This document summarizes carbohydrate digestion. It explains that carbohydrates are broken down into monosaccharides like glucose and fructose through digestion by salivary amylase in the mouth and pancreatic amylase in the pancreas. The monosaccharides are then absorbed into the bloodstream through the small intestine, either through facilitated diffusion down a concentration gradient or active transport against a gradient, powered by sodium-glucose cotransporters.

1. By; Ömer ASLANKAN
Digestion of Carbohydrates
The major source of carbohydrate is found in plants.
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Dietary carbohydrates mostly comes from starch -Amylose and amylopectin
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Dietary carbohydrate principally consist of…
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1) Polysaccharides :- Starch, glycogen & cellulose.
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2) Disaccharides :- Sucrose and Maltose.
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3) Monosaccharides :- glucose and fructose.
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4) oligosaccharides; short polymer so 3-10 monosaccharides
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Monosaccharides does not need digestion.
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Have two important bonds in the Polysaccharides (a-1,6 and a-1,4 glycosidic bond)
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Amylopectin; a-1,6 and a-1,4 glycosidic bond
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Amylose; a-1,4 glycosidic bond
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Digestion in Oral cavity
Digestion Starts in the oral cavity and continues in the GI tract all the way to the stomach
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So oral cavity- pharynx - esophagus- stomach
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Salivary amylase is inactiveted by gastric acid
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Salivary a-amylase is ptyalin
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Mainly secreted by extrinsic glands
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Only targets the a-1,4 glycosidic bonds and breaks
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down amylopectin and amylose
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amylose is broken down into (maltose-disaccharides and maltotriose- oligosaccharides)
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Amylopectin is broken down into (maltose- disaccharides, maltotriose- oligosaccharides and a-limit dextrins-
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oligosaccharides)
Salivary amylase Is responsible for 15% of the chemical break down of carbohydrates
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Digestion In pancreas
Acinar cells- pancreatic amylase- hydrolyses a-1,4 glycosidic bonds
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Maltose , Matlotriose, a-limit dextrins
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Cholecystokinin;
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Stimulate acinar cells to produce pancreatic amylase
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Relaxes the sphincter of oddi- ejection of the pancreatic amylase to the duodenum
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Digestion in small Intestine
Further digestion of carbohydrate occurs in small intestine by pancreatic enzymes.
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Enterocytes- epithelial cell found in the small intestine
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Most of the absorption occurs in the small intestine
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Water and electrolytes can be absorbed from the large intestine
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Structural modifications that increase surface area in the small intestine-increase digestion and increase
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absorption. ( circular folds, villi, microvilli)
Enterocyte; little cytoplasmic extensions, increase the surface area for chemical digestion and absorption
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High concentration of brush border enzymes
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Brush border enzymes (lactase, maltase, sucrase, isomaltase,)
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The enzymes & their reactions are as follows…
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Maltose—Maltase— Glucose + Glucose
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Isomaltose—Isomaltase— Glucose + Glucose
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Sucrose — Sucrase — Glucose + Fructose
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Lactase —Lactase— Glucose + Galactose
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Limit dextrin—Dextrinase— Glucose+ Maltose + Maltotriose
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2. Digestion in Stomach
Digestion of carbohydrate temporarily stops in the stomach.
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The action of salivary amylase stops in stomah because of high acidity of stomach.
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No carbohydrate splitting enzymes available in gastric juice.
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ABSORPTION OF CARBOHYDRATES
The end product of carbohydrate digestion are Glucose, Fructose galactose
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These are readily absorbed through the intestinal mucosal cells into the blood stream.
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Two mechanism are responsible for the absorption of these sugars…
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1) Facilitated transport, with conc gradient
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2) Active transport, against conc. gradient.
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1) Facilitated transport.
This is depends on the conc. of sugar across the intestinal lumen and mucosal cells.
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All the monosaccharide are absorbed o some extent by facilitated diffusion.
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2) Active Transport.
The transport of glucose and Galactose across the brush boarder of mucosal cells occur by active transport.
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It is an energy requiring process that requires transport protein and presence of sodium ions.
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A sodium dependent glucose transporter (SGLT-1) binds both glucose and sodium at separate sites and
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transports them into the cell.
The sodium transport down conc. gradient & glucose transported against conc. gradient.
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This process is called cotransport or symport.
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The energy for this reaction is provided by ATP linked to sodium pump.
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