A person whose diet lacks iodine may develop a goitre because
Correct answer: C. the thyroid cannot make enough thyroxine and enlarges under continued stimulation by the pituitary
- A. iodine is needed to make insulin
- B. iodine destroys the thyroid gland directly
- C. the thyroid cannot make enough thyroxine and enlarges under continued stimulation by the pituitary
- D. excess iodine accumulates in the neck
Explanation
Thyroxine contains iodine, so a shortage means output falls, and the low blood level removes the negative feedback on the pituitary, which keeps releasing thyroid stimulating hormone until the gland swells visibly. This is why iodised salt is used to prevent goitre in areas where the soil is deficient. Insulin is made in the pancreas and contains no iodine at all.
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Chemical coordination uses hormones released by endocrine glands and carried in blood to specific target cells. Coverage includes the pituitary, thyroid, pancreas, adrenal glands, ovaries and testes, feedback control, and the contrast between slower, longer-lasting hormonal responses and rapid nervous coordination.
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