Your amazing body
Your body is like a busy city with teams of workers. Each team is a body system: a group of organs that work together to do one big job.
The skeletal system
The skeletal system is made of your bones. Adults have 206 bones.
Jobs:
- holds your body up and gives it shape
- protects soft organs (your skull protects your brain; your ribs protect your heart and lungs)
- works with muscles to help you move
- makes blood cells inside some bones
The muscular system
The muscular system has more than 600 muscles.
- Skeletal muscles move your bones. They work in pairs: one pulls, then the other pulls back. When you bend your arm, your biceps tightens.
- Heart muscle pumps blood.
- Smooth muscle pushes food through your stomach and intestines.
The digestive system
The digestive system breaks food into tiny pieces called nutrients that your body can use.
| Organ | Job |
|---|---|
| Mouth | Teeth chew; saliva starts breaking down food |
| Esophagus | Tube that carries food to the stomach |
| Stomach | Mixes food with acid and juices |
| Small intestine | Absorbs nutrients into the blood |
| Large intestine | Absorbs water; forms waste |
The respiratory system
The respiratory system brings in oxygen and gets rid of carbon dioxide.
- Air goes in through your nose or mouth.
- It travels down your windpipe (trachea).
- It fills your lungs.
- Oxygen moves into your blood; carbon dioxide moves out.
- You breathe out the carbon dioxide.
A muscle under your lungs called the diaphragm helps you breathe.
The circulatory system
The circulatory system is your heart, blood and blood vessels.
- The heart pumps blood about 100 000 times a day.
- Arteries carry blood away from the heart.
- Veins carry blood back to the heart.
- Capillaries are tiny vessels where oxygen and nutrients pass to cells.
The nervous system
The nervous system is your brain, spinal cord and nerves. It is the body’s control centre. Nerves carry messages between your brain and the rest of your body very quickly.
Systems work together
No system works alone. When you run:
- your nervous system tells your muscles to move
- your muscular and skeletal systems move your legs
- your respiratory system breathes faster to get more oxygen
- your circulatory system pumps faster to carry oxygen to your muscles
- your digestive system provides the energy from food
Staying healthy
| Healthy habit | Helps which system? |
|---|---|
| Eating fruits and vegetables | Digestive |
| Running and playing | Muscular, circulatory, respiratory |
| Drinking milk or eating calcium-rich foods | Skeletal |
| Not smoking | Respiratory |
| Getting enough sleep | Nervous |
Common mistakes
- Thinking the stomach does all the digesting. Most nutrients are absorbed in the small intestine.
- Thinking systems work alone. They depend on each other.
Try it yourself
- Count your heartbeats for 15 seconds, then multiply by 4.
- Do 30 jumping jacks and count again.
- Which systems were working harder? Explain why your heart rate changed.
Quick recap
- A body system is a group of organs with one big job.
- Skeletal: support and protection. Muscular: movement.
- Digestive: breaks down food. Respiratory: brings in oxygen.
- Circulatory: carries blood. Nervous: controls the body.
- All systems work together to keep you alive.