BLOOD

Humans can't live without blood. Without blood, the body's organs couldn't get the oxygen and nutrients they need to survive, we couldn't keep warm or cool off, fight infections, or get rid of our own waste products. Without enough blood, we'd weaken and die.
Here are the basics about the mysterious, life-sustaining fluid called blood.
There are two types of blood vessels carry blood throughout our bodies:
The arteries carry oxygenated blood (blood that has received oxygen from the lungs) from the heart to the rest of the body. The blood then travels through the veins back to the heart and lungs, where it receives more oxygen.
As the heart beats, you can feel blood traveling through the body at pulse points like the neck and the wrist, where large, blood-filled arteries run close to the surface of the skin.

The blood that flows through this network of veins and arteries is called whole blood, and it contains three types of blood cells:
1. red blood cells (RBCs)
2. white blood cells (WBCs)
3. platelets