I
Growth projecting from the wall of a cavity lined with a mucous membrane.
Shape varies widely; it may have a stalk or many lobes. Polyps most often occur in the nose, urinary bladder, and digestive tract, especially in the rectum and colon. Symptoms, if any, depend on location and size; they may result from pressure or from blockage of a passage. Polyps occasionally bleed. Because a small percentage are precursors to cancers or actually contain cancers, it is advisable to have them removed and examined microscopically and to undergo routine colonoscopy after age 50.
II
In zoology, one of two principal cnidarian body forms and, sometimes, an individual in a bryozoan colony.
The cnidarian polyp body is a hollow cylindrical structure. The lower end attaches to another body or surface. The upper, or free, end is directed upward and has a mouth surrounded by extensible tentacles that bear stinging structures called nematocysts. The tentacles capture prey, which is then drawn into the mouth. The polyp may be solitary (see sea anemone ) or colonial (see coral ). The body wall consists of three dermal layers. The other cnidarian body form is the medusa .