Three patients have a swelling in the neck…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Three patients have a swelling in the neck. Their blood tests show these levels.
Patient P: thyroid hormone low, TSH high.
Patient Q: thyroid hormone high, TSH low, and the eyes bulge.
Patient R: thyroid hormone low, TSH low.
- Which patient has a goitre from a lack of iodine? Explain the TSH.
- Which patient has exophthalmic goitre?
- Which patient is likely to have a fault in the pituitary, not in the thyroid?
Need a reminder? The key ideaShow
The thyroid makes T4 and T3, which need iodine. TSH controls the thyroid, and the thyroid hormones act back on the hypothalamus and pituitary by negative feedback. Too little iodine gives a goitre with a high TSH. Too much thyroid hormone, as in Graves' disease, gives a high metabolic rate.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Patient P. With too little iodine the thyroid hormone is low. The feedback is weak, so the pituitary releases more TSH. The TSH makes the gland grow.
Step 2. (b) Patient Q. A high hormone level with low TSH and bulging eyes is Graves' disease, which is exophthalmic goitre. The high hormone level switches TSH down.
Step 3. (c) Patient R. The hormone is low, but TSH is not high, so the pituitary does not respond. The fault lies in the pituitary, which makes too little TSH.
Answer: (a) P; (b) Q; (c) R.
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