What is the function of white blood cells?
White blood cells or WBCs are components of blood which play a vital role in protecting the body against infections by varied pathogens. Also referred to as leukocytes, WBCs aid the immune system by detecting, destroying, and eliminating germs, malignant cells, damaged cells, and foreign materials from the body. White blood cells are produced in the stem cells of the bone marrow and circulate in lymph fluid and blood.
WBCs also have the ability to migrate from the blood vessels to the tissues in the body. They are classified as per the obvious absence of presence of granules in their cytoplasm. Granules are sacs filled with digestive enzymes or other types of chemical matter. A WBC can be termed as agranulocyte or as an agranulocyte.
White blood cells: Production, functions, and components
White blood cells are manufactured by bone marrow inside bones. Some leukocytes mature in the spleen, lymph nodes, or thymus gland. Mature WBCs usually live for a few hours to many days. The production of blood cells is typically regulated by varied body organs like the spleen, lymph nodes, kidneys, and liver.
WBCs help the body in fighting and overcoming infections. They circulate throughout the body via the blood stream, thereby allowing them to easily go to an area which has been affected by an infection.
A normal healthy adult body usually has about 4,000 to 10,000 white blood cells per microliter of blood, with the average being about 7,000. Any rise in the WBC count in the blood is an indication of an underlying infection in the body, leukemia, anemia, tissue damage, or stress; while a low WBC count can indicate bone marrow dysfunction, exposure to radiation, or an underlying disease.
The average percentage of the 6 major types of WBCs in the blood is given below:
- Neutrophils: 58 percent
- Lymphocytes: 4 percent
- Monocytes: 4 percent
- Bands: 3 percent
- Eosinophils: 2 percent
- Basophils: 1 percent
Structure and functioning of each type of WBC
Granulocytes: Granulocytes are of 3 main types, i.e., neutrophils, basophils, and eosinophils. When microscopically examined, the granules occurring in these WBCs are evident when stained.
- Neutrophils: It has a unitary nucleus which seems to have many lobes. They are the most abundant type of leukocyte cells in the blood stream. Neutrophils are chemically attracted to bacteria and can pass via tissue to the area of infection.They ingest the target damaged or bacterial cell via a process called phagocytosis and thus destroy it. Upon release, the granules of neutrophils act as lysosomes so as to engulf cellular macromolecules. During this process, the neutrophils also get destroyed.
- Basophils: They are the least abundant of the WBCs. Basophils have a nucleus with multiple lobes and their granules have materials like heparin and histamine. Functions of histamine include dilation of blood vessels, increasing the capillaries permeability, and enhancing the flow of blood, which in turn facilitate the passage of white blood cells to the affected regions; while heparin thins blood and prevents it from clotting.Basophils play an important role in allergic responses of the body.
- Eosinophils: The cells have a double-lobed nucleus. In blood smears, they often appear as U-shaped. Eosinophils are typically present in the connective tissues of the intestines and the stomach. They are phagocytic and mainly attack antibody-antigen complexes. Such complexes develop when antibodies attach to antigens to classify them as matter which have to be destroyed. Eosinophils are very active during allergic reactions and parasitic infections.
Agranulocytes: Also callednon-granular leukocytes, agranulocytes are of 2 types, i.e., monocytes and lymphocytes. These WBCs seem to contain no apparent granules. The lack of cytoplasmic granules means that agranulocytes usually come with a large nucleus.
- Monocytes: They are the biggest in size amongst all white blood cells. Monocytes contain a single large nucleus which can be of varied shapes. Often, the nucleus may have the shape of a kidney. Monocytes travel from the blood stream to the tissues and become dendritic cells and macrophages. Dendritic cells are usually present in tissues occurring in regions that get exposed to antigens from the environment external to the body. They are present within the nose, and in the skin, the gastrointestinal tract, and lungs. Their main function is to report all types of antigenic data to lymphocytes present in lymph organs and lymph nodes. This helps in the formation of antigen immunity. Dendritic cells get their name from their unusual appearance characterized by the presence of projections that look like the dendrites of neurons. Macrophages are big cells that occur in almost all tissues. They actively carry out phagocytic functions.
- Lymphocytes: They are the most abundant kind of white blood cells after neutrophils. Lymphocyte cells are spherically shaped with minuscule amounts of cytoplasm and big nuclei. Lymphocytes occur in three major forms, i.e., B cells, T cells, and natural killer cells. The first two are crucial for specific immune system responses, while the natural killer cells offer generic immunity.