Like all animals, amphibians need a way to remove waste materials from their body so it doesn’t build up and become toxic. The amphibian excretory system is similar to other vertebrates, but read this lesson to learn more.
Purpose of an Excretory System
Amphibians are vertebrates, or animals with a backbone, that begin life as aquatic organisms. When they undergo metamorphosis they develop lungs.
Mature amphibians may live in water, on land, or a combination of the two.Like any vertebrate, amphibians have an excretory system. What is the purpose of an excretory system? Well, the body produces waste products through cellular respiration, and these wastes need to be excreted from the body. If wastes aren’t removed from an organism, they will become toxic, so the body works to efficiently eliminate it. Eliminating waste also allows the body to maintain the proper balance of salts and other nutrients.
Excretory System in Amphibians
The most common type of waste produced through metabolic processes is nitrogenous wastes.
Nitrogenous wastes form from the natural breakdown of proteins in the body. Amphibians have two kidneys, just like humans, and those kidneys filter wastes out of the blood and combine them with water to form urine. Urine then travels from the kidneys via the ureters to the bladder, and then out through the cloaca.
The cloaca, or vent, is an opening used for the excretory, intestinal, and reproductive tracts of amphibians. Urine leaves the body through the cloaca when the bladder is full.Nitrogenous wastes can take one of three forms: ammonia, uric acid, and urea. Due to different life stages or strategies, different groups of amphibians produce different forms.
Let’s go over these waste forms and how they’re dealt with by different groups.Ammonia is water soluble and is the most toxic form of nitrogenous waste. It becomes harmful if not diluted quickly. Ammonia changes the pH in cells to rise to dangerous alkaline levels if too much of it remains in the body.Juveniles, like frog and toad tadpoles, and aquatic species of amphibians excrete their nitrogenous wastes as ammonium because they aren’t worried about conserving water, because they live in it, and the ammonia is quickly taken away by the current.
With a little energy investment, ammonia can be turn into urea by enzymes in the liver. Urea is a less toxic form of nitrogenous waste. It requires less water to excrete, doesn’t affect the pH the same as ammonia can, and so is safer to have in the body. Terrestrial amphibians have less access to water than the aquatic ones, so the majority of them produce urea.Uric acid is the least toxic of all three forms of nitrogenous waste.
It is insoluble and so needs the least amount of water, but is the most energetically expensive to make. A few species of tree frogs excrete uric acid because they have very limited access to water.
Who knew there was so much to learn about an amphibian’s excretory system? Nitrogenous wastes are formed through normal metabolic processes, and the kidneys are responsible for filtering these wastes out of the blood. The kidneys produce urine that is excreted from the body through the cloaca, an opening in amphibians used for the excretory, intestinal, and reproductive tracts.
Nitrogenous wastes can be present as ammonia, urea, or uric acid. There are different energetic costs for developing each form and they require different quantities of water. However, some forms are less toxic than others, so ecology dictates which type is formed.Aquatic species excrete ammonia because they are not worried about not having enough water to dilute it.
Terrestrial species convert waste to urea because it requires less water and decreases the probability of waste becoming toxic in the body. Arboreal species like tree frogs excrete uric acid to conserve limited water.