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Chordata Excretory System

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Chordates produce waste products through metabolic processes, and these wastes are removed from the body with the excretory system. In this lesson we'll discuss the types of wastes produced and just how these animals deal with them.

Phylum Chordata

You have likely heard of the phylum Chordata because you yourself are part of this diverse group of animals. Ranging from the very small to the very large, from animals with shells to animals with fur, from those that fly to those that swim in the sea, Chordata incorporates a vast group of animals all over the planet.

And while they may not all look the same, they are similar in that they produce wastes through metabolic processes and these wastes need to be removed from their bodies. This is accomplished in a number of different ways depending on the animal. These processes are performed by the excretory system, which quite literally serves to excrete wastes from the body.

Nitrogenous Wastes

The body of a chordate is constantly working, and a lot of waste is produced during that metabolic work. Nitrogenous wastes are one such product, and different chordates excrete it in different ways. For example, some animals excrete their nitrogenous waste as ammonia, while others excrete it as urea, and others still as uric acid.

Ammonia is a very toxic metabolic waste product, while urea and uric acid are both relatively non-toxic. Because of its toxicity, ammonia excretion occurs most often in animals that live in aquatic environments. Here, they have plenty of water to dilute the ammonia, which is not possible for land animals. Despite its toxicity, ammonia is a very efficient form of waste excretion for these animals because it readily leaves the body in aquatic environments.

Ammonia is best released into aquatic environments because it can be diluted.
fish swimming

Urea, which is about 100,000 times less toxic than ammonia, does not need to be diluted with so much water, so we tend to see this type of metabolic waste excreted from land animals, such as mammals, adult amphibians (their juveniles live in aquatic environments and may excrete ammonia during that life phase), and turtles. Uric acid is less toxic than both ammonia and urea and requires less water in order to be excreted from the body. Birds and reptiles usually excrete uric acid.

Water Regulation

Animals need water in their bodies. but they need just the right amount: too much water and their cells will burst, too little water and they will shrivel and die. The excretory system is a big part of maintaining this critical balance, which we call osmoregulation. During this active process, animals control how much water is in their bodies by excreting salts and other solutes that they take in from food, water, and the surrounding environment. For example, a tuna lives in very salty water, and that salt enters its body when it drinks. When there is too much salt, the tuna excretes it through a very concentrated urine, releasing those salts from its body and back into the sea.

Solid Excretion

Some chordates are special in that they can excrete liquids and solid wastes from food separately, yet other chordates do not have this ability. For example, mammals excrete solid food waste through their large intestine and anus. They excrete liquid wastes separately through the urinary system (which we'll get to in a moment). But animals like reptiles and birds simply excrete everything together through one opening, creating a very liquidy feces-like substance.

Birds excrete solids and wastes together in one substance.
bird excreting waste

How Wastes are Excreted

The human urinary system is a critical component of the excretory system.
human urinary system

So, now that we know about types of waste removed from the body, let's talk about how these wastes are excreted. For many chordates, the urinary system is a critical component of the excretory system. It is made up of organs such as the kidneys and bladder, structures such as a urethra or cloaca, and even arteries such as the aorta.

The urinary system is responsible for both creating and excreting urine, which it does to regulate the amount of water and solutes within the body. Amazingly enough, the urinary system also works closely with hormones in your body that signal when you start to become dehydrated or when there is too much fluid in your body.

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