2 different alleles controlling that trait.
(See also inheritance; genetic disorders.)
hookworm infestationAn infestation
of the small intestine by small, round,
blood-sucking worms of the NECATOR
AMERICANUSor ANCYLOSTOMA DUODENALE
species. Hookworm infestation occurs
mainly in the tropics.
The larvae penetrate the skin of the
feet or are ingested. They migrate
throughout the body and mature in the
small intestine. Adult worms lay eggs,
which pass out in the faeces.
When larvae penetrate the skin, a red,
itchy rash may develop on the feet. In
light infestations, there may be no fur-
ther symptoms. In heavier infestations,
migration of the larvae through the lungs
may produce cough and pneumonia;
adult worms in the intestines may
cause abdominal discomfort. The most
important problem is iron-deficiency
anaemiadue to loss of blood.
Diagnosis is made by microscopic ex-
amination of the faeces for worm eggs.
Anthelmintic drugskill the worms. (See
also larva migrans.)
hordeolumThe medical name for a stye.
hormonal disordersConditions caused
by malfunction of an endocrine gland.
hormoneA chemical released into the
bloodstream by a gland or tissue that
has a specific effect on tissues else-
where in the body.
Many hormones are produced by endo-
crine glands. Hormones are also secreted
by other organs, including the brain,
kidneys, intestines, and, in pregnant
women, the placenta. They control many
body functions, including metabolismof
cells, growth, sexual development, and
the body’s response to stress or illness.
hormone antagonist A drug that blocks
the action of a hormone.
hormone replacement therapy (HRT)
The use of a synthetic or natural hor-
moneto treat a hormone deficiency.
Most commonly, HRT refers to the use
of female hormones to relieve symptoms
associated with the menopause, such as
hot flushes and vaginal dryness. HRT
also reduces the risk of the long-term
effects associated with low oestrogen
levels, such as osteoporosis. An oestro-
gen is usually taken in combinationwith a progestogen. The hormones may
be taken orally or released into the
bloodstream from a hormonal implant,
skin patch, or gel.
Minor adverse effects of HRT include
nausea, breast tenderness, fluid reten-
tion, and leg cramps. In some women,
oestrogen therapy may increase the risk
of abnormal blood clotting. Women tak-
ing HRT in the long term are thought to
be at a slightly increased risk of breast
cancer, but are thought to be less likely
to develop coronary artery disease.
horn, cutaneousA hard, noncancer-
ous protrusion occasionally found on
the skin of elderly people and caused by
an overgrowth of keratin.
Horner’s syndromeA group of phys-
ical signs (narrowing of the eye pupil,
drooping of the eyelid, and absence of
sweating) affecting 1 side of the face
that indicates damage to part of the
sympathetic nervous system (see auto-
nomic nervous system).
horseshoe kidneyA congenitalabnor-
mality in which the 2 kidneys are fused
at the base, forming a horseshoe shape.
The joined kidneys usually function
normally, but may be associated with
other congenital kidney defects.
hospiceA hospital or part of a hospital
devoted to the care of patients who are
terminally ill (see dying, care of the).
hospitals, types ofMost of the hospitals
in the UK are part of the National Health
Service. Each NHS district has a general
hospital providing services that include
medicine, surgery, gynaecology, obstetrics,
and paediatrics. Some more specialist
services are concentrated in fewer cen-
tres. Many of the UK’s private hospitals
are nursing homes for the elderly; others
cater for nonemergency surgery, obstetric
care, or inpatient care for the mentally ill.
hot flushesTemporary reddening of the
face, neck, and upper trunk that is
accompanied by a sensation of heat
and is often followed by sweating. Hot
flushes are usually caused by decreased
oestrogenproduction during or after the
menopause, and they sometimes occur
following removal of the ovaries (see
oophorectomy). Hot flushes can often
be alleviated by treatment with hor-
mone replacement therapy (HRT).HOOKWORM INFESTATION HOT FLUSHESH