The insect digestive system has three main parts - the foregut, midgut, and hindgut. The foregut contains structures like the mouth, pharynx, esophagus, crop, and gizzard. The midgut is where most digestion occurs, aided by structures like the peritrophic membrane and gastric caecae. The hindgut absorbs water and nutrients from waste before it is excreted. The insect circulatory system consists of a fluid called hemolymph that circulates through the open circulatory system. Hemolymph is pumped through the dorsal blood vessel by the heart. It carries nutrients, removes waste, and fights pathogens but does not carry oxygen.