Glossary try the best to avoid the use of medical terms that could make it more difficult to understand the information on this website. Still, there are a number of terms that can't be avoided and that are useful to know because they are so often used by the doctors, nurses, and other medical professionals with whom you might speak. The list below includes the terms used on for which we have provided definitions.

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Term Definition

A large molecule consisting of multiple identical or similar chemical units that are linked together


Increase in the number of erythrocytes (red cells, RBCs) in the blood

Polyclonal antibody

Antibody produced by or derived from many types (clones) of plasma cells


An inflammation of the lungs; usually caused by a hypersensitive allergic reaction to repeated exposure to organic particles such as molds, grain dust, and chemicals


Also known as: Pleura

One of the two membranes that surrounds each lung and lines the chest cavity


Also known as: Pleurae (plural)

One of the two membranes that surrounds each lung and lines the chest cavity

Plasma cell

Mature lymphocyte (B cell) that produces and secretes antibodies


Straw-colored, fluid part of blood and lymph


1. Deposit on the inner arterial walls in atherosclerosis
2. Flat, raised patch on the skin or mucous membrane
3. Deposit of saliva and bacteria on teeth that encourages the development of caries


The organ that connects a pregnant woman with her developing baby in the uterus; blood from the mother and baby do not mix directly, but a thin membrane within the placenta allows nutrients from the mother to pass to the baby and waste products to pass from the baby to the mother for elimination.

Pituitary gland

Pea-sized gland located in the center of the head behind the sinus cavity at the base of the brain; the pituitary consists of two parts that produce different hormones: 1) in the anterior portion, growth hormone (GH), adrenocorticotropin (ACTH), thyroid-stimulating hormone (TSH), lutenizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) are produced; 2) in the posterior portion, oxytocin and antidiuretic hormone (ADH) (produced in the hypothalamus) are stored for release.


A substance in the body that contains both lipid (fat) and phosphorous; phospholipids are found in all cells throughout the body because they are a major component of the cell membrane, the outermost layer of a cell.


tumor located in one or both of the adrenal glands that releases excess hormones called catecholamines (e.g., dopamine, epinephrine (adrenaline), norepinephrine and their metabolites, such as metanephrines)


The observable physical or biochemical characteristics of a person, as determined by both their genetic makeup and environmental influences


Measurement of the acidity or alkalinity of a substance. A pH of 7.0 is neutral. A substance with a pH less than 7.0 is an acid, with increasing acidity as the pH decreases toward zero. Likewise, a substance with a pH greater than 7.0 is a base (alkali), with increasing alkalinity as the pH moves toward 14.0.