The endocrine system is made up of organs and tissues that produce hormones. The hormones control the target organs.
Some organ systems have their own internal control systems instead of, or in addition to, hormones.
With aging, changes naturally occur in the way that body systems are controlled. Some target tissues become less sensitive to their controlling hormone. The amount of hormones produced can change. Blood levels of some hormones increase, some decrease, and some are unchanged. Hormones are also broken down slower.