To some degree, sharks digest food similarly to humans. Food is taken into the stomach, where enzymes and other bio-agents break it down. Once this process has been accomplished, the resulting substance is guided into the intestines; however, the shark's system has the capability to distinguish things it has ingested but which supply no nutritional value or which are too big for digestion. In these cases, the excess is expelled.
Sharks frequently swallow things whole or in considerably large pieces. Because of this all of the breakdown must occur in the shark's U-shaped stomach. Some sharks, such as the Great White, have extensions in the esophagus that prevent food or prey from escaping before reaching the stomach. Enzymes and other acids in the stomach then work to form the ingested material into a thick, sludgy substance that is ready to be digested in the intestines. It is necessary for this soupy material to be as mushy as possible, because the valve leading from the shark's stomach to its intestines, the pyloric valve, is quite tiny and will not admit the material otherwise. The shark is capable of vomiting out any material, such as bones, that does not break down easily enough to pass through the valve. The nutrients are then absorbed through the shark's intestines, and excess waste is expelled.