Digestive enzyme
Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tracts of animals (including humans) and in the traps of carnivorous plants, where they aid in the digestion of food, as well as inside cells, especially in their lysosomes, where they function to maintain cellular survival. Digestive enzymes of diverse specificities are found in the saliva secreted by the salivary glands, in the secretions of cells lining
Parasitic nutrition
Endoparasites have various anatomical and biochemical adaptations, typically at the host-parasite interface, to maximise nutrient acquisition. One such adaptation is the tegument, a metabolically active external cover that plays an important role in nutrient extraction from the host. The parasite tegument is permeable to various organic solutes and has transporters for the facilitated or active uptake of nutrients. Various studies have attempted to characterise these transporters in a number of parasites e.g. the amino acid transporter molecules in protozoa. Cestodes do not have a gut so the tegument is therefore critical for nutrient uptake. In cestodes the tegument is highly efficient with spine-like microtriches, similar to microvilli, to increase the surface area available for nutrient acquisition. In many parasites the tegument structure has folds or microvilli to maximise the surface area available for diffusion and uptake of nutrients. The tegument also commonly has additional organelles and features with important functions in metabolism including the glycocalyx. The glycocalyx is a carbohydrate-rich layer that enhances nutrient absorption and secretes enzymes to aid primary digestion.