Brain is the part of nervous system. All body organs send messages through the nerves, and nerves send them to brain. Brain orders all our actions like walking, talking, crying, laughing, reading, loving people and memorising things. 

We have 8 organ systems in our body. These are digestive, respiratory, skeletal, nervous, circulatory, excretory, reproductive and muscular system.

Nerves are the part of nervous system. Nerves act like electric wires in the human body as they spread all over the body and send messages to brain. If we touch a hot cup, the nerves in the skin send message to the brain and then brain orders the hand to withdraw itself from the cup.

Heart is mainly a muscle. The heart muscle has arteries and veins attached to it, and it basically pumps blood to circulate through the body.

Here all organs belong to digestive system. Food pipe helps food to reach to the stomach, liver produces bile juice that helps carry away waste and broken down fats in the small intestine during digestion.

Rib cage is a cage-like structure consisting of 14 bones. It protects our lungs and heart from injury.

The reproductive system helps in producing young ones with the help of reproductive organs present in human body.

This system controls the whole body and gives direction to do things which are right or wrong. When we see danger somewhere, immediately our brain sends message to move away from there.

Skeletal and muscular systems help him in running, jumping and hitting the ball. As muscles are attached to bones, so with the help of both muscles and bones, he is playing football.

Carbon dioxide is the gas that we breathe out during the respiration process. It is one of the major waste products of our body which get removed through this process.

External organs are responsible for protecting the body from most physical and environmental changes, and help us in sensing these changes. Nose, mouth, ears and eyes all are external organs and are present outside the body.

Lungs belong to our respiratory system, and are responsible for breathing in and out. We breathe in oxygen, and we breathe out carbon dioxide.

Sense organs help us to see, hear, smell, taste and feel things. These five senses are the gateways through which we experience everything that happens around. The things that the sense organs respond to are called stimuli.

Muscles are one of the crucial organs of our body. They are incredibly sophisticated and can expand and contract when they relax. Our stomach is made up of muscles, so it expands when food goes inside and it contracts when the food goes out. They are long-lasting, self-healing and are able to grow stronger with practice. They do everything from allowing us to walk to keeping our blood flowing.