A sex chromosome in certain animals, such as chickens, turkeys, and moths. In humans, males are XY and females XX, but in animals with a Z chromosome, males are ZZ and females are WZ.

Zeta-chain-associated protein kinase 70. A member of the protein tyrosine kinase family, ZAP-70 is normally expressed in T cells and natural killer cells and has a critical role in the initiation of T-cell signaling. ZAP-70 is expressed in T cells and tumors of T-cell lineage. A high level of ZAP-70 expression appears restricted to T-cell […]

‘When you hear hoof beats, think of horses, not zebras.’ For example, when someone develops a mild transient cough, a virus infection is the most logical and likely cause, and tuberculosis is a zebra.

A gene that is lethal (fatal) for the zygote, the cell formed by the union of a sperm (male sex cell) and an ovum (female sex cell). The zygote would normally develop into an embryo, as instructed by the genetic material within the unified cell. However, a zygotic lethal gene scotches prenatal development at its […]

A technique in which a woman’s egg is fertilized outside the body, then implanted in one of her fallopian tubes. This technique is one of the methods used to overcome infertility, the inability of couples to produce offspring on their own. First, the egg and the male sperm needed to fertilize it are harvested. Then […]

One of the four valves of the heart, this one is situated between the left atrium and the left ventricle. It permits blood to flow one way only, from the atrium into the ventricle. The valve is more commonly called the mitral valve because its two flaps (cusps) makes it look like a bishop’s miter […]

Auditory prosthesis: A device that enhances the ability to hear or substitutes for it. More commonly called a hearing aid. See: Hearing aid.

The orbital cavity is drained by paired veins called the superior and inferior ophthalmic veins. The superior ophthalmic vein arises at the inner angle of the orbit and follows the course of the ophthalmic artery into the cavernous sinus, a large channel of venous blood. The inferior ophthalmic vein arises from a venous network at […]

A test group that is selected solely by chance.

Biliary: Having to do with the gallbladder, bile ducts, or bile. The biliary system itself consists of the gallbladder and bile ducts and, of course, the bile. For example, biliary atresia is the absence or closure of the major bile ducts, the ducts that drain bile from the liver.