The city that never sleeps
Tanmay was lying on the floor after a cricket match, puffing and panting.
"My heart is going dhak-dhak-dhak," he said. "Why won't it calm down?"
Dadi sat down beside him. "Because your body is a busy city, and you just made every worker in it run overtime. Let me give you a tour."
1. The pump station: your heart
"Your heart is the city's pump station," said Dadi. "It's a muscle about the size of your fist. It pushes blood through tubes called blood vessels, the city's roads, all day and all night."
"What does the blood carry?" asked Tara.
"Like delivery trucks, it carries oxygen and food to every part of the city, and picks up waste to take away."
The rule: the heart pumps blood; blood delivers oxygen and food and collects waste.
2. The gas-swap office: your lungs
"Where does the oxygen come from?" asked Tanmay, still panting.
"From the air you breathe. Your lungs are a swap office. Oxygen from the air goes into your blood, and a waste gas called carbon dioxide comes out of your blood and leaves when you breathe out."
"So lungs clean the air?" asked Tara.
"Not quite. They swap gases. The tiny hairs and sticky mucus in your nose catch most of the dust before it gets far. That's why you should breathe through your nose when you can."
The rule: lungs take oxygen into the blood and send carbon dioxide out. It's a swap, not a filter.
3. The food factory: stomach and intestines
"And the food the trucks carry?"
"That starts at the mouth, where your teeth chop it and saliva makes it soft. Then the stomach, the mixing tank, churns it with strong juices. After that, a long, coiled tube called the small intestine breaks it down even more and passes the useful parts into the blood. What your body can't use moves on and leaves as waste."
"How long is that tube?" asked Tanmay.
"In a grown-up, the small intestine is several metres long, all folded up inside your tummy."
The rule: most of the food's goodness gets into your blood in the small intestine.
4. The control room and the city wall
"Who's in charge of all this?"
"The brain, the control room. It sends and receives messages along nerves, the city's telephone wires, faster than you can blink. And around the whole city is the skin, the city wall. It keeps germs out and keeps you at the right temperature."
"What about when germs get in anyway?"
"Then the city's guards, the white blood cells, go after them. Sometimes the control room turns up the city's thermostat: that's a fever. A mild fever is part of how your body fights germs."
"So a fever is good?" asked Tanmay.
"It's a sign that your body is fighting. But a high fever, or one that won't go away, means tell a grown-up straight away. They'll decide if a doctor is needed."
The rule: the brain controls the body through nerves; skin and white blood cells protect it. A fever is a sign to tell a grown-up.
5. Your turn: think like a city planner
- You breathe faster after running. Which two city workers are rushing, and why?
- Your hand touches a hot tawa and pulls back before you even think. Which city system sent that message so fast?
- Why does washing your hands before eating protect the city?
- Fatima's pulse was 88 and Tanmay's was 76, both sitting still. Does that mean one of them is unhealthy?
Check your answers
- The lungs (taking in more oxygen, sending out more carbon dioxide) and the heart (pumping it round faster). The muscles needed more oxygen, faster.
- The nerves, the city's telephone wires. For quick escapes like this, the message takes a shortcut through your spinal cord, which is why you move before you think.
- Hands carry germs. Washing stops them getting past the city gates, the mouth, along with your food.
- No. Healthy children's heartbeats differ from person to person and from day to day. One number on its own doesn't tell you much. Only a doctor should judge someone's health.
Fun fact: the longest roads
If all the blood vessels in a grown-up's body were laid end to end, scientists estimate they would stretch about 1,00,000 km: more than twice around the Earth. Most of that length is tiny vessels, thinner than a hair.
Where the story stops being true
- The body isn't really separate buildings. Every part works together and depends on the others.
- Cells aren't little workers who think. They follow chemical signals, not orders.
- A real city doesn't grow and repair itself. Your body does, every day: it heals cuts and replaces old cells.
- The "1,00,000 km" is a rough estimate. Different scientists give different numbers.
🧠 Logic corner
You used if-then and a fair test:
- If muscles work harder, then they need more oxygen, so then the heart should beat faster. That's a prediction.
- You tested it by measuring the same person, the same way, before and after marching. Changing only one thing is what makes it a fair test.
- In puzzle 4, you avoided jumping to a conclusion from just one number. That's careful reasoning.