The role of the pituitary gland in the endocrine system is to act as a master gland. It regulates and controls the activity of other endocrine glands by secreting various hormones. The pituitary gland influences growth, metabolism, and reproductive functions through the release of hormones like GH (growth hormone), TSH (thyroid-stimulating hormone), and LH (luteinizing hormone). Its function is vital for maintaining homeostasis and coordinating various physiological processes throughout the body.