Dictionary

range of motion The full movement potential of a joint, usually its range of flexion and extension. For example, a knee might lack 10 degrees of full extension due to an injury.

rapid eye movement sleep See REM sleep.

rash Breaking out (eruption) of the skin. A rash can be caused by an underlying medical condition, hormonal cycles, allergies, or contact with irritating substances. Treatment depends on the underlying cause of the rash. Medically, a rash is referred to as an exanthem.

Rasmussen syndrome A rare brain disorder that is caused by inflammation of brain cells in one hemisphere. Rasmussen syndrome, whose cause is unknown, features seizures that can be difficult or impossible to control with medication, and it eventually results in brain shrinkage (atrophy). Treatment is surgery, if possible. The inflammation seems to stop of its…

RAST Radioallergosorbent test, an allergy test that is done on a sample of blood. RAST is used to check for allergic sensitivity to specific substances.

rat-flea typhus See typhus, murine.

rattlesnake bite A poisonous bite from a member of the pit viper family. All rattlesnakes are venomous and secrete poisonous venom, and they are the main culprit in deaths from snakebites in the US. Emergency treatment is essential: With proper care, rattlesnake bites are rarely fatal. The affected body part should be kept immobile and…

Raynaud’s disease A condition that results in discoloration of the skin on the fingers and/or toes when a person is exposed to changes in temperature or to emotional events. Raynaud’s disease, also known as primary Raynaud’s phenomenon, can accompany other diseases; when it does, it is called Raynaud’s phenomenon or secondary Raynaud’s phenomenon. The skin…

Raynaud’s phenomenon A condition that results in discoloration of fingers and/or toes when a person is exposed to changes in temperature or emotional events and that occurs with a number of conditions, including rheumatic diseases such as scleroderma, rheumatoid arthritis, and systemic lupus erythematosus; hormone imbalance, including hypothyroidism and carcinoid imbalances; trauma, such as from…

reabsorption Being absorbed again. For example, the kidney selectively reabsorbs substances it has already secreted into the renal tubules, such as glucose, protein, and sodium. These reabsorbed substances are returned to the blood.

reaction kinetics The rate of change in a biochemical (or other) reaction.

reactive airway disease A term used to refer to several lung conditions that are characterized by transient narrowing (spasm) of the airways in the lungs, for example, asthma. The narrowing limits the ability of air to be expelled from the lungs through the airways and leads to wheezing. See also asthma.