PARASITES AND PARASITIC DISEASES OF DOMESTIC ANIMALS


The Nematodes

Digestive System

The digestive system of nematodes is usually a simple tube with the majority of variations occurring in the sizes of the mouth opening,  buccal capsule (syn = buccal cavity) and esophagus.

The mouth may be a simple opening with a tiny buccal cavity leading directly to the esophagus as shown in the accompanying image of Nematodirus ( a small nematode found in the small intestine of ruminants).

At the other extreme, the mouth opening may be quite large leading to a prominent buccal cavity with thick walls and often containing teeth ( e.g. Strongylus vulgaris).

The type of mouth opening and accompanying buccal cavity appears to be related to diet. A large mouth opening and prominent buccal cavity is found in those nematodes that feed by taking a bite of mucosa, and drawing it into the buccal cavity where it is digested (e.g the large strongyles of horses). These nematodes are often called "plug feeders".

In nematodes that feed by simple ingestion of host fluids the mouth opening and accompanying buccal cavity are generally quite small.(e.g. Ostertagia in which the mouth opening and buccal cavity are so small they can only be viewed effectively by scanning electron microscopy and, Nematodirus spp).

In nematodes that are described as mucosal grazers, rather then plug feeders, the mouth opening and its buccal cavity are usually intermediate in size
(e.g. Oesophagostomum radiatum a nematode found in the large intestine of swine).

In most nematodes, the esophagus is muscular and is used to pass food into the intestine by a pumping action. The shape of the esophagus may be used as an initial screening characteristic for identification. For example, adult nematodes belonging to the Superfamily Strongyloidea have a club-shaped (strongyliform) esophagus which, as the name suggests, is shaped like a club. Adult members of the Superfamily Oxyuroidea have an esophagus which has a prominent posterior bulb separated from the rest of the esophagus by a narrow isthmus.

The intestine is a straight tube roughly circular in cross section and with a wall consisting of a single layer of columnar (rectangular-shaped) cells. The lumen surfaces of these cells consist of multitudes of projecting microvilli used in absorption and because of their vast numbers provide an immense absorptive capacity. The intestine terminates in a rectum in females and a cloaca in males. The cloaca is a common termination for the intestinal tract and the vas deferens in adult males. In either case, the cloaca (males) and rectum (females) leads to an anus which usually opens to the outside at the posterior end of the body.

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Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)

Copyright 1998 University of Pennsylvania
This page was last modified on February 12, 2004