Osmosis is producing medical tutorials of consistently excellent quality. They start out explaining concepts in understandable layman's terms, but go on to delve into topics at a level more appropriate for college or graduate study. This makes them particularly useful if you're somewhat knowledgeable about a topic, but want to review and build on what you already know.
This video on opioid addiction is a concise introduction to the subject that doesn't get terribly technical. Videos on more specialized topics, such as cardiac dysrhythmias, are far more detailed and complex.