The skeletal system is made of bones and joints which are your elbow bones and knee bones.

Bones have 3 layers the outside one is the compact bone second one is the spongy bone and the middle one is the bone marrow.

You have 206 bones in your body and bands called ligaments keep them in place. Your smallest bone is in your middle ear called ossicles and your biggest one is in your thigh.

Joints are made out of cartilage and fluid. Different joints move differently.

Your upper arm connects to the shoulder blade and in between is a ball joint and socket joint which lets your arm move

You need muscles for the skeletal system to work and stretchy tendons connect muscles with bones , if the brain send a message it travels through nerves and then muscles tighten to help you move. 

Your skull protects your brain and other organs in your body. Your spine has about 33 bones called vertebra which protect your nerves.

If you want to move your bone your voluntary muscle will move them because you wanted it to.

Circular muscles help you move your eye lids or blink and hold your lips together.

You use a hundred muscles when you walk to push your feet on the floor and move your knee

You have many body organs which are smooth muscles like your stomach.

Cardiac muscles are involuntary muscles which work without you wanting it to. Cardiac muscles and smooth muscles never get tired.

Lungs or respatory system

When you breath hard your lungs work harder and you can breath in more oxogen and your heart has to work harder to spread blood and oxogen in your body.

When you inhale oxogen goes down your wind pipe also called the trachea.

At the end of the trachea there are 2 tubes called bronchi which lead 2 big organs called lungs which is where the oxogen gets picked up by blood and spread around your body.

The lungs inhale air with help of your diaphragm a  muscle under the lungs.

The lungs have a lot of small tubes called bronchioles which lead to the alveoli where all the oxogen gets absorbed into our blood. (There are 600 million alveoli in our body).

Each alveoli has a mesh like covering of blood vessels capillaries

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Your veins carry blood to your heart and your arteries spread blood throughout your body. Arteries and veins (blood vessels) are what carry blood to the heart and spread it throughout your body.

There are cells in your body which need oxogen to help your body and it is the bloods job to get the oxogen to them.

When you breath you breath in oxogen which go into your lungs from there with help of the heart and blood they have to go to the other parts of your body and the blood gets them there.

The blood also goes around your body and collects carbon dioxide which is a waste so the blood goes back to the lungs to leave the carbon dioxide we breath out and it picks up more oxogen.

Blood goes to the right atrium where the blood goes into the heart then the blood goes to the tricuspid valve. Valves are there so that the blood flows in the right direction. After the valve the blood goes to the right ventricle then the blood goes through the pulmonary valve and through the pulmonary artery and then to the lungs where all the oxogen gets picked up.

The blood goes through the pulmonary vain and then to the left atrium then finally through the mitral valve and to the left ventricle.