The circulatory system is your body's transport network. It moves blood around your body, delivering oxygen and nutrients to every cell and removing waste products like carbon dioxide.
Check: What two things does blood deliver to your body's cells?
Flowchart
Use the pathway to build a clear mental model. Open each node and answer the check question.
1) What is the circulatory system?
2) The three main components
The circulatory system has three main parts: the heart (the pump), blood vessels (the tubes), and blood (the transport fluid). These work together non-stop, 24 hours a day.
Check: What job does the heart do in the circulatory system?
3) The double circulation
Blood travels in two loops: one to the lungs (to collect oxygen) and one to the rest of the body (to deliver oxygen). This is called double circulation. The heart pumps blood through both loops.
Check: Why does blood need to go to the lungs?
4) Why we need a circulatory system
Every cell in your body needs oxygen and nutrients to produce energy. The circulatory system is the delivery service that reaches all 37 trillion cells! Without it, cells would die within minutes.
Check: Why can't cells just get oxygen directly from the air?
Explanation
What is the circulatory system?
The circulatory system (also called the cardiovascular system) is the body's transport network. It carries blood to every part of your body, delivering essential supplies and removing waste. Your blood travels about 19,000 km every day - that's almost halfway around the Earth!
The Three Main Components
- The Heart - A muscular pump about the size of your fist. It beats around 100,000 times per day, pushing blood through your blood vessels. It never stops working, even when you sleep.
- Blood Vessels - The tubes that carry blood. There are three types: arteries (carry blood away from the heart), veins (carry blood back to the heart), and capillaries (tiny vessels that connect arteries and veins).
- Blood - The transport fluid. It carries oxygen, nutrients, hormones, and waste products. An adult has about 5 litres of blood; a child has about 3 litres.
Double Circulation
Humans have a double circulatory system - blood passes through the heart twice on each complete circuit:
- Loop 1 - Pulmonary circulation: Heart → Lungs → Heart (blood picks up oxygen and drops off carbon dioxide)
- Loop 2 - Systemic circulation: Heart → Body → Heart (blood delivers oxygen and nutrients, picks up waste)
Key Vocabulary
- Circulatory system: the heart, blood vessels, and blood working together.
- Heart: the muscular organ that pumps blood around the body.
- Blood vessels: tubes that carry blood (arteries, veins, capillaries).
- Artery: a blood vessel that carries blood away from the heart.
- Vein: a blood vessel that carries blood towards the heart.
- Capillary: a tiny blood vessel where exchange happens with cells.
Examples
Example 1: Feeling your pulse
When you feel your pulse on your wrist or neck, you're feeling an artery expand each time your heart beats. Each pulse is one heartbeat pushing blood through your arteries. A resting pulse of 70-100 beats per minute is normal for children.
Example 2: Why exercise makes you breathe faster
When you run or play sports, your muscles need more oxygen. Your heart beats faster to pump more blood, and you breathe faster to get more oxygen into your blood. This shows how the circulatory and respiratory systems work together.
Example 3: Why cuts bleed
When you cut yourself, you damage blood vessels. Blood leaks out because the heart is constantly pumping it through your vessels. Small cuts stop bleeding because blood contains special cells that form clots to seal the wound.
Example 4: William Harvey's discovery
In 1628, English doctor William Harvey proved that blood circulates around the body in a continuous loop, pumped by the heart. Before this, people thought blood was made fresh by the liver! Harvey's discovery changed medicine forever.
Practice
Answer all questions, then check your answers. Your quiz result is saved on this device.
Common Mistakes
Mistake 1: Thinking arteries always carry oxygenated blood
Wrong thinking: "Arteries carry oxygen-rich blood, veins carry oxygen-poor blood." Correct: Arteries carry blood AWAY from the heart, veins carry blood TO the heart. The pulmonary artery carries oxygen-poor blood to the lungs!
Mistake 2: Thinking blood is blue in veins
Wrong thinking: "Blood is blue when it has no oxygen." Correct: Blood is ALWAYS red. It's bright red with oxygen and dark red without. Veins look blue through your skin because of how light passes through skin, not because the blood is blue.
Mistake 3: Thinking the heart is on the left side
Wrong thinking: "The heart is on the left side of your chest." Correct: The heart is in the CENTRE of your chest, slightly tilted to the left. About two-thirds of it is on the left side, which is why we feel it beating there.
Mistake 4: Confusing the circulatory and respiratory systems
Wrong thinking: "The circulatory system is about breathing." Correct: The respiratory system handles breathing (lungs). The circulatory system transports blood. They work together - the lungs add oxygen to blood, and the circulatory system delivers it around the body.
Summary
- The circulatory system transports blood around the body.
- It has three main components: heart (pump), blood vessels (tubes), and blood (fluid).
- Blood delivers oxygen and nutrients to cells and removes waste.
- Humans have double circulation: blood goes to lungs, then to the body.
- Arteries carry blood away from the heart; veins carry blood to the heart.
Skills Checklist
- I can name the three main components of the circulatory system.
- I can explain the function of the heart, blood vessels, and blood.
- I can describe the difference between arteries and veins.
- I can explain why we need a circulatory system.