Medical Dictionary: L

labile hypertension: Blood pressure that frequently fluctuates between normal and abnormal during the course of a day, often within only a few minutes.

labyrinth: The inner ear structure that contains the balance organs.

lacrimal gland: The gland that produces tears; located in the upper, outer section of the eye’s orbit.

lactic acidosis: Rare but potentially lethal condition in which blood lactic acid levels increase.

lactose intolerance: The inability of the body to break down lactose; results in gastrointestinal distress.

lacunar stroke: A small ischemic stroke caused by the blockage of one of the smaller blood vessels in the brain; the most common effect is weakness or disability on one side of the body.

lamina: One of the two thin, plate-like parts of each vertebra that join in the midline and form the base of the spinous process of that vertebra (plural: laminae).

lamina: One of the two thin, platelike parts of each vertebra that join in the midline and form the base of the spinous process of that vertebra.

laminectomy: An operation in which all or part of one or both laminae is removed to gain access to the spinal canal or to decompress the spinal cord or nerve roots.

laser: A word derived from the acronym of “light amplification by the stimulated emission of radiation.” Lasers produce intense beams of light energy that generate localized heat used in surgery, removal of vascular and pigmented lesions, and skin rejuvenation.

latex allergy: An allergic reaction to the proteins found in natural rubber.

LED photomodulation: Nonthermal technique for enhancing skin tone and texture using a panel of bright light–emitting diodes (LEDs).

left ventricular hypertrophy: Thickening of the wall of the left ventricle, the chamber of the heart that pumps blood to the body.

leukotriene blockers: Asthma medications that work by blocking the production or action of leukotrienes, chemicals made in the body as part of an allergic reaction.

leukotrienes: Chemicals responsible for inflammation of the airways in diseases such as asthma.

levothyroxine sodium: The active ingredient in synthetic thyroxine (T4) pills (see “thyroxine (T4)”).

libido: Sexual desire.

ligament: a band of fibrous tissue that stabilizes and connects bones.

limbic system: A group of brain structures associated with emotions, such as anger, pleasure, sorrow, fear, and sexual arousal.

liothyronine sodium: The active ingredient in synthetic triiodothyronine (T3) pills (see “triiodothyronine (T3)”).

lipids: Fats, oils, and waxes that serve as building blocks for cells of the body or as energy sources; also capable of accumulating in the artery walls to form the plaques of atherosclerosis. Cholesterol and triglycerides are types of lipids.

lipoprotein(a): A type of lipid that is similar in structure to LDL.

lipoprotein: A combination of fat (lipid) molecules and protein molecules bound together as packages that enable other fats and cholesterol to move easily through the blood. See low-density lipoprotein and high-density lipoprotein.

liposuction: A technique for suctioning fat from areas that resist fat loss by exercise and diet.

live attenuated vaccines: Vaccines containing a live but weakened microbe that can no longer cause disease.

living will: A type of advance directive for health care that lists the kinds of medical treatment a person would and wouldn’t want if he or she is no longer mentally or physically able to make health care decisions.

lobar hemorrhage: An intracerebral hemorrhage that occurs in the white matter beneath the cerebral cortex.

lobules: Milk-producing glands of the breast.

locus ceruleus: An area of the brainstem that helps determine which stimuli are worth paying attention to. A malfunction of the locus ceruleus may contribute to anxiety.

long-term memory: A memory that lasts from a few minutes to decades.

low-calorie diet: A weight-loss diet that allows only 800–1,500 calories a day.

low-density lipoprotein (LDL): So-called “bad” cholesterol because high levels are associated with a high risk for heart attack. It is a lipoprotein that transports cholesterol from the liver to the rest of the body, which can cause the buildup of plaque in the arteries.

lumbar puncture: A procedure in which a hollow needle is inserted into the lower part of the spinal canal to withdraw fluid for testing. Also called a spinal tap.

lumbar spine: The five lowermost vertebrae of the spine.

Lyme disease: An infectious disease transmitted by a tick bite; characterized by rash, flulike symptoms, and inflammation of the heart, nerves, and joints.

lymph nodes: Small, bean-shaped organs, linked by lymphatic vessels. As part of the immune system, they filter out germs and foreign matter. Also called lymph glands.

lymphatic system: A system of channels that drains extracellular fluid to the blood. The system includes the lymph nodes and other lymphoid tissues.

lymphedema: An accumulation of lymph fluid in the arm, hand, or breast that may develop when lymphatic vessels or nodes have been removed or blocked by surgery, or after radiation therapy. It can appear immediately after treatment or many years later.

lymphocyte: A type of white blood cell that can recognize antigens. B lymphocytes produce antibodies. T lymphocytes destroy abnormal cells and interact with B lymphocytes.