This document provides an overview of endocrinology and the endocrine system. It discusses the key endocrine glands including the thyroid gland, parathyroid glands, pancreas, and adrenal glands. For each gland, it describes the hormones produced, their normal functions in maintaining homeostasis, and disorders that can result from too much or too little hormone secretion. The cellular mechanisms of hormonal action are also summarized, focusing on second messengers like cyclic AMP and calcium.