U

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Ulcer

An ulcer is a break in the skin or in the mucous membrane lining the alimentary tract that fails to heal and is often accompanied by inflammation.

Ulna

The ulna is the inner and longer bone of the forearm.

Ultrasound

Ultrasound is the use of sound with a frequency higher than 20,000 Hz to obtain images for medical diagnostic purposes.

Ultrastructure

Ultrastructure is the arrangement of the smallest elements making up a body, or the arrangement of ultramicrons making up a substance.

Ultraviolet (UV)

Ultraviolet light is the part of the electromagnetic spectrum that has wavelengths shorter than visible light but longer than X-rays; it lies outside the visible spectrum at its violet end. Ultraviolet light (radiation) is harmful to humans.

Umbilical

An umbilical is any of various external electrical lines or fluid tubes which connects one portion of a system to another.

Umbilicus

Umbilicus is the scientific term for naval.

UMS

UMS is the acronym for the Urine Monitoring System. The UMS space flight hardware supports metabolic experiments by preparing urine samples for return to ground for analysis after flight. It automatically collects, measures, and samples individual urine samples in either a microgravity or normal gravity environment and accommodates both male and female users.

Upper respiratory infection

An upper respiratory infection is any infectious disease of the upper respiratory tract. These infections include the common cold, laryngitis, pharyngitis, rhinitis, sinusitis, and tonsillitis.

Urea

Urea is a nitrogen-containing substance that is normally cleared from the blood into the urine by the kidney. It is the chief solid component of mammalian urine and an end product of protein decomposition. Diseases that compromise the function of the kidney often lead to increased blood levels of urea, measured by the blood urea nitrogen (BUN) test.

Urethritis

Urethritis is the inflammation of the urethra (the canal through which urine is discharged in most mammals).

Uric acid

Uric acid is the end product of urine breakdown; it is the major form in which metabolic nitrogen is excreted from the body.

Urinalysis

A urinalysis is the chemical analysis of urine.

Urine specific gravity

Urine specific gravity is a measure of the degree of concentration of a sample of urine, and usually indicates fluid intake. The higher the specific gravity, the less the fluid intake.

Urokinase

Urokinase is a proteinase found in mammalian urine, which cleaves plasminogen to plasmin. Urokinase is used to treat people suffering from blood-clot conditions.

Utricle

The utricle is the larger of the two membranous sacs within the vestibule of the ear; it forms part of the membranous labyrinth.

Utricular

Utricular refers to the utricle, the larger of the two membranous sacs within the vestibule of the ear, which forms part of the membranous labyrinth.

UV radiation

Ultraviolet (UV) radiation results from wavelengths of energy from just beyond the violet in the visible spectrum to the border of the X-ray region. Exposure to types of UV radiation can cause damage to the body, namely the skin. The layer of ozone in the Earth's stratosphere normally forms a protective shield, blocking the majority of harmful UV rays from the sun.