Webster's New World Medical Dictionary

hypoplasia of the thymus and parathyroids
See 
DiGeorge syndrome.
hypoplastic left heart syndrome
A form of
congenital heart disease in which the whole left half
of the heart, including the aorta is underdeveloped
(hypoplastic). Blood returning from the lungs has
to flow through an opening in the wall between the
upper chambers of the heart (an atrial septal
defect). The right ventricle pumps blood into the
pulmonary artery, and blood reaches the aorta
through a shunt (the ductus arteriosus). A child
with hypoplastic left heart syndrome may appear
normal at birth, but symptoms appear within the
first few days of life when the ductus arteriosus
closes. The infant becomes ashen, has difficulty
breathing, and has problems with feeding. This
heart defect is usually fatal unless treated by a series
of surgeries or a heart transplant. See also 
atrial
septal defect; ductus arteriosus.
hypospadias
A birth defect in which the urethra
opens on the underside of the penis or below the
penis. Treatment involves surgery to repair and
reconstruct the urethra.
hypotension
Blood pressure that is below the
normal expected for an individual in a given envi-
ronment. Blood pressure normally varies greatly
with activity, age, medications, and underlying med-
ical conditions. Hypotension can result from condi-
tions of the nervous system, conditions that do not
begin in the nervous system, and drugs.
Neurological conditions that can lead to low blood
pressure include changing position from lying to a
more vertical position (postural hypotension),
stroke, shock, Parkinson’s disease, neuropathy,
and fright. Nonneurological conditions that can
cause low blood pressure include bleeding, sepsis,
dehydration, heart disease, adrenal insufficiency,
pregnancy, prolonged bed rest, poisoning, and
blood transfusion reactions. Severe hypotension is
referred to as shock or hypovolemic shock.
Treatment of mild hypotension may not be neces-
sary, although the severe lowering of blood pressure
known as shock is life-threatening and requires
immediate medical treatment. Hypotension is the
opposite of hypertension (abnormally high blood
pressure). See also 
hypotension, orthostatic.