Webster's New World Medical Dictionary

Pickwickian syndrome
A syndrome that is
characterized by obesity, sleepiness, hypoventila-
tion, and a reddened face. It occurs because of
reduced blood oxygen levels due to breathing insuf-
ficiency. The syndrome is named for the “fat and
red-faced boy in a state of somnolency” whom
Charles Dickens described in his novel 
The
Pickwick Papers.
Also known as obesity hypoventi-
lation syndrome (OHS).
PID
Pelvic inflammatory disease.
pigeon breast
Having a prominent breastbone
and chest. Also known as pectus carinatum.
pigment
A substance that gives color to tissue.
Pigments are responsible for the colors of skin, eyes,
and hair.
pigmentation
The coloring of the skin, hair,
mucous membranes, and retina of the eye.
Pigmentation is due to the deposition of the pigment
melanin, which is produced by specialized cells
called melanocytes. Other pigment-related terms
include hyperpigmentation (too much pigment),
hypopigmentation and underpigmentation (too little
pigment), and depigmentation (loss of pigment).
piles
See 
hemorrhoids.
pill, the
See 
oral contraceptive.
piloerection
Erection of the hair of the skin due
to contraction of the tiny arrectores pilorum muscles
that elevate the hair follicles above the rest of the
skin and move the hair vertically, so the hair seems
to “stand on end.”
pilonidal cyst
An abscess that occurs in the cleft
between the buttocks at the base of the tailbone
(coccyx). Pilonidal cysts are common in adoles-
cence, often after long trips that involve sitting.
pimple
An inflamed area of the skin with pus for-
mation that results from an oil gland being infected
with bacteria. Pimples are due to overactivity of the
oil glands located at the base of the hair follicles,
especially on the face, back, chest, and shoulders.
pineal gland
A small gland that is located near
the center of the brain. This gland secretes mela-
tonin, and it may therefore be part of the body’s
sleep-regulation apparatus. Also known as pineal
body.