Medical Definitions - O

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Oliguria - abnormally slight or infrequent urination.

Omphalocele - a congenital hernia in which a small portion of the fetal abdominal contents, covered by a membrane sac, protrudes into the base of the umbilical cord.

Opacification - the process of becoming opaque or cloudy.

Osseous structures - composed of or containing bone; bony.

Organ donation - the removal of the tissues of the human body from a person who has recently died, or from a living donor, for the purpose of transplanting. Organs and tissues are removed in procedures similar to surgery. People of all ages may be organ and tissue donors.

Orogastric tube - also known as an OG tube; passing a stomach tube via the mouth.