Final answer:
The cecum is the pouchlike structure that joins the ileum at the ileocecal valve, and it is the part of the large intestine that the appendix attaches to.
Step-by-step explanation:
The pouchlike structure that joins the ileum at the ileocecal valve is the cecum. The cecum is the first part of the large intestine and a sac-like structure that is situated inferiorly to the ileocecal valve. It measures about 6 cm (2.4 inches) in length and is responsible for receiving the contents of the ileum and continuing the absorption of water and salts. The appendix, or vermiform appendix, which is considered to have a minor role in immunity, is a winding tube that attaches to the cecum. Particularly, during diarrheal illness, the appendix may serve as a bacterial reservoir to repopulate the gut flora for those surviving the illness.