Bodily functions one must be comfortable with when teaching Human Physiology

1.  Formation of urine
2.  The defecation reflex
3.  The menstrual cycle

We are covering the digestive system right now in my Physiology classes, and yes, today I told them about #2 (pun intended).  While it is something we all do (as the saying goes, "everybody poops"), it is a little weird talking about pooping to a room full of 19-22 year olds.