What Your Blood Does for You

On average, men have about 12 pints of blood in their bodies, and women have about 9. It typically accounts for around 8% of your total weight.

This vital fluid has four main parts, each with a specific job. All four together are called “whole blood.”

Red Blood Cells

Most of the cells in your blood are this type. They’re also called RBCs or erythrocytes.

These doughnut-shaped cells have a chemical called hemoglobin. It’s what makes them -- and your blood -- red, and it helps RBCs carry oxygen from your lungs throughout your body. These cells also bring carbon dioxide to your lungs, where you breathe it out.

Red blood cells -- like all parts of your blood -- are made in your bone marrow. They flow through your body for about 120 days before they wear out.

White Blood Cells

These cells are an important part of your body’s defense system. They’re also called leukocytes or WBCs. You don’t have nearly as many white cells as red ones, at least not when you’re healthy. But when your body notices a problem, like a virus or an infection, it makes more white blood cells to help you fight it off.

There are a few different types of WBCs:

  • Granulocytes: These help stop infections and boost healing. They can destroy germs and other things that aren’t supposed to be in your body.
  • Lymphocytes: There are two types of these, B cells and T cells. B cells make proteins called antibodies to fight a specific virus or bacteria. Even after the threat is gone, the antibodies stick around, in case that specific germ comes back. T cells attack infected cells and help your immune cells work together.
  • Monocytes attack and destroy viruses and bacteria in your body.

Most white blood cells have a lifespan of one to three days.


These are also called thrombocytes. Their job is to help your blood clot when you have an injury.

Platelets move to the break in a blood vessel and stick together to plug the leak. They also send out signals to other substances in your body that help your blood clot, calling them to the scene of the injury. The platelets and these other substances -- called clotting factors -- form a little dam that keeps more blood from leaking out.

Platelets flow through your body for about 9 days before they’re cycled out of your system by your spleen.



This is the liquid part of your blood. It’s made mostly of water. It also has fats, sugars, and proteins.

Plasma makes up about 60% of your blood. On its own, it’s a pale yellow.

It delivers nutrients, proteins, and hormones throughout your body, and it carries away waste. Substances your cells don’t need dissolve into your plasma and wash away.

WebMD Medical Reference



Dean, L. Blood Groups and Red Cell Antigens, National Center for Biotechnology Information, 2005. 

American Society of Hematology: “Blood Basics.”

American Red Cross: “Blood Components.”

KidsHealth from the Nemours Foundation: “What’s Blood?”

© 2022 WebMD, LLC. All rights reserved.


091e9c5e813ea7dd091e9c5e822761fbnl-ctr-responsivemodule_nl-ctr-responsive_091e9c5e813ea7dd.xmlwbmd_pb_sharedmodule091e9c5e801c9c6f0144010/13/2021 12:58:100HTML