discuss the role of endogenous factors on body rhythms?

Answer 1

haven't a clue.

Answer 2

This looks like a good lead-in question for an A-level assignment!

As far as the Endocrine system (namely steroids and hormones) is concerned there are many endogenous chemicals that can be ascribed as affecting body rhythms. A major part of this is homeostasis - the fluctuations between two ideal boundaries.
Insulin (Beta Islets of Langerhans) and Glucagon, two hormones that control Glucose levels.
Adrenalin and Noradrenalin, stress hormones that affect among other things cardiovascular efficiency, vascular-dilation, pupil dilation...