The alimentary canal of Fasciola hepatica is incomplete. The digestive system begins with mouth surrounded by the oral sucker, pharynx, oesophagus and intestine but does not terminate in anus, that is why it is referred as incomplete.
Mouth: Mouth opening is situated on the ventral side at the anterior end and is surrounded by an oral sucker. It leads into a mouth or buccal cavity that opens into a ovoid or round, highly muscular pharynx.
Pharynx and oesophagus: The pharynx is a thick, robust organ with very thick wall and a narrow lumen. The pharyngeal wall is composed of radial muscles and number of pharyngeal glands are embedded within it. The pharynx leads into a short, narrow oesophagus that opens into an intestine.
Intestine: The intestine immediately forks to form right and left limbs or branches that run along the either side of the body up to the posterior extremity and terminate blindly. These branches of the intestine are called as crura or intestinal caeca. These caecae give out numerous irregular.blindly terminating, side branches, or diverticulae all along their length on the outer as well as the inner side.
The diverticulae on the outer side of the caeca, the lateral diverticulae are long and are profusely branched while those on the inner side, the median diverticulae are short and simple with no further ramifications. The extensively branched intestinal caeca serve to transport digested food to all the parts of the body.
The digestive system from the mouth up to the oesophagus is lined by cuticle. This region of the alimentary canal is the fore gut region that serves as efficient suctorial apparatus. The intestine is lined by columnar epithelial cells that are endodermal in origin. Numerous secretory gland cells surrounded by a thin muscular layer consisting of circular and longitudinal muscle fibers are present in the caecal epithelium.
Feeding and Digestion: The fluke often migrates into the bile ducts and the capillaries of the host for nourishment. It feeds on blood, lymph, inflammatory exudates and bile juice which it sucks from the wall of the host’s bile passages. The fluke also feeds on the cell debris and pieces of tissue rasped off by the oral sucker. The sucking of food is facilitated by the muscular pharynx.
The physiology of digestion of liver-fluke is not very well understood. Liquid food is sucked up by the muscular pharynx and is pumped into the intestine through the oesophagus. Digestion is extracellular and takes place in the intestinal caeca which also help in absorption of the food. The digested food diffuses into the parenchyma from where it is distributed to the rest of the body through the lateral and median diverticulae of the intestine. These diverticulae thus serve the purpose of the circulatory system, the circulatoy
system being absent in the fluke.
The substances like monosaccharides such as glucose and fructose available in the host’s body are known to diffuse directly into the body of the fluke through its general surface. The numerous folds of the tegument aid in the absorption and diffusion. The waste materials diffuse into the surrounding parenchyma which also helps in its transportation.
Anus is absent, so the undigested wastes are thrown out through the mouth only. The reserve food is stored mainly in the form of glycogen and the fats in the parenchyma and the muscles.