Oral Sex -The difference between insertive and receptive

Question

Why is their a difference in the risk for insertive vs receptive oral sex and anul sex. Does'nt thethe uretha have a very thin membrane that can be penetrated from bacteria such as blood from the mouth or feces from the rectum?

Answer

The difference in risk for insertive vs receptive only applies to anal intercourse as far as I know. The reason the receptive partner is at higher risk is because of the possible of tears and breaks in the rectal mucosa (see other recent answers on this topic).