I asked my step mom about the nurse thing. She as been in nursing for over 30 years and she says that when you see that many naked people it become common place. I believe this is true and think about what I am going to say if it applies to you. When I was a teenager I would get hard from seeing an JC Penny catalog. To see a Playboy was even more exiting. Now to see a Playboy does nothing for me. Those are some good looking girls, but porn as become a drug to me. I see out the kinker and harder type porn, because it is something new to see. But I believe your question depends on the person.
That's what I always wondered about, say, a Playboy photographer. He's seeing the most beautiful women nude all the time, does that get boring? Are you desensitized to beauty? Maybe the only time you'd jackoff to a model you shot may be if you were able to have an intelligent conversation with her, making her more attractive and out of the norm. Not that I'm saying beautiful women wouldn't be able to have an intelligent conversation. Just that maybe you connect differently with one. I still get turned on by Playboy models.
As a nurse I wondered the same thing. Maybe seeing a number of elderly men nude all the time becomes common place. But what if a good looking 25 year old becomes her patient? It's something more out of the norm so does that change her feelings?