Endocrinology is the branch of science that deals with internal organ chemistry and function as well as hormonal chemistry and the physiological effects of hormones.
Doctors Theodore Wallace and Janet Wallace were 23rd century Federation scientists whose expertise included endocrinology and cell structure. (TOS: "The Deadly Years")
In 2372, The Doctor offered Denara Pel access to the ship's medical database, where she could find "several interesting texts on comparative endocrinology." (VOY: "Lifesigns")