TSH is produced by the pituitary gland and stimulates the thyroid gland to produce T4 and T3. Elevated TSH levels usually indicate hypothyroidism, where the thyroid gland is underactive. Conversely, low TSH levels suggest hyperthyroidism, where the thyroid gland is overactive. Histologically, hypothyroidism may show reduced follicular activity, while hyperthyroidism could present with increased follicular activity and colloid depletion.
