Question about how colitis works

Im wondering if when a person has say Left sided colitis if a person will experience "aggravation" on the entire left side of the colon including the rectal area at the same time or if the aggravation can affect only a certain part of the colon, like say just the rectal area. I know I'm doing a terrible job of explaining what I'm trying to ask so bare with me. Another example of what I'm getting at is if a person with left sided colitis can experience only upper left quadrant "flares" or "aggravation" or would the entire colon up until the top left quadrant be affected every single time.

I know with crohns the flares can happen anywhere at any time, but I dont understand how colitis works. I know with procolitis it's just the rectal area, but does this mean that left sided colitis is the entire left side EVERY time or are there periods where a person with left sided colitis will only experience upper left quadrant flares or only rectal flares, or does the entire colon up until the top of the left side flare every single time.

You can have a flare that involves less, or more, of the colon than what you've had in the past. For instance, I was diagnosed with pancolitis. I had a very mild flare about a year ago, and while I didn't have a scope to confirm, my GI and I both thought that it was highly likely just a small portion of my colon was affected, because my symptoms were so mild. I also know of people who were diagnosed with pancolitis, to have subsequent flares only involve the left side, etc.

Generally, though, with UC, the inflammation always starts at the rectum and moves up from there. It's quite rare for UC to be "patchy." So your example of UC only affecting the upper left quadrant would not often happen - it could show up that way on a scope if the patient had been using rectal meds, though, and the rectal meds healed the portion of the colon they can reach.

Thanks for all your input guys. Just something I've always wondered and when you look up the disease online sites make it very ambiguous as to how it actually works.