The Thyroid

Discussion Assignment:

1. Thyroid hormones exert their effects on cells in a mannersimilar to steroid hormones; describe the mechanism of action ofthyroid hormones.
2. Why would an imbalance in thyroid hormones have such widespreadeffects on the body?
3. Why was goiter observed in George’s case?
4. Why would calcium homeostasis be impaired in response toremoval of the thyroid gland?
5. What could be used to specifically destroy the thyroid glandand have minimal effects on other cells and tissues in thebody?

Case Study:

George is a thirty five year old hardware clerk. During hisroutine physical he casually mentions to his physician that heseems to be sweating more profusely than normal and most rooms thatonce were comfortable are now too \"hot\". At home a room that hiswife and children find to be comfortable causes him to sweatprofusely. George also reports that he seems to be losing weighteven though his appetite has increased. He also complains that hehas a shortened attention span and that he always wants to bemoving around. Despite the fact that he feels fatigued, Georgeclaims to have difficulty sleeping and seems to have more frequentbowel movements, occasionally accompanied by diarrhea. Thephysician discovers George has lost 15 pounds since his lastphysical. In checking his chart, the physician finds that Georgehas a negative history for chronic illnesses, does not smoke, andhas a low risk for cardiovascular disease. He does however have apositive family history for autoimmune diseases.His father suffers from idiopathicthrombocytopenia, his mother has been diagnosedwith rheumatoid arthritis and his oldest sisterwas recently diagnosed with systemic lupus erythematosus.

Results of George's physical examination were within normalranges with the exception of the following: he demonstratedtachycardia, loud heart sounds, and apparent cardiac arrhythmiasaccompanied by slight hypertension. These arrhythmias wereconfirmed by electrocardiogram to be supraventricular in origin.George's eyeballs appeared large and protruding and his hair wasfine and soft. He was also beginning to demonstrate some degree ofalopecia. George was also observed to have palmarerythema. palpation of the neck revealed thepresence of goiter. Results of blood testsindicated elevated concentrations of thyroid hormones (thyroxin andtriiodothyronine), hypercalcemia, and decreasedcirculating concentrations of lipids. Based on the physicalcharacteristics and the results of the blood tests, George'sphysician suspected that George was suffering from some form ofhyperthyroidism and sent him to an endocrinologistto confirm the initial diagnosis.

Following the initial consultation and examination, theendocrinologist ordered tests to determine whether George wasindeed hyperthyroid. The test results indicated an elevation in theconcentration of thyroid hormones in the blood and the presence ofthyroid-stimulating antibodies. These antibodies specificallystimulate the thyroid gland by binding with the thyroid stimulatinghormone receptor located on the plasma membrane of the follicularcells of the thyroid gland. Based on these results, theendocrinologist concluded that George had Grave's disease, a formof hyperthyroidism believed to be autoimmune in nature. George waspresented with a number of possible treatment options. Theseincluded treatment with chemicals (propylthiouracil andmethimazole) that decrease the production of thyroid hormones bythe thyroid gland, radioisotopic destruction of the thyroid glandby the use of ¹³¹I, and surgical removal of the thyroidgland. After considering all the options, especially the possibleeffects of radiation on gamete development, George chose surgery.Following successful surgery, George was prescribed syntheticthyroid hormone to ensure that his body was receiving adequatethyroid hormone and told to return within 2 months for a follow-upevaluation of circulating thyroid hormone concentrations. He wasalso cautioned to carefully monitor his calcium intake.

Subject Pathophysiology