The Endocrine System

The endocrine system is a complex network of glands and hormones (chemical messengers) that regulate and control many short and long term bodily functions. Hormones are produced and released into the bloodstream by a variety of endocrine glands including the testes, the ovaries, the pancreas, the adrenal glands, the thyroid, the parathyroid, the thymus, the pituitary gland, hypothalamus and pineal gland. Hormones such as estrogen and testosterone are well-known as the "sex hormones". Others may be well-known but not readily identified as hormones. For instance, adrenalin is the hormone responsible for "fight or flight" responses, insulin is necessary for metabolism, and progesterone is essential for maintaining pregnancy. All vertebrates have an endocrine system.

For more information, see the Environmental Estogens section of Envinronmental Concepts Made Easy.

The endocrine system and nervous system work together to control bodily functions and to relay information and instructions throughout the body.

The Body's Messengers

Hormones - produced and released into the blood stream by endocrine glands - are essential for the regulation of numerous biological processes in the body. They also play an important part in the normal development of the growing fetus. In the womb or egg, hormones guide the development of sexual characteristics, the immune and nervous systems, the brain, behavioural characteristics and growth. Thyroid hormones, for instance, are essential for brain development. Testosterone, progesterone and estrogen are essential for reproductive organ development and functioning. Insulin regulates blood sugar in the body.

Natural hormones are extremely potent and operate at minute concentrations in the body. For example, estradiol, the body's key estrogen hormone, operates at concentrations in the parts per trillion range.

Hormones Activate Genes

Hormones do not alter or damage genes. Rather, they cause the gene to act in a specific way, telling it when to reproduce or activate. It is much like a transmitter sending signals to a cellular phone or radio. If the hormone system works properly, then the right message is sent and is received by genes within the cell. If something happens to damage the hormone system, then the wrong messages, or no messages, are sent to the cell, similar to a fault in the transmission system not connecting properly to the receiver even though the phone or radio is in good working order.

Specialized Action

To relay information throughout the body, hormones bind with specifically tailored cell proteins called receptors. There are hundreds of different kinds of receptors, each one designed for a particular chemical signal. Within one cell there are at least 10,000 types of receptors, although only a small number need to be activated to elicit a response. The hormone and its receptor have an intricate and precise fit, like a lock and key. The hormone-receptor complex then binds to specific regions of DNA in the cell to activate specific genes. If the binding is disrupted at certain stages, normal hormonal signals are derailed.

Humans and Wildlife 'Share' an Endocrine System

In many instances, specific hormones and the biological processes they control are chemically identical in animals and humans. This is an amazing fact considering the years of evolution and differences in physical structure between animal species. For example, estradiol, a hormone critical to sexual development and behaviour, is chemically identical in both turtles and humans. As put by Dr. Lou Gillette, "people like to think that we are different from animals, especially from insects, but at the cellular level we are all the same". This means that a chemical which affects some component of the endocrine system of an insect can be expected to similarly affect a mammal.