Webster's New World Medical Dictionary

achlorhydria
A lack of hydrochloric acid in the
digestive juices in the stomach.
achondroplasia
A genetic disorder of bone
growth and the most common cause of short stature
with disproportionately short arms and legs (known
as dwarfism). The individual has a large head with
a prominent forehead (frontal bossing); underde-
velopment (hypoplasia) of the midface, with cheek-
bones that lack prominence; and a low nasal bridge
with narrow nasal passages. The fingers are short,
and the ring and middle fingers diverge to give the
hand a trident (three-pronged) appearance. The
brain is entirely normal in people with achon-
droplasia, but complications can damage the brain
and spinal cord. Achondroplasia is an autosomal
dominant trait, affecting boys and girls equally. Most
cases are due to new gene mutations that appear for
the first time in the affected child. Achondroplasia is
caused by mutation in the fibroblast growth factor
receptor-3 gene (FGFR3), and prenatal diagnosis is
possible. See also 
dwarfism; dwarfism, hydro-
chondroplastic.
acentric chromosome
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acid, pantothenic
Vitamin B5. See also
Appendix C, “Vitamins.”
acid indigestion
Excessive secretion of
hydrochloric acid by the stomach cells. Medically
known as hyperchlorhydria. Sometimes used inter-
changeably with heartburn. See also 
heartburn.
acid phosphatase
An enzyme that acts to liber-
ate phosphate under acidic conditions and is made
in the liver, spleen, bone marrow, and prostate
gland. Abnormally high serum levels of acid phos-
phatase may indicate infection, injury, or cancer of
the prostate.
acidophilus
Bacteria found in yogurt with “live
cultures” that can help restore supportive bacteria
to an intestinal tract whose normal bacterial popu-
lation (flora) has been disturbed by disease or
antibiotics. Eating yogurt with acidophilus may also
be useful in preventing overgrowth of yeast
(Candida) in the intestinal tract, mouth (thrush),
and vagina. See also 
probiotic.
acidosis
Too much acid in the blood and body.
Acidosis is an abnormal condition resulting from
the accumulation of acid or the depletion of alkaline
reserves. The pH of a body with acidosis is below
normal. For a person with diabetes, this can lead to
diabetic ketoacidosis. The opposite of acidosis is
alkalosis. See also 
pH.