人体系统的奥秘
本文深入探讨了人体的主要系统，包括循环系统、消化系统、神经系统、呼吸系统和免疫系统。心脏通过血管泵血，消化系统分解食物提供能量，神经系统控制肌肉和器官，呼吸系统交换氧气和二氧化碳，免疫系统抵御感染。
The body's circulatory system includes the heart and blood vessels.
The heart pumps blood to all ports of the body through a network of arteries and veins.
The digestive system breaks down and absorbs food into the body.
It supplies the energy that the body needs for growth and repair.
After digestion, excess food is turned into waste and eliminated from the body.
The nervous system includes the brain, spinal cord and nerves.
This is your body's control system.
It controls your muscles and organs, including your circulatory and digestive systems.
The respiratory system includes the nose and lungs.
It brings air and oxygen into the body and removes carbon dioxide.
The lungs are where oxygen enters the bloodstream and carbon dioxide is removed.
The immune system protects the body against infections and diseases.
Sneezing and fever are examples of how the immune system works.
If an infection invades the body, the immune system attacks it.
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