“The Devil made me do it,” said comedian Flip Wilson in the ’70s. These days, though, it’s hormones that get the blame. Teenagers becoming uncontrollable as spring kicks into high gear? Hormones. Blowing up at your boss/spouse/children for no reason? Hormones. Overweight? Hormones. Underweight? Hormones. Feeling depressed? Euphoric? Romantic? Hormones, hormones, hormones.
All of which begs the question, “Just what is a hormone?”
Hormones get their name from a Greek word meaning “to urge on,” and that’s just what they do: they urge cells in the body to perform in certain ways. They’re messengers from one part of the body to another, and are essential to the regulation of many different biological processes, from brain development to reproduction to regulating blood sugar.
Hormones are produced by various glands that make up the endocrine system. These glands–principally the pituitary, thyroid, parathyroid and adrenal glands, plus the pancreas and the reproductive glands–release their hormones directly into the bloodstream. Although the body’s response to a release of hormones isn’t as immediate as it is to a signal sent through the nervous system, a hormonal response typically lasts a lot longer. (In other words words, if you see something that frightens you in a flash of lightning, you’ll still be feeling the hormone-induced effects of your fear long after you can no longer see the frightening sight.)
Hormones achieve their effects in amazingly tiny quantities; the body is exquisitely sensitive to them because such sensitivity is vital to survival. For example, estradiol, the body’s key estrogen hormone, works just fine at a concentration in the blood in neighborhood of one part per trillion–the equivalent of one drop of estradiol in 660 rail tank cars of blood.
There are dozens of different hormones coursing through your bloodstream all the time. Each of the glands that produces them does so for a different reason. The pituitary gland, located in the brain, is the master gland of the system. It’s anterior (front) lobe controls skeleton growth and helps regulate the various other hormone-producing glands, among other things, while the posterior lobe’s hormones include some that increase blood pressure, prevent excessive secretion of urine and stimulate contractions of the uterus.
The thyroid gland’s hormone stimulates general metabolism and plays an important role in the process of growing from a child to an adult. The parathyroid gland’s hormone controls the concentration of calcium and phosphate in the blood. The pancreas’s primary hormones, insulin and glucagon, regulate the body’s use of carbohydrates: insulin regulates blood sugar levels and glucagon helps the liver and muscles store glucose.
The outer layer of the adrenal glands produce hormones that, among other things, control the concentration of salts and water in the body fluids, maintain our resistance to stress, and affect secondary sexual characteristics. The inner part of the adrenal gland is famous for producing adrenaline, which stimulates the circulatory and nervous systems.
The reproductive glands, or gonads, are probably the organs we most often associate with hormone production. Their hormones control sexual development and the various processes of reproduction. The testes’ hormones, for example, control the development of men’s secondary sexual characteristics (i.e., chest hair), while the ovaries produce the aforementioned estradiol and other estrogens, which control the cycle of ovulation.
Although these glands are the primary producers of hormones, they aren’t the only ones. The mucous membrane of the small intestine releases hormones during certain stages of digestion, for example, and the placenta produces its own hormones during pregnancy that, along with the estrogens, contribute to the development of the mammary glands (in preparation for nursing) and inhibit ovulation. Some methods of pregnancy testing look for these placental hormones.
Each hormone has specific target tissues that it effects. The cells of these target tissues have special “receptor sites” into which molecules of the hormone fit very precisely, like a key slipping into a lock. These sites are very specific: they’ll only accept the hormone they’re designed for, which keeps cells from getting confused by the many different hormones that go zipping by in the bloodstream every second.
Hormones can have either short-term or long-term effects on their target tissues. Short-term effects are changes to the metabolism of the target tissues’ cells. Insulin, for example, is believed to make the membranes of skeletal muscle cells more permeable, so they can transport glucose rapidly. Long-term effects are achieved by telling the target tissues’ cells what proteins they should manufacture. This is how hormones produce the changes associated with puberty.
Many hormones work together to keep the body regulated. Some hormones inhibit the effects of other hormones, some increase the effects of other hormones, and some, while apparently exerting no effect on certain tissues, are actually influencing that tissue’s reaction to other hormones.
When this rich mixture of hormones gets out of whack, medical problems can occur–ask a diabetic, who must take regular injections of the hormone insulin in order to be able to properly metabolize sugars. Recently, however, there’s been a trend toward self-medication with hormones: steroids, for example. Some people seem to think that just because hormones are “natural” substances, they can’t hurt you; but the fact is, the level of hormones in your body is carefully balanced by your body itself. Dose yourself with hormones of any sort, without medical supervision, and you run the risk of upsetting that balance, with unfortunate or even disasterous results.
In fact, one of the biggest environmental threats we face is the fact that many man-made chemicals are apparently able to disrupt the delicate hormonal balance. Some chemicals mimic hormones so well they’re able to cause the same bodily changes as hormones; some stimulate the formation of extra hormone receptors; some keep hormones from working by plugging up the cells’ receptor sites. Abnormalities in many different types of wildlife have been linked to these hormone-mimicking chemicals. The jury is still out on how much risk is posed to humans, but the concern is that even if the risk to adult humans isn’t great (yet), unborn children face a greater hazard, because any disruption of the normal flow of hormones during pregnancy can result in developmental problems.
It’s amazing, really, how much of our day-to-day existence is dependent on almost-undetectable amounts of chemicals flowing through our veins. Yet there’s no denying the power of hormones.
It’s spring. Ask any teenager.