Subject headings are terms that a database uses to keep descriptions consistent. Sometimes these headings are not necessarily the first terms that come to mind when starting your research. Headings could be discipline specific and include specialized language. So, how do do you find these terms so you, too, can find the best sources?
Start by conducting your own search with the terms you came up with. Also, use the synonyms you listed to see what additional resources are returned. From there, read the abstract and choose an article that looks like it might work for your research. Click on the title of the article, which will take you to the full record. There is a lot of information here that can help with your research.
You might see a section labeled Subject Terms, or MeSH (Medical Subject Headings) terms, or Author-Supplied Keywords. Any of these can be helpful; these are terms that either the database supplied, the medical field uses, or the author provided. By clicking on the given terms, you'll be taken to a new search specific to that term. This will produce more results which can help you get to the best sources for your research.