Webster's New World Medical Dictionary

DiGeorge syndrome
A congenital disorder
characterized by low blood calcium because of
underdevelopment of the parathyroid glands
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DiGeorge syndrome
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needed to control calcium; immunodeficiency due
to hypoplasia of the thymus (an organ behind the
breastbone in which lymphocytes mature and multi-
ply); and defects involving the outflow tracts from
the heart. DiGeorge syndrome is caused by a very
small deletion in chromosome band 22q11.2. The
key gene that is lost is Tbx-1. Tbx-1 is a master con-
trol gene that regulates other genes required for the
connection of the heart with the blood circulation.
Tbx-1 also controls genes involved in the develop-
ment of the parathyroid and thymus glands and the
shape of the face. Also known as hypoplasia of the
thymus and parathyroids and as third and fourth
pharyngeal pouch syndrome.
digestive system
The system of organs responsi-
ble for getting food into and out of the body and for
making use of food to keep the body healthy. The
digestive system includes the salivary glands, mouth,
esophagus, stomach, liver, gallbladder, pancreas,
small intestine, colon, and rectum. The digestive sys-
tem’s organs are joined in a long, twisting tube from
the mouth to the anus. Inside this tube is a lining
called the mucosa. In the mouth, stomach, and small
intestine, the mucosa contains tiny glands that pro-
duce juices to help digest food. Two solid organs, the
liver and the pancreas (both of which are embry-
ologically derived from the digestive tract), produce
digestive juices that reach the intestine through small
tubes known as ducts. In addition, parts of other
organ systems (for instance, nerves and blood) play
a major role in the digestive system.