Lamina muscularis mucosa

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. 

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],... 

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. 

Fig. 8. Fore-stomach of a normal rat. Note normal squamous keratinizing epithelium, thin and relatively avascular lamina propria, well-developed muscularis mucosae, submucosa with less connective tissue and numerous blood vessels, and circular and longitudinal layers of the muscularis externor.

Fig. 9. Fore-stomach of a vitamin A-deficient rat, showing severe epithelial hyperplasia and hyperkeratosis, thickening and papillary prolongation of lamina propria, atrophy and penetration by blood vessels of muscularis mucosae. Continuity of muscularis mucosae is unbroken.

The mouth and esophagus are composed of two layers, the mucosa and submucosa (Figure 3.5). The mucosa is lined on its outer surface by a stratified squamous epithelium with layers of polyhedral cells of the intermediate layers and low columnar cells of the basal layer. Below the cellular layer is the lamina propria containing loose connective tissue with blood vessels and small aggregates of lymphocytes. Smooth muscle within the mucosa (muscularis mucosal layer) is seen as small bundles. The submucosa... 

Figure 3.5. Structure of oral tissues. The mouth and esophagus are composed of two layers the mucosa and submucosa. The mucosa is composed of layers of squamous epithelium, lamina propria, and muscularis. The submucosa contains blood vessels, nerves, adipose tissue, and skeletal muscle.

Figure 3.15. Structure of small intestine. In small intestine, the mucosa contains villi or surface projections, lamina propria, and muscle fibers. Submucosa contains duodenal glands, and the muscularis contains muscle fibers.

In contrast, in the small intestine (Figure 3.15), the mucosa is composed of surface projections or villi with a core of lamina propria and muscle fibers. In the lamina propria itself are found intestinal glands, fine connective tissues, reticular cells, and lymphatic tissue. The submucosa is filled with glands in the duodenum whereas in the muscularis externa an inner circular layer and an outer longitudinal layer of muscle are present. Parasym-... 

The structure of the bladder, ureter, and urethra are similar in that they contain three layers, the mucosa, muscularis, and serosa. In the bladder (Figure 3.16) the inner layer (mucosa) when empty is infolded and it is made up of transitional epithelium. The lamina propria that is found below contains collagen and elastic fibers in the deeper layer. The muscularis is prominent and contains muscle fibers that are arranged in branching bundles separated by connective tissue. Muscular contraction causes expulsion of fluid from the bladder into the ureter. The connective tissue between the muscle fiber bundles merges with the connective tissue of the serosa. The serosa is continuous with the peritoneal lining. 

Figure 3.16. Structure of bladder. This structure is composed of mucosa, muscularis, and serosa. In the bladder, the mucosa is infolded when empty and is supported by connective tissue in the lamina propria. Muscularis contains smooth muscle bundles, and the serosa is continuous with the peritoneum.

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