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The hormonal system is the second important control system in the body. It is closely connected with the nervous system, but is also distinct.
The pituitary gland in the base of the brain has a key role in secreting many hormones. It acts as a controlling gland that influences many others.
Hormones have the advantage of having a widespread, powerful and long-lasting effect on the body's cells. The disadvantage is that the effect is often slower than the nervous system. But together, they are perfect!
Hormones are proteins that act as chemical messengers.
They are secreted - that is they are released from glands into the blood stream. Hormones are then carried around the blood so that they can reach every cell.
They are an easy way to communicate with every cell in the body.
Not every cell has the right receptor molecules on the surface of its cell membrane. The hormone molecules only bind to those cells that do have the receptor molecules. This effects enzymes inside the cells and causes changes to the cell's function.
This is similar to the way that enzyme molecules bind to their substrates.
Hormones control a wide variety of things in the body including the amounts of water and glucose (see separate pages).
Hormones also control important functions including the production of eggs and sperm. They effect our growth, repair our cells, produce heat, and so on.
The pituitary gland controls the volume of water in the body by secreting anti-diuretic hormone (ADH) as part of homeostasis. The pituitary gland also controls other glands throughout the body.
Hormones form an essential part of our body's control system.
This diagram shows some of the important glands: