• Z chromosome

    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.

  • ZAP-70

    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 […]

  • Zebra

    ‘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.

  • Zygotic lethal gene

    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 […]

  • Zygote intrafallopian transfer (ZIFT)

    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 […]

  • Xerophagia

    Having a tendency to eat a dry diet.

  • Uterine contraction

    (1) they cause the cervix to thin and dilate (open); and (2) they help the baby to descend into the birth canal. Uterine contractions also occur during the monthly menstrual cycle and are recognized as menstrual cramps.

  • Epilepsy, Jacksonian

    Epilepsy, Jacksonian:A brief alteration in movement, sensation or nerve function caused by abnormal electrical activity in a localized area of the brain. Seizures of this type typically cause no change in awareness or alertness. They are transient, fleeting, ephemeral. Jacksonian seizures are extremely varied and may involve, for example, apparently purposeful movements such as turning […]

  • Vitiligo

    A condition in which the skin turns white due to the loss of pigment from the melanocytes, cells that produce the pigment melanin that gives the skin color. In vitiligo, the melanocytes are destroyed, leaving depigmented patches of skin. The hair that grows in areas affected by vitiligo may also turn white. The skin is […]

  • Xanthosis

    Yellowing of the skin without yellowing of the eyes. In jaundice there is yellowing of both the skin and the whites of the eyes. Xanthosis is associated sometimes with malignancies.