xerostomia Dry mouth. Xerostomia can be associated with systemic diseases, such as Sjogren’s syndrome, systemic lupus erythematosus, and rheumatoid arthritis; and it can be a side effect of medication and poor dental hygiene. Xerostomia results from inadequate function of the salivary glands, such as the parotid glands. Treatment involves adequate intake of water, use of…
xiphoid process The lower part of the breastbone. The xiphoid process has no particular function and ranges in size from miniscule to several inches in length.
X-linked A gene on the X chromosome that is located on the X chromosome. An X-linked disorder is associated with or caused by a gene on the X chromosome.
X-linked dominant An X-linked trait that is expressed when one copy of the gene for that trait is present. In the case of an X-linked dominant disease, a single copy of the mutant gene on the X chromosome can cause the disease in a female. An example is a type of hereditary rickets called hypophosphatemic…
X-linked recessive A mode of genetic inheritance characterized by a gene on the X chromosome being expressed only when there is no different gene present at that spot (locus) on a second X chromosome. This means that X-linked traits are expressed in males and in females who are homozygous for the gene (they have a…
X-ray High-energy radiation with waves shorter than those of visible light. X-ray is used in low doses to make images that help to diagnose diseases and in high doses to treat cancer.
X-ray, AP An X-ray picture in which the beams pass through the patient anteroposteriorly (from front to back).
X-ray, lateral An X-ray picture that is taken from the side.
X-ray, PA An X-ray picture in which the beams pass through the patient posteroanteriorly (from back to front).
X-ray therapy The use of X-ray radiation to treat cancer. X-rays may be used inside or outside the body, depending on the type of tumor involved. See also radiation therapy.
XX The sex chromosome complement of a normal human female. See also X chromosome.
XXX syndrome A chromosome condition that is present in 1 in 1,000 females, due to the presence of three X chromosomes rather than the usual two. The condition is associated with increased height but no malformations. Intelligence ranges from above normal to mild mental retardation. Also known as triple X and triplo-X.