Tuesday, April 14, 2026

Biology – Excretory System

Excretion 

- The process of removing waste products from the body.  
- Metabolic wastes such as urea and carbon dioxide are poisonous, so they must be excreted regularly.  

Skin as an organ of excretion  

- The skin removes excess salts and water through sweat.  
- In summer, more water is lost through sweating, so less water is available for urine formation.  
- In winter, sweating is reduced because the body needs to conserve heat.  

Urine formation and control  

- The sphincter muscles contract tightly to close the opening of the urethra, controlling the release of urine.  

Key points to remember  

- Excretion maintains balance in the body by removing harmful substances.  
- Sweating helps regulate both temperature and salt/water balance.  
- The excretory system works continuously to keep the internal environment safe and stable.  

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