Webster's New World Medical Dictionary

Zollinger-Ellison syndrome
A rare disorder
caused by a tumor called a gastrinoma, most often
occurring in the pancreas. The tumor secretes the
hormone gastrin, which causes increased produc-
tion of gastric acid leading to severe recurrent
ulcers of the esophagus, stomach, and the upper
portions of the small intestine. Gastrinomas result-
ing in the Zollinger-Ellison syndrome may also
occur in the stomach, duodenum, spleen, and
lymph nodes. Treatment can include the use of H2
antagonist medications, proton pump inhibitors, or
surgical removal of the tumor.
zona pellucida
The strong membrane that forms
around an ovum as it develops in the ovary. The
membrane remains in place during the egg’s travel
through the fallopian tube. To fertilize the egg, a
sperm must penetrate the thinning zona pellucida. If
fertilization takes place, the zona pellucida disap-
pears, to permit implantation in the uterus.
zoonosis
An infection that is known in nature to
infect both humans and lower vertebrate animals.
zooparasite
A living parasite, such as a worm or
protozoa.
zoophilia
A sexual disorder (paraphilia) that
involves an abnormal desire to have sexual contact
with animals. See also 
paraphilia.
zygoma
The bone that forms the prominence of
the cheek. Also known as zygomatic bone, zygo-
matic arch, malar bone, and yoke bone.
zygomatic arch
See 
zygoma.
zygomatic bone
See 
zygoma.
zygomycosis
A potentially fatal, dangerous infec-
tion that is caused by various fungi from the class
Zygomycetes. Zygomycosis is seen most often in
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patients who are already ill with diseases that sup-
press the immune system, such as AIDS, burn
patients, patients taking corticosteroids, and those
with poorly controlled diabetes. If unchecked, the
fungal infection can spread to the lungs and other
organs, the blood, the eyes, and the brain. Treatment
involves controlling the underlying condition and
attacking the infection with antifungal medications.
zygote
The cell that is formed by the union of a
male sex cell (sperm) and a female sex cell (an
ovum). The zygote develops into the embryo, as
instructed by the genetic material within the unified
cell. The unification of a sperm and an ovum is
called fertilization. See also 
ovum; sperm.