The gastrointestinal tract, also known as the gut or alimentary canal, is a tube by which bilaterian animals (including humans) transfer food to the digestion organs. In large bilaterians, the gastrointestinal tract generally also has an exit, the anus, by which the animal disposes of solid wastes. Some small bilaterians have no anus and dispose of solid wastes by other means (for example, through the mouth).
Animals that have gastrointestinal tracts are classified as either protostomes or deuterostomes. The digestive tract evolved separately in these two clades, an example of convergent evolution. The clades are distinguished based on their embryonic development: protostomes develop their mouths first, while deuterostomes develop their mouths second. Protostomes include arthropods, molluscs, and annelids, while deuterostomes include echinoderms and chordates.
For more specific information on digestive organs, see specialized organs and behaviours.
Uses of animal guts by humans
- The stomachs of calves have commonly been used as a source of rennet for making cheese.
- The use of animal gut strings by musicians can be traced back to the third dynasty of Egypt. In the recent past, strings were made out of lamb gut. With the advent of the modern era, musicians have tended to use strings made of silk, or synthetic materials such as nylon or steel. Some instrumentalists, however, still use gut strings in order to evoke the older tone quality. Although such strings were commonly referred to as "catgut" strings, cats were never used as a source for gut strings.
- Sheep gut was the original source for natural gut string used in racquets, such as for tennis. Today, synthetic strings are much more common, but the best gut strings are now made out of cow gut.
- Gut cord has also been used to produce strings for the snares that provide a snare drum's characteristic buzzing timbre. While the modern snare drum almost always uses metal wire rather than gut cord, the North African bendir frame drum still uses gut for this purpose.
- "Natural" sausage hulls, or casings, are made of animal gut, especially hog, beef, and lamb.
- The wrapping of kokoretsi, gardoubakia, and torcinello is made of lamb (or goat) gut.
- Haggis is traditionally boiled in, and served in, a sheep stomach.
- Chitterlings, a kind of food, consist of thoroughly washed pig's gut.
- Animal gut was used to make the cord lines in longcase clocks and for fusee movements in bracket clocks, but may be replaced by metal wire.
- The oldest known condoms, from 1640 AD, were made from animal intestine.