A 64-year-old steel worker presents to his Primary Care Provider PCP with a chief complaint of passing bright red blood when he had a bowel movement that morning

A 64-year-old steel worker presents to his Primary Care Provider (PCP) with a chief complaint of passing bright red blood when he had a bowel movement that morning. He stated the first episode occurred last week, but it was only a small amount after he had eaten a dinner of beets and beef. The episode today was accompanied by nausea, sweating, and weakness. He states he has had some left lower quadrant pain for several weeks but described it as “coming and going”. He says he has had a fever and abdominal cramps that have worsened this morning. The likely diagnosis is lower GI bleed secondary to diverticulitis.

Question:

What can cause diverticulitis in the lower GI tract?