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Glossaries - M

We've defined thousands of terms related to health care. This page discusses glossary terms with the letter M.


a large immune system cell in the tissues that devours invading pathogens and other intruders. Macrophages stimulate other immune cells by presenting them with small pieces of the invaders. Macrophages also can harbor large quantities of viruses like HIV without being killed, acting as reservoirs of the virus.

Magnetic Resonance Imaging (MRI) (mag-NEH-tik REH-zuh-nuns IM-uh-jing)

A test that takes pictures of the soft tissues in the body. The pictures have advantages over x-rays.

Malabsorption Syndromes (MAL-ub-SORP-shun sin-drohmz)

Conditions that happen when the small intestine cannot absorb nutrients from foods.


Impaired digestion, which can cause uncomfortable gastrointestinal symptoms and overall poor health.

Mallory-Weiss Tear (MAH-luh-ree-WYSS tair)

A tear in the lower end of the esophagus. Caused by severe vomiting. Common in alcoholics.

Malnutrition (mal-noo-TRISH-un)

A condition caused by not eating enough food or not eating a balanced diet.

Manometry (muh-NAW-muh-tree)

Tests that measure muscle pressure and movements in the GI tract. See also Esophageal Manometry and Rectal Manometry.

Mast cell

a type of granulated cell found in connective tissue.


the arithmetic average, or the sum of all the values divided by the number of values.

Meckel's Diverticulum (MEH-kulz dy-vur-TIK-yoo-lum)

A birth defect in which a small sac forms in the ileum.


the midpoint value obtained by ranking all values from highest to lowest and choosing the value in the middle. The median divides a population into two equal halves.

Median Time to Elimination

the time it takes one half of a drug to be eliminated from the body.

Mediate (MEE-dee-ate)

accomplished indirectly.

Medulla Oblongata (muh-DULL-ah ob-long-GAH-tah)

the part of the brain stem located just above the spinal cord; means "rather long and narrow;" acting as kind of a "telephone exchange," the medulla oblongata links the higher brain centers with several senses.

Megacolon (MEG-uh-koh-lun)

A huge, swollen colon. Results from severe constipation. In children, megacolon is more common in boys than girls. See also Hirschsprung's Disease.

Melena (muh-LEE-nuh)

Blood in the stool.

Memory cell

memory cells are a subset of T cells and B cells that have been exposed to specific antigens and can then proliferate (recognize the antigen and divide) more readily when the immune system re-encounters the same antigens. (See also anamestic response.

Menetrier's Disease (may-NAY-tree-ayz duh-zeez)

A long-term disorder that causes large, coiled folds in the stomach. Also called giant hypertrophic gastritis.

Metabolism (muh-TAH-buh-lih-zum)

The term for the way cells chemically change food so that it can be used to keep the body alive. It is a two-part process. One part is called catabolism - when the body uses food for energy. The other is called anabolism -when the body uses food to build or mend cells. Insulin is necessary for the metabolism of food.

Metaphase (MEH-tah-faze)

the second stage of mitosis in which the chromosomes are aligned along the center of the dividing cell.


<oncology, pathology> The change in the type of adult cells in a tissue to a form which is not formal for that tissue.

Metastasis (meh-TASS-tah-sis)

the transfer of a disease from one part of an organ to another or to a different organ by the transfer of causative organisms or, as in the case of cancer, by the transfer of cells.

Metastasize (me-TASS-tah-size)

to form a new focus of a disease (e.g., cancer) in another part of the body by the process of metastasis.

Microtubule (my-kro-TOO- b'you'l)

one of a number of small tubular structures found inside nearly all cell.

MHC (major histocompatibility complex)

the gene cluster that controls certain aspects of the immune response. Among the products of these genes are the histocompatibility antigens, such as HLA class I antigens, which are present on every cell with a nucleus and serve as markers to distinguish self from non-self. (See also HLA antigens).


A tiny living organism such as bacteria or yeast that has the potential to trigger chronic illness and disease.


Microwave therapy is a type of deep heat therapy. The electromagnetic waves pass between electrodes placed on the patient's skin. This creates heat that increases blood flow and relieves muscle and joint pain.


surrounded by a thin layer of biodegradable substance referred to as a microsphere. A means of protecting a drug or vaccine antigen from rapid breakdown. Microencapsulation may also enhance an antigens absorption and the immune response to that antigen.


An often familial (occurring in families) symptom complex of periodic attacks of vascular (pertaining to blood vessels or indicative of a copious blood supply), headache, usually temporal (of or pertaining to the temple or temples) and unilateral (occurring on one side)  in onset, commonly associated with irritability, nausea, vomiting, constipation or diarrhea, and often photophobia (sensitivity to light), attacks are preceded by constriction of the cranial arteries (arteries in the head), usually with eye symptoms and commence with the vasodilation that follows.

Origin: Gr. Hemikrania = an affection of half of the hea.

Mitosis (mi-TOE-sis)

a microtubular (see microtubule) structure that connects chromosomes during metaphase of mitosis.

Monoclonal antibody (mon-uh-KLOH-nul)

Chemically and immunologically homogeneous antibodies produced by a single clone of antibody-secreting cells; a monoclonal antibody against glycoprotein IIb/IIIa is undergoing investigation as a platelet function inhibitor.


a large white blood cell in the blood that ingests microbes or other cells and foreign particles. When a monocyte passes out of the bloodstream and enters tissues, it develops into a macrophage.

Morbidity Rate

The sickness rate; the number of people who are sick or have a disease compared with the number who are well.

Mobilization therapies

A group of treatments that include traction, massage, and manipulation. When used by a trained professional, these methods can help control pain and increase joint and muscle motion.


A study of the configuration the structure of animals and plants.

Mortality Rate

The death rate; the number of people who die of a certain disease compared with the total number of people. Mortality is most often stated as deaths per 1,000, per 10,000, or per 100,000 persons.

Motility (moh-TIL-uh-tee)

The movement of food through the digestive tract.

Motility Disorders (moh-TIL-uh-tee dis-or-durz)

Mucosal immunity

resistance to infection across the mucous membranes. Mucosal immunity depends on immune cells and antibodies present in the linings of reproductive tract, gastrointestinal tract and other moist surfaces of the body exposed to the outside world.

Mucosal Protective Drugs (myoo-KOH-zul proh-TEK-tiv drugz)

Mucous Colitis (MYOO-kus koh-LY-tis)

Mucosal Lining (myoo-KOH-zul LY-ning)

The lining of GI tract organs that makes mucus.

Mucus (MUOO-kus)

A clear liquid made by the intestines. Mucus coats and protects tissues in the GI tract.

Myalgia (my-AL-gee-ah)

muscular pain.


relating to the muscular coat of the intestine.

Myocardial Infarction (my-oh-KAR-dee-al)

An infarction caused by obstruction of circulation to a region of the heart; also called a heart attack; results from permanent damage to an area of the heart muscle. This happens when the blood supply to the area is interrupted because of narrowed or blocked blood vessels.


inflammation of a muscl.

Myringotomy (mir-ing-GOT-oh- my)

draining fluid from within the eardrum by means of a needle.

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