polyp

—polypous, adj.

/pol"ip/, n.

1. Zool.

a. a sedentary type of animal form characterized by a more or less fixed base, columnar body, and free end with mouth and tentacles, esp. as applied to coelenterates.

b. an individual zooid of a compound or colonial organism.

2. Pathol. a projecting growth from a mucous surface, as of the nose, being either a tumor or a hypertrophy of the mucous membrane.

[1350-1400; ME polip, short for polipus nasal tumor (later, also cephalopod, now obs.) < ML, L polypus < dial. Gk poulýpous octopus, nasal tumor (Attic polýpous, gen. polýpodos; see POLY-, -POD)]

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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.

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▪ medicine

      in medicine, any growth projecting from the wall of a cavity lined with a mucous membrane. A polyp may have a broad base, in which case it is called sessile; or it may be a pedunculated polyp, i.e., one with a long, narrow neck. The surface of a polyp may be smooth, irregular, or multilobular. The most common locations of polyps in the human body are the nose, the urinary bladder, and the gastrointestinal tract, especially the rectum and colon.

      Symptoms of polyps depend upon their location and size. There may be no symptoms, or there may be symptoms resulting from pressure or from mechanical obstruction of all or part of a channel, such as that of the nose or a bowel. Polyps occasionally may bleed. Usually polyps are simple, benign growths, but a small percentage may be either precursors to cancers or may actually contain cancers. For that reason, it is advisable, when possible, to have all polyps removed and examined microscopically.

▪ zoology

 in zoology, one of two principal body forms occurring in members of the animal phylum Cnidaria. The polyp may be solitary, as in the sea anemone, or colonial, as in coral, and is sessile (attached to a surface). The upper, or free, end of the body, which is hollow and cylindrical, typically has a mouth surrounded by extensible tentacles that bear complex stinging structures called nematocysts. The tentacles capture prey, which is then drawn into the mouth. The lower end of the polyp typically is adapted for attachment to a surface. The body wall consists of an ectodermal, or outer, layer and an endodermal, or inner, layer.

      Members of one class of cnidarians, the Anthozoa, exhibit only the polyp body form; most species of the other three classes (hydrozoans, scyphozoans, and cubozoans) alternate in their life cycles between polypoid and medusoid (medusa) (free-swimming) body forms. In general, the jellyfish-shaped medusae are produced asexually by the polyp, whereas sperm and eggs are produced by the medusae. Compare medusa.

      The term polyp also is sometimes applied to an individual in a colony of invertebrate aquatic animals belonging to the phylum Bryozoa, although those individuals are usually called zooids.

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