Blood

A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.

PubMed Health Glossary
(Source: NIH - National Cancer Institute)

What Does Blood Do?

The blood is a vitally important fluid for the body. It is thicker than water, and feels a bit sticky. The temperature of blood in the body is 38° C, which is about one degree higher than body temperature. How much blood you have depends mostly on your size and weight. A man who weighs about 70 kg (about 154 pounds) has about 5 to 6 liters of blood in his body. Blood has three important functions:

  • Transportation: The blood transports oxygen from the lungs to the cells of the body, where it is needed for metabolism. The carbon dioxide produced during metabolism is carried back to the lungs by the blood, where it is then exhaled. Blood also provides the cells with nutrients, transports hormones and removes waste products, which the liver, the kidneys or the intestine, for example, then get rid of.
  • Regulation: The blood helps to keep certain values of the body in balance. For instance, it makes...

Read more about the Blood

Terms to know

B-Lymphocytes (B-Cells)
A type of white blood cell that makes antibodies. B lymphocytes are part of the immune system and develop from stem cells in the bone marrow. Also called B cell.
Basophils
A type of immune cell that has granules (small particles) with enzymes that are released during allergic reactions and asthma. A basophil is a type of white blood cell and a type of granulocyte.
Blood Plasma
The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clots are in plasma.
Blood Vessels
Tubes that carry blood to and from all parts of the body. The three main types of blood vessels are arteries, capillaries, and veins.
Bone Marrow
The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.
Eosinophils
A type of immune cell that has granules (small particles) with enzymes that are released during infections, allergic reactions, and asthma. An eosinophil is a type of white blood cell and a type of granulocyte.
Erythrocytes (Red Blood Cells)
A cell that carries oxygen to all parts of the body.
Granulocytes
A type of immune cell that has granules (small particles) with enzymes that are released during infections, allergic reactions, and asthma. Neutrophils, eosinophils, and basophils are granulocytes. A granulocyte is a type of white blood cell.
Hematocrit
A measure that tells what portion of a blood sample consists of red blood cells. Low hematocrit suggests anemia or massive blood loss.
Hematopoiesis
The formation of new blood cells.
Hematopoietic Stem Cells (Blood Stem Cells)
A stem cell that gives rise to all red and white blood cells and platelets.
Hemoglobin
A protein inside red blood cells that carries oxygen from the lungs to tissues and organs in the body and carries carbon dioxide back to the lungs.
Leukocytes (White Blood Cells)
A type of immune cell. Most white blood cells are made in the bone marrow and are found in the blood and lymph tissue. White blood cells help the body fight infections and other diseases. Granulocytes, monocytes, and lymphocytes are white blood cells.
Lymphoblasts
A lymphocyte that has gotten larger after being stimulated by an antigen. Lymphoblast also refers to an immature cell that can develop into a mature lymphocyte.
Lymphocytes
A lymphocyte is a type of white blood cell that is part of the immune system. There are two main types of lymphocytes: B cells and T cells. The B cells produce antibodies that are used to attack invading bacteria, viruses, and toxins. The T cells destroy the body's own cells that have themselves been taken over by viruses or become cancerous.
Lymphoid
Referring to lymphocytes, a type of white blood cell. Also refers to tissue in which lymphocytes develop.
Macrophages
A type of white blood cell that surrounds and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells.
Monocytes
A type of immune cell that is made in the bone marrow and travels through the blood to tissues in the body where it becomes a macrophage. Macrophages surround and kill microorganisms, ingest foreign material, remove dead cells, and boost immune responses. A monocyte is a type of white blood cell and a type of phagocyte.
Myeloblasts
A type of immature white blood cell that forms in the bone marrow. Myeloblasts become mature white blood cells called granulocytes (neutrophils, basophils, and eosinophils).
Myeloid
Having to do with or resembling the bone marrow. May also refer to certain types of hematopoietic (blood-forming) cells found in the bone marrow. Sometimes used as a synonym for myelogenous; for example, acute myeloid leukemia and acute myelogenous leukemia are the same disease.
Natural Killer Cells (NK Cells)
A type of immune cell that has granules (small particles) with enzymes that can kill tumor cells or cells infected with a virus. A natural killer cell is a type of white blood cell. Also called NK cell and NK-LGL.
Neutrophils
A type of immune cell that is one of the first cell types to travel to the site of an infection. Neutrophils help fight infection by ingesting microorganisms and releasing enzymes that kill the microorganisms. A neutrophil is a type of white blood cell, a type of granulocyte, and a type of phagocyte.
Phagocytes (Scavenger Cells)
A large white blood cell that contributes to immune defenses by ingesting microbes or other cells and foreign particles.
Platelets (Thrombocytes)
A tiny piece of cell that is made by breaking off of a large cell in the bone marrow. Platelets are found in the blood and spleen. They help form blood clots to slow or stop bleeding, and to help wounds heal. Also called thrombocyte.
Rh Factor
Rh factor is a protein on red blood cells. If you have Rh factor, you're Rh-positive. If you don't have it, you're Rh-negative. Rh factor is inherited (passed from parents to children through the genes). Most people are Rh-positive.
Stem Cells
A cell from which other types of cells develop. For example, blood cells develop from blood-forming stem cells.
T-Lymphocytes (T-Cells)
A type of white blood cell. T-lymphocytes are part of the immune system and develop from stem cells in the bone marrow. They help protect the body from infection and may help fight cancer. Also called T cell and thymocyte.

Terms to know

B-Lymphocytes (B-Cells)
A type of white blood cell that makes antibodies. B lymphocytes are part of the immune system and develop fro...
Basophils
A type of immune cell that has granules (small particles) with enzymes that are released during allergic reac...
Blood Plasma
The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clot...
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