Which of the following is the most likely explanation for hypothyroidism in a patient whose iodine level is normal? A) a disproportionate production of T3 to T4 B) hyposecretion of TSH C) hypersecretion of TSH D) hypersecretion of MSH E) a decrease in the thyroid secretion of calcitonin

The correct answer: B) hyposecretion of TSH

Hypothyroidism is a disorder of the endocrine system when the thyroid gland does not work properly, meaning that the production of thyroid hormone is decreased. This disorder is manifested by poor ability to tolerate cold, tiredness, constipation, depression, and weight gain. The causes of hypothyroidism are:

• Low iodine in diet

• autoimmune condition Hashimoto's thyroiditis

• treatment with radioactive iodine

• injury (or surgery) that affects hypothalamus or the anterior pituitary gland

• medications ...

The diagnosis of hypothyroidism includes blood tests measurements of thyroid-stimulating hormone (TSH) and thyroxine levels.