Peyer's patches
From Wikipedia, the free encyclopedia
Peyer's patches are secondary lymphoid organs named after the 17th-century Swiss anatomist Hans Conrad Peyer. They are aggregations of lymphoid tissue that are usually found in the lowest portion of the small intestine (ileum) in humans; as such, they differentiate the ileum from the duodenum and jejunum in that the number of Peyer's patches increase further down the intestine (ie. terminal ileum contains most Peyer's patches).
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[edit] Location and appearance
Grossly, Peyer's patches are observable as elongated thickenings of the intestinal epithelium measuring a few centimeters in length. Microscopically, Peyer’s patches appear as oval or round lymphoid follicles (similar to lymph nodes) located in the mucosa and extending into the submucosa of the ileum.
In adults, B lymphocytes are seen to predominate in the follicles' germinal centers. T lymphocytes are found in the zones between follicles.
[edit] Function
Because the lumen of the gastrointestinal tract is exposed to the external environment, much of it is populated with potentially pathogenic microorganisms. Peyer's patches thus establish their importance in the immune surveillance of the intestinal lumen and in facilitating the generation of the immune response within the mucosa.
Pathogenic microorganisms and other antigens entering the intestinal tract encounter macrophages, dendritic cells, B-lymphocytes, and T-lymphocytes found in Peyer's patches and other gut-associated lymphoid tissue (GALT).
Peyer's patches contain specialized cells called M cells which sample antigen directly from the lumen and deliver it to antigen-presenting cells (located in a unique pocket-like structure on their basolateral side. B-cells and memory cells are stimulated upon encountering antigen in Peyer's patches. These cells then pass to the mesenteric lymph nodes where the immune response is amplified. Activated lymphocytes pass into the blood stream via the thoracic duct and travel to the gut where they carry out their final effector functions.
[edit] Pathology
Although important in the immune response, excessive growth of lymphoid tissue in Peyer’s patches is pathologic, as hypertrophy of Peyer’s patches has been closely associated with idiopathic intussusception.
[edit] External links
- Histology at BU 12006ooa - "Lymphoid Tissues and Organs: ileum, Peyer's patches"
- Organology at UC Davis digestive/mammal/intestine0/intestine3 - "Mammal, small intestine (LM, Low)"
- Peyer's patches at thehealthnews.org
Bone marrow | Thymus (Hassall's corpuscles) | Spleen (White pulp, Periarteriolar lymphoid sheaths, Marginal zone, Red pulp) | Tonsils/Waldeyer's tonsillar ring (Palatine, Lingual, Adenoid)
Mucosa-associated lymphoid tissue: Gut-associated lymphoid tissue | Peyer's patches
Lymph nodes: Subcapsular sinus | Paracortex | Lymph vessels
Lymph | Lymphocytes | High endothelial venules | Immune system
Anatomy of torso, digestive system: Gastrointestinal tract |
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Upper gastrointestinal tract Mouth • Pharynx (nasopharynx, oropharynx, hypopharynx) • Esophagus • Crop • Stomach (rugae, gastric pits, cardia/gland, fundus/gland, pylorus/gland, pyloric antrum) Lower gastrointestinal tract Large intestine: Cecum • Colon (ascending colon, transverse colon, descending colon, sigmoid colon) • Rectum (Houston valve, rectal ampulla, pectinate line) • Anal canal (anal valves, anal sinuses, anal columns) Anus: Sphincter ani internus muscle • Sphincter ani externus muscle GALT: Peyer's patches • M cells intestinal villus • crypts of Lieberkühn • circular folds • taenia coli • haustra • epiploic appendix |