Digestion, the process of converting food into chemical substances that can be absorbed and assimilated, begins in the mouth, where food is broken apart by the teeth, a process aided by the tongue. Meanwhile, food is moistened and softened by (an unchanged Latin word of the same meaning), which contains certain digestive enzymes. This is produced primarily by three types of gland, all named for their location: “sublingual,” “submandibular,” and “parotid” (Grk. “next to the ”).

Food then passes through the pharynx, where the blocks the passage into the lungs, forcing the food into the esophagus (Grk. oisophagus, “gullet”; probably from ois- [“to carry”] and phag- [“to ”]). The esophagus is a muscular tube that is divided into three parts (cervix, thorax, abdomen) and that leads into the stomach. It terminates in the esophageal sphincter (Grk. sphinc-, “to , to tighten”), which keeps food from going back from the stomach into the esophagus. The stomach serves as a storage tank for food waiting to be digested by the intestines and contains digestive enzymes of its own; food then passes through the (Grk. “gatekeeper”) and the pyloric sphincter, which keeps food from going back into the stomach.

The (Lat. intestinum tenue, “slender innard”) varies in length but is generally about 20 feet long and is heavily coiled, which gives maximum time for nutrients to be absorbed from food that is being digested. It consists of three major parts, the first of which is the (Lat. “twelve,” for its assumed length in fingerbreadths). The next portion is called the “jejunum,” a Latin word meaning “,” so called probably because this portion of the intestine is generally found to be empty upon postmortem dissection (as is the case with several intestinal elements, the name itself is an adjective, with the noun intestinum being understood). The last is known as the “,” from the Latin ilia (“flanks, guts”); the term may show conflation with the Greek-derived ileus, an intestinal obstruction (which perhaps explains the spelling of and its specific use for the small intestine instead of entrails in general).

Other organs do not come directly into contact with food but even so aid in the digestive processes of the small intestine. The liver (Lat. iecur, Grk. hepar) performs many functions, among which is the creation of bile, which helps to break down fat. Excess bile is stored by the (a Germanic word; in Latin it is called the vesica biliaris, in Greek cholecystis). The pancreas (see p. 224) releases digestive enzymes that digest protein.

The large intestine (Lat. intestinum crassum, “thick innard”) is about 5 feet long and helps with the absorption of water. It originates at the terminus of the “ileum,” where the is found (Lat. “blind spot, cul-de-sac”) along with the vermiform (“worm-shaped hanger-on”). There are four major sections of the large intestine: , , , and sigmoid. The first three are so named because they carry food “up,” “sideways,” and “down.” In between the first two is the “ flexure,” which means “bending point at the liver,” so called because of its location near that organ (Grk. hepar). Similarly, the transverse colon meets the descending colon at the “splenic flexure,” which is near the spleen (Grk. splen). The final part of the colon is called “sigmoid” because of its serpentine curvature (“like a ”). Finally, food passes into the (“straight [intestine],” a misnomer given that this structure is actually somewhat cortorted) and then to the anus, thought by some to get its name from the Latin word anus meaning “,” though it is also suggested that the term is connected with the Sanskrit word meaning “to sit.”