Your body is made of systems, teams of parts that work together. They all have to work at once, even while you sleep.
| System | Main parts | Job |
|---|---|---|
| Skeletal | bones (206 in an adult) | hold you up and protect organs |
| Muscular | muscles | move the bones and pump the heart |
| Circulatory | heart, blood, blood vessels | carry oxygen and food all around the body |
| Respiratory | nose, windpipe, lungs | take in oxygen, breathe out carbon dioxide |
| Digestive | mouth, stomach, intestines | break food into pieces the body can use |
| Nervous | brain, spinal cord, nerves | sense, think and send messages |
Key idea
Body systems work together. When you run, your muscles need more oxygen, so you breathe faster (respiratory) and your heart beats faster (circulatory), all controlled by your brain (nervous).
Why it works
Muscles can only pull, not push. That is why they work in pairs: one muscle bends your elbow, another straightens it.
Worked example: Which system?
Which system carries the oxygen from your lungs to your toes?
- Blood carries oxygen.
- The heart pumps the blood through blood vessels.
Answer: The circulatory system.
Common mistake
Thinking the heart sits far over on the left. It is near the middle of the chest, tipped a little to the left, and about the size of your fist.
Try it at home
- Find your pulse: press two fingers gently on the inside of your wrist below your thumb.
- Count the beats in 15 seconds and multiply by 4. Now jump in place for one minute and count again. What changed, and why?
Going further. William Harvey discovered how blood goes around the body: Harvey: On the Motion of the Heart and Blood. Later: Body Systems Working Together in Life Science.