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Urinary / Excretory System

Our bodies are constantly making things and breaking them down. This generates a lot of waste. Of course, we can’t just keep it all! Fortunately, we have the urinary/excretory system to clean up. The urinary/excretory system is the organ system which processes and gets rid of waste. It’s kind of like the body’s own garbage disposal.

Illustration of the excretory system in a transparent human.

How do we generate waste?

On the surface, we are stable organisms. Sure, you might look a little different from day to day. Still, you’ll appear more or less the same a few weeks from now.

But, we have to be careful: This stability can fool us! In reality, our bodies are in constant operation. It takes a lot of work to maintain a solid organism.

On the microscopic level, our cells act like little workers. They constantly build new things and tear others down in a process called metabolism. Metabolism is the set of cell-level, chemical reactions which keep our body working.

Our cells are like tiny builders. They work all the time to maintain our stable bodies.

Our cells are like tiny builders. They work all the time to maintain our stable bodies.

These reactions are messy! When we break things down, like food for energy, we make things we don’t need. You can see this is in everyday life, too. For example, when you eat a banana, you’re left with the peel, which is waste.

A banana peel is the waste leftover from eating a banana. We can just throw away the peel, but when our cells eat they cannot

A banana peel is the waste leftover from eating a banana. We can just throw away the peel, but when our cells eat they cannot

This is because not every part of a food is useful. The same is also true on a microscopic level. But, when cells ‘eat,’ they leave their waste inside of our body. So, we need a way to get rid of it.

How do we get rid of the different kinds of waste?

Solid Waste

Solid waste is usually leftover from food. This leaves the body after going through the digestive system. When we digest food, we’re just taking the useful parts from it. After it has been fully digested, all that’s left is the solid waste.

This ends up in the large intestines. The large intestine are part of both the digestive and excretory organ systems. As part of the excretory system, their job is to take solid waste and form feces. It’s kind of gross, but that’s the main way we get rid of solid waste. This waste leaves the body through the rectum.

Liquid Waste

The disposal of liquid waste is where the urinary system comes into play. Our bodies actually generate a lot of dangerous liquid waste. For one, the process of metabolism makes what are called nitrogen compounds. These are toxic waste products which will circulate in our blood until disposed of. Additionally, water itself can be waste! If we have too much, our body will get rid of some of it through the urinary system.

The urinary system starts with the kidneys. These organs are like filtration devices for the body. They separate waste and excess water out of our blood for removal. When blood passes by a kidney, it is ‘cleaned.’ This means that waste compounds separate out into the kidney. The kidney will then reabsorb any non-waste material trapped with the waste. The leftover waste product is called urine.

A diagram showing the location of the kidneys

A diagram showing the location of the kidneys

When all that’s left is urine, it will leave the kidney through a tube called the ureter. The ureter connects to the bladder, an organ which stores urine until the body is ready to get rid of it. When there is enough urine in the bladder, it will exit the body through another tube called the urethra.

Gaseous Waste

Finally, there’s a pretty simple kind of waste removal we do every few seconds: breathing. When we breathe out, we’re getting rid of carbon dioxide. This is a waste product generated by metabolism in our cells. After being made by our cells, it dissolves in the blood and moves to the lungs. There, it is converted into a gas so that we can exhale it.

Urinary / Excretory System

When we exhale in the cold, we can see the gaseous waste leave our body.

Other Great Resources:

How the Kidneys Work:

Organs that Get Rid of Waste: https://sciencing.com/organs-rid-wastes-produced-cells-6785572.html
The Urinary/Excretory System and Homeostasis: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/homeo/homeostasis1.shtml
The Excretory System: http://www.mcwdn.org/body/excretory.html

Written by: Noah Louis-Ferdinand