Final answer:
Peyer's patches are the large collections of lymphoid tissue found in the submucosa of the small intestine. They serve to provide immune responses against ingested substances.
Step-by-step explanation:
The large collections of lymphoid tissue found in the submucosa of the small intestine are called Peyer's patches. Peyer's patches are aggregations of mucosa-associated lymphoid tissue (MALT) that serve to provide immune responses against ingested substances. They contain specialized cells called M cells that sample material from the intestinal lumen and transport it to nearby follicles, initiating adaptive immune responses.