Bma Illustrated Medical Dictionary

structure in the body to be inspected

directly. The endoscope is inserted

through a natural body opening, such

as the mouth or vagina, or into a small

incision. The operator can inspect and

photograph the organ and carry out a

biopsy. Many operations can be per-

formed by passing surgical instruments

down an endoscope. (See also minimal-

ly invasive surgery.)

endotheliumThe layer of cells that

lines the heart, blood vessels, and lym-

phatic ducts (see lymphatic system). The

cells are squamous (thin and flat), pro-

viding a smooth surface that aids the

flow of blood and lymph and helps pre-

vent the formation of blood clots. (See

also epithelium.)

endotoxinA poisonproduced by cer-

tain bacteriathat is not released until

the bacteria die. Endotoxins that are

released in infected people cause fever.

They also make the capillarywalls more

permeable, causing fluid to leak into

the surrounding tissue, sometimes re-

sulting in a drop in blood pressure, a

condition called endotoxic shock. (See

also enterotoxin; exotoxin.)

endotracheal tubeA tube that is passed

into the tracheathrough the nose or

mouth that enables delivery of oxygen

during artificial ventilationor of anaes-

thetic gases (see anaesthesia) during

surgery. An inflatable cuff around the

lower end of the endotracheal tube pre-

vents secretions or stomach contents

from entering the lungs.

enemaA procedure in which fluid is

passed into the rectumthrough a tube

inserted into the anus. An enema may

be given to clear the intestine of faeces,

to relieve constipation or in preparation

for intestinal surgery. Enemas are also

used to administer medicine, such as

corticosteroid drugsto treat ulcerative

colitis. A barium enema is used to diag-

nose disorders of the large intestine

(see barium X-ray examinations).

energyThe capacity to do work or effect

a physical change. Nutritionists refer to

the fuel content of a food as its energy.

There are many forms of energy, in-

cluding light, sound, heat, chemical,

electrical, and kinetic, and most of them

play a role in the body. For instance, the

retinaconverts light energy to electrical

nerve impulses, making vision possible.

Musclesuse chemical energy obtained

from food to produce kinetic energy,

movement, and heat.

Energy is measured in units called cal-

oriesand joules. Because these units are

extremely small, more practical units used

in dieteticsare the kilocalorie (kcal, 1,000

calories), and kilojoule (kJ, 1,000 joules).

Carbohydratesand proteinsprovide 4 kcal

per gramme (g), fatsprovide 9 kcal per g

(see metabolism). In general, the energy

liberated from the breakdown of food is

stored as chemical energy in ATPmol-

ecules. The energy in these molecules is

then available for processes that con-

sume energy, such as muscle contraction.

energy requirementsThe amount of

energythat is needed by a person for

cell metabolism, muscular activity, and

growth. This energy is provided by the

breakdown of carbohydrates, fats, and

proteinssupplied by food in the diet

and by stored nutrientsin the liver,

muscles, and adipose tissue.

Energy is needed to maintain the heart-

beat, lung function, and constant body

temperature. The rate at which these

processes use energy is called the basal

metabolic rate (BMR). Any form of move-

ment increases energy expenditure above

the BMR. A person’s energy require-

ment increases during periods of growth

and during pregnancy and lactation.

When more energy is ingested as food

than is used, the surplus is stored and

ENDOTHELIUM ENERGY REQUIREMENTS

E

Endotracheal

tube

Nasal cavity

Epiglottis

Trachea

Lung

ENDOTRACHEAL TUBE