Is there any format for official Physiological/Medicine answers?
Given the highly variable nature of such processes and systems, it's unlikely that a common standard is feasible or sensible. In medical questions, a bottom-up order like in your example usually makes sense, starting with the most specific known cause and deriving from there until you arrive at the symptoms. Treatments can branch off or into the order at the point where they apply logically.

If your exam instructions ask for flow text, your question is alreay unnecessary - but if you believe you have the choice, use a note format that is appropriate by common sense. You are essentially creating a diagram, and like any diagram you have to ensure that it is self-contained and comprehensive.

You can shorten the amount of time it takes to write sentences by reducing the literary quality. Of course a well-written text is more pleasing to read and mark, but the main emphasis in your grading will usually be content, meaning that you can afford to form sentences of repetitive structures or lacking logical connection if it is difficult to figure out quickly whether there is one or how to express it etc.