Hormones 101

May 4, 2011 No Comments by Scott Isaacs MD

When I was in the seventh grade, I remember my friend Michael Root’s science project on the endocrine system.   He made a detailed poster of all the glands in the body with little arrows coming out, representing the various hormones.  He gave his presentation to the class, describing the intricacies of this elegant system.  As a twelve-year-old, I remember thinking to myself, what a complicated system.  How do all these glands know what hormones to make and how do those hormones know what to do?  At the time, the whole thing seemed fixed, unchangeable, just another bodily function.  I didn’t realize how dynamic and adaptable our hormones can be.

In my first year of medical school, I rediscovered the remarkable endocrine system.  I studied glands and hormones and learned how hormones really worked.  Over the years, I have continued to think about glands and hormones in their most basic terms.  I think that understanding the very basics of the endocrine system helps when you contemplate the hormonal disorders that people have. For example, to understand the difference between type 1 and type 2 diabetes, you must have a fundamental understanding of the hormone insulin and the insulin receptor.

Insulin is just one of many hormones, but in many ways all hormones are the same.  Hormones are made by glands.  There two types of glands, those that make hormones, known as endocrine glands and those that make other substances, like sweat and saliva, known as exocrine glands.  Endocrine means that substances are secreted directly into the bloodstream.  Exocrine means that substances are secreted somewhere other than the bloodstream.  So this means that hormones are substances produced by glands that are secreted directly into the blood stream.  Seems simple right?

But what do they do?  Hormones travel throughout the circulatory system like tiny chemical messengers looking for their target “receptor” located in the brain and on virtually every organ and every cell in the body.  Insulin, for example, has a specific insulin receptor.  Thyroid hormone has its own receptor too.  Every hormone has its own receptor.  A hormone receptor is like a light switch.  Some receptors naturally are in the “off” position and the hormone turns it “on.”  Other receptors are naturally in the “off” position and the receptor turns it “on.”   The point is that a hormone is a signal to turn on or to turn off a receptor.

Hormone receptors are found everywhere in the body and are responsible for the effects of a hormone.  Thyroid hormone receptors on the heart, for example, respond to thyroid hormone by making the heart beat faster.  Insulin receptors in the liver and on muscle cells direct the cell to take in glucose from the blood.  Hungry hormone receptors in the brain respond to various hungry hormones like leptin, PYY and ghrelin, turning on or off appetite.

Hormones are the body’s way of communicating with itself.  They are the chemical messengers that transmit information from one part of the body to another.  The blood is the superhighway for these signals.  I’ve joked with my cardiologist friends, that the main purpose of the heart is to pump all those hormones around the body.

Many medical problems have ties to glands, hormones and hormone receptors.  There are so many things that can go wrong.  Next week, I’ll blog about some of the things that can go wrong with hormones.

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