The title of my question seems simple but here is an example of what I want to do:

http://www.mayoclinic.com/health/infant-jaundice/DS00107

What happens on that page is whenever you click on a link to go a section (e.g. "Symptoms") in the article on "Infant Jaundice", it provides a URL parameter like this:

http://www.mayoclinic.com/health/infant-jaundice/DS00107/DSECTION=symptoms

As the DESCTION parameter changes, you get different content on the same page DS00107. The content changes as well as <meta keywords>.

Can someone please tell me how this is achieved? I was thinking it was an if/else situation programmed into the page itself to display different properties depending on the URL parameter.

Any help or suggestions are very much appreciated and my thanks to you for reading my question.