What Does the Thyroid Do?

What does the thyroid gland do? What do thyroid tests mean?

Rob Lamberts, MD,
May 26, 2010
Episode #048

Page 2 of 4

The Thyroid and Pituitary Work Together

The pituitary controls the thyroid by putting out something called TSH, or thyroid stimulating hormone. TSH tells the thyroid how much thyroid hormone the body needs; if the body needs a lot of thyroid hormone, the TSH level goes up, and if the body has enough, the TSH level goes down. 

That’s a really important thing to remember, because it gets many people confused. A high TSH means there isn’t enough thyroid hormone, whereas a low TSH means there’s too much. It’s much like a thermostat that tells the furnace to get hot when the house is cold, and to cool down when the house is hot.

What Do Thyroid Hormones Do?

The best analogy I could find to explain the function of thyroid hormone comes from an unlikely place: auto mechanics. Your car needs fuel to run; most cars use gasoline as their fuel. Gas gets burned in the engine, which ultimately turns the wheels of the car so you can drive to the petting zoo, or wherever else you want to go.

The speed of the car depends on how much gas is let in the engine to be burned. The more gas, the more the engine revs. The carburetor, or the fuel injectors, are the parts of the car that control the amount of gas going to the engine, telling the engine how high to rev.

In the same way, the body needs fuel for you to do things, like getting out of your car and petting the llamas. It also needs energy to keep the heart beating, the lungs breathing, and the spleen, well, spleening. The burning of energy to do all of these things is called the metabolism. Thyroid hormone is much like the carburetor. Low thyroid hormone levels make the body burn less energy, whereas high levels make the body burn more energy. 


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