Dictionary

X-ray, PA An X-ray picture in which the beams pass through the patient posteroanteriorly (from back to front).

X-ray, lateral An X-ray picture that is taken from the side.

X-ray, AP An X-ray picture in which the beams pass through the patient anteroposteriorly (from front to back).

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-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-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 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.

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.

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…

xerosis Abnormal dryness of the skin, mucous membranes, or conjunctiva (xerophthalmia). There are many causes of xerosis, and treatment depends on the particular cause.

xerophthalmia Dry eyes. Xerophthalmia can be associated with systemic diseases, such as Sjogren’s syndrome, systemic lupus erythematosus, and rheumatoid arthritis; deficiency of vitamin A; and use of some medications. It results from inadequate function of the lacrimal glands, which produce tears. When xerophthalmia is due to vitamin A deficiency, the condition begins with night blindness…

xerophagia Having a tendency to eat a dry diet.