Pineal Gland: Functions and Hormones The pineal gland is a small, pea-shaped endocrine gland located in the brain, between the two hemispheres, in a groove where the two halves of the thalamus join. It plays a crucial role in regulating biological rhythms and certain endocrine functions. Functions of the Pineal Gland Hormones Secreted by the Pineal Gland 1. Melatonin: 2. Serotonin (Precursor of Melatonin): Disorders Associated with Pineal Gland Dysfunction