The endocrine system is made up of glands that secrete hormones which tell cells what to do. The major endocrine glands are located in the brain, neck, abdomen, and groin. The pituitary gland, though small, is called the "master gland" and regulates other glands. The pancreas is the largest endocrine gland and produces insulin which is important for regulating blood sugar levels. Common problems with the endocrine system include diabetes.