Mucosal surface area

Diarrhea is a common problem that is usually self-limiting and of short duration. Increased accumulations of small intestinal and colonic contents are known to be responsible for producing diarrhea. The former may be caused by increased intestinal secretion which may be enterotoxin-induced, eg, cholera and E. col] or hormone and dmg-induced, eg, caffeine, prostaglandins, and laxatives decreased intestinal absorption because of decreased mucosal surface area, mucosal disease, eg, tropical spme, or osmotic deficiency, eg, disaccharidase or lactase deficiency and rapid transit of contents. An increased accumulation of colonic content may be linked to increased colonic secretion owing to hydroxy fatty acid or bile acids, and exudation, eg, inflammatory bowel disease or amebiasis decreased colonic absorption caused by decreased surface area, mucosal disease, and osmotic factors and rapid transit, eg, irritable bowel syndrome. 

Permezel NC, Web ling DD (1971) The length and mucosal surface area of the small and large gut in young rats. J Anat 108 295-296... 

Q1 The mucosa is a mucous membrane which forms the innermost layer of the intestine. In the small intestine the mucosal surface area is increased greatly by folds and by villi, finger-like projections containing a core with a lymph capillary (lacteal) and blood vessels. Villi are covered by absorptive columnar epithelial cells whose luminal surface is further increased by microvilli (brush border) on which digestive enzymes and transport mechanisms for inorganic ions are located. 

The mucosal layer, comprising the lumenal surface of the small intestine, is responsible for the digestive and absorptive functions of the small intestine. The mucosal surface area is much larger than predicted for a simple cylinder. Circular folds account for this amplification. The mucosal surface area is extended further by fingerlike projections called villi and depressions called crypts. The villi are 0.5-1.0 mm in height. Each villus and crypt is lined by epithelial cells that are covered with many closely packed microvilli that project into the intestinal lumen. If the small intestine is viewed as a simple cylinder, its mucosal surface area would be on the order of half of a square meter. However, in reality, the mucosal surface area of the small intestine is approximately 250 square meters, comparable with size of a tennis court. 

For non-invasive drug administration, particulate delivery systems offer the advantage of providing a prolonged residence time oti mucosal membranes [65] and the possibility to reach greater mucosal surface areas, leading to a comparatively higher... 

The use of a bioadhesive, polymeric dosage form for sustained dehvery raises questions about swallowing or aspirating the device. The surface area is small, and patient comfort should be addressed by designing a small (less than 2 cm ), thin (less than 0.1 mm (4 mil) thick) device that conforms to the mucosal surface. The buccal route may prove useful for peptide or protein dehvery because of the absence of protease activity in the sahva. However, the epithelium is relatively tight, based on its electrophysiological properties. An average conductance in the dog is 1 mS/cm (57) as compared to conductances of about 27 and 10 mS/cm in the small intestine and nasal mucosa, respectively (58,59) these may be classified as leaky epitheha. 

Diarrhea Drug related Antibiotic-induced bacterial overgrowth Hyperosmolar medications administered via feeding tubes Antacids containing magnesium Malabsorption Hypoalbuminemia/gut mucosal atrophy Pancreatic insufficiency Inadequate GIT surface area Rapid GIT transit Radiation enteritis Tube feeding related Rapid formula administration Formula hyperosmolalty Low residue (fiber) content Lactose intolerance Bacterial contamination... 

V represents the volume of the mucosal compartment and A the surface area of the mucosal barrier. Passive paracellular solute flux is also proportional to mucosal solute concentration, where the proportionality constant is the ratio of the... 

Carrier-mediated transport is linear with mucosal solute concentration until this concentration exceeds the number of available carriers. At this point the maximal solute flux (7max) is independent of further increases in mucosal solute concentration. In the linear range of solute flux versus mucosal concentration (C), the proportionality constant is the ratio of / to the solute-carrier affinity constant (Km). This description of Michaelis-Menten kinetics is directly analogous to time changes in mass per unit volume (velocity of concentration change) found in enzyme kinetics, while here the appropriate description is the time change in solute mass per unit surface area of membrane supporting the carrier. 

The plicae circulares, or circular folds, form internal rings around the circumference of the small intestine that are found along the length of the small intestine. They are formed from inward foldings of the mucosal and submucosal layers of the intestinal wall. The plicae circulares are particularly well developed in the duodenum and jejunum and increase the absorptive surface area of the mucosa about threefold. Each plica is covered with millions of smaller projections of mucosa referred to as villi. Two types of epithelial cells cover the villi ... 

In the area of a gastric or duodenal peptic ulcer, the mucosa has been attacked by digestive juices to such an extent as to expose the subjacent connective tissue layer (submucosa). This self-digestion occurs when the equilibrium between the corrosive hydrochloric acid and acid-neutralizing mucus, which forms a protective cover on the mucosal surface, is shifted in favor of hydrochloric acid. Mucosal damage can be promoted by Helicobacter pylori bacteria that colonize the gastric mucus. 

Exposure of rats to 800 ppm for 15 minutes was fatal, but nearly all survived when exposed for 13 minutes. There was severe inflammation of all exposed mucosal surfaces, resulting in lacrimation, corneal ulceration, and burning of exposed areas of skin. In another study, exposure of rats to 480 ppm for 40 minutes or to 96ppm for 3.7 hours was fatal in the latter group, effects were pulmonary edema and marked irritation of the bronchial mucosa. Chronic exposure of dogs and rats to about Ippm, 6 hours/day for up to 6 months caused severe pulmonary irritation and some deaths. ... 

After the tablet disintegrates in the stomach the drug molecules are dispersed in gastric juice with or without partially digested food, and normally only a small proportion will penetrate the gastric mucosa and enter the blood circulation - partly because the stomach presents only a small surface area for absorption. Drugs are absorbed across mucosal surfaces but there are factors which determine how much is absorbed and at what rate in any particular site. The first set of factors is to do with the dmg molecule itself. 

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