Excretion

Your kidneys are bean-shaped organs that filter waste from your blood to make urine. Each kidney contains about one million tiny units called nephrons. These nephrons work like sieves, allowing useful substances like glucose and water back into your blood while waste products like urea pass into the bladder. Think of it like how women in Lagos markets sort beans—keeping the good ones and removing the bad ones.

Your skin also excretes waste through sweat glands, releasing water, salt, and a tiny amount of urea. When you exercise or feel hot, like during harmattan season in northern Nigeria, your skin produces more sweat to cool your body down while removing these wastes simultaneously.

Both organs work together to maintain your body's water balance and remove nitrogen waste. Without them, poisonous substances would build up and damage your cells.

Your kidneys produce urine through three main stages. First comes **filtration**, where blood enters the kidney and useful substances like glucose and water get separated from waste products at the glomerulus. Next is **reabsorption**, where your kidney tubules bring back things your body needs—glucose, water, and salts—into the bloodstream. What remains is mostly urea and extra water, which forms urine. Finally, **collection** happens as this urine moves through the ureter into your bladder, where it's stored until you urinate.

Think of it like a market woman sorting tomatoes: she removes the rotten ones (waste) but keeps the good ones (useful substances). Your kidneys work similarly every single day to keep your body clean.