The lining of the tiny intestine is remarkably adjusted for the duty of absorption by boosting the surface area for transmucosal deliver at three levels (Figure 1):

The within surface has circular folds, which increases the area by roughly 3-fold.

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The mucosa tasks from the folds into the lumen through finger-like structures called villi roughly 1 mm in length. Villi rise the surface area by second 10-fold. The surface ar of every villus is extended with epithelial cells known as enterocytes. Absorption takes place throughout the enterocyte barrier.

Small hair-like filaments known as microvilli project from the luminal surface ar of every enterocyte right into the lumen. Microvilli rise the surface ar area for absorption by an additional 20-fold.


The three structures combine to rise the surface ar area by about 600-fold.


*

Figure 1. Wall of the tiny intestine. The intestinal surface area is intensified by finger-like villi.


Each villus is gave with its very own connective tissue support recognized as the lamina propria, its very own arteriolar and venous microcirculation through capillaries draining the basolateral areas of all the enterocytes, and also its own lymphatic system.


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Small Intestine: Imaging Approach and Differential Diagnosis


In Imaging in Gastroenterology, 2018

Mural little Bowel Anatomy

There are 5 class of the SB wall. The innermost is the mucosa, the absorptive surface ar of the bowel. The jejunal mucosa is extensively plicated (folded) and these transverse ("circular") crease lie perpendicular to the long axis of the bowel. The other layers room the submucosa, one muscle, longitudinal muscle, and serosa. The serosa is the peritoneal lining the the bowel. The mucosal surface of the jejunum is raised by influential villi, which space finger-like projections that mucosa. The submucosa has actually a network the capillaries, lymphatics, and a nerve plexus (of Meissner) within loose areolar tissue.

The ileum has the very same 5 layers, but its wall surface is thinner and also less vascular, through less prominent transverse folds and villi. This fold pattern the the jejunum and ileum can be changed by various an illness processes or also reversed, as seen in some patients v celiac-sprue.


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Imaging approach to the tiny Intestine


In Diagnostic Imaging: gastrointestinal (Third Edition), 2015

Mural little Bowel Anatomy

There room 5 class of the small bowel wall. The innermost is the mucosa, one absorptive surface of the bowel. The jejunal mucosa is generally plicated (folded) and these transverse (“circular”) crease lie perpendicular to the lengthy axis that the bowel. The other layers space the submucosa, one muscle, longitudinal muscle, and serosa. The serosa is the peritoneal lining of the bowel. The mucosal surface ar of the jejunum is increased by prominent villi, which space finger-like projections that mucosa. The submucosa has a network of capillaries, lymphatics, and also a nerve plexus (of Meissner) within loosened areolar tissue.

The ileum has actually the exact same 5 layers, but its wall surface is thinner and less vascular, v less influential transverse folds and also villi. This wrinkles pattern the the jejunum and also ileum deserve to be transformed by various disease processes or also reversed, as seen in some patients v celiac-sprue.


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Developmental anomalies that the lids


Hélène Dollfus, Alain Verloes, in Pediatric Ophthalmology and Strabismus (Fourth Edition), 2013

Initial development

During the first month the embryonic development, the optic vesicle is extended by a thin layer of surface ectoderm. During the 2nd month, active cellular proliferation of the surrounding mesoderm results in the development of a circular fold of mesoderm lined by ectoderm. This wrinkles constitutes the rudiments that the eyelid, which gradually elongates over the eye. The mesodermal portion of the top lid arises from the frontal sleep process, the reduced lid indigenous the maxillary process. The covering layer of ectoderm becomes skin ~ above the outside, conjunctiva ~ above the inside. Tarsal plate, connective, and also muscles the the eyelids are obtained from the mesodermal core.


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Anatomy and also Physiology that the small and huge Intestines


Rose Lee, Ethan A. Mezoff, in Pediatric Gastrointestinal and also Liver disease (Sixth Edition), 2021

Mucosa

The muscularis mucosae is the deepest class of mucosa, lying beside the submucosa. It consists of an external longitudinal and inner circular layer of smooth muscle cells. That is a fairly thin layer, being just 3 to 10 cell thick, prolonging into the circular folds (plicae circularis). The colonic muscularis mucosae is thicker, and the thickness boosts progressively from the cecum to the anal canal.5

Lying above the muscularis mucosae, the lamina propria offers structural assistance for the basement membrane of the epithelium. It is composed of a thin layer that connective tissue that embraces the crypts and also extends right into the villous protrusions. The lamina propria is wealthy in arterioles, veins, lacteals, nerve fibrils, and fibroblasts, as well as various cell types, consisting of lymphocytes, macrophages, eosinophils, mast cells, and neutrophils.

The mucosa is thick and highly vascularized in the proximal portion of the little intestine, yet thinner and also less vascular in the distal small intestine. The mucosa is thrown right into crescentic folds, the plicae circulares (also termed the valves of Kerckring). The little intestinal surface ar is studded with finger-like or leaflike protrusions, the minister villi. These two striking morphologic and physiologic features, in addition to the formation of microvilli on the epithelial cabinet surface, combine to produce a 400- to 500-fold boost in the surface area of the mucosa.19 The mucosa the the colon is there is no of villi that characterize the tiny intestine however contains crypts of Lieberkühn (which are bigger than those uncovered in the ileum) and also crescentic folds (plicae circulares) the correspond come the outside sacculations termed haustra.

The luminal surface of small intestine is extended by numerous tiny, hairlike, highly vascularized structures referred to as villi (Fig. 30.3). The villi job for about 0.5 to 1.5 mm right into the lumen, providing it a velvety appearance and feel. The height of the villi decreases increasingly from the duodenum come the ileum. Villi are larger and also denser in the duodenum and also jejunum, and also smaller and also fewer in the ileum.5 lock are broader and ridge-shaped in the proximal duodenum, vice versa, in the distal duodenum and also proximal jejunum lock are predominantly leaf-shaped and only occasionally finger-shaped. Finger-shaped villi predominate in the distal jejunum and ileum. Villi space covered generally with mature absorptive enterocytes, interspersed with couple of mucus-secreting goblet cells and rare enteroendocrine cells. Every villus has a central arteriole, a venule, and also a central lacteal. A cascading capillary bed is developed at the advice of the villi in proximity come the basal surface of the epithelium, allowing for rapid clearance of absorbed nutrients, fluids, and electrolytes right into portal flow then systemic circulation. The capillary walls room fenestrated with diaphragmatic covers, greatly facilitating the absorptive process.20 The core of the villus likewise contains some little nerve fibers, plasma cells, macrophages, mast cells, lymphocytes, eosinophils, and fibroblasts. The bases the the villi room surrounded by numerous pitlike crypts, the crypts the Lieberkühn, expanding down v the lamina propria to the muscularis mucosa.

The epithelial cabinet lining the the small intestine is continuous, yet the cell populace differs in between the villi, the crypts, and also the epithelium overlying the Peyer patches. The crypts, the bases of i m sorry contain the intestinal stem cell (ISC) niche, are occupied primarily by regardless of whether columnar epithelial cells, with a boy scattering of goblet cells, Paneth cells, tuft cells, cuplike cells, and also enteroendocrine cells. The villous epithelium has the same array of cells, through the exemption of Paneth cells. The undifferentiated cell are replaced with maturation enterocytes. The epithelial cells overlying the Peyer job contain all of the aforementioned cells plus functionally and also structurally unique membranous cell (M cells), which are thought come be crucial sites that antigen and luminal bacteria sampling because that the mucosa-associated lymphoid system.22 M cells space responsible for transepithelial transport, delivering foreign antigens and microorganisms to the mucosal lymphoid tissue for recognition and handling, an attribute currently being exploited in vaccine production.23 Structurally distinct, the M cells typically assume one oval or globular configuration, but with a widened base and narrowed apex. The M cell are also found in other parts that the body, particularly where over there is one interface in between the mucosa and also the outside environment; this sites include, however are not restricted to, the tonsils, adenoids, airways, and ocular mucosa.24 The apical microvilli overlying Peyer patches room randomly shortened and also occasionally fused right into folds or ridges.

The mucosal epithelial cells are turned over every 5 come 7 days; therefore, intense mitotic task occurs in ~ the minister crypts. Every intestinal epithelial cells are thought to derive from long-lived, resides progenitors or “stem cells.” these ISCs are located near the basic of the crypts, where they divide to produce added stem cell (to keep their numbers) and rapidly dividing progenitors, termed “transit amplifying” cells, the will identify into the various epithelial cabinet types. The transit amplifying cells undergo several additional cell divisions as they move upward along the minister crypt wall. Cell cycle arrests and also differentiation happen as distinct cell varieties (terminal differentiation) type near the top of the crypt. In the little intestine, many terminally identified cells migrate out of the crypt and also onto the villi and are fully mature by the moment they reach the upper third of the villus; Paneth cells move to the basic of the crypt whereby they reside in proximity to the stem cells. In the big intestine, terminal differentiation wake up in the top one-third of the crypt, and also most cells move onto the mucosal surface; in some areas of the huge intestine, terminally distinguished cells likewise migrate to the crypt base, displacing the proliferating cell upward. Old and spent cells room extruded right into the intestinal lumen in a process termed anoikis, usually at the reminder of the villi or the surface of the colon, to confront the very same fate of digestion and also absorption in addition to the ingesta. Overlying the Peyer patches, epithelial cabinet differentiation has the production of M cells from surrounding stem cells.

Differentiation and also homeostasis that the minister epithelium room regulated through several key developmental pathways including the WNT (wingless), NOTCH, BMP (bone morphogenetic protein), and HEDGEHOG pathways.25,26 this pathways show off signaling between epithelial cells as well as between the epithelium and also the underlying lamina propria, specifically the myofibroblasts.27 In addition, the growth and integrity the the minister mucosa are kept under the affect of the ingesta and also several luminal factors and also autocrine, endocrine, and paracrine secretion from the surrounding cells. Thus, enteral, humoral, and tissue factors are all important for the well-being of the minister mucosa.

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Peptides secreted native enteroendocrine cells play a significant cytoprotective and reparative role in the survival and proliferation the the intestinal mucosa, such together the glucagon-like peptides.28-31 Glucagon-like peptide (GLP) 1 and GLP2 are released native enteroendocrine cell in solution to nutrient ingestion. GLP1 improves glucose-stimulated insulin secretion and inhibits glucagon secretion, gastric emptying, and also feeding. Recently, GLP1 receptor agonists have been used to treat kind 2 diabetes.32 It additionally has proliferative and antiapoptotic results on pancreatic β cells. GLP2 is a 33-amino-acid peptide, encoded carboxy-terminal come the sequence of GLP1 in the proglucagon gene. That is an intestinal trophic peptide that stimulates cabinet proliferation and inhibits apoptosis in the intestinal crypts. Current clinical trials using GLP2 suggest that it may have actually utility in treating patients with brief bowel syndrome and also Crohn disease.33-35

Intestinal epithelial cells add to the gut’s homeostatic setting for commensal bacteria and act as a barrier against external pathogens, in part, v the production and also maintenance that a glycocalyx. Recent studies have displayed that minister epithelial glycoconjugates, such as α 1,2-fucose, play an essential role in host-microbe interactions.36 Selected symbionts such together Bacteroides fragilis and also Bacteroides thetaiotaomicron catabolize α 1,2-fucose, utilizing the byproduct to keep their moving structure and also liberalizing short chain fat acids which, in turn, contribute to the power balance the the host and support mucosal health.37,38 Fucosylated glycans may likewise act together a physiologic barrier, interfering through the attachment of details pathogenic bacteria, such as Salmonella typhimurium, to epithelial cells.39 Fucosylated, sialylated, and other epithelial membrane-bound glycans play a vital role in the intestinal immune system and also maintenance that gut microbial communities.