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lecithin

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(lĕs′ĭth-ĭn) [Gr. lekithos, egg yolk] A phospholipid (phosphoglyceride) that is part of cell membranes; also found in blood, egg yolk, and soybeans. On hydrolysis, it yields stearic acid, glycerol, phosphoric acid, and choline on hydrolysis. SYN: phosphatidycholine. lecithal, adj.

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lecithinase

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(lĕs′ĭ-thĭn-ās) An enzyme that catalyzes the decomposition of lecithin.

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cobra l. An enzyme present in certain snake venoms.

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lecithin: sphingomyelin ratio

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(lĕs′ĭ-thĭn sfĭng″gō-mī′ă-lĭn rā′shē-ō) ABBR: L : S ratio. The ratio of lecithin to sphingomyelin in the amniotic fluid. It is used to assess maturity of the fetal lung. Until about the 34th week of gestation, the lungs produce less lecithin than sphingomyelin. As the fetal lungs begin to mature, they produce more lecithin than sphingomyelin. Delivery before the reversal of the ratio is associated with an increased risk of hyaline membrane disease in the infant. The use of this test enables the obstetrician to determine the best time for elective termination of pregnancy. Other tests commonly used for this purpose include the amniotic lamellar body count, phosphatidylglycerol presence, and the shake test. SEE: amniocentesis.

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lectin

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(lĕk′tĭn) [L. legere, to pick and choose] One of several plant proteins that stimulate lymphocytes to proliferate. Phytohemagglutinin and concanavalin A are lectins. SEE: mitogen.

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lectual

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(lĕkt′ū-ăl) [L. lectus, bed] Confining to a bed or couch, said of certain diseases.

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LED

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light-emitting diode.

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leech

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(lēch) A bloodsucking water worm, belonging to the phylum Annelida, class Hirudinea, parasitic on humans and other animals. Leeches are a source of hirudin, an anticoagulant secreted by their buccal glands. In addition to hirudin, leech saliva contains several active substances including inhibitors of platelet aggregation, that have been synthesized for use as anticoagulants in clotting disorders. SEE: Annelida; hirudin; Hirudinea.

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Leeches were used as a means of bloodletting, common until the mid-19th century but now almost completely abandoned.

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medicinal l. Any of several species of leech, esp. Hirudo medicinalis, used to evacuate periorbital hemorrhage (black eye) and to remove congested venous blood from the suture lines of reimplanted fingers. SEE: Hirudo.

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Lee ganglion

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(lē) [Robert Lee, Brit. gynecologist and obstetrician, 1793–1877] A cervical uterine ganglion formed from the third and fourth sacral nerves and the hypogastric and ovarian plexuses.

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LEEP

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loop electrosurgical excision procedure.

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Leeuwenhoek disease

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(lā′vĕn-huk) [Antoni van Leeuwenhoek, Dutch microscopist, 1632–1723] Repetitive involuntary contractions ("fluttering") of the diaphragm and accessory muscles of respiration. The patient may experience shortness of breath and epigastric pulsations. The disease is caused by an abnormality of the respiratory control system of the brainstem. SYN: diaphragmatic ...

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