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What Is a Cloaca?

By Cindy Quarters
Updated Jun 04, 2024
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A cloaca is a chamber that is found on some types of animals, especially birds and reptiles. Instead of having separate openings in the body for fecal matter, urine and reproductive fluids, all of these systems discharge their contents into the chamber, where they are eliminated through a single opening. This means that the cloaca is used for both elimination of waste and for breeding.

The cloaca is found in all kinds of birds, including everything from chickens, pigeons and geese to hummingbirds and eagles. Some mammals, such as the duck-billed platypus and the echidna, also have one, but most mammals have much more advanced reproductive and digestive systems. Reptiles such as lizards, snakes, turtles and crocodiles have a cloaca, but the males have some type of a penis as well, though the penis is only used for breeding and not for excreting urine.

When animals that have a cloaca breed, the manner in which the breeding is accomplished varies depending on the specific anatomy of the animal. In some cases they simply press their cloacae together, and the male passes sperm to the female through the openings. Other animals, particularly birds, have modified cloacae. The male has bumps or ridges in or near the area that help him to connect securely with the female to pass his sperm to her.

Reptiles and other animals with both a penis and a cloaca mate when the male inserts his penis into the female’s opening. His sperm then flows into her, where it provides the genetic material for the next generation. This mating can be very quick in many species, but in others the process can take a relatively long time.

All developing human embryos have cloacae, which fetuses use as they grow. Eventually the normal human reproductive and excretory systems form, replacing the single chamber. By the time a baby is born, it has no longer any visible signs of having had this primitive body system.

In some cases, the fetus does not develop the usual human systems, and a baby is born with a single opening in its body to handle all bodily excretions. In many cases the presence of a cloacal deformity indicates other significant and life-threatening problems in the baby’s anatomy, and in such cases immediate surgery is required in order to save the baby’s life. It is often possible for doctors to correct the problem and allow the patient to have a normal life, though in some cases he or she will always require assistance with elimination of body wastes.

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Discussion Comments
By croydon — On Oct 22, 2014

@pleonasm - It's fascinating that a human fetus will have a cloaca for a while as part of its development though. I've always thought there was something almost eerie about the fact that we go through different stages of evolution in the womb.

Although I don't know how they could possibly help a child born with a persistent cloaca. It seems like that would be a recipe for disaster.

By pleonasm — On Oct 21, 2014

@irontoenail - Well, it works for the animals who have it. They aren't the kind of animals that enjoy sex so much as just do it on instinct, however. And from what I remember, they often have problems in this area as well. Birds, particularly domestic birds, can become egg-bound very easily, which is when the egg gets stuck in the cloacal passage and it's almost always fatal without human intervention.

Honestly, I am happy that humans are mammals and reproduce the way we do. Laying eggs seems to be a very dangerous business from the start to the finish. Being pregnant isn't safe by any means, but I think it's safer than that.

By irontoenail — On Oct 21, 2014

I remember reading somewhere that this was actually a sort of proof that people weren't made from a clever design, because the 'playground' was so close to the 'sewage system' that it could cause problems. But I guess we've actually evolved to the point where there is a distinct difference between the two (or actually more than two) and cloacae show how bad it the alternative could be.

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