My Brother Calls Me 'Bug Eyes'": A Case Study on the Endocrine System Nineteen-year-old Krista waited impatiently as Dr. Weisman scribbled in his...

My Brother Calls Me 'Bug Eyes'": A Case Study on the Endocrine System

Nineteen-year-old Krista waited impatiently as Dr. Weisman scribbled in his chart. She hoped he was scribbling an explanation of what was wrong with her. She was tired of not feeling like herself and tired of being so stressed about it. She was particularly tired of how her eyes seemed to bulge outward, so much that her 10-year-old brother had started calling her "Bug Eyes." 

Dr. Weisman finally put down his pen and looked at Krista. "Well, your blood pressure and pulse are elevated. You've lost weight without trying, you have difficulty sleeping, you perspire more than usual and you've had continuing bouts of diarrhea. Those things, combined with the swelling in the front of your neck, suggest that you may be suffering from more than the stress of college life. I think we need to run some blood tests to check your thyroid function."

Krista blinked in surprise. "All of those things can be caused by a problem with my thyroid? Even the way my eyes look?"

Dr. Weisman nodded. "Your thyroid secretes several hormones that have widespread and varied effects. The protrusion of your eyes is a condition called exophthalmos - it is an inflammatory response to abnormal levels of thyroid hormones. The fact that you have this condition in addition to your other symptoms makes me fairly certain this is a thyroid problem."

Krista hoped Dr. Weisman was right. Having a medical explanation for her symptoms would mean that she wasn't losing her mind.

Several days later, Krista met again with Dr. Weisman.  

"Let's talk about your test results," he said. "Your thyroid hormone levels are elevated, but your level of thyroid-stimulating hormone (TSH) is lower than it should be. Those results suggest that you probably have Graves' disease, which means that your thyroid is overactive. But there's good news too—this is a condition that we can treat relatively easily."

Krista felt a twinge of relief at the doctor's words, but a flurry of questions poured out of her mouth. "What made my thyroid go crazy? And what is TSH? If it's a thyroid hormone, why is it low instead of high like everything else? And what kind of treatment do I need? Will it fix my thyroid? Will I..."

Dr. Weisman laughed and held up his hand to stop the barrage of questions. "Hold on, Krista. I'll explain everything, and with the right treatment, your brother may not be able to call you 'Bug Eyes' much longer." 

1. Name the two hormones commonly referred to as "thyroid hormone" and describe their general actions.
2. Why would an overactive thyroid cause Krista's weight loss, sweating, and elevated heart rate?
3. Krista wonders if TSH is a "thyroid hormone," and Dr. Weisman explains that it is not. State the action of thyroid-stimulating hormone (TSH) and name the gland that secretes it.
4. How is the secretion of TSH regulated under normal conditions?
5. In Graves' disease, the immune system makes antibodies that stimulate TSH receptors on the thyroid gland. What effect does this have on Krista's thyroid?
6. Why is Krista's TSH level low instead of high?
7. If Krista had been diagnosed with hypothyroidism, what would happen to her levels of TSH and thyroid hormone?
8. A common treatment for Graves' disease involves ingesting a dose of radioactive iodine, which slowly destroys the thyroid gland. Why are other tissues unaffected?