The ______ layer of the GI tract contains blood vessels, so it can be the site of an inflammatory response that leads to inflammatory bowel disease.

Explanation : Can affect any part of the GI tract (from the mouth to the anus)—Most often it affects the portion of the small intestine before the large intestine/colon. Occurs in the large intestine (colon) and the rectum. 

Inflammatory bowel disease (IBD) is a group of disorders that cause chronic inflammation (pain and swelling) in the intestines. IBD includes Crohn's disease and ulcerative colitis. Both types affect the digestive system. 

 Crohn’s disease and ulcerative colitis are the main types of IBD. Types include:

• Crohn's disease causes pain and swelling in the digestive tract. It can affect any part from the mouth to the anus. It most commonly affects the small intestine and upper part of the large intestine.
•  Ulcerative colitis causes swelling and sores (ulcers) in the large intestine (colon and rectum).
• Microscopic colitis causes intestinal inflammation that’s only detectable with a microscope.