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.

[edit] Blood Basics

Two types of blood vessels carry blood throughout our bodies:

• Arteries carry oxygenated blood (blood that has received oxygen from the lungs) from the heart to the rest of the body.
• Blood then travels through 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 whole blood, which contains three types of blood cells:

• red blood cells (RBCs)
• white blood cells (WBCs)
• platelets

In babies and young kids, blood cells are made within the bone marrow (the soft tissue inside of bones) of many bones throughout the body. But, as kids get older, blood cells are made mostly in the bone marrow of the vertebrae (the bones of the spine), ribs, pelvis, skull, sternum (the breastbone), and parts of the humerus (the upper arm bone) and femur (the thigh bone).

The cells travel through the circulatory system suspended in a yellowish fluid called plasma, which is 90% water and contains nutrients, proteins, hormones, and waste products. Whole blood is a mixture of blood cells and plasma.