• Why we bleed when the skin is cut
• What blood carries, and how food and medicines reach it
• How the heart pumps blood to the lungs and the body
• Why heartbeat and breathing become faster when we exercise
• How to keep our heart healthy

Place your hand on your chest and feel your heart beating. Now place two fingers on your wrist and feel your pulse. Something inside you is moving all the time. What do you think it is carrying, and where is it going?

1. Blood and Blood Vessels

Blood is a very important fluid that keeps us alive and healthy. It flows through all parts of the body inside special tubes called blood vessels. On the back of your hand you can see some of them as faint lines under the skin.

What does blood carry?

• Oxygen from the lungs to every cell.
• Nutrients from food: glucose, fats, proteins, vitamins, minerals and water.
• Carbon dioxide and other wastes away from the cells.
• Medicines to the part of the body that needs them.

What is blood made of?

• Red blood cells contain haemoglobin, which carries oxygen.
• White blood cells help the body fight germs.
• Platelets help blood to clot and stop bleeding.

Why can blood reach every cell?

Our body is made of tiny cells, so small that you need a microscope to see them. Big arteries and veins cannot reach every cell. They branch into thinner and thinner tubes called capillaries, and capillaries reach all the cells. This is why a small cut anywhere on the skin can bleed. The hair we cut and the free edge of a nail do not contain blood vessels, so they do not bleed.

Reading a blood report

When someone is ill, a doctor may ask for a blood test. The report lists parts of the blood and a standard range for each. This is Rizu’s report:

All of Rizu’s values are inside the range. If a value is outside the range, the doctor looks for the reason and may suggest food, medicine or another test.

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2. How Food and Medicines Reach the Blood

Food is broken down by the digestive system. The nutrients from the food are absorbed into the blood mainly through the walls of the small intestine. The blood then carries glucose, fats, proteins, vitamins, minerals and water to every cell. Cells use glucose and oxygen to make energy. That is why we feel hungry after running or swimming: the body has used up a lot of energy.

What about medicines?

Khoji wondered how a medicine given in his hand could help his stomach. Simba wondered how a syrup could help his injured leg. The answer is the same for both: the blood carries medicine around the body.

• Syrup or tablet: it is swallowed, absorbed through the small intestine and enters the blood.
• Drip: a needle in the hand puts the medicine straight into a vein.
• Some injections go into a muscle first, and then the medicine enters the blood.
• Then the blood carries the medicine to the part of the body that needs it.

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3. The Heart and the Journey of Blood

The heart is a strong muscle that pumps blood. It is about the size of your fist and lies slightly to the left of the middle of your chest. It is divided into four chambers.

Your textbook calls the upper chambers auricles. Scientists usually call them atria. Valves in the heart keep the blood moving in one direction only, from the atria to the ventricles. Blood cannot flow backwards. The right side of the heart handles oxygen-poor blood, and the left side handles oxygen-rich blood.

Arteries, veins and capillaries

There is one special pair. The pulmonary artery carries oxygen-poor blood from the heart to the lungs, and the pulmonary veins carry oxygen-rich blood from the lungs to the heart. The whole network of the heart, blood and blood vessels is the circulatory system.

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4. Heartbeat, Breathing and a Healthy Heart

A heartbeat is one cycle of the heart squeezing and relaxing. When you listen to the heart, you hear a lub-dub sound. A doctor uses a stethoscope to hear it. The pulse is the throb of an artery that is pushed open by each heartbeat. You can feel it at your wrist, where an artery is close to the skin.

After running or jumping, your heartbeat and breathing become faster. Your muscles need more energy, and so they need more oxygen. Breathing brings oxygen into the body, and the heart pumps oxygen-rich blood to the muscles. So the heart beats faster to supply more oxygen where it is needed most.

How to take care of your heart

• Eat healthy food: fruits, vegetables, whole grains and nuts. Dates, figs, spinach and raisins have iron, which helps make haemoglobin.
• Limit salty and fried food: do not add extra salt, and eat fried or packet foods like chips only now and then. Baked or grilled food is better for the heart.
• Be active: try for 30 minutes of running, playing, swimming or cycling every day, in a way that suits your age.
• Drink water: about seven to eight glasses a day, especially when you are active.
• Sleep enough: rest lets your heart recover and stay strong.

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Picture Card 1: Blood Vessels in the Hand

Tube-like lines under your skin are blood vessels. Blood flows inside them.
Key idea: Blood travels inside tubes called blood vessels.

Picture Card 2: The Farm Pipe Idea

One big pipe splits into small pipes so that every sapling gets water.
Key idea: Artery ➜ capillaries ➜ vein. Capillaries are tiny vessels that reach every cell.

Picture Card 3: Food Enters the Blood

Digested food passes into the blood through the small intestine.
Key idea: Blood carries food nutrients to every cell.

Picture Card 4: Medicine on the Move

Syrup and tablets are absorbed in the small intestine, and a drip goes into a vein.
Key idea: Blood carries medicine to the part that needs it.

Picture Card 5: The Four-Chambered Heart

The heart has two atria on top and two ventricles below.
Key idea: The right side holds oxygen-poor blood and the left side holds oxygen-rich blood.

Picture Card 6: The Journey of Blood

Blood goes from the heart to the lungs, back to the heart and then to the body.
Key idea: Blood always passes through the heart between the lungs and the body.

Picture Card 7: Pulse and Stethoscope

Two fingers on the wrist feel the pulse. A stethoscope lets us hear lub-dub.
Key idea: The pulse matches the heartbeat.

Picture Card 8: Exercise and the Heart

Running and cycling make the heart beat faster and make us breathe faster.
Key idea: Muscles need more oxygen when we move.

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CIRCULATORY SYSTEM

Heart + Blood + Blood vessels

Case 1: Aarav and the Scraped Knee

Aarav was riding his bicycle in his society garden in Borivali when he fell and scraped his knee. Blood came out at once. His friend Meher ran to call his mother. Mummy washed the knee with clean water and pressed a clean cloth on it. Soon the bleeding slowed. That evening Aarav had a haircut, and he asked the barber, ‘Why does my knee bleed but my hair does not?’ The barber smiled and said, ‘Ask your science teacher!’ Aarav asked her the next day.

Answer these questions:

1. Why did blood come out of Aarav’s knee?
2. Why does a haircut not make Aarav bleed?
3. Which part of the blood helped the bleeding to slow down?
4. What should Aarav do first after a fall like this?
5. Name the tiny vessels found almost everywhere in the skin.

Case 2: Sneha’s Cricket Match

Sneha plays cricket for her school team in Pune. In the final, she ran many quick runs between the wickets. After the match her heart was thumping and she was breathing fast. Coach Patil asked her to find her pulse. She counted 30 beats in 15 seconds. Before the match, her pulse had been 20 beats in 15 seconds. After some rest, her breathing slowed down and she felt very hungry. The coach gave her a banana and a glass of water.

Answer these questions:

1. Why did Sneha’s heart beat faster?
2. Why did she breathe faster?
3. How many beats per minute did Sneha have before and after the match?
4. Why did Sneha feel hungry after the match?
5. What happened to her heartbeat and breathing after rest?

Case 3: Rohan’s Blood Report

Rohan from Nagpur often felt tired, so his doctor asked for a blood test. A nurse took a little blood from a vein in his hand. The next day the report came. It showed haemoglobin 11 g/dl, while the standard range is 12 to 15 g/dl. All other values were normal. The doctor told Rohan not to worry. She asked him to eat dates, spinach, figs and raisins, and to come back for another test. Rohan wondered how one small tube of blood could tell the doctor so much.

Answer these questions:

1. Why was blood taken from a vein in Rohan’s hand?
2. Which part of the blood carries oxygen?
3. Is Rohan’s haemoglobin inside the standard range?
4. Name two foods that help the body make haemoglobin.
5. Why can one small blood sample tell the doctor so much?

Case 4: Tanvi’s Syrup

Tanvi twisted her ankle during a kabaddi game in Nashik. The doctor gave her a syrup to drink. Her younger brother Yash said, ‘The syrup goes into your tummy, not your ankle. How will it help your leg?’ Tanvi was puzzled. Their grandmother remembered the drip she had needed in hospital last year. ‘That medicine went into my hand, but it helped my whole body,’ she said. Tanvi wondered if the syrup and the drip worked the same way. She decided to ask her science teacher the next day.

Answer these questions:

1. Where is the syrup absorbed into the body?
2. What carries the medicine to Tanvi’s ankle?
3. Is Yash right that the syrup stays in the tummy?
4. How is a drip different from a syrup?
5. Who should give medicines to a child?

Case 5: Heart Health Week

Class 5 in a school in Thane did a Heart Health Week. Each child filled a chart. Kabir ate chips and fried snacks daily, played no outdoor games, watched screens for three hours and slept late. Meera ate fruit every day, played outside for 30 minutes, drank seven glasses of water and slept on time. At the end, the teacher asked the class to compare the two charts and give advice. The children discovered that small daily choices can make the heart stronger.

Answer these questions:

1. Which of Kabir’s habits can harm the heart?
2. Which of Meera’s habits help the heart?
3. Why are baked or grilled foods better than fried foods?
4. Suggest three changes for Kabir.
5. How many minutes of activity should we try for every day?