close   X


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 life-sustaining fluid called blood.

What Is Blood and What Does It Do?

Blood brings oxygen and nutrients to all the parts of the body so they can keep working. Blood carries carbon dioxide and other waste materials to the lungs, kidneys, and digestive system to be removed from the body. Blood also fights infections, and carries hormones around the body.

Blood is made up of blood cells and plasma. Plasma (PLAZ-muh) is a yellowish fluid that has nutrients, proteins, hormones, and waste products. The different types of blood cells have different jobs.

What Are the Types of Blood Cells?

Red blood cells: Red blood cells (RBCs, also called erythrocytes; ih-RITH-ruh-sytes) are shaped like slightly indented, flattened disks. RBCs contain hemoglobin (HEE-muh-glow-bin), a protein that carries oxygen. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the different body parts.

Each RBC lives for about 4 months. Each day, the body makes new RBCs to replace those that die or are lost from the body. RBCs are made in the inside part of bones called the bone marrow.

White blood cells: White blood cells (also called leukocytes; LOO-kuh-sytes) are a key part of the immune system. The immune system helps the body defend itself against infection. Different types of white blood cells (WBCs) fight germs, such as