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.