Bma Illustrated Medical Dictionary

in which both inheritance and environ-

ment probably play a part.

A rough estimate of heritability can be

obtained from the known incidence of a

disorder in the first-degree relatives of

affected people compared with the inci-

dence of the disorder in a population

exposed to similar environmental influ-

ences. Estimates of heritability are

useful in genetic counselling. (See also

genetic disorders.)

hermaphroditismA congenitaldisor-

der in which gonadsof both sexes are

present, and the external genitalia are

not clearly male or female. True herm-

aphroditism is extremely rare and its

cause unknown. A more common con-

dition is pseudohermaphroditism, in

which the gonads of only 1 sex are

present, but the ex-

ternal genitalia are

not clearly either

male or female.

herniaThe protru-

sion of an organ or

tissue through a weak

area in the muscle

or other tissue that

normally contains it.

The term is usually

applied to a protru-

sion of the intestine

through the abdom-

inal wall. In a hiatus

hernia,the stomach

protrudes through the

diaphragm and into

the chest.

Abdominal hernias

are usually due to a

congenitalweakness

in the wall of the ab-

domen. The hernias

may result from dam-

age caused by lifting

heavy objects, per-

sistent coughing, or

straining to defae-

cate, or may develop

after an operation.

There are several types of hernia, and

they are classified according to their lo-

cation in the body. The most important

are inguinal hernias,which mainly affect

men; femoral hernias,which are more

common in overweight women; and

umbilical hernias, which occur in babies.

The 1st symptom of an abdominal

hernia is usually a bulge in the abdomi-

nal wall. There may also be abdominal

discomfort. Sometimes the protruding

intestine can be pushed back into place.

Severe pain occurs when the hernia

bulges out and cannot be put back;

surgery (see hernia repair) is usually nec-

essary. If the blood supply to a twisted,

trapped portion of intestine becomes

impaired (a strangulated hernia), gan-

greneof the bowel may develop. A

strangulated hernia requires urgent

treatment. Umbilical hernias in babies

can usually be left untreated as they

tend to disappear naturally by age 5.

hernia repairSurgical correction of a

hernia. Surgery is usually performed to

treat a hernia of the abdominal wall that

is painful or cannot be pushed back into

place. A strangulated hernia requires an

emergency operation. During surgery, the

protruding intestine is pushed back into

the abdomen and the weakened muscle

wall is strengthened. Either open or

minimally invasive surgerymay be used.

herniated discSee disc prolapse.

herniorrhaphySurgical correction of a

hernia. (See hernia repair.)

heroinA narcotic drugsimilar to mor-

phine. When used for medical purposes,

it is generally known as diamorphine.

Heroin is a white or brownish powder

that can be smoked, sniffed, or dis-

solved in water and injected.

As well as having an analgesic effect,

heroin produces sensations of warmth,

calmness, drowsiness, and a loss of

concern for outside events. Long-term

use of the drug causes toleranceand

psychological and physical dependence

(see drug dependence; heroin abuse).

Sudden withdrawal produces shivering,

abdominal cramps, diarrhoea, vomiting,

and restlessness.

heroin abuseNonmedical use of hero-

in. Heroin addiction has many adverse

effects on the user, including injection

scars, skin abscesses, weight loss,

impotence, and the risk of infection

with hepatitis B, hepatitis C, and HIV

through sharing needles. Death com-

monly occurs from accidental overdose.

HERMAPHRODITISM HEROIN ABUSE

H

FEMORAL HERNIA

HERNIA

INGUINAL HERNIA

UMBILICAL HERNIA