The Excretory System for Middle School Science

May 8

11 min read

Think of your body as a busy city. Just like a city produces trash that needs to be collected and taken away, your body also creates waste as it performs its daily functions. If that waste isn’t removed, it can cause problems, just like garbage piling up on city streets. The excretory system is your body’s waste management system. It includes organs like the kidneys, bladder, lungs, and skin, which all work together to collect and remove unwanted materials. This system keeps everything clean and balanced inside your body, helping you stay healthy and feeling good. In this chapter, you’ll discover how the excretory system works and why it plays such a vital role in keeping your body city running smoothly.

You can check out the pages of my body system unit from Teachers Pay Teachers below. You can also continue on to read more about the respiratory system.

The Excretory System

Every moment, your body is hard at work—breaking down food for energy, repairing tissues, and supporting countless chemical reactions that keep you alive. But just like a busy engine or factory, these processes create waste products. If these wastes were left to build up, they could become toxic and harmful to your health. That’s where the excretory system comes in. This essential system is responsible for filtering out and removing unwanted materials from the body, including extra water, salts, carbon dioxide, and other waste chemicals.

The excretory system isn’t made up of just one part—it includes several organs that work together to keep your internal environment clean and balanced. The kidneys filter waste from the blood to form urine, which is then stored in the bladder until it’s released. The lungs help remove carbon dioxide, a waste gas created when cells use oxygen. Even your skin plays a role by releasing waste through sweat.

Without the excretory system, your body wouldn’t be able to function properly. It helps maintain homeostasis, the stable conditions your cells need to survive. In this chapter, you’ll explore the parts of the excretory system, how they work together, and why this system is one of the most important for keeping your body safe, clean, and healthy.

Functions of the Excretory System

Your body is always working to keep everything running smoothly. As it digests food, uses energy, and repairs cells, it also creates waste that must be removed. If this waste builds up, it can make you sick. That’s why the excretory system is so important. It keeps your body clean on the inside by removing waste and keeping important balances just right. Let’s explore the major functions of this system.

Removing Waste Products

The excretory system’s most important job is to get rid of waste your body doesn’t need. When cells do their work, they create waste products like urea and carbon dioxide. The kidneys remove urea from the blood and send it out as urine. The lungs remove carbon dioxide when you breathe out. Your skin also helps by sweating out some waste products along with water and salt.

Maintaining Homeostasis

The excretory system helps keep the body in balance, or in homeostasis. For example, your kidneys control how much water, salt, and acid are in your blood. If you drink a lot of water, your kidneys make more urine to get rid of the extra water. If you don’t drink enough, they save water to keep you from getting dehydrated. This balance keeps your cells healthy.

Regulating Blood Pressure

Your blood pressure depends on how much fluid is in your blood and how wide your blood vessels are. The kidneys help control this by deciding how much water to keep or release. They also make hormones that signal your blood vessels to tighten or relax, helping to keep your blood pressure at a healthy level.

Cooling the Body

When you exercise or it’s hot outside, your body uses sweat to cool down. Your sweat glands, which are part of the skin, release water mixed with small amounts of salt and waste. This not only lowers your temperature but also helps the excretory system remove extra materials.

The excretory system does much more than help you go to the bathroom. It plays a key role in removing harmful waste, keeping your body’s fluids balanced, supporting healthy blood pressure, and even helping you stay cool. Without it, your body couldn’t stay clean or function properly. That’s why the excretory system is one of the body’s most important helpers in keeping you safe and healthy every day.

Parts of the Excretory System

The excretory system is made up of several organs that work together to remove waste and keep the body in balance. Each part has a special job, and together they form a powerful cleaning system for your body.

Kidneys

You have two kidneys, located on either side of your spine, just below your ribcage. These bean-shaped organs act like filters for your blood. They remove waste like urea, extra salts, and extra water, turning it into urine. Kidneys also help control your blood pressure, body fluid levels, and electrolyte balance.

Ureters

The ureters are thin tubes that carry urine from the kidneys to the bladder. Each kidney has its own ureter. The urine travels down these tubes using small muscle movements.

Bladder

The bladder is a stretchy, muscular sac that stores urine until you are ready to go to the bathroom. When it fills up, your body sends a signal to your brain, letting you know it’s time to release the urine.

Urethra

The urethra is the tube that carries urine out of the body from the bladder. It has muscles that control when urine is released, so you don’t go until the right time.

Skin

The skin is also part of the excretory system. It gets rid of some waste through sweat glands. Sweat helps cool your body down and removes small amounts of salt, water, and waste products.

Lungs

The lungs are usually known for breathing, but they also help remove waste. When you breathe out, your lungs release carbon dioxide, a gas waste made by your body’s cells.

Liver

The liver helps break down harmful substances in the blood, like drugs and toxins. It also changes some waste into forms the kidneys can remove more easily.

Each of these parts plays a role in keeping your body clean and working well. Together, they make sure waste is removed and your body stays in balance.

All About the Liver

The liver is one of the largest and most important organs in your body. Located on the right side of your abdomen, just below your lungs, the liver plays a key role in keeping your body clean and healthy. While it does many things, one of its most important jobs is to help the excretory system remove harmful substances from the body.

Filtering Toxins

Every day, your liver filters your blood to remove toxins—harmful chemicals that can come from foods, drinks, medicines, or even things your body naturally makes. The liver changes these toxins into less harmful substances that can be removed by your kidneys, intestines, or sweat glands.

Breaking Down Waste Products

The liver breaks down old red blood cells and turns part of them into a yellow substance called bilirubin. This is sent to the intestines in bile and removed from the body through solid waste (feces). If bilirubin builds up, it can cause a yellowing of the skin and eyes called jaundice.

Processing Medicines and Alcohol

When you take medicine or drink alcohol, your liver goes to work right away. It helps break down these substances so they don’t harm your body. This is why doctors are careful about how much medicine people take—too much can overwhelm the liver.

Producing Urea

Your body makes waste when it digests protein from food. The liver changes this waste into a substance called urea, which is then sent to the kidneys to be removed in urine.

Storing Nutrients

Even though this isn't a waste-removal job, it's worth mentioning: the liver stores vitamins, minerals, and sugars to give your body energy when it needs it. This helps keep your body in balance, which is part of how the excretory system works too.

The liver is like a built-in chemical lab and storage unit all in one. Without it, your body couldn’t safely get rid of many of the substances it doesn’t need. That’s why taking care of your liver—by eating well, drinking water, and avoiding harmful substances—is so important!

What Your Urine Can Tell You

Urine is more than just waste—it's a helpful sign of what's going on inside your body! Doctors often use urine tests to check health. Here are some important things your urine can tell you:

Hydration Level

One of the easiest things to learn from your urine is whether you’re drinking enough water.

Clear or pale yellow = You’re well hydrated.
Dark yellow or amber = You might need more water.
Very dark or brownish = Could be a sign of dehydration or a medical issue.

Signs of Infection

Cloudy urine, or urine that smells bad, can be a sign of a urinary tract infection (UTI). A doctor may test your urine for bacteria or white blood cells to confirm it.

Kidney Health

If your kidneys aren't working properly, proteins or blood may show up in your urine. This can be a warning sign that your kidneys need help.

Blood Sugar Levels

If someone has diabetes, sugar might appear in their urine. Normally, urine does not contain sugar, so this is something doctors look for in tests.

Color and Diet

Sometimes, the food you eat can change the color of your urine. For example:

Eating beets might turn urine pink or red.
Taking vitamins can make urine bright yellow or even orange.This isn’t usually a problem—it just shows how closely your body reacts to what you eat and drink!

Urine is like a window into your body's health. It helps your body get rid of waste, but it also gives doctors useful clues. That’s why urine tests are common during checkups—your body may be sending important messages!

Sweat

When you exercise, get nervous, or it’s a hot day, your body starts to sweat. But sweat does more than just cool you off—it’s also part of your excretory system and helps your body stay healthy.

Why Do We Sweat?

Sweat helps control your body temperature. When your body gets too hot, your sweat glands release water through your skin. As the sweat evaporates, it cools you down.

What’s in Sweat?

Sweat is mostly water, but it also contains small amounts of:

Salt (sodium)
Urea (a waste product also found in urine)
Other minerals and waste chemicals

This means that when you sweat, your body is not just cooling off—it’s also getting rid of waste!

Where Does Sweat Come From?

Your skin has millions of sweat glands, especially on your hands, feet, underarms, and forehead. These glands are part of your integumentary system (skin system), but they work closely with your excretory system to help remove waste.

Does Everyone Sweat the Same?

Not exactly. Some people sweat more than others, and things like temperature, exercise, emotions, and even what you eat can change how much you sweat.

Sweating is a natural and healthy way your body keeps cool and cleans itself. If you didn’t sweat, your body could overheat or hold onto waste it needs to release. So while it may not always feel great, sweating is a sign that your body is doing its job!

The Kidneys

The kidneys are two bean-shaped organs located in your lower back, just below your rib cage—one on each side of your spine. Though small (about the size of a fist), the kidneys do an incredibly important job: they help clean your blood and keep your body balanced.

Filtering Waste

Every day, your kidneys filter about 50 gallons of blood! They remove waste products, extra water, and toxins that your body doesn’t need. This waste leaves your body as urine.

Balancing Body Fluids

Your kidneys help keep the right balance of water, salt, and minerals in your blood. This balance is important so that your muscles, nerves, and other organs can work properly.

Controlling Blood Pressure

The kidneys also help regulate your blood pressure by controlling the amount of fluid in your body and by releasing hormones that tighten or relax your blood vessels.

Producing Important Hormones

Besides filtering, the kidneys produce hormones that:

Help make red blood cells
Keep your bones healthy
Control your blood pressure

Even though you only need one working kidney to survive, keeping both healthy is important. Drinking water, eating healthy, and avoiding too much salt or sugar can help protect your kidneys.

Understanding Dialysis

Sometimes, a person’s kidneys stop working properly. Since the kidneys are in charge of filtering waste and extra fluid from the blood, it’s a big problem if they stop doing their job. That’s where dialysis comes in.

When kidneys fail, waste builds up in the blood. This can make someone very sick. Dialysis is a medical treatment that does the job of the kidneys—it cleans the blood when the kidneys can’t.

There are two main types of dialysis:

Hemodialysis: A machine is connected to a person’s blood vessels. The machine pulls out the blood, filters it, and then sends the clean blood back into the body.
Peritoneal Dialysis: A special fluid is put into the belly through a soft tube. This fluid soaks up waste and extra water from the blood vessels in the body’s abdomen. Then the fluid is drained out, taking the waste with it.

Most people who use hemodialysis go to a clinic three times a week for a few hours each time. People using peritoneal dialysis may do it at home, often once or several times each day, or overnight while they sleep.

Dialysis helps people live longer and stay healthier, but it’s not a cure. Some people may need dialysis for the rest of their lives, while others might get a kidney transplant, which could allow them to stop dialysis altogether.

Dialysis is a critical treatment for people with kidney failure. It takes the place of their kidneys and keeps their blood clean and balanced. Thanks to dialysis, many people with kidney disease can live active, full lives.

How the Excretory System Interacts with Other Body Systems

The excretory system doesn’t work alone—it’s part of a team of systems that keep your body healthy. It helps remove waste, but it relies on other systems to do its job. Let’s look at how they work together.

Circulatory System

The blood carries waste materials—like carbon dioxide, extra water, and urea—from all parts of the body to the organs of the excretory system. The kidneys filter these wastes out of the blood, and the cleaned blood goes back into circulation.

Respiratory System

Your lungs, which are part of the respiratory system, are also part of the excretory system! They remove carbon dioxide, a gas your body doesn’t need. You breathe it out every time you exhale.

Digestive System

The digestive system breaks down food and absorbs nutrients, but it also creates solid waste. The large intestine collects and removes this leftover waste, working as a partner with the excretory system to keep your body clean.

Integumentary System (Skin)

Your skin has sweat glands that help remove excess salt, water, and some waste products. Sweating is one way the excretory system cools your body and gets rid of waste at the same time.

Nervous System

The brain controls when and how you get rid of waste. It tells your bladder when it’s full and sends signals to help you urinate or sweat. Without the nervous system, your excretory system couldn’t react at the right times.

Your body systems work together like parts of a machine. The excretory system depends on other systems to deliver waste and to help remove it. That’s how your body stays clean, balanced, and healthy!

Flashcards on the Excretory System

Flashcards are the best way to practice remembering new information. You can get digital and printable flashcards at Teachers Pay Teachers, or you can use the flashcards here for free!