Hormones are chemicals that travel around the bloodstream. They carry messages to different parts of your body. There are more than 50 different kinds of hormone. They are produced in small organs called glands (you can see some of them in the diagram opposite). The glands release the hormones into the bloodstream, which carries them to certain cells or organs. Hormones control activities such as growth, how fast your body uses up energy, stress, sleep and hunger.

How hormones work

The brain controls the release of many of the hormones in the body. When a hormone reaches a cell, it brings about a change in the way that the cell works. They may cause it to work faster or slower, or to release its products. For example, when you are frightened, a gland in the body makes a hormone called adrenaline. This makes the heart beat faster and more blood flow to the muscles, so the body is ready for action.

The time when children start to become adults is called the age of puberty. The pituitary gland near the brain makes growth hormones. These signal to the muscles, bones and organs that it is time for them to grow. Different hormones for girls and boys are released, which is why women and men look different. Female hormones make girls grow breasts. Their bodies also change so they can have children. Male hormones make boys’ voices sound lower and hair grow on their faces.