What does the kidney do in the body?

In one line

The rule

The kidney is an organ in the excretory system that filters blood to remove waste products and excess water, helping to maintain the body's internal balance of water, salts, and nutrients. (NCERT, Class 10)

Let's understand it simply

Imagine your house has a water filter. Dirty water goes in, clean water comes out, and the dirt is thrown away. Your kidney works like that filter. Blood flows into the kidney. The kidney removes the 'dirt' (waste and extra water) from your blood. This waste leaves your body as urine.

How it works

1. Blood enters the kidney through a blood vessel.
2. Tiny filters inside the kidney (called nephrons) separate waste and extra water from the blood.
3. Clean blood goes back into your body.
4. The waste and extra water become urine.
5. Urine travels down tubes (ureters) to the bladder, where it is stored until you pee.

The story behind it

Scientists have studied kidneys for centuries, but the real breakthrough came in the 1800s when doctors learned how kidneys filter blood. The invention of the microscope helped them see the tiny nephrons inside the kidney. Today, we know a healthy kidney is vital for life.

Where you see it in real life

• After drinking a lot of water → you pee more → kidneys remove extra water.
• When you eat salty food → kidneys balance the salt in your blood.
• If you have not drunk enough water (like on a hot day) → your urine is dark yellow → kidneys save water for the body.
• People with kidney problems need dialysis (a machine cleans their blood) → shows how important kidneys are.
• When you feel tired and weak after not peeing for long → waste is building up in your blood.

Why it matters

• Keeps your blood clean and healthy.
• Controls the amount of water and salts in your body.
• Removes harmful substances, so you don't get sick.
• Without kidneys, waste would poison your body.
• Many medicines and treatments depend on healthy kidneys.

Common mistakes

• Thinking kidneys only make urine—they also balance water and salts.
• Believing you can live normally with no kidneys—you need at least one, or a machine (dialysis).
• Forgetting that kidneys also help control blood pressure.

Remember it

Kidneys are your body's natural filter—cleaning blood and making urine.