Medical Dictionary

X Chromosome

The X chromosome is a sex gene. The female egg always carries one X chromosome. The sex of an embryo is determined by the sex chromosome carried by the sperm that fertilises the egg. The sperm can either bring another X chromosome (XX) in which case the embryo will develop into a female or the sperm can carry an Y chromosome (XY) in which case the embryo will develop into a male.

Xanthelasma

A xanthelasma (plural xanthelasmata) is a deposit of cholesterol underneath the skin, usually on or near the eyelids. Xanthelasmata appear as yellowish plaques. They can be a sign of high cholesterol.

Xanthines

Xanthines are a type of bronchodilator medication. There are three main active, naturally occurring methylxanthines - theophylline, theobromine and caffeine. Theophylline is the most commonly used xanthine in treatment of asthma.

Xenical

Xenical is a weight- reducing medicine that contains 120mg of the active ingredient Orlistat. It is used in obese patients with a Body Mass Index greater than 30, as well as overweight patients with BMI's greater than 27 and other risk factors (hypertension, diabetes, and high lipids). Doses need to be taken 3 times a day with breakfast, lunch and dinner, and a healthy, low fat diet must be consumed.

Xerosis

Xerosis is the techncial term for dry skin. Xerosis resulting from cold, dry weather with low humidity is often referred to as winter xerosis. Dry skin may also be caused by inherited factors or skin conditions such as ichthyosis, as well as increasing age, excessive bathing or swimming, air conditioning, central heating or contact with soap or detergents.

Xerostomia

Xerostomia is the subjective feeling of oral dryness, which may or may not be actually associated with a problem with the salivary glands.

X-ray

An X-ray is an electromagnetic ray having an extremely short wavelength that ranges from about o.1 to 10 nanometers. It is formed by the bombardment of a metal target with high-speed electrons in a vacuum tube or by the transfer of electrons to the inner shells of heavy atoms.