Bma Illustrated Medical Dictionary

margin of the eye orbit and drains on to

the conjunctiva. It secretes tears during

crying and when the eye is irritated. The

accessory gland lies within the conjunc-

tiva, and maintains the normal tear film,

secreting it directly onto the conjunctiva.

Tears drain through the lacrimal puncta,

tiny openings towards the inner ends of

the upper and lower eyelids. The puncta

are connected by narrow tubes to the lac-

rimal sac, which lies within the lacrimal

bone on the side of the nose. Leading

from the sac is the nasolacrimal duct,

which opens inside the nose.

lactase deficiencyA condition in which

there is an absence of lactase, an en-

zymethat breaks down lactose(milk

sugar), in the cells of the small intes-

tine. Lactase deficiency results in a

reduced ability to digest lactose, also

known as lactose intolerance. The condi-

tion may be permanent, or may occur

temporarily after gastroenteritis, par-

ticularly in young children. Symptoms

include abdominal cramps, bloating,

flatulence, and diarrhoea, all of which

are caused by the laxative effect of the

undigested sugar in the intestines.

Treatment is with a lactose-free diet.

lactationThe production and secretion

of breast milk (see breast-feeding).

lactic acidA weak acid that is produced

when body cells break down glucoseby

anaerobicmetabolism in order to pro-

duce energy. Lactic acid is produced by

muscles during vigorous exercise and is

one of the factors that contribute to

cramp. The acid is also produced in

body tissues when they receive insuffi-

cient oxygen due to impairment of their

labetalolA beta-blocker drug that is

used to treat hypertensionand angina

pectoris. Possible adverse effects include

indigestion, nausea, and, in rare cases,

depressionand temporary impotence.

labiaThe folds of skin of the vulvathat

protect the vaginal and urethral open-

ings. There are 2 pairs of labia. The

outer pair, the labia majora, are fleshy

folds that bear hair and contain sweat

glands. They cover the smaller, hairless

inner folds, the labia minora, which

meet to form the hood of the clitoris.

labileA term meaning unstable or likely

to undergo change.

labourSee childbirth.

labyrinthThe collective term for the

convoluted structures of the inner ear.

The first part of the labyrinth is the coch-

lea, which contains the mechanism of

hearing. Situated behind the cochlea

are 2 sacs (the saccule and the utricle)

and 3 fluid-filled semicircular canals, all

of which are concerned withbalance.

labyrinthitisInflammation of the laby-

rinth. The condition is almost always

caused by bacterial or viral infection.

Viral labyrinthitis may develop during

illnesses such as influenza. Bacterial

labyrinthitis is commonly a complica-

tion of otitis media. The main symptom

is vertigo, sometimes with nausea,

vomiting, nystagmus,tinnitus, and hear-

ing loss. Viral labyrinthitis clears up on

its own, but symptoms are relieved by

antihistamine drugs. Immediate treat-

ment with antibiotic drugsis needed for

bacterial labyrinthitis, otherwise perma-

nent deafnessor meningitismay result.

lacerationA torn, irregular wound.

lacrimal apparatusThe system that

produces and drains tears. The lacrimal

apparatus of the eye includes the main

and accessory lacrimal glands and the

nasolacrimal drainage duct. The main

gland lies just within the upper and outer

LABETALOL LACTIC ACID

L

LACRIMAL APPARATUS

Lacrimal

(tear)

gland

Lacrimal

puncta

Lacrimal

sac

Nasolacrimal

duct

L