Final answer:
Peyer's Patches and appendices are parts of the digestive system that have important immune functions.
Step-by-step explanation:
Peyer's Patches are patches of lymphoid tissue found in the lining of the small intestine. They play an important role in the immune system by detecting and preventing the entry of harmful microbes into the body. When foreign substances are detected, Peyer's Patches produce antibodies to destroy them.
Appendices are small, finger-like projections located at the beginning of the large intestine. While the exact function of the appendix is still not fully understood, it is believed to have immune functions similar to Peyer's Patches. Additionally, it may also act as a reservoir of beneficial gut bacteria.