Peyer's patches

Recommended video: Introduction to the lymphatic system [14:10]

Overview of the anatomy, function and main structures of the lymphatic system.

Peyer’s patches are small clusters of lymphatic tissue found in the wall of the small intestine. Specifically, they reside within the lamina propria and extend into the submucosa of the ileum.

Peyer's patches act as the immune system's first line of defense against microbial and dietary antigens. They monitor intestinal microbial populations and can prevent the growth of pathogenic bacteria in the intestines.

Peyer’s patches are an important part of the GALT (gut-associated lymphoid tissue), the largest lymphatic organ of the human body containing more than 50% of its lymphocytes. GALT comprises both isolated and aggregated lymphoid follicles. In the case of Peyer's patches, also known as submucous aggregated lymphoid nodules, these are oval in shape and contrary to standard lymph node structure, they are not surrounded by a connective tissue capsule.

Peyer's patches are irregularly distributed in the small intestine. They are highly concentrated in the distal ileum, where they form a distinct lymphoid ring. One patch is around 2 to 5 centimeters long and consists of about 300 aggregated lymphoid follicles and the parafollicular lymphoid tissue. The dome-like bulge above one follicle is called dome area. M cells (microfold cells) line the dome epithelium of Peyer's patches. Their function is to absorb antigens from the intestinal lumen via endocytosis and transport them to the antigen-presenting cells (APC) to initiate an immune response.