Many Animals Have a Cloaca, But Humans Should Not

By: Alia Hoyt
A cross-section illustration of the internal anatomy of a male frog shows how all roads lead to the cloaca for urination, defecation and reproduction. Dorling Kindersley/Getty Images

Unless you've studied human or animal biology in depth, you've likely never heard of the cloaca (pronounced klow·ei·kuh). The norm in animals like reptiles, amphibians, birds and sharks, the cloaca is a common chamber where multiple body systems come together (the genital, intestinal and urinary tracts). From there, the cloaca has only one opening. So instead of having a separate anus, reproductive organ and urethra all with their own exterior access, as is typical with placental mammals, their systems empty out into the cloaca.

Although the cloaca sounds efficient, when it occurs in humans it presents major challenges. All human fetuses start off with a cloaca, but during a normal pregnancy it separates, forming the all-important urethra, anus and reproductive organ. Unfortunately, this doesn't go according to plan in roughly one in 50,000 female babies, leaving them with varying levels of cloacal deformity. Since the organs of both sexes have to pass through the stage of having a cloaca, anomalies occur in both, though the occurence in males is far less common than in females.


Why Don't Humans Have a Cloaca?

One of the reasons that a cloaca can't work in humans is because we have a bladder, whereas those other animals do not. "In an animal cloaca the ureter empties directly into the cloaca," explains Dr. Richard Wood, chief of the department of Pediatric Colorectal and Pelvic Reconstructive Surgery at Nationwide Children's Hospital in Columbus, Ohio. "There's no bladder, so that common area doesn't have a stasis of urine." In other words, the typical bladder holds urine in stasis until you're ready to let it out, so it's just sitting there.

This non-moving collection of urine that humans have is a big deal if a cloaca is present. "In the kids with cloacas the problem is mostly that they get bacteria from stool into their bladder and then the urine is static in their bladder," Wood says, noting that this causes recurrent bladder infections. "They also reflux urine commonly, [so it] can travel back up the ureters into the kidneys and that gives them kidney infections."


This is more than just a minor setback for these kids. According to Wood, between 20 and 50 percent of patients will end up with renal problems because of recurring damage to the kidneys. Many of those wind up requiring a kidney transplant. "That's why very early on, in the first couple of days of life, we start to fix it," Wood says.

Stool and urine blockages aren't the only problem with having a cloaca, however. Sexual intercourse is impossible without reconstruction, but in most cases proper treatment will help the patient to eventually lead a normal sex life.

As Wood says, surgery in the first days of life is necessary to stabilize the patient. A loop colostomy is done to redirect stool to an opening in the abdomen. A catheter is also used to help the bladder drain urine. The vagina may also suffer from urine build-up, and thus could require decompression.

The visible cloaca of a kākā parrot (Nestor meridionalis septentrionalis).
Judi Lapsley Miller/Wikimedia Commons (CC BY 4.0)

Reconstruction is the next step, but the process depends on how high up the deformity is and how long the common channel is. Typically, this begins between 6 months to 1 year of age. Reconstruction involving a child with a common channel of more than 1 inch (3 centimeters) is more complex than in a child with a smaller channel. However, the goal is the same. "At the end of it if you have a separate urethra, separate vagina and a separate anus," Wood says.

Although quality of life can be dramatically improved with proper reconstruction, it's really a lifelong process to treat a patient with cloacal deformation. "Many of these kids will need help with their function," Wood says, noting that the children especially need help at age 4 or 5 when it's time to focus on continence. "They're taken care of to be sure that they're clean and dry at school." The focus shifts as they approach maturity, especially when they start menstruating and becoming sexually active. Adults often also need help with fertility issues.

"They get care from beginning to end, which hopefully means less kidney problems long-term and less psychological problems," Wood says.

Nobody knows for sure why some children are born with cloacas. However, Nationwide Children's has set up a consortium of 15 sites around the United States to gather information. "Genetics is an area where we're going to concentrate research going forward," Wood explains. Thanks to this cooperative effort, there are now more than 2,500 patients enrolled nationwide, and doctors also track patients lifelong to find out the challenges that adult patients are facing. "The key to doing this research is understanding that the greater goal is to help the kids," Wood says.


Cloaca FAQ

What is the function of the cloaca?
The cloaca is a common chamber with only one opening where multiple body systems come together, including the genital, intestinal, and urinary tracts. Simply put, there is no separate anus, reproductive organ, and urethra all with their own exterior access — everything empties into the cloaca.
Do humans have a cloaca?
Adults don't have a cloaca — they simply wouldn't work, in large part because we have a bladder. But fetuses start off with one in the womb. During a normal pregnancy it separates, forming the urethra, anus, and reproductive organ. However, this separation doesn't happen for roughly one in 50,000 female babies who are born with a cloaca and suffer serious health complications because of it.
What does a cloaca look like?
A cloaca is just an orifice that, on many animals, isn't visible until it's open. In some animals, it's just a hole that looks a lot like an anus. For other animals, like snakes, it's a small slit or vent.
What animals have a cloaca?
All amphibians, reptiles, birds, sharks, and a few mammals (monotremes, tenrecs, golden moles, and marsupial moles) have a cloaca.
What does cloaca mean?
The word cloaca is from the Latin verb cluo, "to cleanse". Therefore the noun means "sewer".
Do turtles breathe through their cloaca?
Some turtles rely on cloacal respiration when diving for long periods of time or hibernating in bodies of water during winter when the temperatures drop below freezing and become covered in ice. These creatures have a pair of accessory air bladders that are connected to the cloaca that can absorb limited amounts of oxygen from the water keeping them alive. Technically, it's respiration, not breathing.