Final answer:
The ileocecal valve is the most distal short portion of the small intestine that precedes the large intestine, located at the end of the ileum and the beginning of the cecum.
Step-by-step explanation:
The most distal short portion of the small intestine, just before it joins the large intestine, is the ileocecal valve. The ileum is the third and final part of the small intestine, ending at the ileocecal valve, where it meets the first part of the large intestine - the cecum. Not only does the ileum absorb essential nutrients like vitamin B12 and bile salts, but it also passes the remaining undigested material into the large intestine through the ileocecal valve. The appendix, a small tube located at the ileocecal valve, is thought to be a vestigial organ with a minor role in immunity and may serve as a bacterial reservoir during illness.