The<unk> <unk> , digestive<unk> , alimentary canal) is the<unk>  or passageway of the digestive system that leads from the mouth to the anus. The<unk>  contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as feces.<unk>  is an adjective meaning of or pertaining to the stomach and intestines. Most animals have a "through-gut" or complete digestive<unk> . Exceptions are more primitive ones: sponges have small pores (ostia) throughout their body for digestion and a larger dorsal pore (osculum) for excretion, comb jellies have both a ventral mouth and dorsal anal pores, while cnidarians and acoels have a single pore for both digestion and excretion. The human<unk>  consists of the esophagus, stomach, and intestines, and is divided into the upper and lower<unk> s. The<unk>  includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. The complete human digestive system is made up of the<unk>  plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). The<unk>  may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment. The whole human<unk>  is about nine metres (30 feet) long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis. The<unk>  contains the gut microbiota, with some 4,000 different strains of bacteria having diverse roles in maintenance of immune health and metabolism, and many other microorganisms. Cells of the<unk>  release hormones to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
Gastrointestinal tract
Peripheral nervous system
Stomach
Central nervous system
Enteric nervous system
Reproductive system
Urinary system
Genitourinary system