Excretory system in Humans

Excretory system in Humans

Table of Contents

Introduction of Excretory system in Humans


Imagine your body as a busy factory. Just like any factory, it produces waste products during its everyday operations. Excretion is the vital process by which our body gets rid of these unwanted materials.

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  • Removing excess water and salts: Too much water or salt disrupts the balance in our body fluids, affecting functions like blood pressure. Excretion keeps these levels in check.
  • Eliminating harmful byproducts: Cellular processes create waste products that can be toxic if allowed to accumulate. Excretion ensures their timely removal.

Human Excretory System

This amazing system acts like our body’s personal cleaning crew, consisting of several organs working together:

  • Kidneys: These bean-shaped wonders filter waste products and excess water from the blood, forming urine.
  • Ureters: These tubes transport the urine from the kidneys to the bladder.
  • Bladder: This muscular sac stores urine until it’s released from the body.
  • Urethra: This tube acts as the final exit point for urine to leave the body.

Main Organs of the Excretory System


Two bean-shaped organs located just below the rib cage, on either side of the spine. They are about the size of a clenched fist.

Diagram showing human kidney anatomy

  • Nephrons: Microscopic filtering units within each kidney. There are about 1 million nephrons in each kidney.

The Nephron

Function of Kidneys

The kidneys are vital organs responsible for several crucial bodily functions:

  • Blood filtration and waste removal: They filter waste products, excess fluid, and toxins from the blood. These wastes are then excreted in urine.
  • Regulation of blood pressure, blood pH, and electrolyte balance: Kidneys maintain a healthy balance of water, salts, and minerals like sodium, potassium, and calcium in the blood. This balance is essential for proper nerve and muscle function.
  • Production of hormones: Kidneys produce hormones like erythropoietin, which stimulates red blood cell production, and renin, which helps regulate blood pressure.


Nephrons are the functional units of the kidneys, acting as tiny filters. Each nephron consists of two main parts:

  • Glomerulus: A network of tiny blood vessels where the initial filtration happens. Blood pressure pushes fluid and waste products from the blood into a capsule surrounding the glomerulus.
  • Tubule: A long, winding tube where reabsorption and secretion occur. Here, the filtered fluid is further processed:
    • Reabsorption: Essential components like water, glucose, and electrolytes are reabsorbed back into the bloodstream.
    • Secretion: Waste products like urea, uric acid, and excess minerals are secreted into the filtrate, forming urine.

Filtration process within a nephron:

  1. Blood enters the glomerulus: Blood pressure forces fluid and waste products from the blood into the glomerular capsule. Blood cells and large proteins stay behind in the bloodstream.
  2. Filtration: The filtered fluid, now called filtrate, contains water, waste products, and some electrolytes.
  3. Reabsorption: As the filtrate travels through the tubule, essential elements like water, glucose, and electrolytes are selectively reabsorbed back into the bloodstream.
  4. Secretion: Waste products like urea, uric acid, and excess minerals are actively secreted from the blood into the filtrate.
  5. Urine formation: The remaining fluid, now containing mostly waste products, becomes urine. This urine flows out of the kidney through thin tubes called ureters to the bladder for storage and eventual elimination.


Paired tubes: There are two ureters, one for each kidney. They are thin, muscular tubes about 20-30 cm (8-12 inches) long and 3-4 mm wide.

The Urinary System - Wellspect


  • The ureters start at the renal pelvis (funnel-shaped area) of each kidney.
  • They travel down the abdomen behind the peritoneum (lining of the abdominal cavity).
  • They then enter the pelvis (bowl-shaped cavity at the base of the spine) and curve towards the bladder.
  • Finally, they enter the bladder at an angle to prevent urine from flowing back up to the kidneys.


  • The ureters act as pipelines, carrying urine produced by the kidneys down to the bladder for storage.
  • The muscular walls of the ureters help to propel urine through peristalsis (wave-like muscle contractions).

Urinary Bladder

Bladder, internal human organ. Anatomy of the human organ. Medicine, healthcare and science. infographic banner

Structure and Location:

  • Imagine a muscular balloon in your lower belly, close to your pelvic bone. That’s your bladder!
  • It’s mostly hollow with stretchy walls that allow it to expand as it fills with urine.


  • The bladder acts like a storage tank for urine.
  • As waste products are filtered by your kidneys, they travel down thin tubes called ureters and empty into the bladder.
  • A healthy adult bladder can hold around two cups (400-600 ml) of urine for several hours.

Micturition Reflex (Emptying the Bladder)

Given below is a diagram showing the functioning of the micturition reflex in humans. Identify the correct statements: I: The region designated as 'X' in the diagram is the sacral region of

  1. Filling Up: As the bladder fills with urine, it stretches, sending signals to your brain.
  2. Feeling the Urge: When the stretch gets strong enough, your brain sends messages back down.
  3. Muscle Action:
    • The bladder muscles (detrusor) squeeze to push urine out.
    • At the same time, circular muscles around the urethra (sphincters) relax to open the passage.
  4. Emptying: Urine flows out of the bladder through a tube called the urethra and exits the body.


  • Function: This tube acts like a highway, carrying urine from the bladder out of the body.
  • Location: It’s found in the pelvic region, below the bladder.

The Differences:


  • Length: Think longer straw – around 15-25 cm (6-10 inches).
  • Path: The tube runs through the prostate gland and then travels along the underside of the penis.

Urethra: Location, Anatomy, Function, & More - Healthroid


  • Length: Think shorter straw – around 4 cm (1.5 inches).
  • Path: Straighter route – directly from the bladder to the opening between the labia minora (the folds of skin around the vagina).

Physiology of Excretion

Waste Products

  • Category: Nitrogenous waste
  • Origin: Breakdown of proteins in the body.
  • Examples:
    • Urea: Main waste product, produced in the liver.
    • Uric Acid: Formed during the breakdown of nucleic acids.
    • Creatinine: A waste product from muscle metabolism.

These waste products contain nitrogen, which can be harmful if allowed to accumulate in the body.

Blood Filtration

Imagine your kidneys as giant filtration units. Here’s what happens inside:

  • Glomerulus: Tiny cluster of blood vessels acting as a filter.
  • Filtration Membrane: A thin barrier within the glomerulus that allows water and small molecules to pass through, but blocks larger blood cells and proteins.


  1. Blood enters the glomerulus: Blood pressure pushes fluid and waste products through the filtration membrane.
  2. Water and small molecules: Pass freely into a collecting tubule.
  3. Large molecules (blood cells, proteins): Remain in the bloodstream.

Urine Formation

Blood filtrate is not urine yet. Here’s the additional journey:

  1. Filtration: As mentioned earlier, water and small molecules move into the collecting tubule.
  2. Reabsorption: The body reabsorbs essential things like water, glucose, and salts back into the bloodstream through the tubule walls.
  3. Secretion: If there’s excess waste or unwanted substances, they are secreted from the blood into the collecting tubule.

Importance of Reabsorption

  • Water conservation: Most of the filtered water (around 99%) is reabsorbed. This prevents dehydration and maintains body fluid balance.
  • Essential nutrients: Glucose, amino acids, and salts are reabsorbed to prevent their loss from the body.

Disorders of the Excretory System

Here are some common excretory system disorders:

Kidney stones: Hard deposits of minerals and salts that form in the kidneys. These stones can cause severe pain when they pass through the urinary tract.

Kidney Stones: Symptoms, Diagnosis, Precautions & Treatment - KDAH Blog -  Health & Fitness Tips for Healthy Life
  • Urinary tract infections (UTIs): Infections that occur in any part of the urinary system, including the kidneys, ureters, bladder, and urethra. UTIs are most common in women.


Best Urinary Tract Infections Treatment & Diagnosis India – RG Hospital
  • Kidney failure: When the kidneys can no longer properly filter waste products and excess fluid from the blood. This can be caused by a variety of factors, including diabetes, high blood pressure, and autoimmune diseases.

    Bladder and kidney problem illustration


Here’s a conclusion summarizing the human excretory system:

The human excretory system acts as a silent guardian, continuously working behind the scenes to maintain a healthy internal environment.

  • Kidneys, the powerhouses of this system, meticulously filter blood, removing nitrogenous wastes, excess water, and other unwanted substances.
  • Through a coordinated effort of ureters, the bladder, and urethra, these waste products are efficiently eliminated as urine.
  • This process not only expels harmful toxins but also plays a crucial role in:
    • Regulating blood pressure and blood volume
    • Maintaining electrolyte balance
    • Controlling blood pH


The excretory system doesn’t solely focus on five specific functions, but rather plays a vital role in maintaining a healthy internal environment through several key actions:

  • Filtering waste products: The excretory system primarily removes excess substances, like ammonia and urea, produced during cellular processes.
  • Balancing water and electrolytes: It regulates the body’s water content and maintains a healthy balance of salts and minerals essential for various bodily functions.
  • Regulating blood pressure: The kidneys play a crucial role in controlling blood pressure by influencing blood volume and electrolyte composition.
  • Contributing to red blood cell production: The excretory system produces a hormone called erythropoietin (EPO) that stimulates the bone marrow to generate red blood cells.
  • Maintaining pH balance: The kidneys help regulate the body’s acid-base balance by eliminating excess acid and conserving essential chemicals.

The main excretory organs work together to eliminate waste and maintain internal balance:

  • Kidneys: These bean-shaped organs act as filtration units, removing waste products and excess water from the blood.
  • Ureters: These thin tubes transport the filtered urine from the kidneys to the bladder.
  • Urinary bladder: This muscular sac serves as a temporary storage reservoir for urine until it’s expelled from the body.
  • Urethra: This tube acts as the final pathway, allowing urine to exit the body.

Excretion involves a continuous process:

  1. Blood filtration: Waste products and excess fluids in the blood pass through tiny filters within the kidneys called nephrons.
  2. Selective reabsorption: Essential nutrients and water are reabsorbed back into the bloodstream.
  3. Urine formation: Waste products and excess water that are not reabsorbed form urine.
  4. Transportation and storage: Urine travels down the ureters to the bladder for temporary storage.
  5. Elimination: When the bladder reaches a certain fullness, muscles contract, and urine flows out through the urethra.

There are three main ways the body eliminates waste products:

  • Urinary excretion: The primary mode, where the excretory system removes water-soluble wastes like urea and excess water through urine.
  • Respiratory excretion: The lungs eliminate carbon dioxide, a gaseous waste product of cellular respiration.
  • Sweat: The skin excretes sweat, containing water, salts, and some waste products, helping regulate body temperature and eliminate some toxins.

Urine formation boils down to three key steps in the kidneys:

  1. Filtration: Blood pressure pushes water and waste products through tiny filters.
  2. Reabsorption: Essential elements like water and salts are returned to the blood.
  3. Secretion: Unwanted materials are added to the filtrate.


  1. What is the primary function of the excretory system in humans?

    • a) To remove waste products from the body
    • b) To regulate body temperature
    • c) To produce hormones
    • d) To aid in digestion
  2. Which organ in the human body is primarily responsible for filtering blood and producing urine?

    • a) Liver
    • b) Kidneys
    • c) Lungs
    • d) Heart
  3. What is the functional unit of the kidney responsible for filtering blood and forming urine?

    • a) Glomerulus
    • b) Nephron
    • c) Ureter
    • d) Bladder
  4. Where is urine temporarily stored before it is eliminated from the body?

    • a) Kidneys
    • b) Ureters
    • c) Bladder
    • d) Urethra
  5. What is the name of the process by which waste products are removed from the blood and transported to the kidneys?

    • a) Digestion
    • b) Circulation
    • c) Filtration
    • d) Respiration
  6. Which of the following is NOT a waste product excreted by the kidneys?

    • a) Urea
    • b) Creatinine
    • c) Insulin
    • d) Uric acid
  7. The tubes that carry urine from the kidneys to the bladder are called:

    • a) Nephrons
    • b) Ureters
    • c) Urethra
    • d) Bladders
  8. The process of expelling urine from the bladder is known as:

    • a) Excretion
    • b) Micturition
    • c) Digestion
    • d) Circulation
  9. Which of the following organs is NOT part of the human excretory system?

    • a) Liver
    • b) Stomach
    • c) Skin
    • d) Lungs
  10. What is the role of the urethra in the excretory system?

    • a) To filter blood
    • b) To produce urine
    • c) To carry urine from the bladder to the outside of the body
    • d) To store urine temporarily
  11. Which hormone regulates the concentration of water excreted by the kidneys?

    • a) Insulin
    • b) Antidiuretic hormone (ADH)
    • c) Estrogen
    • d) Testosterone
  12. Which of the following substances is reabsorbed by the kidneys back into the bloodstream during urine formation?

    • a) Glucose
    • b) Urea
    • c) Creatinine
    • d) Uric acid
  13. The outer layer of the kidney is called the:

    • a) Cortex
    • b) Renal cortex
    • c) Medulla
    • d) Renal medulla
  14. Which of the following is a function of the excretory system?

    • a) Producing enzymes for digestion
    • b) Removing nitrogenous wastes
    • c) Regulating body temperature
    • d) Storing vitamins
  15. What is the functional significance of the loop of Henle in the nephron?

    • a) Filtration of blood
    • b) Secretion of hormones
    • c) Concentration of urine
    • d) Absorption of nutrients
  16. Which blood vessel carries blood to the kidneys for filtration?

    • a) Renal vein
    • b) Renal artery
    • c) Aorta
    • d) Inferior vena cava
  17. Which of the following is a common symptom of kidney dysfunction?

    • a) Increased urine production
    • b) Presence of blood in urine
    • c) Decreased thirst
    • d) Increased appetite
  18. Which of the following is the primary component of urine?

    • a) Glucose
    • b) Protein
    • c) Red blood cells
    • d) Water
  19. Which of the following conditions is characterized by the formation of kidney stones?

    • a) Hemophilia
    • b) Diabetes mellitus
    • c) Nephrolithiasis
    • d) Osteoporosis
  20. What is the normal pH range of human urine?

    • a) 5-7
    • b) 8-10
    • c) 4.6-8
    • d) 2-4

Answer Key:

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