Muscularis mucosae

The mucosa of the small intestine can be divided into three distinct layers. The muscularis mucosa, the deepest layer, consists of a thin sheet of smooth muscle... 

Structurally, the large intestine is similar to the small intestine, although the luminal surface epithelium of the former lacks villi. The muscularis mucosa, as in the small intestine, consists of inner circular and outer longitudinal layers. Figure 6 illustrates a photomicrograph and diagrammatic sketches of this region. 

Mucosa. The innermost layer of the wall is the mucosa, which consists of a mucous membrane, the lamina propria, and the muscularis mucosa. The mucous membrane provides important protective and absorptive functions for the digestive tract. The nature of the epithelial cells lining the tract varies from one region to the next. Rapidly dividing stem cells continually produce new cells to replace worn out epithelial cells. The average life span of these epithelial cells is only a few days. The lamina propria is a thin middle layer of connective tissue. This region contains the capillaries and small lymphatic vessels that take up the digested nutrient molecules. The muscularis mucosa is a thin layer of smooth muscle. Contraction of this muscle may alter the effective surface area for absorption in the lumen. 

The ability of such a protein to access the muscularis externa and thereby influence peristalsis in vivo has to be called into question, but a role for regulation of local spasm via inhibition of the muscularis mucosa is feasible. Similarly, a role for parasite AChEs in the latter phenomenon cannot yet be discounted. 

Peptic ulcer disease (PUD) refers to a group of ulcerative disorders of the upper GI tract that require acid and pepsin for their formation. Ulcers differ from gastritis and erosions in that they extend deeper into the muscularis mucosa. The three common forms of peptic ulcers include Helicobacter pylori (HP)-associated ulcers, nonsteroidal antiinflammatory drug (NSAID)-induced ulcers, and stress-related mucosal damage (also called stress ulcers). 

Figure 8.1 (A) Cross-sectional view of the organization of the small intestine, illustrating the serosa, the longitudinal and circular muscle layers (=muscularis externa), the submucosa, and the intestinal mucosa. The intestinal mucosa consists of four layers, the inner surface cell monolayer of enterocytes, the basal membrane, the lamina propria (connective tissue, blood capillaries), and the muscularis mucosae, (B) Schematic representation of an enterocyte (small intestinal epithehal cell) (according to Tso and Crissinger [151], with permission).

The tracheo-bronchial epithelium forms the interface between the conducting airways and inspired air. As described above, the epithelium is layered upon a connective tissue substratum consisting of a basement membrane, lamina propria, and submucosa [6], The submucosa contains elastic fibres, a muscularis mucosa, connective tissues and seromucous glands. Lymphatics are also located in the bronchial walls [2],... 

Ulcerative or inflammatory lesions may affect the physiology of the small and large intestine. Ulcer formation entails a circumscribed loss of tissue from the surface of an organ, which results from necrosis following cell destruction by chemicals and the like, or by restriction of the blood supply. Ulcers are among the most common and important lesions. Those that do not penetrate the muscularis mucosa are called erosions. Ulcerative conditions in humans must be differentiated from malignant ulcers, which are associated with neoplasia. Among... 

Both the parasympathetic and sympathetic nervous systems provide extrinsic gastrointestinal innervation. Parasympathetic stimulation increases muscle contraction of the gut, while sympathetic stimulation inhibits contractions. Stimulation of either a- or 13-adrenoceptors will result in inhibition of contractions. The intramural nervous system consists of a myenteric (Auerbach s) plexus between the circular and longitudinal muscle areas and a submucosal (Meissner s) plexus between the muscularis mucosa and the circular muscle layers. These two plexuses contain stimulatory cholinergic neurons. 

Bieger, W. S., and Triggle, C. R. (1990). NO Possible role in 1 TX-sensitive field-stimulated relaxations of the rat oesophageal tunica muscularis mucosae. Eur, ]. Pharmacol. 183, 2419. 

As mentioned above, the villi of the small intestine (Figure 1.2) house a dynamic, self-renewing population of the epithelial cells that includes absorptive cells (enterocytes), secretory cells, and endocrine cells. The thin lining (height 25 p,M height of the microvilli is 1.5 pM) of the columnar enterocytes is the only barrier between the intestinal lumen and the muscularis mucosa, which represents, in this context, the entire body interior. The entire epithelial lining of the intestine replaces itself every 3-5 d [128], It is the enterocyte and its neighboring cells where absorption processes occur and it will therefore be the focus of the mechanistic discussions below. 

Ford AP, Baxter GS, Eglen RM, Clarke DE. 5-Hydroxytryptamine stimulates cyclic AMP formation in the tunica muscularis mucosae of the rat oesophagus via 5-HT4 receptors. Eur J Pharmacol 1992 211 117-120. 

Traditional endoscopic and surgical procedures provide whole tumor samples well suited for microscopic examination and analysis in the pathology laboratory. The use of whole tissue tumor biopsies for proteomic studies has, however, raised several important issues that have been well demonstrated in CRC [9]. These include cellular heterogeneity in the different bowel parietal layers (mucosa, submucosa, muscularis mucosa, serosa) that may or may not be infiltrated, epithelial cell diversity in the mucosa itself, tissue infiltration by inflammatory cells such as lymphocytes, contamination with other body fluids, and protein degradation following tumor necrosis. In fact, epithelial cell content was found to vary between 9 and 67% in whole biopsies of normal mucosa and between 7 and 95% in tumor biopsies [10]. This study clearly demonstrates the likelihood of large cellular variation between tissue samples. 

This is divided, histologically, into three layers an epithelial surface, a supporting connective tissue layer (the lamina propria), and a thin smooth muscle layer (the muscularis mucosae). The latter produces local movements and folding of the mucosa. 

The epithelium is supported underneath by lamina propria and a layer of smooth muscle called muscularis mucosa (3-10 cells thick). These three layers, i.e., the epithelium, lamina propria, and muscularis mucosa, together constitute the intestinal mucosa.On the apical surface, the epithelium along with lamina propria projects to form villi. The cell membranes of epithelial cells that comprise the villi contain uniform microvilli, which give the cells a fuzzy border, collectively called a brush border. These structures, although greatly increase the absorptive surface area of the small intestine, provide an additional enzymatic barrier since the intestinal digestive enzymes are contained in the brush border. In addition, on the top of the epithelial layer lies another layer, the UWL, as previously described. The metabolic and biochemical components of the epithelial barrier will be discussed. 

Mucous Surface. The mucosa of the small intestine consists of three layers (Fig. 2) an absorptive layer, a continuous single sheet of columnar epithelium the lamina propria, a layer heterogeneous in composition and cell type and the muscularis mucosa, a muscular layer separating the mucosa and submucosa. 

MRT mean residence time (drug turnover time), mucosa The lining of the gut. consisting of three layers the inner epithelium lamina propria muscularis mucosae, mucous membrane (mucosa) The moist membrane lining internal structures, e.g. respiratory tract, mucus The fluid secreted by mucous membranes, multideterminant Antigen carrying more than one antigenic determinant. 

The epithelial layer is in immediate contact with the lumen of the gastrointestinal tract. The lamina propria, which functions as a structural support for the epithelial layer, is situated on the basolateral side of the epithelial layer. The lamina propria contains lymph vessels, smooth muscle cells, nerves, and blood vessels, which nourish the epithelium. The muscularis mucosa makes up the deepest layer, which is thought to be involved in contractility.8 A more detailed description of the forces that hold together the epithelial layer is provided below. 

Tis includes cancer cells confined within the glandular basement membrane (intraepithelial) or lamina propria (intramucosal) with no extension through the muscularis mucosae into the submucosa. 

Leiomyoma of the muscularis mucosae is the most common mucosal-based mesenchymal lesion of the GI tract that may present as a polypoid mass." ° " ° These tumors often arise in the colon leiomyomas are also likely to occur within the wall of the esophagus.Unlike many of the previously mentioned lesions, this tumor displaces the colonic crypts and does not grow between crypts. As with leiomyomas elsewhere, these lesions stain strongly with smooth muscle actin and desmin and are negative for c-kit. 

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