External, originating outside of an organ, tissue, cell or the body. It may refer to a substance that is administered to the body, such as exogenous insulin or testosterone.
Darkening and thickening of the skin around the neck, underarms, and skin folds; can be caused by elevated levels of insulin in the blood and is often associated with obesity
Originating in or produced within an organ, tissue, cell or by the body. The term may be used to distinguish between an internal or external source of a substance, such as insulin or testosterone.
Specialized cells in the pancreas that produce and secrete one of several hormones that affect certain body functions; some examples include alpha cells that produce glucagon and beta cells that produce insulin.