Meet Your Thyroid Part 1

Know Your Thyroid Gland's Job Description

Do you know what your thyroid gland looks like? If you're female, you may view it as a butterfly-shaped organ found in your neck hugging your windpipe (trachea). If you belong to the opposite sex, it will appear more of like a shield to you. You may be surprised to know that even if it looks beautiful or it could seem as if it protects your windpipe, it performs none of those functions.

This article is divided into three parts:

Part 1 – Your Thyroid's Responsibilities (Its Job Description) (Dear Reader, You're already here)

Part 2 – How Do You Know If Your Thyroid is Having Problems with its Job?

Part 3 – How to Help Your Thyroid

The adult thyroid gland weighs between 25 to 35 g. It's made up of two lobes (right and left) connected by the isthmus (from an Ancient Greek word which means “neck”). This gland is located in front of your thyroid cartilage. In adult males, you can easily locate the thyroid cartilage. It's where you commonly describe the location of your “Adam's apple”. The “Adam's apple” is actually a part of the thyroid cartilage called the thyroid prominence. Below that, is your thyroid gland. In females, the location is less prominent. Sorry ladies, there's no such thing as an “Eve's apple”. Rest assured, if you're functioning normally right now, your thyroid gland is there.
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Each lobe of the thyroid is divided into lobules (smaller lobes). The lobules are comprised of follicles (small glands) which are the functional units of the thyroid. They're called functional units because they perform the main function of the thyroid gland which is the production of thyroid hormones. The follicles are filled with a substance called colloid. The colloid acts like a storage area (a bit like a refrigerator) for raw materials utilized in the production of thyroid hormones. Iodine, the amino acid tyrosine, and thyroglobulin (a protein which stores iodine) are among these raw materials tucked away in the colloid. Scattered in between the follicles are “C cells” or parafollicular cells. The C stands for calcitonin. These “C cells” secrete calcitonin, a hormone which reduces the blood levels of calcium ions in your body. It accomplishes this by communicating with three other organs in your body namely your small intestine (decreased absorption), bones (decreased breakdown), and kidneys (decreased reabsorption).

You may not be aware of it, but your thyroid gland is a generous endocrine organ. It provides refuge to your parathyroid glands. Are you confused? Don't be. The parathyroid glands are also endocrine glands located at the back of the left and right lobes of the thyroid. There is usually a total of 4 parathyroid glands, a pair in each lobe. They were discovered by a Swedish medical student named Ivar Viktor Sandstorm who was humble enough not to name the organs after himself (I would, IF I had discovered them). Instead he gave them the prefix para- (which means beside), the thyroid in this case. The parathyroid gland produces parathyroid hormone. This hormone increases the levels of calcium ions in the blood. If you analyze it, parathyroid hormone has opposing actions

with calcitonin. Like calcitonin, it communicates with the same three organs in your body (small intestine, bones, kidneys) to maintain the blood levels of calcium within a narrow range. But enough of the parathyroid glands...back to the thyroid.

The principal function of the thyroid gland is to produce and secrete thyroid hormones. When it's time to secrete the hormones, thyroglobulin from the colloid is reabsorbed into the follicular cells. Inside these cells, they undergo cleavage (a special separation process) and thyroxine (T4) and triiodothyronine (T3) come out and are released into your blood. Both thyroid hormones are derivatives of the amino acid tyrosine. Enumerated below are the physiologic effects of both thyroid hormones:

1. Heart. Thyroid hormones make your heart pump more blood (increase cardiac output) by increasing your heart rate and the force of contraction made by the muscles of your heart. This delivers more blood (which contains nutrients and O2) to the different organs of your body. In addition, heat is also produced, resulting in a small rise in body temperature (a process called calorigenesis).

2. Nervous system. Thyroid hormones are required during development of the brain as children grow. Deficiencies in thyroid hormones can result in mental retardation, deaf-mutism and motor rigidity (fancy term for muscle stiffness). As an adult, if you're deficient in thyroid hormones (a state called hypothyroidism), your ability to think is very slow. Don't get any funny ideas by buying thyroid hormone supplements thinking that you'll be a grade A level genius like Einstein. It's never that simple. So just can that idea. Thyroid hormones increase your brain's sensitivity to catecholamines (neurotransmitters) making them respond better.

3. Carbohydrate Metabolism. Your thyroid hormones can increase how fast your digestive system absorbs carbohydrates from the food you eat.

4. Cholesterol Metabolism. It's interesting to know that thyroid hormones can decrease your blood cholesterol levels. This is primarily accomplished by telling your liver to increase the removal of cholesterol from your circulation. Unfortunately, the amount of cholesterol removed doesn't produce significant clinical effects. In other words, thyroid hormones can't be medicinally used to lower your cholesterol.

5. Growth. Your thyroid hormones are very much needed to optimize your growth. Thyroid hormones increase the secretion of growth hormone. All three hormones (T3, T4 and growth hormone) have a significant impact on your height by increasing bone growth potential.

6. Everything Else. T3 and T4 have effects on the maturation and differentiation of all the cells in your body. This means that to fully realize their capabilities and specializations, the cells need thyroid hormones.

What Controls Your Thyroid Gland?

To cut a long story short, there are two anatomical brain regions which control your thyroid, your hypothalamus and your pituitary gland. These structures secrete thyroid releasing hormone (TRH) and thyroid stimulating hormone (TSH) respectively, to tell your thyroid to secrete thyroid hormones (T3 and T4). Low blood sugar (hypoglycemia), exercise, surgery and changes in temperature are examples of stimuli which can promote the secretion of your thyroid hormones.

Appreciate Your Thyroid

From the preceding paragraphs, I hope you realize the tremendous amount of responsibility bestowed on your thyroid gland. You need it to reach your full mental capabilities, increase your metabolic rate and interact with two other important hormones, epinephrine and norepinephrine (catecholamines). All the cells in your body need your thyroid in order to function optimally. To know if you may have a problem with your thyroid gland, watch out for Part 2 of this series!