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Labia - the folds of skin at the opening of the vagina (and other organs).

Labyrinth - the bony structure of the inner ear. The labyrinth consists of three semicircular canals, the cochlea, and the vestibule. The functions of the labyrinth include both hearing and balance. 

Labyrinthine hydrops - excessive fluid in the organ of balance (labyrinth) that can cause pressure or fullness in the ears, hearing loss, dizziness, and loss of balance.

Labyrinthitis - viral or bacterial infection or inflammation of the inner ear that can cause dizziness, loss of balance, and temporary hearing loss.

Lactase - an enzyme in the small intestine needed to digest lactose, a sugar found in milk and milk products.

Lactase deficiency - lack of an enzyme made by the small intestine called lactase, which prevents the body from digesting lactose (a sugar found in milk and milk products) properly.

Lactose - sugar found in milk and milk products, which the body breaks down into galactose and glucose.

Lactose intolerance - inability to digest lactose, the sugar in milk, because the body does not produce the lactase enzyme.

Lactose tolerance test - a test that determines the body's ability to digest lactose (a sugar found in milk and milk products).

laminectomy - surgical procedure which includes removal of a portion of the lamina to provide more room in the vertebral canal; usually for disc herniation or spinal canal stenosis.

Landau-Kleffner syndrome - a childhood disorder of unknown origin that can be identified by gradual or sudden loss of the ability to understand and use spoken language.

Language - system for communicating ideas and feelings using sounds, gestures, signs, or marks.

Language disorders - problems with verbal communication and the ability to use or understand the symbol system for interpersonal communication.

Lanugo - fine, downy hair that covers the fetus until shortly before or after birth.

Laparoscope - a long, thin tube with a camera lens attached that allows the physician to examine the organs inside the abdominal cavity - to check for abnormalities, and to operate through small incisions.

Laparoscopic cholecystectomy - an operation to remove the gallbladder. The physician inserts a laparoscope, and other surgical instruments, through small holes in the abdomen. The camera allows the physician to see the gallbladder on a television screen. The physician removes the gallbladder through the holes.

Laparoscopic lymph node sampling - lymph nodes are removed through a viewing tube called a laparoscope, which is inserted through a small incision in the abdomen.

Laparoscopic lymphadenectomy - the removal of pelvic lymph nodes with a laparoscope performed through small incisions in the lower abdominal region.

Laparoscopy - use of a viewing tube with a lens or camera (and a light on the end), which is inserted through a small incision in the abdomen to examine the contents of the abdomen and remove tissue samples.

Laparotomy - a surgical procedure that involves an incision from the upper to lower abdomen; often used when making a diagnosis by less invasive tests is difficult.

Large intestine (also called the colon) - part of the intestine that goes from the cecum to the rectum.

Laryngeal neoplasms - abnormal growths in the larynx (voice box) that can be cancerous or non-cancerous.

Laryngeal nodules - non-cancerous, callous-like growths on the inner parts of the vocal folds (vocal cords).

Laryngeal paralysis - loss of function or feeling of one or both of the vocal folds.

Laryngectomy - surgery to remove part or all of the larynx (voice box).

Laryngitis - hoarse voice or the complete loss of the voice because of irritation to the vocal folds (vocal cords).

Laryngoscopy - inspecting the larynx (voice box) with a mirror or viewing tube.

Larynx - valve structure between the trachea (windpipe) and the pharynx (the upper throat) that is the primary organ of voice production.

Laser resurfacing - uses high-energy light to burn away damaged skin. Laser resurfacing may be used to minimize wrinkles and fine scars.

Laser surgery - a type of surgery using a device that emits a beam of light radiation to cauterize a wound, repair damaged tissue, or cut through tissue.

Lateral collateral ligament (LCL) - the ligament that gives stability to the outer knee.

Lateral epicondylitis (also known as tennis elbow) - pain is caused by damage to the tendons that bend the wrist backward away from the palm.

Lavage - washing or rinsing out a body cavity for diagnostic or therapeutic purposes. For example, ductal lavage involves inserting fluid into a milk duct in the breast, removing the fluid, then examining it in the lab for the presence of cancer cells. Gastric lavage is putting fluid into the stomach through a tube, then pumping it out to remove a toxic substance or blood when there has been bleeding in the stomach.

Laxatives (also called cathartics) - medications to relieve long-term constipation.

Lead poisoning - a condition caused by breathing or swallowing substances that contain lead. Exposure to lead over a long period of time can cause serious health conditions, especially in children. 

Learning disability (LD) - a disorder that affects a person's ability to either interpret what he or she sees and hears, or to link information from different parts of the brain. These limitations are characterized by difficulty in reading, writing, and arithmetic.

Lens (also called crystalline lens) - the transparent structure inside the eye that focuses light rays onto the retina.

Lesion - a destructive change in body tissue, such as a wound, injury, or inflammation.

Leukapheresis - a procedure to remove white blood cells (leukocytes) from the body.

Leukemia - a cancer of the blood-forming tissue. Leukemic cells look different than normal cells and do not function properly.

Leukoplakia - a whitish patch of mucous membrane inside the mouth; it is considered to be a precancerous lesion that can develop into oral cancer .

Leukorrhea - whitish vaginal discharge during pregnancy.

Levator syndrome - a feeling of fullness in the anus and rectum with occasional pain, caused by muscle spasms.

Levodopa (L-dopa) - the single most effective anti-Parkinson drug; it is changed into dopamine in the brain.

Lewy bodies - tiny protein deposits in the part of the brain associated with movement and memory. They are associated with the development of nervous disorders such as Parkinson's disease and Lewy body dementia.

Lice - tiny parasites that can infest the skin; characterized by intense itching.

Lichenification - skin that has thickened.

Ligament - a white, shiny, flexible band of fibrous tissue that binds joints together and connects various bones and cartilage.

Lipid - a fatty substance in the blood.

Lipomas - round or oval lumps under the skin caused by fatty deposits.

Lipoproteins - transporters of fatty substances in the blood.

Liposuction - type of cosmetic surgery in which localized areas of fat are removed from beneath the skin using a suction-pump device inserted through a small incision.

Lithotripsy, extracorporeal shock wave (ESWL) - method of breaking up kidney stones, bile stones, and gallstones with a specialized tool and shock waves.

Liver - largest organ in the body, which carries out many important functions, such as making bile, changing food into energy, and cleaning alcohol and poisons from the blood.

Liver enzyme tests (also called liver function tests) - blood tests to determine how well the liver and biliary system are working.

Living will - a legal document that states a person's medical preferences for treatment and resuscitation in the event that person can no longer speak for himself or herself.

LMP - last menstrual period.

Lobe - a roundish projection of any structure. In the breast, lobes of the mammary glands radiate from the central area to the nipple area like wheel spokes.

Lobectomy - removal of an entire lobe of the lung.

Lobule - a subdivision of a lobe in the breast.

Local anesthesia - anesthetic medicine injected into the site of the operation to temporarily numb that area.

Locally invasive - a tumor which can invade the tissues surrounding it by sending out "fingers" of cancerous cells into normal tissue.

Locking clip - a special device used when the vehicle's lap/shoulder belts do not lock. A locking clip will help secure a child safety seat tightly into a vehicle.

Loop electrosurgical excision procedure (LEEP) - a procedure that uses an electric wire loop and low-energy current to remove abnormal tissue from the cervix.

Loose body - name given to an object, located within a joint, that has become detached.

Lordosis (Also called sway-back.) - an exaggeration of the forward curve of the lower part of the back.

Low blood glucose - a condition that occurs when blood glucose levels are too low.

Low-density lipoprotein (LDL) - a type of cholesterol that can build up in the walls of arteries; the "bad" cholesterol.

Lower back (also called lumbar spine) - a complex structure that connects the upper body to the lower body; consists of vertebrae, disks, spinal cord, and nerves.

Lower esophageal sphincter - muscle between the esophagus and stomach.

Lower GI (gastrointestinal) series (also called barium enema) - a procedure that examines the rectum, the large intestine, and the lower part of the small intestine. A fluid called barium (a metallic, chemical, chalky, liquid used to coat the inside of organs so that they will show up on an x-ray) is given into the rectum as an enema. An x-ray of the abdomen shows strictures (narrowed areas), obstructions (blockages), and other problems.

Lumbar puncture (also called spinal tap) - a procedure in which a special needle is placed into the lower back, into the spinal canal. This is the area around the spinal cord. The pressure in the spinal canal and brain can then be measured. A small amount of cerebral spinal fluid (CSF) can be removed and sent for testing to determine if there is an infection or other problems. CSF is the fluid that bathes the brain and spinal cord.

Lumpectomy - a surgical procedure to remove a tumor and surrounding tissue.

Lung volume - the amount of air the lungs hold.

Luteinizing hormone (LH) - hormone secreted by the pituitary gland in the brain that stimulates the growth and maturation of eggs in females and sperm in males.

Lyme disease (LD) - a bacterial infection caused by the spirochete Borrelia burgdorferi, a spiral-shaped bacterium that is most commonly transmitted by a tick bite.

Lymph - part of the lymphatic system; a thin, clear fluid that circulates through the lymphatic vessels and carries blood cells that fight infection and disease.

Lymph node biopsy - a procedure performed to remove tissue or cells from the body for examination under a microscope.

Lymph nodes (also called lymph glands) - small organs located in the channels of the lymphatic system which store special cells to trap bacteria or cancer cells traveling through the body in lymph. Clusters of lymph nodes are found in the underarms, groin, neck, chest, and abdomen.

Lymph vessels - part of the lymphatic system; thin tubes that carry lymph fluid throughout the body.

Lymphadenectomy - a procedure in which lymph nodes are taken from the body for purposes of diagnosing or staging cancer.

Lymphangiogram - an X-ray that uses a special dye to determine whether cancer has spread to the lymph nodes.

Lymphangioma - a lump of entwined lymph and blood vessels that may be found in various locations in the body.

Lymphatic system - a complex network of capillaries, thin vessels, valves, ducts, nodes, and organs that helps to protect and maintain the fluid environment of the body by filtering and draining lymph and by producing blood cells.

Lymphedema - a disorder in which lymph accumulates in the soft tissues, resulting in swelling. Lymphedema may be caused by inflammation, obstruction, or removal of the lymph nodes during surgery.

Lymphocytes - part of the lymphatic system; white blood cells that fight infection and disease.

Lymphocytic leukemia - a type of leukemia in which the cancer develops in the lymphocytes (lymphoid cells).