White blood cell facts for kids
Quick facts for kids White blood cell |
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| A scanning electron microscope image of normal circulating human blood. In addition to the irregularly shaped leukocytes, both red blood cells and many small disc-shaped platelets are visible. | |
| System | Immune system |
White blood cells, also called leukocytes or leucocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. White blood cells include three main subtypes; granulocytes, lymphocytes and monocytes.
All white blood cells are produced and derived from multipotent cells in the bone marrow. Leukocytes are found throughout the body, including the blood and lymphatic system. All white blood cells have nuclei, which distinguishes them from the other blood cells.
Contents
Etymology
The name "white blood cell" derives from the physical appearance of a blood sample after centrifugation. White cells are found in the buffy coat, a thin, typically white layer of nucleated cells between the sedimented red blood cells and the blood plasma. The scientific term leukocyte directly reflects its description. It is derived from the Greek roots leuk- meaning "white" and cyt- meaning "cell".
Function
White blood cells are part of the body's immune system. They help the body fight infection and other diseases. Types of white blood cells are granulocytes (neutrophils, eosinophils, and basophils), and agranulocytes (monocytes, and lymphocytes (T cells and B cells)). Produced in the bone marrow, white blood cells defend the body against infections and disease. An excess of white blood cells is usually due to infection or inflammation. Less commonly, a high white blood cell count could indicate certain blood cancers or bone marrow disorders.
The number of leukocytes in the blood is often an indicator of disease, and thus the white blood cell count is an important subset of the complete blood count. White blood cells make up approximately 1% of the total blood volume in a healthy adult, making them substantially less numerous than the red blood cells at 40% to 45%. However, this 1% of the blood makes a large difference to health, because immunity depends on it. x
Types of white blood cells
Lymphocytes
Lymphocytes are round white blood cells a bit bigger than a red blood cell. Their center is round and they have little cytoplasm. Part of the lymphatic system, these target specific germs or poisons using their antibodies. There are three known types of lymphocytes, called T-cells, B-cells, and natural killer cells (NK cells).
B-cells make antibodies, which are little molecules that attach to viruses or bad cells. These tell other cells to destroy the viruses or bad cells, like a flag.
T-cells can either help make more B-cells, or kill cells with antibodies.
Natural killer cells kill cells in the body that have been infected by a virus or that are part of a tumor. They are part of the innate immune system.
Monocytes
Monocytes are reserve cells which turn into macrophages and dendritic cells, which work together in tissues to fight disease. Monocytes have a kidney bean shaped center and lots of cytoplasm. They may appear as macrophages in a non-round shape when they pass through tissue to eat germs, "junk" cells, and dead cells.
Granulocytes
The next three types of white blood cells are referred to as granulocytes since they all contain rough, grain-like particles that assist in attacking viruses and bacteria. Granulocytes are also called polymorphonuclear leukocytes because of the shape of the nucleus, which has three segments.
Neutrophils
Neutrophils are the most abundant type of white blood cells in mammals, 70% of leukocytes. They are an essential part of the immune system. They get to the site of an injury within minutes, and make up much of the content of pus. They have a short life-span of a couple of days.
The nucleus, which looks like a string of beads, does not take up stain strongly. Like phagocytes, they actually eat the bacteria and dead cells. They also release a bunch of proteins which work to damage the bacteria.
Basophils
Basophils, or basophil granulocytes, are rare granulocytes. If you collected 1000 white blood cells, only 1–3 of them would be basophils. Their nucleus is hidden by granules which turn dark blue in color when stained. Basophils carry histamine and heparin. They appear at the sites of ectoparasite infection, or allergies. We don't know exactly how they work.
Eosinophils
Eosinophils, or acidophils, are leukocytes. They are one of the immune system components which combat parasites and certain infections. As with mast cells and basophils, they part causes of allergy and asthma. Eosinophils are round cells with a lobed nucleus and granules which turn red when stained. These granules are packed with proteins that can be poured out to help destroy invaders.
Cell testing
A test called a differential count shows how many white blood cells there are in a person's blood, and how many of each type are there.
Disorders
The two commonly used categories of white blood cell disorders divide them quantitatively into those causing excessive numbers (proliferative disorders) and those causing insufficient numbers (leukopenias). Leukocytosis is usually healthy (e.g., fighting an infection), but it also may be dysfunctionally proliferative. Proliferative disorders of white blood cells can be classed as myeloproliferative and lymphoproliferative. Some are autoimmune, but many are neoplastic.
Another way to categorize disorders of white blood cells is qualitatively. There are various disorders in which the number of white blood cells is normal but the cells do not function normally.
Neoplasia of white blood cells can be benign but is often malignant. Of the various tumors of the blood and lymph, cancers of white blood cells can be broadly classified as leukemias and lymphomas, although those categories overlap and are often grouped together.
Images for kids
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Neutrophil engulfing anthrax bacteria
See also
In Spanish: Leucocito para niños
