Thyroid hormones exert their effects on cells in a manner similar to steroid hormones; describe the mechanism of action of thyroid hormones.
Why would an imbalance in thyroid hormones have such widespread effects on the body?
Why was goiter observed in Georges case?
Why would calcium homeostasis be impaired in response to removal of the thyroid gland?
What could be used to specifically destroy the thyroid gland and have minimal effects on other cells and tissues in the body?
Case Study:
George is a thirty five year old hardware clerk. During his routine physical he casually mentions to his physician that he seems to be sweating more profusely than normal and most rooms that once were comfortable are now too “hot”. At home a room that his wife and children find to be comfortable causes him to sweat profusely. George also reports that he seems to be losing weight even though his appetite has increased. He also complains that he has a shortened attention span and that he always wants to be moving around. Despite the fact that he feels fatigued, George claims to have difficulty sleeping and seems to have more frequent bowel movements, occasionally accompanied by diarrhea. The physician discovers George has lost 15 pounds since his last physical. In checking his chart, the physician finds that George has a negative history for chronic illnesses, does not smoke, and has a low risk for cardiovascular disease. He does however have a positive family history for autoimmune diseases. His father suffers from idiopathic thrombocytopenia, his mother has been diagnosed with rheumatoid arthritis and his oldest sister was recently diagnosed with systemic lupus erythematosus.
Results of George’s physical examination were within normal ranges with the exception of the following: he demonstrated tachycardia, loud heart sounds, and apparent cardiac arrhythmias accompanied by slight hypertension. These arrhythmias were confirmed by electrocardiogram to be supraventricular in origin. George’s eyeballs appeared large and protruding and his hair was fine and soft. He was also beginning to demonstrate some degree of alopecia. George was also observed to have palmar erythema. palpation of the neck revealed the presence of goiter. Results of blood tests indicated elevated concentrations of thyroid hormones (thyroxin and triiodothyronine), hypercalcemia, and decreased circulating concentrations of lipids. Based on the physical characteristics and the results of the blood tests, George’s physician suspected that George was suffering from some form of hyperthyroidism and sent him to an endocrinologist to confirm the initial diagnosis.
Following the initial consultation and examination, the endocrinologist ordered tests to determine whether George was indeed hyperthyroid. The test results indicated an elevation in the concentration of thyroid hormones in the blood and the presence of thyroid-stimulating antibodies. These antibodies specifically stimulate the thyroid gland by binding with the thyroid stimulating hormone receptor located on the plasma membrane of the follicular cells of the thyroid gland. Based on these results, the endocrinologist concluded that George had Grave’s disease, a form of hyperthyroidism believed to be autoimmune in nature. George was presented with a number of possible treatment options. These included treatment with chemicals (propylthiouracil and methimazole) that decrease the production of thyroid hormones by the thyroid gland, radioisotopic destruction of the thyroid gland by the use of 131I, and surgical removal of the thyroid gland. After considering all the options, especially the possible effects of radiation on gamete development, George chose surgery. Following successful surgery, George was prescribed synthetic thyroid hormone to ensure that his body was receiving adequate thyroid hormone and told to return within 2 months for a follow-up evaluation of circulating thyroid hormone concentrations. He was also cautioned to carefully monitor his calcium intake.
