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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.
Zebra
The term "zebra" in medicine does not refer to the striped African animal but to an unlikely diagnostic possibility. It comes from an old saying in teaching medical students about how to think logically in regard to the differential diagnosis: "When you hear hoof beats, think of horses, not zebras."
For example, when someone develops a mild transient cough, tuberculosis is a "zebra." For another example, following the discovery of West Nile fever in New York City in September, 1999, the Centers for Disease Control and Prevention warned doctors to expect more infectious disease "zebras" (diseases due to rare microbes).
Zeitgeber
German for "time-giver", Zeitgeber refers to an environmental agent or event such as the occurrence of light or dark that provides the stimulus setting or resetting a biological clock.
Zellweger syndrome
A congenital disorder (birth defect), also called the cerebrohepatorenal syndrome, characterized by the reduction or absence of peroxisomes (cell structures that rid the body of toxic substances) in the cells of the liver, kidneys, and brain. Zellweger syndrome is one of a group of genetic disorders called the leukodystrophies that affect growth of the myelin sheath, the fatty covering which acts as an insulator on nerve fibers in the brain.
The most common features of Zellweger syndrome include an enlarged liver, high levels of iron and copper in the blood, and vision disturbances. Some affected infants may show prenatal growth failure. Symptoms at birth may include lack of muscle tone and an inability to move. Other symptoms may include unusual facial characteristics, mental retardation, seizures, and an inability to suck and/or swallow. Jaundice and gastrointestinal bleeding may also occur.
There is no cure for Zellweger syndrome and there is no standard course of treatment. Infections are guarded against to prevent such complications as pneumonia and respiratory distress. Other treatment is symptomatic and supportive.
The prognosis for individuals with Zellweger syndrome is poor. Death usually occurs within 6 months after onset, and may be caused by respiratory distress, gastrointestinal bleeding, or liver failure.
The condition is named for the pediatrician Hans Zellweger. The Zellweger syndrome is caused by mutations (changes) in any of several different genes involved in peroxisome formation. These genes lie on at least two different chromosome locations including chromosome 2 (region 2p15) and chromosome 7 (region 7q21-q22).
Zidovudine
A drug used against human immunodeficiency virus (HIV), the virus that causes AIDS. Formerly called azidothymidine and abbreviated AZT. Usually used in combination with other drugs.
Uses: Zidovudine is the pharmacologic mainstay for preventing the transmission of HIV by infected women to their babies during birth. In the U.S. zidovudine is now recommended for health care workers with needle stick exposures and cautiously suggested in rape cases in which there is a high risk of exposure to HIV. Zidovudine crosses the blood-brain barrier and therefore may be effective against the syndrome of AIDS dementia.
Toxicity: Zidovudine has some toxicity but for the 30-day time period it is used for PEP (post-exposure prophylaxis) there is an extremely low risk of long-term problems. The biggest issues are cost and uncertainty about efficacy, not its toxicity.
Technical: Zidovudine acts as a nucleoside (thymidine) analog drug. It suppresses the replication of HIV by terminating DNA synthesis.
ZIFT
Stands for zygote intrafallopian transfer, a method used to treat infertility in which an egg fertilized in vitro (outside the body) is placed into a woman's fallopian tube. This technique is one used to overcome infertility, the inability of couples to produce offspring on their own.
The egg and the male sperm needed to fertilize it are harvested. Then the egg and the sperm are united in a petri dish, a multi- purpose glass or plastic container with a lid. If all goes well, the sperm fertilizes the egg, and the physicians then implant it in a fallopian tube. From there, nature takes its course, and the egg eventually is deposited by the fallopian tube into the uterus (womb) for development.
A zygote is the combined cell resulting from the union of sperm and egg. A zygote develops into an embryo. An embryo, a mass of cells with no recognizable human features, begins formation of a human body. After about seven or eight weeks, the embryo exhibits recognizable features such as a mouth and ears. At this stage, the developing human becomes known as a fetus. The word "zygote" is derived from the Greek word "zygon" (yoke).
The term "intrafallopian" means "inside the fallopian tubes." ("Intra," a Latin word, means "within" or "inside.") Thus, the term "zygote intrafallopian transfer" refers to the transfer of a zygote into a fallopian tube.
Zinc
A mineral essential to the body, zinc is a constituent of many enzymes that permit chemical reactions to proceed at normal rates. It is involved in the manufacture of protein (protein synthesis) and in cell division. Zinc is also a constituent of insulin, and is concerned with the sense of smell.
Food sources of zinc include meat, particularly liver and seafood; eggs; nuts; and cereal grains.
Deficiency of zinc is associated with short stature, anemia, increased pigmentation of skin (hyperpigmentation), enlarged liver and spleen (hepatosplenomegaly), impaired gonadal function (hypogonadism), impaired wound healing, and immune deficiency. (For a genetic disorder that impairs zinc uptake, please see Acrodermatitis enteropathica).
Too much zinc can cause gastrointestinal irritation (upset stomach), interfere with copper absorption and cause copper deficiency, and (like too little zinc) cause immune deficiency.
According to the National Academy of Sciences, the Recommended Dietary Allowance of zinc is 12 milligrams per day for women and 10 milligrams per day for men.
Zinc acetate
A form of zinc that has been used as an emetic.
Zinc deficiency
According to the National Academy of Sciences, the Recommended Dietary Allowances of zinc are 12 milligrams per day for women and 10 milligrams per day for men. Food sources of zinc include meat including liver, eggs, seafood, nuts and cereal.
Deficiency of zinc is associated with short stature, anemia, increased pigmentation of skin (hyperpigmentation), enlarged liver and spleen (hepatosplenomegaly), impaired gonadal function (hypogonadism), impaired wound healing, and immune deficiency.
In a genetic disease called acrodermatitis enteropathica, there is impaired zinc uptake from the intestine. The condition is characterized by the simultaneous presence of dermatitis (skin inflammation) and diarrhea. The skin on the cheeks, elbows and knees and the tissues about the mouth and anus are inflammed. There is balding of the scalp, eyebrows and eyelashes. Wound healing is delayed. And there are recurrent bacterial and fungal infections due to immune deficiency. The key laboratory finding is an abnormally low blood zinc level reflecting the impaired zinc uptake. Treatment with zinc is curative.
Zinc deficiency dermatitis and diarrhea
Among the consequences of zinc deficiency, dermatitis (skin inflammation) and diarrhea are particularly prominent features.
A genetic disease called acrodermatitis enteropathica in which there is impaired zinc uptake from the intestine is, in fact, characterized by the simultaneous presence of dermatitis (skin inflammation) and diarrhea. The skin on the cheeks, elbows and knees and the tissues about the mouth and anus are inflammed. There is balding of the scalp, eyebrows and eyelashes. Wound healing is delayed. And there are recurrent bacterial and fungal infections due to immune deficiency. The key laboratory finding in acrodermatitis enteropathica is an abnormally low blood zinc level reflecting the impaired zinc uptake. Treatment with zinc is curative.
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