Complex sentence: Upregulation and downregulation can also happen as a response to toxins or hormones, for example in pregnancy, hormones cause cells in the uterus to become more sensitive to oxytocin.
Split into simpler sentences: Upregulation and downregulation can also happen as a response to toxins or hormones. An example of upregulation in pregnancy, is hormones cause cells in the uterus to become more sensitive to oxytocin.