If I can accomplish this with LR, as you suggested, that would be great! I'll wait for your followup with the rest of the detailed information you referred to. Being able to accomplish this without having to install third party software would be the way I'd want to go. Lightroom, my D7100 and my MBP would be awesome!
I have tethered to my D800 using LR 4 and LR 5 using the cable that comes with my Nikon that connects to the camera and to the USB port on the MacBook Pro. I am assuming that the D7100 comes with an appropriate cable?
In LR, go to the File menu at the top of LR, and then down to Tethered Capture, and then Start Tethered Capture. You will get a menu that comes up where you can and should name the Session, Naming Template, and choose the destination where the pictures will be uploaded and saved to your computer. Once you do that and click OK, you will get another smaller window that asks you to put in the initial shot name. That can be anything you want; such as Shot 1, or Martha's Portrait, or whatever.
As Catfish252 posted, your D7100 can be tethered using LR based on the link he provided.
From that point, you just start shooting and the images should appear on your MacBook Pro. As Bobbee said, LR is actually a third party software program (not a Mac OSX installed program) which is an image editing and cataloging program from Adobe. I guess most people think of it as not being a third party program because it is used so much and kind of like an industry standard, perhaps. Another 'third party program'
you can download off the internet that is free, that I previously mentioned, is called Sofortbild at http://www.sofortbildapp.com
. It works very well and has some nifty features for controlling your camera from your MacBook Pro. Just as a FYI, LR also has controls for your camera, as well, from your MacBook Pro.
You can find tether cable extensions (16 feet long) for connecting to your laptop at http://www.bhphotovideo.com/c/search?Ntt=Tether+cable+Extensions+D7100&N=0&InitialSearch=yes&sts=ma&Top+Nav-Search=
. Hope this helps you out a bit with both LR and the cable extensions. :)