Excretory System: Function, Parts, and Main Organs

2.3.2025 0 comments

Author: Trisha Houghton, CNS, ASIST

The human excretory system is one of the most crucial of your internal systems.

Every function of the human body—from processing of nutrients to absorbing oxygen to producing cellular energy—produces some form of waste.

If all those waste products remained in your body, they would gum up the works and impede the efficient functioning of your internal organs, tissues, and systems.

Thanks to your excretory system, though, your body can get rid of all the waste byproducts and keep your body running optimally.

In this article, we’re going to take a deep dive into excretory system function and structure. We’ll look at the various excretory organs that do the work of purging wastes from your body and what role each plays.

We’ll examine the basic step-by-step process by which waste is eliminated, look at some of the most common excretory system disorders, and last of all, look at solutions for maintaining good excretory system health.

By the end, you’ll have a much better understanding of just how important this particular system is and what you can do to keep it running smoothly for better overall health!

Introduction to the Excretory System

To maintain balance, the excretory system relies on both passive and active processes. An example of a passive process in the body is diffusion, where water and small particles move without the use of energy.

Oppositely, an example of an active process in the body is when our kidneys reabsorb glucose or electrolytes, or naturally fine tune our pH levels. These required the use of energy.

Both processes collaborate to ensure our systems are getting rid of waste in an energy efficient manner so that homeostasis is maintained throughout the body.

Eliminating waste, in the form of both liquid and gaseous matter, is crucial for maintaining chemical homeostasis in the body and preventing the damage that an accumulation of waste byproducts can cause.

Typically, the term “excretory system” is used primarily to refer to the urinary system. However, given that other organs and glands also participate in waste elimination, it’s important to understand the full scope of this crucial system.

Primary Functions of the Excretory System

Below are the main functions of the human excretory systems explained.

Waste Elimination

Waste is a natural byproduct of every cellular process, from breaking down sugar for energy to producing ATP energy to power your muscles. Left in your body, waste products can cause damage or slow down internal functions.

Removing the metabolic wastes from your body ensures your internal systems can run smoothly and efficiently.

Regulation of Blood Composition

The excretory system also plays a role in maintaining a good electrolyte balance.

Electrolytes are minerals like calcium, potassium, chloride, sodium, magnesium, and phosphate that contain an electric charge, and they all contribute to healthy bodily function.

There is a delicate balance between all of these minerals, but that balance can be altered or thrown off when you are dehydrated or overhydrated. Kidney problems, excessive sweating, diarrhea, vomiting, and certain medications can also impact your electrolyte balance.

One of your excretory system’s functions is to restore that balance and make sure your body has enough fluid, salt, and minerals.

Detoxification

A truly crucial function of the excretory system is to eliminate toxins, chemicals, and harmful substances from your blood.

Your kidneys are made up of millions of filtering units (while we’ll explore more fully below) that detect and eliminate harmful substances present in your bloodstream. Those toxins and chemicals are then excreted via your urine before they can damage your body.

pH Balance

Maintaining the right pH balance (a balance between acidity and alkalinity) is crucial for healthy bodily function.

The human body has an average pH level of 7.4, but each organ has its own pH level. The stomach, for example, is incredibly acidic with a pH between 1.5 and 2.0, while the colon tends to be far more alkaline with a pH between 7.9 and 8.5.

Each organ functions optimally at its specific pH level. Certain digestive enzymes require a low pH in order to break down the food you eat, while others require a high pH level.

Your excretory system works to regulate the pH level of extracellular fluid in your body. If your body senses your pH levels are too high or too low, your kidneys work to restore them to optimal levels (a process that takes a few days).

Homeostasis

Ultimately, the human body functions best when in chemical homeostasis, or a “stable internal environment”.

Removing wastes and chemical byproducts is a crucial function that contributes to homeostasis.

Main Organs of the Excretory System

The excretory system is made of multiple functional units that contribute to its overall function. Below is a breakdown of the main organs involved in the process.

Kidneys

The primary organs involved in urinary system function are the kidneys, two bean shaped organs located next to your spinal column.

Each human kidney is about 10 to 12 centimeters long, 5 to 7 centimeters wide, and weighs anywhere from 120 to 170 grams. But though small, the kidneys are incredibly complex and powerful organs. They filter an average of 113 to 142 liters of blood per day and produce anywhere from 0.95 to 1.95 liters of urine per day.

Blood vessels, nerves, and the ureter enter the two kidneys on the inner concave side. The blood that flows into your kidneys passes through nephrons, which are the filtering units in the kidneys.

Millions of nephrons (made up of glomerulus and renal tubules) act to filter the chemicals, toxins, and waste products out of the blood. The filtered blood then continues on through the renal vein to be distributed to the body.

The wastes that the nephrons filtered from the blood are combined with the salts, excess water, and urea likewise filtered. That combination is called urine. Urine passes through the ureters and out the kidney to continue their journey down the excretory system.

Kidney Function and Urine Production

The kidneys filter waste, balance fluids, and produce urine to maintain overall health.

This process involves several key stages:

• Filtration: Blood flows through the nephrons in the kidneys, where glomeruli filter out excess fluid and waste products.
• Reabsorption: The tubules in the nephrons use active transport to return essential nutrients, such as glucose and electrolytes, to the bloodstream, maintaining proper chemical and fluid balance.
• Secretion: Remaining waste combines into urine, which the kidneys transport through the ureters to the bladder for storage.
• Excretion: Once the bladder is full, the body expels urine through the urethra, removing waste in liquid form.

This structured process ensures that the body effectively manages waste elimination while preserving essential nutrients, fluid, and ionic balance.

Ureters

Ureters are thin muscular tubes (called ducts sometimes) that transport urine produced in the kidneys to the bladder. Each ureter is about 25 to 30 centimeters long, long enough to pass through the pelvic bones and enter the bladder.

Valves (called the ureterovesical valves) ensure that the transport of urine remains one-way and prevents backflow.

Bladder

The bladder, also called the “urinary bladder”, is another of the urinary system organs. Its main function is to store the urine and waste produced by the kidneys.

The hollow, muscular organ can expand (distend) to make space for more urine. The triangle-shaped balloon-like organ can usually store around 500 milliliters of urine. They filter an average of 113 to 142 liters of blood per day and produce anywhere from 0.95 to 1.95 liters of urine per day.

Urethra

Once the bladder fills up and the micturition (urination) process is triggered, the urine flows from the bladder down the urethra, which serves as the exit for liquid waste.

(Note: In males, sperm also exits the body via the urethra.)

Sphincter muscles in the urethra prevent backflow of urine, ensuring the chemicals and liquid wastes travel on a one-way trip to excretion.

Other Organs Involved in Excretion

The body relies on multiple organs to efficiently remove waste and maintain internal balance. Beyond the kidneys, ureters, bladder, and urethra, several other organs play important roles in the excretion of waste products.

Lungs

Your lungs are absolutely crucial for healthy excretory system function. Their job is to excrete the carbon dioxide that is a waste product of cellular respiration (absorbing and utilizing oxygen).

Carbon dioxide is pulled from the blood via the alveoli in the lungs, then expelled via your exhalations. Water vapor and trace levels of other “waste gases” are also expelled as you breathe out.

Removing carbon dioxide and these gaseous wastes from the bloodstream is crucial for maintaining homeostasis.

Skin

The skin is part of your body’s integumentary system which protects the body from damage, but it also plays a crucial role in excretion.

The sweat glands in your dermis produce sweat, which helps your excretory system maintain homeostasis by excreting excessive salt and fluid. The skin even excretes small amounts of urea via your sweat (which is why sweat can smell bad).

Liver

The liver gets into the action before the kidneys, breaking down toxins and chemicals so your kidneys can absorb and excrete them.

The liver also breaks down ammonia (which is produced when amino acids are catabolized) and turns it into urea for the kidneys to excrete. The liver also plays a key role in detoxifying harmful substances, such as alcohol and drugs, from the bloodstream. It processes bilirubin, a byproduct of red blood cell breakdown, and excretes it into bile, which is eventually eliminated through the digestive system.

The bile and bilirubin produced by the liver play a central role in the elimination of solid waste (fecal matter) via the large intestine.

Large Intestine

While the kidneys and bladder deal with liquid waste, your large intestines excrete solid waste—typically fiber and undigested food.

The large intestine’s job is to remove the last of the water from waste matter from the small intestine so it’s easier to excrete. It also mixes in the bilirubin that contains the waste byproducts collected by and excreted from the liver.

It’s both one of your most important excretory organs and a crucial component of your digestive tract.

How the Excretory System Works: Step-by-Step Process

The excretory system follows a precise sequence to filter waste and maintain the bodys internal balance.

Below is a step-by-step overview of how this system functions:

• Step 1: Blood flows into the kidneys via the renal artery.
• Step 2: Nephrons in the kidneys filter excess fluids, salts, chemicals, and harmful substances from the blood.
• Step 3: Tubules return critical nutrients and fluids to the blood, which exits the kidneys through the renal vein. The kidneys produce urine by combining the leftover waste products with urea.
• Step 4: Urine flows down the ureter and into the urinary bladder, which serves to store urine prior to excretion.
• Step 5: When full, the bladder works to eliminate urine via the urethra.

At the same time all of this is happening, excess urea is excreted via the skin, carbon dioxide is expelled from the lungs with every exhalation, and the liver and large intestine work together to filter out and excrete harmful substances via fecal matter.

Together, all of these organs work to maintain internal homeostasis.

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Common Excretory System Disorders

Disruptions in the excretory system can lead to waste buildup and severe health problems. Below are common disorders that affect this system.

Kidney Stones

Kidney stones are clusters of crystals formed from the minerals, salts, and acids filtered out of your bloodstream. These stones tend to form as a result of too much uric acid, calcium-oxalate, or calcium phosphate present in your body.

Kidney stones can be small enough to pass through the urinary tract unnoticed, but when larger, can cause severe pain and trigger other symptoms (including fever, vomiting, bloody pee, and nausea). People who don’t drink enough fluids, eat a lot of protein-rich and high-sodium foods, or take certain medications (like antacids or diuretics) may be at higher risk of kidney stones.

Urinary Tract Infections (UTIs)

UTIs are infections that affect parts of the urinary system, including the kidneys, bladder, urethra, and sometimes the renal pelvis. They are caused by bacteria in your urine.

Bacteria typically enter the urinary tract through the urethra and can spread upward to the bladder, ureters, and even the kidneys.

Symptoms of a UTI include localized pain, pressure in your lower pelvis, urinary incontinence, pain when you pee, fever, nausea, vomiting, and chills.

Chronic Kidney Disease (CKD)

Chronic Kidney Disease, or CKD, is a condition in which your kidneys are damaged (either by an injury or a chronic condition like diabetes or high blood pressure) and their function diminishes.

The damage reduces their ability to filter waste from the blood. The greater the damage, the more your kidney function is reduced, and the more serious the long-term risks to your body overall.

Symptoms of chronic kidney disease include tiredness, low energy, loss of appetite, weakness, shortness of breath, swelling in your hands, feet, and ankles, puffy eyes, dry and/or itchy skin, and sleeping difficulties, among others.

Liver Cirrhosis

Liver cirrhosis is scarring caused by chronic inflammation in your liver. It is typically the result of excessive alcohol consumption, excess fat storage, hepatitis C, hepatitis B, cardiovascular disease, autoimmune disease, or genetic disorders.

The scarring reduces liver function and prevents it from filtering toxins and wastes out of your bloodstream.

Liver cirrhosis may start with minor symptoms (including fatigue, nausea, loss of appetite, and malaise), but can become serious, even fatal over time.

Respiratory Acidosis

Respiratory acidosis is a condition in which your respiratory system is unable to filter sufficient carbon dioxide from your body, which results in high blood acidity.

It may be caused by a number of respiratory conditions—including acute pulmonary edema, ALS, COPD, asthma, MS, scoliosis, obesity, or pulmonary fibrosis—and can be serious, potentially even fatal.

Maintaining Excretory System Health

Good excretory system health is absolutely crucial for optimal body function. Your body needs the excretory system firing on all cylinders to eliminate wastes and maintain homeostasis.

Here are a few simple yet very effective solutions for keeping your excretory system healthy:

• Drink plenty of water. Sufficient fluid intake is essential for kidney and urinary function, as well as healthy digestion. Dehydration can lead to electrolyte imbalances, decreased kidney function, reduced urination, and a buildup of toxins in the body.
• Eat a balanced diet. Eat a low-sodium diet to reduce kidney stones, and make sure to get enough dietary fiber to facilitate digestive system health and efficient elimination of wastes from your gastrointestinal tract. Anti-inflammatory and antioxidant-rich foods like blueberries, cauliflower, strawberries, olive oil, bell peppers, garlic, cabbage, and arugula will all contribute to better kidney and liver health.
• Exercise. Daily exercise improves blood flow (including to your kidneys) and facilitates the elimination of waste products through your entire excretory system, including your large intestines, lungs, and skin.

• Avoid toxins. Reduce your exposure to harmful chemicals and pollutants, toxic artificial food substances, and UV radiation.
• Get regular health checkups. Monitoring your kidney, liver, and bladder function will help you catch signs of decreased activity or potential damage before it gets serious.

Protecting the excretory system is of great importance because its primary function is to remove waste and maintain the body’s internal balance. A healthy excretory system also supports the central nervous system by preventing toxin buildup that can disrupt overall body function.

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Conclusion

Our excretory systems are responsible for keeping everything running smoothly by clearing away waste products that could slow down organ function.

The kidneys filter the blood, preserving red blood cells while removing excess minerals and other substances, which are then concentrated into urine within the collecting duct. The bladder, along with the skin, lungs, and large intestines, works to eliminate additional wastes and harmful substances that would otherwise build up.

By adopting the habits we suggested above, you can maintain good excretory system health and ensure your body can always get rid of harmful wastes.

FAQs

Which side is your bladder on?

The bladder is located in the center of the pelvis, between your hip bones. Pain or discomfort resulting from a full or infected bladder will typically be felt in the middle of your pelvis or lower abdomen, not on either side of the body.

What happens if waste is not removed from the body?

If waste products, especially nitrogenous waste, aren’t removed from the body, cells stop functioning properly, and toxic substances can damage tissues and organs. Excess water retention can raise blood pressure, and waste buildup can overwhelm the lymph nodes and bone marrow, weakening the immune system and blood cell production. Your skin may develop disorders or bumps as a sign of poor waste elimination, and symptoms like bad breath, fatigue, and constipation can also indicate ineffective waste removal.

How do you know if you have too much waste in your body?

Signs of too much waste in the body include fatigue, sleep problems, food intolerances, weight gain or loss, digestive issues, heartburn, headaches, mood changes, and bad breath, to name just a few.

How does the excretory system know when to release urine?

The excretory system uses nerve impulses and brain signals to control urination. As the bladder fills, stretch receptors send nerve impulses to the brain. In response, the brain sends signals to trigger the urge to urinate. These signals also coordinate the relaxation of the bladder muscles and the urethral sphincter, allowing urine to be released.

What is the role of afferent and efferent arterioles in kidney function?

Afferent arterioles carry blood into the glomeruli of the nephrons for filtration. After filtration, efferent arterioles transport the filtered blood away from the glomeruli. This process helps regulate blood pressure in the kidneys and controls how much blood is filtered to remove waste and maintain fluid balance.

How does the kidney filter and process waste in the nephron?

The filtration process in the nephron begins in the Bowmans capsule, which surrounds the glomerulus and collects filtered blood plasma. From there, the filtrate moves into the renal tubule, starting with the proximal convoluted tubule, where water, glucose, and essential nutrients are reabsorbed. It then passes through the distal convoluted tubule, where the balance of salts, water, and pH is further adjusted before waste continues to the collecting duct for excretion.

Resources

Urinary System

Excretory System

Excretory System

Introduction to the Urinary System

16.2 Organs of Excretion

pH in the Human Body

Your Kidneys & How They Work

Urinary Tract Infections

Kidney Stones

Chronic Kidney Disease

Cirrhosis of the Liver

Respiratory Acidosis

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