Which hormone is released by the posterior pituitary?

The hormone released by the posterior pituitary is antidiuretic hormone (ADH), also known as vasopressin. ADH plays a crucial role in regulating water balance within the body. It is produced in the hypothalamus and then transported to the posterior pituitary, where it is stored and released into the bloodstream in response to various signals, such as high blood osmolarity. Once released, ADH acts primarily on the kidneys to promote water reabsorption, thereby reducing urine output and helping to maintain fluid balance and blood pressure.

In contrast, other hormones listed have different sources and functions. For example, insulin is secreted by the pancreas to regulate blood glucose levels, thyroxine is produced by the thyroid gland to regulate metabolism, and estrogen is primarily secreted by the ovaries and is involved in the reproductive system and secondary sexual characteristics. Understanding the specific origins and functions of hormones is essential in biology, particularly in the context of endocrine regulation.