THYROID INTRODUCTION

What Your Thyroid Gland Does and Why You Should Care

 

By:  Zana Carver, PhD

Updated 2/23/2018

Thyroid Function

The thyroid gland is part of the endocrine (communication) system that sends out hormones to affect different organs within the body.  The thyroid gland is the largest purely endocrine organ in the body and its major function is to produce two thyroid hormones, thyroxine (T4) and triiodothyronine (T3).  T4 makes up the majority of thyroid hormone produced by this butterfly-shaped gland, yet it is T3 that is more active in tissues.

Thyroid Gland

Thyroid Gland

Thyroid hormones control your metabolism but in order to do this, they have to enter tissue cells, the functional units of life.  It is in tissues, a group of cells of the same type, that these hormones exert an effect.  Thyroid hormones change gene transcription within cells in a way that allows them to utilize more oxygen and nutrients to produce more energy.  All tissues have the ability to respond to thyroid hormone, thus these hormones control the metabolism of all cells in the body.  So why should you care about your metabolism?

Why You Should Care

When thyroid levels are low (hypothyroidism) you can feel tired, exhausted, unable to handle stress, or not able to keep up with co-workers, family, and friends.   You may feel cold most of the time when others are not, or have cold hands and feet.  You could also notice a change in your weight, hair loss, gut issues, depression, or anxiety.  Perhaps your doctor has told you that your cholesterol, blood pressure, or blood sugar levels are abnormal.  All of these symptoms are caused by metabolic dysfunction and therefore, may be thyroid related.

According to the Centers for Disease Control, National Institutes of Health, and the American Thyroid Association twenty million Americans may be affected by thyroid disorders, yet an estimated sixty percent are unaware.  Thyroid disorders are more common in women and the vague, non-specific symptoms are often mistaken for other disorders or not taken seriously.  Thyroid awareness is lacking and accurate, relevant, and current information is time consuming to find and hard to access.

Adaptability and Homeostasis

The ability of the human body to adapt to change is truly remarkable.  The more I learn, the more impressed I am with the body’s ability to maintain a stable internal environment despite constantly changing conditions.  From blood pressure regulation to fluid and electrolyte balance to maintaining stable blood sugar levels, this process of maintaining a stable internal environment is relentless.  A good example of homeostasis is building a tolerance to chemicals or medications.

One example that many people are familiar with is building a tolerance to alcohol.  When someone consumes alcohol in excess or for extended periods of time the number of enzymes in their liver that break down the alcohol (alcohol dehydrogenases) increases.  This makes the person more efficient at breaking down the alcohol and they will need higher and higher doses of alcohol to produce the desired effect.

Tissue Communication

Tissue Communication

Thyroid hormones do not work in isolation.  Not only do thyroid hormones affect other tissues but other tissues affect the levels of thyroid hormones, both in the blood and in tissues.

Thyroid Feedback

The thyroid gland is controlled by a complex feedback loop; the following diagram is simplified for clarity.  The pituitary gland responds to signals from the brain (hypothalamus) to produce thyroid stimulating hormone (TSH).  TSH causes the thyroid gland to release both T4 and T3 thyroid hormones.  When thyroid hormone levels are high they shut off the system to decrease TSH, T4, and T3.

Simplified Thyroid Feedback

Simplified Thyroid Feedback

This feedback process can be disrupted by many factors including insulin resistance and leptin resistance, as well as environmental factors.  My next post will describe common laboratory tests for thyroid disorders and which types of thyroid problems are detected with these tests.  It will also explore alternative thyroid testing and what you can do to get more accurate lab results.  Subscribe to the newsletter to read the latest thyroid health information.

References:

  1. Yen, P., Brent, G. (2013). Werner & Ingbar’s The Thyroid, A Fundamental and Clinical Text. Philadelphia, Wolters Kluwer/Lippincott Williams & Wilkins.
  2. American Thyroid Association. (2018) https://www.thyroid.org/  Accessed 2/18/18.
  3. Hollowell, J. G., et al. (2002). “Serum TSH, T4, and Thyroid Antibodies in the United States Population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III).” The Journal of Clinical Endocrinology & Metabolism 87(2): 489-499.
  4. Canaris, G. J., et al. (2000). “The Colorado thyroid disease prevalence study.” Arch Intern Med 160(4): 526-534.
  5. Ladenson, P. W., et al. (2000). “American thyroid association guidelines for detection of thyroid dysfunction.” Arch Intern Med 160(11): 1573-1575.
  6. Vanderpump, M. P. J., et al. (1995). “The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey.” Clinical Endocrinology 43(1): 55-68.
  7. Sinaii, N., et al. (2002). “High rates of autoimmune and endocrine disorders, fibromyalgia, chronic fatigue syndrome and atopic diseases among women with endometriosis: a survey analysis.” Human Reproduction 17(10): 2715-2724.
  8. Malik, R. and H. Hodgson (2002). “The relationship between the thyroid gland and the liver.” QJM: An International Journal of Medicine 95(9): 559-569.

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