Small intestine electrolytes

As we have seen in this chapter steroids have a number of functions in human physiology Cholesterol is a component part of cell mem branes and is found in large amounts in the brain Derivatives of cholic acid assist the digestion of fats in the small intestine Cortisone and its derivatives are involved in maintaining the electrolyte balance in body fluids The sex hormones responsible for mascu line and feminine characteristics as well as numerous aspects of pregnancy from conception to birth are steroids... 

Castor oil is a cathartic only after Hpolysis in the small intestine Hberating ricinoleic acid. Ricinoleic acid inhibits the absorption of water and electrolytes. It is commonly used for preparation of the large bowel for diagnostic procedures. 

Gum arabic. (GA) modifies paracellular water and electrolyte transport in the small intestine. Digestive Diseases and Sciences, Vol. 48, No.4, (April 2003), pp. 755-760, ISSN 0163-2116. 

WINGERTZAHN M A, TEICHBERG s, WAPNIR R A (2001) Stimulation of non-sodium-dependent water, electrolyte, and glucose transport in rat small intestine by gum arabic. DigDis Sci. 46 1105-12. 

V. cholerae is a gram-negative bacillus. Vibrios pass through the stomach to colonize the upper small intestine. Vibrios have filamentous protein extensions that attach to receptors on the intestinal mucosa, and their motility assists with penetration of the mucus layer.2 The cholera enterotoxin consists of two subunits, one of which (subunit A) is transported into the cells and causes an increase in cyclic AMP, which leads to a deluge of fluid into the small intestine.20 This large volume of fluid results in the watery diarrhea that is characteristic of cholera. The stools are an electrolyte-rich isotonic fluid, the loss of which results in blood volume depletion followed by low blood pressure and shock.2 Of note, the diarrheal fluid is highly infectious. 

Jackson, M. J. Tai, C.-Y., Morphological correlates of weak electrolyte transport in the small intestine, in Dinno, M. A. (ed.), Structure and Function in Epithelia and Membrane Biophysics, Alan R. Liss, New York, 1981, pp. 83-96. 

Water and electrolytes. Each day in an average adult, about 5.51 of food and fluids move from the stomach to the small intestine as chyme. An additional 3.5 1 of pancreatic and intestinal secretions produce a total of 9 1 of material in the lumen. Most of this (>7.5 1) is absorbed from the small intestine. The absorption of nutrient molecules, which takes place primarily in the duodenum and jejunum, creates an osmotic gradient for the passive absorption of water. Sodium may be absorbed passively or actively. Passive absorption occurs when the electrochemical gradient favors the movement of Na+ between the absorptive cells through "leaky" tight junctions. Sodium is actively absorbed by way of transporters in the absorptive cell membrane. One type of transporter carries a Na+ ion and a Cl ion into the cell. Another carries a Na+ ion, a K+ ion, and two Cl ions into the cell. 

Cholera Toxin that causes the mucosal cells of the small intestine to hypersecrete water and electrolytes into the lumen of the gastrointestinal tract. 

Mechanism of Action A laxative prepared from the bean of the castor plant but the exact mechanism of acfion is unknown. Acts primarily in the small intestine. Maybe hydrolyzed to ricinoleicacid which reduces net absorption of fluid and electrolytes and stimulates peristalsis. Therapeutic Effect Increases peristalsis, promotes laxative effect. 

Most studies have investigated resorption of allergens from the small intestine, whereas little is known about resorption of allergens or other proteins from the large intestine. The large intestine is mainly recognized as the site of resorption of free water, electrolytes, and water-soluble vitamins. However, resorption of streptokinase after rectal application as well as resorption of human albumin from the large intestine have been described [1, 17, 25],... 

The functions of the colon are (1) absorption of water and electrolytes from the chyme and (2) storage of fecal matter until it can be expelled. The proximal half of the colon, illustrated in Figure 12.2, is concerned principally with absorption, and the distal half with storage. Because intense movements are not required for these functions, the movements of the colon are normally sluggish. Although sluggish, the movements still have characteristics similar to those of the small intestine and can be divided into mixing movements and propulsive movements. 

Besides, it has been found3 that Silics possesses some antidiarrheal properties that are not related to sorption of microorganisms or their toxins. A Silics medicinal preparation retards secretion of water in isolated intestinal loops of rats in the case of its combined introduction with diarrhea mediators such as sodium desoxycholate, cyclo-adenosine 3 ,5 -monophosphate (c-AMP), and serotonin (Table 5). The decrease of water release into intestinal segment lumens seems to be related to the modifying action of the preparation on mucosa of bowels, because sorption of the stimulators themselves on Silics does not take place. The modifying action of the preparation on the small intestine mucosa is also attributed to the stimulation exerted by Silics on transport of glucose and electrolytes through bowel walls.3... 

Q2 Unlike the small intestinal mucosa, the colonic mucosa does not contain any villi. There are columnar epithelial cells and mucus-secreting goblet cells in the mucosa the columnar epithelium reabsorbs fluid and electrolytes. 

Q3 The muscular wall of the colon is quiescent for much of the time. The major type of motility is segmentation but this is less frequent than in the small intestine. It mixes and moves colonic contents around to promote reabsorption of water and electrolytes. Peristaltic movements also occur and promote colon emptying. The myenteric plexus in the wall of the colon coordinates both motor and secretory activity and affects activity of the internal sphincter at the junction of the colon and rectum. This sphincter is usually contracted and is maintained closed by sympathetic stimulation. Stimulation of parasympathetic nerves increases motor activity throughout the colon and relaxes the internal sphincter, allowing material to enter the rectum. 

Figure 4.11 Electrolyte movement in secretory crypt cells of the small intestine. Apical Basolateral...

The surface of the mucosa is relatively smooth as there are no intestinal villi. Crypts of Lieberktlhn are present. Goblet cells account for more of the epithehal cells than in the small intestine. The mammalian large intestine is important for the maintenance of water and electrolyte balance. Its primary function is the reabsorption of water, sodium, chloride and volatile fatty acids it secretes potassium and bicarbonate. 

Bile is a complex fluid containing 95% water, electrolytes and organic molecules, including bile acids/salts, cholesterol, phospholipids and conjugated bilirubin that flows through the biliary tract into the small intestine (Table 2.6). 

Oral administration is the most common route of drug administration. Major physiologic processes in the GI system include secretion, digestion, and absorption. Secretion includes the transport of fluid, electrolytes, peptides, and proteins into the lumen of the alimentary canal. Enzymes in saliva and pancreatic secretions are involved in the digestion of carbohydrates and proteins. Other secretions such as mucus protect the linings of the lumen of the GI tract. Digestion is the breakdown of food constituents into smaller structures in preparation for absorption. Both drug and food constituents are mostly absorbed in the proximal area (duodenum) of the small intestinal. The process of absorption is the entry of constituents from the lumen of the gut into the body. Absorption may be considered as the net result of both lumen-to-blood and blood-to-lumen transport movements. 

In diseases of the small intestine, active secretion caused by cyclic nucleotide stimulation can result in a large volume of water and electrolytes moving into the lumen. Additionally, enteric neuron activation of mast cells can increase intestinal capillary permeability and promote passive fluid secretion. Diseases that increase intestinal permeability can result in passive secretion of protein-rich fluid into the intestinal lumen. Active secretion of electrolytes and water is a feature of many diarrheal disorders and can be stimulated by bacterial enterotoxins. Several bacterial enterotoxins interact with intestinal epithelial cell membrane adenylate cyclase or guanylate cyclase, resulting in increased cAMP or cGMP. These, in turn, activate basolateral chloride channels, resulting in an increase in the luminal secretion of chloride, accompanied by sodium and followed by water (Gemmell 1984). Bacterial enterotoxins that stimulate cAMP include cholera toxin, Escherichia coli... 

Enkephalins are pentapeptides that bind to opiate receptors. In the gut, enkephalins promote the absorption of sodium, chloride and water (Dobbins et al 1980). Racecadotril is an oral enkephalinase inhibitor used in France and the Philippines for the treatment of acute diarrhea. It prevents the degradation of endogenous opioids (enkephalins) and thus promotes absorption of water and electrolytes from the intestinal lumen (Matheson Noble 2000). Studies have demonstrated the efficacy of racecadotril in two models of hypersecretory diarrhea infusion of cholera toxin and castor oil induced diarrhea. Moreover, unlike loperamide, racecadotril did not prolong transit time in the small intestine or colon. Further experiments have shown that racecadotril does not promote bacterial overgrowth in the small intestine (Duval-Iflah et al 1999). There are no reports on the use of racecadotril in horses. 

Disorders that cause increased secretion of fluid and electrolytes into the small intestine of the horse are characterized by abdominal discomfort, distension of the small intestine and enterogastric reflux. In young foals with small intestinal secretory disorders, diarrhea may occur. Increased intestinal secretion can result from the active secretion of electrolytes and water, for example the cyclic nucleotide-stimulated secretion that results from exposure to bacterial enterotoxins. Passive secretion of water can result from increased permeability of the intestine, such as in enteritis, distension or ischemia, or decreased absorption of osmoti-caUy active substances, such as with lactose intolerance in foals. Disorders in which there is decreased secretion of fluid into the small intestine are not appreciated, although impactions of ingesta in segments of the small intestine can occur. 

Fluid and electrolyte loss in cholera patients is closely related to elevated concentrations of cAMP, which can stimulate chloride secretion in intestinal epithelial cells (Field, 1971 Moss and Vaughan, 1988a). There is also evidence for the importance of other substances, such as prostaglandin E2 (PGE2) and 5-hydroxytryptamine (5-HT), in CT-induced secretion (Kaper et al., 1995). Nilsson et al. (1983) reported that 5-HT was released from enterochromaffin cells in the cat small intestine upon CT treatment. 5-HT could then stimulate PGE2 synthesis (Beubler etai, 1989) and activate the enteric nervous system (Ekiund et al., 1984). Cholera toxin also caused release of PGE2 into the lumen of intestinal loops in vitro (Peterson and Ochoa, 1989), via an effect on arachidonic acid formation (Peterson et al., 1990 Reit-meyer and Peterson, 1990). The contribution of these, and perhaps other, CT effects to the pathogenesis of cholera remains to be elucidated (Peterson etai, 1994). 

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