noob question regarding while loop and random numbers, in text based RPG style game.

So I started python 2 days ago, complete beginner and I am trying to incorporate combat into a text based game.

I would like to have randomly generated numbers for damage but I don't think I can insert a different number into each loop of a while loop?

Just now I just randomly generate a number and that is the only number I can use to deduct damage.

I would appreciate if someone could show me how to have a random number between 2 set values deducting damage each loop. Thanks in advance, heres what I have just now:

http://pastebin.com/Dp09S9Ck

also if anyone can explain 'sentry variables' to me in a simple way i would appreciate it.