Enteral respiration, also referred to as cloacal respiration or intestinal respiration, is a form of respiration in which

gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a b ...

occurs across the epithelia of the enteral system, usually in the caudal cavity (

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

). This is used in various species as an alternative respiration mechanism in hypoxic environments as a means to supplement blood oxygen.

Turtles

Some

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

s, especially those specialized in diving, are highly reliant on

cloacal A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilaginou ...

respiration during dives. They accomplish this by having a pair of accessory air bladders connected to the cloaca which can absorb oxygen from the water.

Sea cucumbers

Sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

s use cloacal respiration via a pair of "respiratory trees" that branch in the

just inside the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

, so that they "breathe" by drawing water in through the anus, extracting

dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...

from water, and then expelling it. The "trees" consist of a series of narrow tubules branching from a common duct, and lie on either side of the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

Gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a b ...

occurs across the thin walls of the tubules, to and from the fluid of the main body cavity.

Other animals

Various

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

, as well as

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

worms and even

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s, are specialized to take advantage of the constant flow of water through the cloacal respiratory tree of sea cucumbers while simultaneously gaining the protection of living within the sea cucumber itself. At night, many of these species emerge from the anus of the sea cucumber in search of food. The pond loach is able to respond to the periodic drying in their native habitats by burrowing into the mud and exchanging gas through the posterior end of their alimentary canal. Studies have shown that mammals are capable of performing intestinal respiration to a limited degree in a laboratory setting. Mice were subjected to hypoxic conditions and supplied oxygen through their intestines survived an average of 18 minutes compared to 11 minutes in the control group. In 2024

Ig Nobel Prize The Ig Nobel Prize () is a satirical prize awarded annually since 1991 to promote public engagement with scientific research. Its aim is to "honor achievements that first make people laugh, and then make them think." The name of the award is a ...

an award in physiology has been given to a study proving that pigs are capable of this as well. When the intestinal lining was abraded before oxygen was introduced, most of the animals survived for at least 50 minutes. Investigations are planned regarding the effectiveness of the strategy, the safety of this application of

perfluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are ...

s, and the feasibility of application to humans. It has potential application to people with a

respiratory disease Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, ...

or lung damage.

References

{{Reflist Respiration Animal anatomy Digestive system

Turtles

Sea cucumbers

Other animals

See also

References