A Busy Gland
Ever wonder why your best friend can down desserts with reckless abandon and never gain weight? And why you pack on pounds by nibbling on just one or two desserts a week? At least some of the blame — or credit, depending on whom you ask — goes to your thyroid, which produces the hormone that determines your metabolism, or basal metabolic rate (BMR). That's the rate at which your body cells use oxygen and energy to do their jobs. Too much thyroid hormone, and your metabolism speeds up. Too little, and it slows down.
But metabolic rate is only one of the thyroid gland's tasks. It is also responsible for how your body uses the energy sources — carbohydrates, proteins, and fats — that you derive from food. It is responsible for bone growth and muscle function. In addition, the thyroid affects respiration, heart rate, mood, skin, hair, and nails.
For all it does, the thyroid is a modest organ that weighs about half to three-quarters of an ounce in mature adults. On the body, the small butterfly-shaped gland resembles a bowtie, nestled in the front of your neck, just below the larynx — also called your Adam's apple or voice box — and in front of the trachea, the windpipe that carries air to your lungs. The wings of the butterfly are called its left and right lobes, and are wrapped around the trachea. Each lobe measures about an inch and a half. In between is the isthmus, a narrow strip that connects the two wings.
A drop in thyroid hormone can cause depression, malaise, and forgetfulness. An increase in thyroid hormone can cause excitability, wide fluctuations in mood, and crying spells for no reason. Be on the lookout for radical mood changes — they might be thyroid related.
Development of the thyroid begins around the seventeenth day after conception. When the fetus reaches three months gestation, it begins to make its first thyroid hormone. During pregnancy, it also receives thyroid hormone from the mother. Even at these early stages, thyroid hormone is needed for the fetus's development of the brain and nervous system.
The thyroid gland is part of the body's endocrine system, a collection of glands that produce the hormones that regulate your growth, metabolism, and sexual development and function. Hormones — coming from a Greek word meaning “to excite” or “to spur on” — are chemical messengers that act on cells to cause chemical reactions. Once released by specific glands, they travel in the bloodstream to the targeted organ, where they spur the organ to action. Other parts of the endocrine system include the:
Adrenal glands, which are located above the kidney, and affect metabolism, the body's stress response, and salt regulation.
Hypothalamus, a part of the brain that regulates the pituitary gland as well as involuntary bodily functions, sleep, appetite, and hormones.
Ovaries and testicles, which are located in the sex organs, and produce sex hormones involved in influencing female and male sexual characteristics. They regulate the menstrual cycle in women and sperm production in men.
Pancreas, which is located below your stomach, and secretes insulin, a hormone that regulates the body's use of glucose.
Parathyroid glands, which are located near the thyroid, and regulate calcium levels in the blood.
Pineal gland, which is in the back of the brain, and produces melatonin, a hormone that is involved in sleep-wake cycles.
Pituitary gland, which is located near the base of the brain, and produces numerous hormones that affect the other endocrine glands, including the thyroid.
Thymus gland, which is located at the top of the chest, and is involved in the body's immune function.
Each one of these glands plays a vital role in keeping you healthy, and the thyroid is no exception. But the thyroid doesn't work alone. It requires help from other body parts and elements in your diet to perform the critical task of regulating metabolism and promoting healthy growth.