Lemierre’s disease A rare, potentially lethal complication of tonsillitis caused by anaerobic (not requiring oxygen) bacteria including Fusobacteria. The disease usually develops after a bacterial infection has created an abscess near the tonsils. Deep in the abscess, the anaerobic bacteria can flourish. The bacteria penetrate from the abscess into the neighboring jugular vein in the…
Lennox syndrome See Lennox-Gastaut syndrome.
Lennox-Gastaut syndrome A severe form of epilepsy that usually begins in early childhood. It is characterized by frequent seizures of multiple types, mental impairment, and a slow spike-and-wave pattern seen on an EEG. The seizures are notoriously hard to treat and may lead to falls and injuries. Treatment involves anti-epileptic medications.
lens The transparent structure inside the eye that focuses light rays onto the retina.
lens, objective In a microscope, the lens nearest to the object being examined. Most light microscopes now have a turret that bears a selection of objective lenses.
lens, ocular In a microscope, the lens closest to the eye. Also known as eyepiece. Most light microscopes are binocular, with one ocular lens for each eye.
leprosy An infectious disease of the skin, nervous system, and mucous membranes that is caused by the bacteria Mycobacterium leprae. Leprosy is transmitted via person-to-person contact. For thousands of years leprosy was one of the world’s most feared communicable diseases because the nerve and skin damage often led to terrible disfigurement and disability. Today leprosy…
leptin A hormone produced mainly by adipocytes (fat cells) that is involved in the regulation of body fat. Leptin interacts with areas of the brain that control hunger and behavior and signals that the body has had enough to eat. A small number of people have genetic mutations in the leptin gene, leading to a…
leptomeninges The two innermost layers of tissue that cover the brain and spinal cord. The two layers are called the arachnoid mater and pia mater.
lesbian A female homosexual.
lesbianism Female homosexuality. Also known as Sapphism.
Lesch-Nyhan syndrome A rare, inherited disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The lack of HPRT causes a buildup of uric acid in all body fluids, and leads to symptoms such as severe gout, poor muscle control, and moderate retardation, which appear in the first year of life. Affected individuals also…