Hey there!
Your example sentence is very good, and the article is in exactly the right place.
Articles can also be referred to as 'determiners,' since they determine specifically which object (noun) is being talked about. For example, when talking about a boy riding his bicycle, using 'a boy' tells that there is one specific boy that is riding his bike. However, when talking about John riding his bicycle, the name 'John' does not need an article ('a John' is never correct in English). The name itself is enough to tell that there is one specific person riding his bike.
In your sentence, 'organic bowel disease' is the name of a specific disease, so it does not need an article. "A functional condition" refers to a group of conditions, and does not specify which one is being discussed (since that is the task of the person who will answer the question). Since there are multiple functional conditions, and the question is asking for the identification of only one, it requires an article, 'a functional condition.'
Does that make sense?
Also, you are right to second-guess the grammar in your own question. It should be "there is no article," since 'article' is singular.