Hormones & Endocrine System

The endocrine system comprises ductless glands that secrete chemical messengers known as hormones directly into the circulatory bloodstream to regulate metabolism, growth, and reproduction. The pituitary gland, located at the base of the brain in the sella turcica, functions as the 'master gland' under the control of the hypothalamus, secreting growth hormone, ACTH, TSH, and gonadotropins. The thyroid gland produces thyroxine ($T_4$) and triiodothyronine ($T_3$) to regulate basal metabolic rate. The pancreas functions as both an exocrine and endocrine gland; its Islets of Langerhans contain beta cells that secrete insulin to lower blood glucose and alpha cells that secrete glucagon to raise glucose levels.