Cell Disaccharidases

Glucose and galactose enter the absorptive cells by way of secondary active transport. Cotransport carrier molecules associated with the disaccharidases in the brush border transport the monosaccharide and a Na+ ion from the lumen of the small intestine into the absorptive cell. This process is referred to as "secondary" because the cotransport carriers operate passively and do not require energy. However, they do require a concentration gradient for the transport of Na+ ions into the cell. This gradient is established by the active transport of Na+ ions out of the absorptive cell at the basolateral surface. Fructose enters the absorptive cells by way of facilitated diffusion. All monosaccharide molecules exit the absorptive cells by way of facilitated diffusion and enter the blood capillaries. 

Disaccharides Disaccharidases Hydrolyze disaccharides into Absorptive cells of Brush border of... 

Disaccharides are cleaved to monosaccharides by a battery of disaccharidases after absorption into intestinal mucosal cells. 

Source and kinds of disaccharidases The final digestive processes occur at the mucosal lining of the small intestine. Several disaccharidases [for example, lactase (p-galactosidase), sucrase, maltase, and isomal-tase] produce monosaccharides (glucose, galactose, and fructose). These enzymes are secreted by and remain associated with the luminal side of the brush border membranes of intestinal mucosal cells. Absorption of the monosaccharides requires specific trans porters. 

The intestinal oligo- and disaccharidases are fixed components of the cell membrane of the brush border region of the wall of the small intestine. These enzymes digest dietary carbohydrate to monosaccharides which are absorbed through the intestinal wall. They include sucrase, maltase, isomaltase, lactase, trehalase, and hetero-p-glucosidase. In the late 1970s, it was realized that inhibition of all or some of these activities could regulate the absorption of carbohydrate, and that these inhibitors could... 

It can be seen from Table 2 that a large number of the naturally-occurring polyhydroxylated alkaloids are potent inhibitors of the various a-glucosidase-specific disaccharidases involved in mammalian digestion (e.g. sucrase, maltase, isomaltase, etc.,). These enzymes are expressed at the surface of the epithelial cells of the brush border in the small intestine. In the late 1970s it was realised that inhibitors of these enzymes, such as DNJ, could be used therapeutically in the oral treatment of the non-insulin-dependent (type n) diabetes mellitus. ... 

Dextrinases, a-glucosidases, and disaccharidases located on the surface of the brush border of the intestinal epithelial cell complete the conversion of starch to glucose. 

B. Lactose and sucrose are digested by disaccharidases on the brush border of intestinal epithelial cells. Starch is digested by salivary and pancreatic amylase. Therefore, its digestion would be less affected by a lack of pancreatic juice than fat, which is digested mainly by pan-creatic lipase. A common finding in cystic fibrosis is steatorrhea (fatty stools). 

The intestine is also an important site for secretion of digestive enzymes. In A. suum several disaccharidases are abundant on the microvilli, including sucrase, palatinase, maltase and trehalase, with maltase activity predominating. Endopeptidases that break down hemoglobin and other host proteins are also present. Lipases have been detected in intestinal cells of several species, and their activity depends extensively on the diet of the parasite. In Strongylus edentatus, which feeds on host mucosal tissue, lipase activity in the intestine is 12-fold greater than that for A. suum, a saprophagous feeder (141). 

A patient has a genetic defect that causes intestinal epithelial cells to produce disaccharidases of much lower activity than normal. Compared with a normal person, after eating a bowl of milk and oatmeal sweetened with table sugar, this patient will exhibit higher levels of which of the following ... 

The dietary carbohydrates also include sucrose and lactose. Specific disaccharidases which convert these sugars into their constituent monosaccharides are present in the brush border of the intestinal epithelial cells. Only monosaccharides can be absorbed and an active transport system ensures that glucose, galactose and other sugars having the structural features shown below... 

The enzymes that catalyse the hydrolysis of disaccharides (the disaccharidases) are located on the brush border of the intestinal mucosal cells the resultant monosaccharides return to the lumen of the small intestine, and are absorbed together with dietary monosaccharides and glucose arising from the digestion of starch (section... 

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