2- The circulatory system

The circulatory system moves your blood to all the different parts of your body to send oxygen and nutrients to all your cells. In order to work properly, it needs three things: blood , the heart, and blood vessels.

A) Blood 

The blood cells pick up and deliver oxygen, water, and nutrients to all the cells in the body. Blood is made up of:

• Plasma that carries the nutrients and waste products.
• Red blood cells give blood its colour. They carry oxygen and carbon dioxide.
• White blood cells fight infection. 
• Platelets join together when the body is losing blood to stop the bleeding.

B) Heart 

The heart is a strong muscle, that pumps  blood through the body. It usually beats between 60 and 100 times per minute, but can go much faster.

C) The blood vessels are the roads the blood  travel to make their deliveries. There are three types of blood vessels.

• Arteries carry blood from the heart to the rest of the body. This blood contains oxygen.
• Veins carry the blood back to the heart. This blood contains carbon dioxide.
• Capillaries are tiny blood vessels which connect the arteries and the veins, gases and nutrients can easily pass through them to the cells.