iPhone: share with instagram

Sometimes when I take a photo I like to share it with friends and family, so I press the button that points up, which then leads to a screen where I can share the photo with facebook, flickr and several other things that I don't use. Recently I decided to use instagram as a means of sharing photos, since I had noticed some of my friends on facebook doing it. I installed the instagram app on my iphone and have used it a few times to share photos, but it is missing from the list of things to share with immediately after taking a photo navigated to from the photo gallery. How can I get instagram to appear in the list of destinations that I see when I decide t share a photo from my phone?