenated blood quickly.
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The types of Blood Vessels 1 (Arteries)
The first type of blood vessel in your body, is the Artery. These carry blood away from your heart to the organs of your body. This is usually oxygenated blood so it is bright red. The Arteries stretch as the blood is forced through them and go back into shape afterwards. You can feel this as a Pulse when they run close to the surface (Like your wrist)
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The types of blood vessels 2
The second type of blood vessel, is the vein. These carry blood towards your heart, it is usually low in oxygen and so is deeply purply-red colour. They do not have a pulse, but they often have valves to prevent the back flow of blood as it moves from various parts of the body back to the heart.
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The types of blood vessels 3
The final type of blood vessel is the Capillary. In the organs of your body, between the arteries and the veins, your blood flows through a huge network of these capillaries. No cell in the body is more than 0.05mm away from a capillary. They are very narrow with thin walls so the substances needed by your body cells, such as Oxygen and Glucose, can easily pass out of your blood and into your cells by diffusion. In the same way, CO2 can pass easily back into the blood.
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Arteries have; Thick walls and a Small Lumen
Veins have; Thin walls and a Large Lumen
Capillaries have; Walls a single cell thick and a Narrow Lumen
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Your heart is made up of Two Pumps (for double circulation) which beat around 70 times a minute.
The walls of your heart are almost entirely muscle, supplied with oxygen by the Coronary Blood Vessels
The blood in Arteries are usually Bright red, and in Veins a purply-red colour. However, the colour of the blood is swapped around in the Pulmonary Artery and Pulmonary Vein, as the Pulmonary Artery takes Deoxygenated Blood to the lungs, and the Pulmonary Vein returns it, Fully Oxygenated.