Bad quality pics on instagram?

So whenever I take photos on my Nikon the pictures are really full of detail and you can see the HAIR on someone's arm but when I post the pictures onto instagram they become really bad quality? I post them onto tumblr from my computer and then save them when I go to tumblr on my IPad.

However everyone else's pictures are full of detail and they don't seem to have the problems I do?

It probably needs to convert the image and make it much much smaller. Probably a poor compression on the site itself. Lousy phone pictures don't need to be compressed because they are already small enough to post. Maybe if you use photoshop to compress before hand. I know that does seem like a lot more work per picture.