chivalry is dead. nothing should be done solely because they're female.
i hold the door open for everyone. if it's with a group of friends, i hold it open for all to pass.
if it's a group for 1-4 strangers, i hold it open for all to pass.
if i see a fairly large group / continuous chain of people, i pass the torch. otherwise you're stuck forever.
and although a "thank you" is generally warranted, you should never expect it. you dont hold open doors thinking, "i'm going go open this door for this young man because he will say thank you to me!" you hold open doors because you want to be nice.
as we're all nurses, i'm sure you do tons of things for your patients and sometimes never get a thank you. dont be annoyed by it, just know you're doing the right thing by helping.