section_path: Morphology and physiology/Internal systems/Digestive
section_name: Digestive
paragraph_text: Digestive
  
  An insect uses its digestive system to extract nutrients and other substances from the food it consumes. There is extensive variation among different orders, life stages, and even castes in the digestive system of insects. The gut runs lengthwise through the body. It has three sections, with paired salivary glands and salivary reservoirs. By moving its mouthparts the insect mixes its food with saliva. Some insects, like flies, expel digestive enzymes onto their food to break it down, but most insects digest their food in the gut. The foregut is lined with cuticule as protection from tough food. It includes the mouth, pharynx, and crop which stores food. Digestion starts in the mouth with enzymes in the saliva. Strong muscles in the pharynx pump fluid into the mouth, lubricating the food, and enabling certain insects to feed on blood or from the xylem and phloem transport vessels of plants. Once food leaves the crop, it passes to the midgut, where the majority of digestion takes place. Microscopic projections, microvilli, increase the surface area of the wall to absorb nutrients. In the hindgut, undigested food particles are joined by uric acid to form fecal pellets; most of the water is absorbed, leaving a dry pellet to be eliminated. Insects may have one to hundreds of Malpighian tubules. These remove nitrogenous wastes from the hemolymph of the insect and regulate osmotic balance. Wastes and solutes are emptied directly into the alimentary canal, at the junction between the midgut and hindgut.