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Immune System

The body's system for protecting itself from viruses and bacteria or any foreign substances.

PubMed Health Glossary
(Source: NIH - National Institute of Diabetes and Digestive and Kidney Diseases)

About the Immune System

The immune system (from the Latin word immunis, meaning: "free" or "untouched") protects the body like a guardian from harmful influences from the environment and is essential for survival. It is made up of different organs, cells and proteins and aside from the nervous system, it is the most complex system that the human body has.

As long as our body's system of defense is running smoothly, we do not notice the immune system. And yet, different groups of cells work together and form alliances against just about any pathogen (germ). But illness can occur if the performance of the immune system is compromised, if the pathogen is especially aggressive, or sometimes also if the body is confronted with a pathogen it has not come into contact before.

The tasks of the immune system

Without an immune system, a human being would be just as exposed to the harmful influences of pathogens or other substances from the outside environment as to changes harmful to health happening inside of the body. The main tasks of the body's immune system are:

  • Neutralizing pathogens like bacteria, viruses, parasites or fungi that have entered the body, and removing them from the body
  • Recognizing and neutralizing harmful substances from the environment
  • Fighting against the body's own cells that have changed due to an illness, for example cancerous cells...

Read more about the Immune System

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.
Bacteria
A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The singular of bacteria is bacterium.
Bladder
The organ that stores urine.
Bone Marrow
The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.
Cells
The basic subunit of any living organism; the simplest unit capable of independent life. Although there are some single-celled organisms, such as bacteria, most organisms consist of many cells that are specialized for particular functions.
Colon (Bowel)
The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus.
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.
Lymph Nodes
A rounded mass of lymphatic tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymph (lymphatic fluid), and they store lymphocytes (white blood cells). They are located along lymphatic vessels. Also called lymph gland.
Lymphatic System
The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels (a network of thin tubes that carry lymph and white blood cells). Lymphatic vessels branch, like blood vessels, into all the tissues of the body.
Mucosa (Mucous Membranes)
The moist, inner lining of some organs and body cavities (such as the nose, mouth, lungs, and stomach). Glands in the mucosa make mucus (a thick, slippery fluid). Also called mucous membrane.
Nose
A part of the upper respiratory tract. It contains the organ of smell. The term includes the external nose, the nasal cavity, and the paranasal sinuses.
Pathogen
A disease-causing organism or virus.
Phagocytes (Scavenger Cells)
A large white blood cell that contributes to immune defenses by ingesting microbes or other cells and foreign particles.
Pharynx (Throat)
The hollow tube inside the neck that starts behind the nose and ends at the top of the trachea (windpipe) and esophagus (the tube that goes to the stomach).
Skin
The outer covering of the body that protects it from the environment.
Spleen
An organ that is part of the lymphatic system. The spleen makes lymphocytes, filters the blood, stores blood cells, and destroys old blood cells. It is located on the left side of the abdomen near the stomach.
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.
Thymus Gland
An organ that is part of the lymphatic system, in which T lymphocytes grow and multiply. The thymus is in the chest behind the breastbone.
Tissue
A group of cells that act together to carry out a specific function in the body. Examples include muscle tissue, nervous system tissue (including the brain, spinal cord, and nerves), and connective tissue (including ligaments, tendons, bones, and fat). Organs are made up of tissues.
Tonsils
Two small masses of lymphoid tissue on either side of the throat.

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...
Bacteria
A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The sin...
Bladder
The organ that stores urine....
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