What is the primary purpose of the hormone thyroxin?

The primary purpose of the hormone thyroxin, also known as T4, is to regulate metabolism. Thyroxin is produced by the thyroid gland, and it plays a pivotal role in the body’s metabolic processes. This hormone influences how cells use energy, affecting the rate at which the body burns calories and produces proteins. Elevated levels of thyroxin can increase the metabolic rate, leading to faster energy use, while lower levels can lead to a slowdown in metabolism.

The other choices focus on different physiological functions. Blood sugar levels are primarily controlled by insulin and glucagon, stress responses are managed by hormones like cortisol and adrenaline, and calcium levels in the body are regulated by parathyroid hormone and calcitonin. Thus, while all these hormones have significant roles in maintaining bodily functions, thyroxin specifically targets metabolic regulation, making it the correct answer.