The menstrual cycle. What more of a classic drawing can you get? Though it has been done a million times over, here’s the Sketchy Medicine version of the classic hormonal interplay that allows for the endometrial lining to build up, shed, build up, shed, build up, shed…
The nice thing is the the pituitary hormones are aptly named so that FSH (follicle stimulating hormone) stimulates the follicle to grow and LH (luteinizing hormone) causes ovulation (the infamous LH surge) and subsequent corpus luteum development.
Meanwhile the developing follicle secretes estradiol which stimulates the proliferative phase of the cycle. Then the corpus luteum secretes estradiol and progesterone to kick things into high gear for the secretory phase.
You can now passively study this all the time (and keep your own notes) on a notebook or a mug. Nothing says “mmm, coffee” like the hormonal phases of the female reproductive system.