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Cardiovascular System

The Role of Blood Vessels

There are three main kinds of blood vessels within the cardiovascular system:
  • Arteries
  • Capillaries
  • Veins.
Arteries are large blood vessels that carry blood from your heart to the rest of your body. This blood is rich in oxygen and nutrients. As arteries get farther away from the heart, they begin to branch and become smaller and smaller.
The smallest branches are called capillaries. Here, oxygen is transferred from the blood into your cells. In exchange, the wastes from your cells, including carbon dioxide (CO2), are transferred into the blood.
Just beyond this area, the capillaries begin to merge together and eventually form larger vessels, called veins, which lead back to the heart. As veins carry the CO2-rich blood back to the heart, other organs filter out and dispose of the waste products.
As the deoxygenated blood makes its way back through the heart and lungs, it picks up oxygen and nutrients. It also releases the CO2 into the air you breathe out. The heart then pumps the blood out through the arteries, and the cycle is repeated.

The Role of Blood

The last main component of the cardiovascular system is blood. Blood flows throughout your entire body, carrying oxygen and nutrients to all of your cells and taking away the waste products that they produce. Blood is a fluid that carries several different kinds of cells. The three types that we will talk about are red blood cells, white blood cells, and special cell fragments called platelets.
  • Red blood cells carry oxygen to your organs and take carbon dioxide away from them.


  • White blood cells help your body fight infection from bacteria and viruses. They play a very important role in your body's immune system.


  • Platelets help to seal off a blood vessel when it has been cut or torn, so they act like your own natural bandage. They clump together to plug a wound inside the body or on the skin. They also stop blood from flowing out of the damaged area. This is the first step in the formation of a "clot." 
Because red and white blood cells and platelets are so important, they are constantly flowing throughout your body in the network of blood vessels.
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