Illustration of a swollen, inflamed Peyer's patch during diarrhoea. Peyer's patches are lymphatic nodules found in the ileum (lower part of the small intestine). They are crucial for monitoring the growth of pathogenic bacteria in the intestine. Inflammation of Peyer's patches can be caused by typhoid or intestinal tuberculosis. Here, the disease has progressed with the muscularis visible in the base of the ulcer.