The Endocrine System

In this topic you will learn about how the endocrine system uses chemicals to control many things.
Certain chemicals in the body react only when they reach a target. Hormones are chemicals that control body functions by influencing how cells work. Only when hormones reach their target can they cause changes in your body. A gland that produces hormones is called an endocrine gland. These glands make up your endocrine system, which, like the nervous system, is a control system of the body.
Endocrine glands are not connected like the parts of the digestive system. They are scattered around the body. Each endocrine gland makes one or more hormones. Every hormone seeks out a target organ—the place in the body where the hormone acts.
The human body makes more than 50 different hormones. They control body activities like growth. Only tiny amounts are needed because hormones are powerful substances. Too little or too much of a hormone can upset how the body works. The body depends on a process called biological feedback to determine when to release a hormone and when to stop.
The pituitary gland is often called the master gland. Some of the hormones it makes control how other endocrine glands in the body work. The pituitary gland is located at the base of the brain.
The thyroid gland is controlled by the pituitary gland. It produces two hormones that affect the rate at which cells use oxygen and release the energy in food. The sum of all chemical reactions that occur in the body is called its metabolism.
The parathyroid glands are four pea-sized glands embedded in the back of your thyroid gland. They make a hormone that helps control how much calcium is in your blood.
The two adrenal glands sit on top of the kidneys. The outer part of each adrenal gland produces 30 different hormones. The inner part of the adrenal gland produces adrenaline. This powerful hormone's main job is to help you deal with emergencies.
The reproductive system starts to develop when the pituitary gland releases hormones that target the reproductive organs. These organs produce sex cells. Ovaries are the female reproductive organs that produce eggs. Testis are the male reproductive organs that produce sperm. These organs also function as endocrine glands. They produce sex hormones.
Above your pituitary gland is a part of the brain called the hypothalamus. The nerve cells in the hypothalamus make hormones that tell your pituitary gland which of its hormones to start or stop.