Human Excretory System

 

Definition

The excretory system is the system responsible for removing metabolic waste products from the body. These wastes must be eliminated to maintain the body’s balance (homeostasis) and prevent poisoning of cells.

Organs of the Human Excretory System

 

1. Kidneys

   • Function: Filter blood to remove urea, excess salts, and water, forming urine.
   • Structure: Each kidney contains millions of nephrons as the functional unit.
   • Urine passes from the kidneys to the bladder through the ureters.

   
   
   
   
    

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      pic taken from hopkinsmedicine.org 

      

      

      pic taken from diseasefix.com

      

     • Process of Urine Formation

       Urine is formed in the nephrons, which are the functional units of the kidneys. The process consists of three main stages:

        

     • Filtration (in the Glomerulus)

       • Blood enters the glomerulus under high pressure.

       • Water, salts, glucose, amino acids, and urea are filtered into Bowman’s capsule.

       • Large molecules (such as proteins and blood cells) remain in the blood.

     • Reabsorption (in the Proximal Tubule and Loop of Henle)

       • Useful substances such as glucose, amino acids, most water, and some salts are reabsorbed back into the blood.

       • This ensures the body does not lose essential nutrients.

     • Secretion (in the Distal Tubule and Collecting Duct)

       • Additional wastes such as hydrogen ions, potassium ions, and drugs are actively secreted into the tubule.

       • This helps maintain the acid-base balance of the body.

     Final Product

     The remaining fluid is urine, which contains:

   • Water (about 95%)

   • Urea (a waste product of protein metabolism)

   • Salts and minerals (Na⁺, K⁺, Cl⁻)

   • Other waste substances

   Urine then flows from the collecting ducts → renal pelvis → ureters → urinary bladder → urethra, and is excreted out of the body.

    

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2. Skin

    

   pic taken from thedermspecs.com 

    

   • Function: Excretes sweat through sweat glands.

   • Sweat contains water, salts, and a small amount of urea.

   • Also helps regulate body temperature.

3. Lungs

    

   Pic taken from byjus.com 

   • Function: Remove carbon dioxide (CO₂) and water vapor as waste products of respiration.

   • Gas exchange occurs in the alveoli.

4. Liver

   • Function: Processes toxic substances and breaks down excess amino acids.

   • Produces urea and bile pigments (from the breakdown of hemoglobin).

      

      

 Pic taken from geeksforgeeks.org

 

Substances Excreted by the Human Body

• Urine (from kidneys): urea, salts, excess water.

• Sweat (from skin): water, salts, small amount of urea.

• Carbon dioxide and water vapor (from lungs).

• Bile pigments (from liver, excreted with feces).

   

  
  

Disorders of the Excretory System

1. Kidney Stones – Solid deposits of minerals in the kidney that block urine flow.

2. Nephritis – Inflammation of the nephrons, often caused by infection.

3. Uremia – Accumulation of urea in the blood due to kidney failure.

4. Jaundice – Liver disorder causing yellowing of the skin due to bile pigment buildup.

5. Emphysema – Damage to the alveoli, reducing lung function.