Labyrinth  - organ of balance located in the inner ear; consists of three semicircular canals and the vestibule.

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.

Lactase - enzyme in the small intestine needed to digest milk sugar (lactose).

Lactase deficiency - lack of the lactase enzyme.

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

Laminectomy - surgical procedure which includes removal of a portion of the lamina, to provide more room in the vertebral canal; usually performed to treat 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.

Laparoscope - thin tube with a tiny video camera attached, used to look inside the body and see the surface of organs. (see also endoscope.)

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

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 through small incisions in the lower abdominal region.

Laparotomy - a surgical procedure that involves an incision into the abdominal cavity; often used when making a diagnosis when less invasive tests are difficult or not possible.

Large intestine - 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 noncancerous.

Laryngeal nodules - noncancerous, 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 or voice box.

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

Lavage - the process of washing (cleaning) of an organ such as the bowel or stomach.

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

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

Lesion - an injury or wound.

Levodopa (l-dopa) - an effective anti-parkinson drug, that is changed into dopamine in the brain.

Lewy body - a pink-staining sphere, found in the bodies of dying cells, that is considered to be a marker for parkinson's disease.

Ligament - a flexible band of fibrous tissue that connects the bones and bind the joints together.

Lipid - a fatty substance in the blood.

Lipoproteins - transporters of fatty substances in the blood.

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

Liver - largest organ in the body; performs 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 that indicate the functioning of the liver and biliary system.

Living will - a legal document which states your medical preferences for treatment and resuscitation in the event you can no longer speak for yourself.

Lobectomy - removal of a lobe of the lung, for cancer, benign tumors, or infections.

Lobule - a subdivision of a lobe or a small lobe.

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

Loop electrosurgical excision procedure (leep) - procedure for treating cervical dysplasia in which a fine wire loop and low-energy current are used to remove abnormal tissue from the cervix.

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

Low blood glucose - a condition that occurs in people with diabetes when their blood glucose levels are too low.

Low density lipoprotein (ldl) - a blood substance with large amounts of cholesterol.

Lower (gastrointestinal) gi series (also called barium enema x-ray.) - x-rays of the rectum, colon, and lower part of the small intestine.

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.

Lumen - the hollow area within a tube.

Lumpectomy - a surgical procedure in which only the tumor and a small area of surrounding tissue are removed.

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.

Lymph nodes (also called lymph glands.) - small glands clustered in the neck, armpits, abdomen, and groin that supply infection-fighting cells to the bloodstream and filter out bacteria and other antigens.

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

Lymphatic system - tissues and organs, including bone marrow, spleen, thymus, and lymph nodes, that produce, store, and carry white blood cells to fight infection and disease.

Lymphocyte - any one of a group of white blood cells of crucial importance to the adaptive part of the body's immune system.