ENDOTHELIUM
ENERGY REQUIREMENTS
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.)
endothelium
The 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.)
endotoxin
A
poison
produced by cer-
tain
bacteria
that is not released until
the bacteria die. Endotoxins that are
released in infected people cause fever.
They also make the
capillary
walls 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 tube
A tube that is passed
into the
trachea
through the nose or
mouth that enables delivery of oxygen
during artificial
ventilation
or 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.
enema
A procedure in which fluid is
passed into the
rectum
through 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 drugs
to treat
ulcerative
colitis
.
A barium enema is used to diag-
nose disorders of the large intestine
(see
barium X-ray examinations)
.
energy
The 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
retina
converts light energy to electrical
nerve impulses, making vision possible.
Muscles
use chemical energy obtained
from food to produce kinetic energy,
movement, and heat.
Energy is measured in units called
cal-
ories
and
joules
.
Because these units are
extremely small, more practical units used
in
dietetics
are the kilocalorie (kcal,
1,000
calories), and kilojoule (kJ, 1,000 joules).
Carbohydrates
and
proteins
provide 4 kcal
per gramme (g),
fats
provide 9 kcal per g
(see
metabolism
).
In general, the energy
liberated from the breakdown of food is
stored as chemical energy in
ATP
mol-
ecules. The energy in these molecules is
then available for processes that con-
sume energy, such as muscle contraction.
energy requirements
The amount of
energy
that is needed by a person for
cell
metabolism
, muscular activity, and
growth. This energy is provided by the
breakdown of
carbohydrates
,
fats
, and
proteins
supplied by food in the diet
and by stored
nutrients
in 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
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