Human Excretory System

Topic: LIVING THINGS AND THEIR ENVIRONMENT — Subject: Integrated Science (Age 12, Kenya)

What is excretion?
Excretion is the process by which the body removes waste products made by cells. These wastes would be harmful if they stayed in the body.

Main jobs of the excretory system

• Remove waste chemicals from blood (like urea and extra salts).
• Keep the amount of water and salts in the body balance (homeostasis).
• Help control blood pressure and keep the internal environment stable.

Important organs

• Kidneys – two bean-shaped organs that filter blood and make urine.
• Ureters – tubes that carry urine from each kidney to the bladder.
• Bladder – a stretchy bag that stores urine until we pass it out.
• Urethra – the tube through which urine leaves the body.
• Skin – gets rid of some water and salts through sweat.
• Lungs – remove carbon dioxide and small amounts of water vapour when we breathe out.

Simple diagram: How urine moves

Inside a kidney (simple)

The kidney filters blood to form urine. Each kidney contains tiny filters called nephrons. Nephrons remove wastes and take back useful substances (like glucose and some water).

How urine is formed — short steps

1. Blood enters the kidney and passes through tiny filters (glomeruli).
2. Filtration: water, salts, and wastes (like urea) pass into nephron.
3. Reabsorption: useful things (glucose, some water, salts) are taken back into blood.
4. Secretion: extra wastes are added into the tubule from blood.
5. Urine collects in the pelvis, goes down the ureter to the bladder and is released via the urethra.

Other ways the body removes wastes

• Skin: sweat removes water and salts.
• Lungs: remove carbon dioxide when we breathe out.
• Digestive system: solid wastes (faeces) leave through the anus.

Why the excretory system is important

• Prevents build-up of harmful wastes like urea.
• Helps keep water and salt balance — important in hot climates like many parts of Kenya.
• Helps control blood pressure and overall health.

How to keep your excretory system healthy (simple tips)

• Drink enough clean water every day (helps kidneys wash out wastes).
• Eat a balanced diet (vegetables, fruits, grains, some protein).
• Wash hands and stay clean to avoid infections (UTIs).
• Avoid too many salty or sugary foods and drinks.
• Go to the toilet when you need to — do not hold urine for too long.
• See a doctor if you have pain when passing urine, blood in urine, or very little urine.

Common problems (very simple)

• Urinary tract infection (UTI) — pain when passing urine; needs treatment from a health worker.
• Kidney stones — hard bits that can cause strong pain; hygienic drinking habits and medical help are needed.
• Dehydration — not enough water; can make urine dark and kidneys work poorly.

Simple classroom activity

Model filtration: Use a clear plastic bottle, cotton/wool, sand, and charcoal. Pour muddy water into the top and let it pass through layers into a cup. Discuss how the layers act like filters — not the same as a kidney but helps show filtering and clean water.

Key words (short)

• Excretion — removing wastes from the body.
• Kidney — organ that filters blood.
• Nephron — tiny filter in the kidney.
• Ureter, bladder, urethra — tubes and storage for urine.
• Homeostasis — keeping internal conditions steady.

Quick check (try answering)

1. Name the two main organs that filter blood.
2. Where does urine collect before leaving the body?
3. Mention one way to keep the excretory system healthy.

Summary: The human excretory system removes wastes and keeps water and salts balanced. The kidneys are the most important organs for this job. Drink safe water, stay clean and eat well to keep your excretory system working properly.