Urea is the primary waste product of protein metabolism in humans, excreted by the kidneys in urine.

Main Excretory Product in Humans
The primary excretory product in human beings is urea, which plays a crucial role in the body's waste elimination process. Here's a detailed explanation:
What is Urea?
- Urea is a nitrogenous compound formed in the liver from ammonia, a toxic byproduct of protein metabolism.
- It is less toxic than ammonia, making it safer for the body to transport and excrete.
Why Urea Over Other Excretory Products?
- Ammonia: Highly toxic and requires large amounts of water for excretion. This is why aquatic animals excrete ammonia directly.
- Uric Acid: Less toxic and conserves water, but it is not the primary excretory product in humans. It is more common in reptiles and birds.
- Creatinine: A breakdown product of creatine phosphate in muscle, but it is not the main waste product the body needs to eliminate.
Formation of Urea
- Urea is produced through the urea cycle in the liver, where ammonia combines with carbon dioxide.
- The kidneys filter urea from the blood, and it is excreted in urine.
Importance of Urea in Excretion
- Urea helps to regulate the body’s nitrogen balance.
- Its excretion is crucial for removing excess nitrogen from the body, maintaining homeostasis.
Conclusion
In summary, urea is the main excretory product in humans due to its less toxic nature and efficient removal from the body through urine. Understanding urea's role helps clarify why it is preferred over other nitrogenous waste products.