ulcer: An area of epithelial sloughing associated with damage to the underlying connective tissues and blood vessels.

ultrasound: A diagnostic visualization procedure that uses high-frequency sound waves.

umbilical cord: The connecting stalk between the fetus and the placenta; contains the allantois, the umbilical arteries, and the umbilical vein.

umbilicus: The navel.

unicellular gland: Goblet cells.

unipennate muscle: A muscle whose fibers are on one side of the tendon.

unipolar neuron: A sensory neuron whose cell body is in a dorsal root ganglion or a sensory ganglion of a cranial nerve.

unmyelinated axon: An axon whose neurilemma does not contain myelin and across which continuous conduction occurs.

uracil: A pyrimidine; one of the nitrogenous bases in the nucleic acid RNA.

uremia: An abnormal condition caused by impaired kidney function; characterized by the retention of wastes and the disruption of many other organ systems.

ureters: Muscular tubes, lined by transitional epithelium, that carry urine from the renal pelvis to the urinary bladder.

urethra: A muscular tube that carries urine from the urinary bladder to the exterior.

urethritis: An inflammation of the urethra.

urinalysis: An analysis of the physical and chemical characteristics of urine.

urinary bladder: The muscular, distensible sac that stores urine prior to micturition.

urination: The voiding of urine; micturition.

urobilin: A compound derived from urobilinogen and ultimately from the bilirubin excreted in bile.

uterus: The muscular organ of the female reproductive tract in which implantation, placenta formation, and fetal development occur.

utricle: The largest chamber of the vestibular apparatus of the inner ear; contains a macula important for static equilibrium.

uvea: The vascular tunic of the eye.

uvula: A dangling, fleshy extension of the soft palate.