Thyroxin is a hormone that increases metabolic activities within various tissue targets. Low levels of circulating thyroxin trigger the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH secretion then stimulates thyroxin production and release by the thyroid gland. The increased level of circulating thyroxin inhibits further secretion of TSH from the anterior pituitary.

Based on the information provided, which of the following can most likely be concluded about the TSH-thyroxin loop?

When thyroxin levels are low, production of TSH is stimulated which in turn stimulates secretion of thyroxin. When thyroxin levels are high, TSH secretion is inhibited so no more thyroxin is secreted. These negative feedback processes ensure a stable amount of thyroxin in the tissue targets.