In fish, birds and amphibians, the cloaca -- also known as the vent -- serves as the exit cavity for the excretory, urinary and reproductive systems. Male and female frogs both have cloacas, which their respective reproductive tracts use as the vehicle for the passage of sperm and eggs.
Urinary and Excretory Functions
A frog's digestive system starts in the mouth and ends at the cloaca. After food enters the mouth, it heads down the esophagus to the stomach. From there, it proceeds to the small intestine, where food becomes processed into nutrients. What remains continues on to the large intestine, which absorbs remaining water. The final step ends with the feces exiting out the cloaca. In both sexes, the bladder connects to the frog's kidneys through the urinary ducts, or ureters, which empty into the cloaca. The bladder stores the urine until the frog excretes it.
Female Frog Cloaca
A female frog's ovaries, clogged with eggs, lie next to her kidneys. Oviducts connect her ovaries to her two "uteruses," which are simple extensions at the end of the oviducts. These extensions open directly into her cloaca. When the female frogs release eggs, these ducts also secrete a gel-like substance that covers the eggs and protects them.
Male Frog Cloaca
A male frog's testes rest near his tail area, one on the front of each of his kidneys. Parts of his urinary ducts serve as vessels that create semen and allow the collection of sperm. When he mates, his sperm is released through the urinary ducts into his cloaca and then out of his body.
Amplexus in Frogs
In frogs, amplexus refers to mating, specifically a mating embrace of the female by the male. The male frog wraps his front legs around the female, holding her just behind her forelegs. This embrace causes the female to release her eggs through her cloaca, which he then fertilizes as his sperm simultaneously leaves his cloaca. The gel covering the thousands of eggs laid by the female swells up after fertilization, protecting the newly emerged eggs. Depending on the species, tadpoles hatch from the eggs in approximately 30 to 40 days.
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