Hormone production and release are primarily controlled by negative feedback, as described in the discussion on homeostasis. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones. Increasing levels of these hormones in the blood then give feedback to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland (Figure 16.14).
Goiter, a disease caused by iodine deficiency, results in the inability of the thyroid gland to form T3 and T4. The body typically attempts to compensate by producing greater amounts of TSH. Which of the following symptoms would you expect goiter to cause?
- Hypothyroidism, resulting in weight gain, cold sensitivity, and reduced mental activity.
- Hyperthyroidism, resulting in weight loss, profuse sweating, and increased heart rate.
- Hyperthyroidism, resulting in weight gain, cold sensitivity, and reduced mental activity.
- Hypothyroidism, resulting in weight loss, profuse sweating, and increased heart rate.