The Body: A Guide for Occupants

by Bill Bryson

Wass is a tireless campaigner for a better appreciation of hormones and what they do for us. “They were the last major system in the body to be discovered,” he says. “And we are still discovering more all the time. I know I am biased, but it is really a terribly exciting field.” As late as 1958, only about twenty hormones were known. No one seems to know quite how many there are now. “Oh, I think it must be at least eighty,” says Wass, “but perhaps as many as a hundred now. We really do keep discovering more all the time.” Until very recently, it was thought that hormones are produced exclusively in the body’s endocrine glands (hence the name endocrinology for this branch of medicine). An endocrine gland is one that secretes its products directly into the bloodstream, as opposed to exocrine glands, which secrete onto a surface (like sweat glands onto skin or salivary glands into the mouth). The principal endocrine glands—the thyroid, parathyroid, pituitary, pineal, hypothalamus, thymus, testes (in men), ovaries (in women), pancreas—are scattered all around the body but work together closely. They are mostly tiny and altogether weigh no more than a few ounces but have an importance to your happiness and well-being that is entirely disproportionate to their modest dimensions.