The gut-associated lymphoid tissues comprise aggregated or isolated lymphoid follicles which form the Peyer’s patches (PPs). Initially, the aggregated lymphoid follicles were described in 1645 in Italy by Marco Aurelio Severino. In 1677, after a detailed explanation by Johann Conrad Peyer, a Swiss pathologist, these follicles were named Peyer’s patches.
Peyer’s patches due to their ability to carry out the transportation of bacterial and luminal antigens were deemed as the immune sensors of the intestine. These patches operate as induction of the immune defense or tolerance against the pathogens, which lead from the complex interplay between immune cells found in the lymphoid follicles and the follicle-associated epithelium.
Peyer’s Patches – Location
These patches are small masses of lymphatic tissues found all through the ileum area (last portion of the small intestine) of the small intestine. Apart from digesting the food you eat further, the ileum also absorbs nutrients and water from food. Peyer’s patches also referred to as aggregated lymphoid nodules form a significant portion of the immune system by supervising the intestinal bacteria population and checking the growth of the pathogenic bacteria in the intestines.
Peyer’s Patches – Shape
Typically, these patches are rectangular or oval in nature located on the antimesenteric border. In the terminal ileum and duodenum, and sometimes in the proximal jejunum, these patches are randomly seen around the walls of the gut. Some differently shaped patches were also invariably seen in the proximal jejunum and around the ileocaecal valve. Sometimes, these patches, in outline, were serpiginous while some had smaller side branches of the width of 2-3 follicles.
Peyer’s Patches – Follicular distribution
Studies indicate the follicular composition of PPs exhibit that its increasing size was associated with an increase in the count of follicles found. If the size of the patch was bigger, the number of follicles in it was found to be greater. A microscopic view indicated that the patches were thick by only one follicle. The thick patches were occasionally found in the terminal ileum of the well-nourished infants and younger children; a complete analysis indicated that such patches were thick by two to three follicles. However, sections taken for histology exhibited a papillary appearance.
Peyer’s Patches – Function
As the lumen of the gastrointestinal tract is disclosed to the exterior, most of this part is occupied by pathogenic microbes. These patches hence set up their significance in the immune surveillance of the intestinal lumen and promote the generation of the immune response in the mucosa.
It is involved in the analysis and in responding to pathogenic microbes in the ileum. In the gut, the antigens from the microorganisms are seen through endocytosis by microfold cells which line the surface of each patch. Such antigens are transported to the lymphoid tissue where it is absorbed by the macrophages and serves to the B and T lymphocytes.
The lymphocytes stimulate an immune response when provided with dangerous pathogenic antigens by the production of pathogen-specific antibodies. This makes them pathogen-killing cytotoxic T lymphocytes. Also additionally, moving via the lymphatic vessels to the lymph nodes to alarm other cells of the immune system. Then the body prepares a full-body immune response to the pathogen ahead of it being able to spread beyond the intestines.
The pathogenic microbes and other antigens which enter the intestinal tract taken on the dendritic cells, macrophages, B-lymphocytes and T-lymphocytes seen in Peyer’s patches and other sites of the gut-associated lymphoid tissue. PPs serve for the gastrointestinal system like the tonsils serve for the respiratory system which traps foreign matter, surveilling and destroying it.
Folds – Plicae Circulares
The inner walls of the small intestine are covered by many folds of the mucous membrane known as plicae circulares. The surface of such folds comprises small projections referred to as microvilli and villi that further increases the total area to absorb. Absorbed nutrients move into circulation by lacteals and blood capillaries or the lymph channels.
Even though small intestines are 3-4 cm in diameter, it is about 7 meters in length and has been approximated that their total absorptive surface area is close to 4500 sq. meters. This huge absorptive surface is rendered by their special structure of the mucosa that is oriented in concentric folds appearing as transverse ridges. Such folds are called plicae circulares which are close to 5-6 cm in length and 3 mm in thickness.
The Plicae circulares are found all through the small intestine barring the bulb or the first part of the duodenum. It is typically a smooth and flat exception being some longitudinal folds. These folds are also referred to as the valves of Kerckring and are the largest structures in the lower part of the duodenum and in the upper portion of the jejunum. It gets smaller and disappears eventually in the lower part of the ileum.
Usually, the folds are one-half to two-thirds of their way around the intestinal wall. In some instances, one fold can spiral through the wall for 3-4 complete turns. It is evaluated that the small intestine comprises close to 800 plicae circulares, and it increases the surface area of the lining of the small bowel by 5-8 folds the surface area of the exterior.
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