How is the admissions process in Spain?

Does anyone know what are the requirements for admission to a Spanish Med school? I know that they vary by school, but what are the most common requirements?

For instance I notice that they ask you to submit the grades from your Bachillor or equivalent (High School), but what if you have a university degree already, would the grades from your uni be more important than your high school grades for the application process?

On that note, I am an EU citizen but got my uni degree from North America, how can I validade my degree in Spain?