Thyroid Gland

January is Thyroid Month, and since so many of our patients have either hypo- or hyperthyroidism, it is important to fully grasp the function of this gland and the effect it has on our body.

The thyroid gland is located in the neck, below the larynx, and regulates the secretion of three different hormones: triiodothyronine (T3), thyroxine (T4), and thyrocalcitonin. (Alspatch, 616)

Hormones in the body function in a dance with one another using feedback loops. The hypothalamus produces thyrotrophic-releasing hormone (TRH) which is then carried to the pituitary gland. This causes the pituitary to increase the production of TSH, triggering the thyroid to release T3 and T4. The hypothalamus also makes somostatin, which slows the production of TSH by the pituitary. The last steps of the dance are controlled by T3 and T4 themselves, as the body senses those levels and releases or withholds TSH based on them. Think of it like your car. The tank (thyroid) carries the gas (T3 and T4), but won’t send it to the engine (the body) unless you step on the gas pedal or the cruise control senses you slowing down (TRH and TSH). When you hit the brakes, that is somostatin.

Thyroxine is made from an amino acid, tyrosine, by an enzyme derived from zinc, iodine, and selenium. (Holford, 216) Amiodarone, the anti-arrhythmic drug can mimic thyroxine in the body. So, what does it do in the body? It increases the metabolic activity of all the cells, driving up oxygen consumption, generating heat, and promoting growth. Thyrocalcitonin targets bone cells, and is given as a therapeutic treatment in cancer and osteoporosis.

In hypothyroidism, the thyroid tissue stops releasing adequate amounts of hormones, leading to chronic fatigue, cold sensitivity, weight gain, slowed mental ability, constipation, and dry skin. It can be autoimmune, as in Hashimoto’s disease, surgically induced, or be congenital. This is remedied by giving thyroid hormones and monitoring blood levels regularly. If hypothyroidism is untreated, complications such as drug overdose can occur due to the inability of the body to metabolize them properly. Another rare complication is myxedema coma, in which the body can no longer compensate for the decreased energy production leading to stupor and heart/kidney failure.

Hyperthyroidism is when the thyroid is overactive and is often caused by the immune system as well, as in Graves Disease. It can also be caused by thyroiditis from a virus or a tumor, usually benign. Goiter is a symptom and is the swelling of the thyroid or nodules. Other symptoms are hyperactivity, palpitations, breathlessness, heat intolerance, and weight loss. Complications of untreated hyperthyroidism are arrhythmias, congestive heart failure, osteoporosis and thyrotoxic crisis (1). Treatment for this can consist of drugs to block hormone release, surgery, or radioactive iodine.

The care of these patients consists mainly of educating them about the importance of medication compliance, signs and symptoms of crises, and stressing lab follow ups. Understanding the effect the thyroid on their energy levels can motivate patients to participate fully in their care. Knowing why you are testing levels of hormones will give you the ability to discuss these values intelligently with the physician and patients.

References:
(1) http://www.mayoclinic.com/health/hyperthyroidism/DS00344/DSECTION=complications

Holford, P. The New Optimum Nutrition Bible. Cross Press, 2004.

Alspach, J. Core Curriculum for Critical Care Nursing, fourth edition. W.B. Sauders Company, 1991.