Excretory System in Humans: quick revision, 15 bites

What Is Excretion?

Waste removal keeps you alive.

Wastes are **toxic or poisonous** and must be removed so a person stays healthy.

Takeaway. Excretion = removal of cell-produced wastes; the excretory system does this job.

The Three Main Waste Products

Your body makes three key wastes.

Urea enters the blood and makes it **impure**; if not removed constantly, the person will soon die.

Takeaway. Carbon dioxide, urea and sweat are the main wastes produced in human body cells.

Organs of Waste Removal

Three organs, three different wastes.

Takeaway. Lungs, kidneys and sweat glands are the three main excretory organs in humans.

The Human Urinary System: 4 Organs

Four organs, one liquid waste.

Takeaway. The urinary system = 2 kidneys + 2 ureters + bladder + urethra.

Inside the Kidney: Cortex, Medulla, Renal Pelvis

Two regions and a funnel-shaped exit.

Each kidney has **millions of nephrons** — its microscopic filtering units.

Takeaway. Kidney = cortex (outer) + medulla (inner) + renal pelvis; functional units are nephrons.

How a Nephron Forms Urine

Filter, reabsorb, collect — that's urine.

Takeaway. Filtration in Bowman's capsule + reabsorption in the tubule = urine formation.

Nephron Parts You Must Name

Bowman's capsule + tubule = nephron.

Bowman's capsule + urinary tubule together make **one nephron**.

Takeaway. Nephron = Bowman's capsule (with glomerulus) + urinary tubule.

Composition of Urine

95% water, 5% waste.

An adult normally passes **1 to 1.8 litres** of urine per day.

Takeaway. Urine is 95% water, 2.5% urea, 2.5% other waste salts.

Other Excretory Organs: Skin, Lungs, Liver

Kidneys aren't the only cleaners.

Takeaway. Skin, lungs and liver are accessory excretory organs alongside the kidneys.

Why Sweat Cools You Down

Sweat isn't just waste — it cools.

Takeaway. Sweat evaporation removes heat, making you feel cool.

Urea vs Urine — Don't Confuse Them

Urea isn't urine.

Takeaway. Blood carries urea; urine is formed only after filtration in the kidney.

UTI vs Kidney Stones

Two very different urinary problems.

Takeaway. UTIs are infections treated with antibiotics; kidney stones are mineral deposits that may need surgery.

Urine Colour Tells Your Hydration

Clear urine = good health.

Pale yellow or clear urine is generally a sign of **good health**. The more water you drink, the clearer your urine looks.

Takeaway. Clear/pale urine signals good hydration and health.

Must-Underline Lines for Exams

These lines score marks.

Takeaway. Memorise these exact definitions and facts for full marks.

Remember the Urinary Path

K-U-B-U: the urine highway.

Urine path: **K**idney → **U**reter → **B**ladder → **U**rethra. Remember as **'KUBU'** — Kids Use Bathroom Urgently.

Takeaway. KUBU = Kidney → Ureter → Bladder → Urethra.