hyperexplexia A rare genetic disorder inherited in an autosomal dominant manner in which babies have an exaggerated startle reflex. Symptoms at birth may include muscle stiffness (hypertonia), an exaggerated response to being startled, and strong brain stem reflexes (especially head-retraction reflex). The startle reflex is sometimes accompanied by sudden stiffness (acute generalized hypertonia), which can…
hyperglycemia Elevated blood glucose (sugar). Hyperglycemia is often found in diabetes mellitus. See also diabetes mellitus.
hyperhidrosis A condition characterized by extreme and excessive sweating. Primary hyperhidrosis affects the hands, feet, and armpits and often has no identifiable cause. If the sweating occurs as a result of another medical condition, it is called secondary hyperhidrosis. In secondary hyperhidrosis, the sweating may be all over the body or may be localized to…
hyperkalemia Elevated potassium in the blood. Hyperkalemia can be caused by taking excessive amounts of potassium, by medications, tissue trauma, and by diseases such as kidney failure. Hyperkalemia may not produce any symptoms, but severe hyperkalemia can lead to potentially fatal arrythmias of the heart.
hyaline membrane disease Synonym for acute respiratory distress syndrome and respiratory distress syndrome. See acute respiratory distress syndrome; respiratory distress syndrome.
hybrid The result of a cross between genetically unlike parents. A hybrid is therefore the offspring of parents who differ in regard to the particular gene in question.
hybridoma A hybrid cell used as the basis for the production of antibodies in large amounts for diagnostic or therapeutic use. Hybridomas are produced by injecting a specific antigen into a mouse, collecting an antibody-producing cell from the mouse’s spleen, and fusing it with a tumor cell called a myeloma cell. The hybridoma cells multiply…
hydatid mole See hydatidiform mole.
hydatidiform mole A tumor that forms in the uterus as a mass of cysts resembling a bunch of grapes. Hydatidiform moles occur during the childbearing years, and they do not spread outside the uterus. However, a malignancy called choriocarcinoma may start from a hydatidiform mole. In its early stages, a hydatidiform mole may look like…
hydro- Prefix meaning related to water.
hydrocele Accumulation of fluid in the coat around the testis. Small hydroceles tend to disappear by 1 year of age. Larger hydroceles may persist and warrant surgery.
hydrocephalus An abnormal buildup of cerebrospinal fluid (CSF) in the ventricles and/or subarachnoid space of the brain. The fluid often increases intracranial pressure, which can compress and damage the brain. Hydrocephalus can arise before birth or at any time afterward. Causes can include birth defects (particularly spina bifida), hemorrhage into the brain, infection, meningitis, tumor,…