What is the Function of the Thyroid in the Body?


Under the direct control of the pituitary gland as well as the feedback control from end organs it supplies, the thyroid controls the rate of all metabolism. This is a brief discussion that will allow you to loosely understand if not interpret your thyroid blood tests when your physician does annual blood screening for wellness sake.


When given your blood test results for safekeeping by your physician, never interpret them on your own without a physician’s guidance.


Is Thyroid TSH Checked in Routine Blood Work?


There is huge value to having annual blood work that looks for the big killers at least, and many other things that your particular region of the country puts you at risk for. The big killers that we need to look for annually nationwide, regardless of your region, are thyroid disease, diabetes, and cancer. This discussion just focuses on thyroid disease.

The thyroid gland is controlled by the pituitary. The pituitary control of it is governed by the master gland, the hypothalamus. All these other topics you should master if you want to get a good handle on your health. For now, all we will discuss is thyroid function.

The thyroid is stimulated by thyroid stimulating hormone (TSH) released by the pituitary in order for the thyroid to function. Then, thyroid hormone goes throughout your body and stimulates tissues. Then, the tissues tell the thyroid and pituitary to back off and function less.

Thyroid function can be excessive for many reasons. Infection, malignancy (cancer), auto immune disease when your body makes antibodies against itself, and incorrect iodine intake are the big ones.

What is Autoimmune Grave’s Disease? 


Autoimmune disease means your body has created an antibody that your own tissue receptors respond to. Autoimmune disease that affects the thyroid gland might mean that antibodies your body is making can increase thyroid function or decrease thyroid function. The hyperthyroidism caused by autoimmune antibodies that your body makes to increase your thyroid function is known as Grave’s disease. Antibodies against the thyroid in Grave’s disease mimic TSH so these antibodies stimulate the thyroid, and excessive thyroid hormone is produced.


What is Hashimoto’s Thyroiditis?


Autoimmune disease in which your body produces antibodies that inhibit thyroid production is known as Hashimoto’s thyroiditis. The antibodies produced in Hashimoto’s disease make the thyroid produce less thyroid hormone, so it’s called hypothyroidism.

Now you might think that if you want to assess thyroid function in annual wellness blood-work, you might want to measure thyroid hormone. Unfortunately that is not as sensitive as looking at TSH, the hormone produced by the pituitary to make the thyroid go. And so that’s what physicians do. 

Hyperthyroid vs Hypothyroid


So, if you were going to be looking at TSH to gauge whether not you have a hypothyroid or a hyperthyroid state (or a euthyroid state which means normal), then you will look at it like this. A high TSH means your pituitary has to work harder to get your thyroid to do anything. So high TSH means hypothyroidism. A low TSH conversely means hyperthyroidism. The thyroid is producing thyroid hormone in excess, so it’s telling the pituitary to back off. Low TSH means hyperthyroidism; high TSH means hypothyroidism.

The thyroid gland also produces calcitonin. It’s function is to “tone” down calcium levels in the body (i’m afraid the only pneumonic in this topic). It does this by making the calcium move into bones. So, we end up with less calcium in the blood stream, more calcium in the bones. So, we should be watching for blood levels of calcium to assess whether not there is a calcitonin problem.

For completeness sake, I should mention that there is an opposing hormone produced by the parathyroid gland (four little glands that live on the thyroid coincidentally) simply called parathyroid hormone that mobilizes calcium from the bones, so increases calcium in the blood stream when it’s needed by destroying bone.


What is TSH?


We follow TSH levels in the blood to assess thyroid function even though TSH is a pituitary hormone. We do this because TSH levels are more sensitive to hypo and hyper thyroidism.

If the pituitary is producing too much TSH, your thyroid function is diminished. And that is an important work up that has to be done by endocrinologist. If your annual TSH is low, that means your thyroid is working too hard. That hyperthyroidism needs to be referred to and worked up by an endocrinologist as well.

Either hyperthyroidism or hypothyroidism must be worked up. It can’t just be blindly treated with extra thyroid hormone for hypo or with drugs that destroy the thyroid because it’s working too much in hyperthyroidism. We need to know why the thyroid is working too little or too much. It will give us clues to your underlying problem which might be an infection or cancer. Stay well!