What makes up blood

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.

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 WBCs are being made or are entering the bloodstream to battle the infection. Platelets: Platelets also called thrombocytes, say: THROM-buh-sytes 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. 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.

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. Sometimes medicine can be given to help a person make more blood cells. And sometimes blood cells and some of the special proteins blood contains can be replaced by giving a person blood from someone else.

This is called a transfusion say: trans-FEW-zyun. People can get transfusions the part of blood they need, such as platelets, RBCs, or a clotting factor. The shape of a red blood cell is a biconcave disk with a flattened center - in other words, both faces of the disc have shallow bowl-like indentations a red blood cell looks like a donut.

Production of red blood cells is controlled by erythropoietin, a hormone produced primarily by the kidneys. Red blood cells start as immature cells in the bone marrow and after approximately seven days of maturation are released into the bloodstream.

Unlike many other cells, red blood cells have no nucleus and can easily change shape, helping them fit through the various blood vessels in your body. However, while the lack of a nucleus makes a red blood cell more flexible, it also limits the life of the cell as it travels through the smallest blood vessels, damaging the cell's membranes and depleting its energy supplies.

The red blood cell survives on average only days. Red cells contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbon dioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their color from the hemoglobin. The percentage of whole blood volume that is made up of red blood cells is called the hematocrit and is a common measure of red blood cell levels.

White blood cells protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of your blood. The most common type of white blood cell is the neutrophil, which is the "immediate response" cell and accounts for 55 to 70 percent of the total white blood cell count. Each neutrophil lives less than a day, so your bone marrow must constantly make new neutrophils to maintain protection against infection.

Transfusion of neutrophils is generally not effective since they do not remain in the body for very long. The other major type of white blood cell is a lymphocyte. There are two main populations of these cells.

T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors. B lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials. Unlike red and white blood cells, platelets are not actually cells but rather small fragments of cells.

Platelets help the blood clotting process or coagulation by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur. This results in the formation of a fibrin clot, which covers the wound and prevents blood from leaking out.

Fibrin also forms the initial scaffolding upon which new tissue forms, thus promoting healing. The solid part of your blood contains red blood cells, white blood cells, and platelets. Red blood cells RBC deliver oxygen from your lungs to your tissues and organs.

White blood cells WBC fight infection and are part of your immune system. Platelets help blood to clot when you have a cut or wound.

Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer.

Also, blood is either Rh-positive or Rh-negative. So if you have type A blood, it's either A positive or A negative. Which type you are is important if you need a blood transfusion. And your Rh factor could be important if you become pregnant - an incompatibility between your type and the baby's could create problems. Blood tests such as blood count tests help doctors check for certain diseases and conditions.