Peyer's patches (or
aggregated lymphoid nodules, or occasionally
PP for brevity) are organized lymphoid nodules, named after the 17th-century
Swiss anatomist
Johann Conrad Peyer. They are aggregations of lymphoid tissue that are usually found in the lowest portion of the
small intestine, the
ileum, in humans; as such, they differentiate the ileum from the
duodenum and
jejunum. The duodenum can be identified by
Brunner's glands. The jejunum has neither Brunner's glands nor Peyer's patches.