What Is Blood, and What Does It Do? Blood is needed to keep us alive. It 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 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? White blood cells: White blood cells are a key part of the immune system. The immune system helps the body defend itself against infection. Different types of white blood cells fight germs, such as bacteria and viruses. Some types of white blood cells make antibodies, which are special proteins that recognize foreign materials and help the body get rid of them. There are several types of white blood cells, and their life spans vary from hours to years. New cells are constantly being formed — some in the bone marrow and some in other parts of the body such as the spleen, thymus, and lymph nodes. Blood contains far fewer white blood cells than red blood cells, although the body can increase white blood cells production to fight infection. The white blood cell count (the number of cells in a given amount of blood) in someone with an infection often is higher than usual because more white blood cells are being made or are entering the bloodstream to battle the infection.
Platelets: Platelets are tiny oval-shaped cells that help in the clotting process. When a blood vessel breaks, platelets gather in the area and help seal off the leak. Platelets work with proteins called clotting factors to control bleeding inside our bodies and on our skin. Platelets survive only about 9 days in the bloodstream and are constantly being replaced by new platelets made by the bone marrow. How Does Blood Travel in the Body? With each heartbeat, the heart pumps blood throughout our bodies, carrying oxygen to every cell. After delivering the oxygen, the blood returns to the heart. The heart then sends the blood to the lungs to pick up more oxygen. This cycle repeats over and over again. The circulatory system is made up of blood vessels that carry blood away from and toward the heart. Two types of blood vessels carry blood throughout our bodies: Arteries carry oxygenated blood (blood that has gotten oxygen from the lungs) from the heart to the rest of the body. Blood then travels through veins back to the heart and lungs, so it can get more oxygen to send back to the body via the arteries. 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. What if Someone Has Low Numbers of Blood Cells? Sometimes medicine can be given to help a person make more blood cells. And sometimes blood cells and some special proteins blood contains can be replaced by giving a person blood from someone else. This is called a transfusion. People can get transfusions of the part of the blood they need, such as platelets, RBC, or a clotting factor. When someone donates blood, the whole blood can be separated into its different parts to be used in these ways.
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