DIGESTION OF VARIOUS FOODS:DIGESTION OF VARIOUS FOODS:Carbohydrates are large polysaccharides or disaccharides Carbohydrates are large polysaccharides or disaccharides which are combination of monosaccharide bounded to one which are combination of monosaccharide bounded to one another by condensation this mean that hydrogen ion has another by condensation this mean that hydrogen ion has been removed from one of monosaccharide , while hydroxyle been removed from one of monosaccharide , while hydroxyle removed from the next , which combined with water to form removed from the next , which combined with water to form water , when carbohydrate are digested back into water , when carbohydrate are digested back into monosaccharides specific enzyme return hydrogen&hydroxyl monosaccharides specific enzyme return hydrogen&hydroxyl ion to the polysaccharides &separate the monosaccharides ion to the polysaccharides &separate the monosaccharides from each other this process called hydrolysis.from each other this process called hydrolysis.Fat consist of triglycerides which are combination of 3 fatty Fat consist of triglycerides which are combination of 3 fatty acids molecules combined with single glycerol molecule , in acids molecules combined with single glycerol molecule , in condensation 3 molecules of water removed , digestion of condensation 3 molecules of water removed , digestion of triglycerides consist of the reverse process , the fat digesting triglycerides consist of the reverse process , the fat digesting enzyme returning molecules of water to the enzyme returning molecules of water to the triglyceridesoleculese &there by splitting the fatty acid triglyceridesoleculese &there by splitting the fatty acid molecules away from the glycerole so that digestive process molecules away from the glycerole so that digestive process is one of hydrolysis .is one of hydrolysis .

Finally proteins are formed from amino acids and bounded Finally proteins are formed from amino acids and bounded together by peptide linkage , in this linkage , a together by peptide linkage , in this linkage , a hydroxyle ion is removed from one amino acid hydroxyle ion is removed from one amino acid &hydrogen ion removed from the next . Thus the &hydrogen ion removed from the next . Thus the amino acid in protein chain are bounded together by amino acid in protein chain are bounded together by condensation ,&digestion occure by the reverse effect condensation ,&digestion occure by the reverse effect called hydrolysis , the proteolytic enzyme returning the called hydrolysis , the proteolytic enzyme returning the water to the protein molecules to split them in to amino water to the protein molecules to split them in to amino acids , therefore,the chemical digestion of the 3 types acids , therefore,the chemical digestion of the 3 types of food is in the same basic process of hydrolysis ,the of food is in the same basic process of hydrolysis ,the only difference lie in the enzyme required to promote only difference lie in the enzyme required to promote

the reaction for each type the reaction for each type of food .of food . All the digestive All the digestive enzymes are proteinsenzymes are proteins

Digestion of CHO:Digestion of CHO:

1- digestion of CHO in month &stomach :1- digestion of CHO in month &stomach :

When food is chewed , it is mixed with saliva , which contains alpha – When food is chewed , it is mixed with saliva , which contains alpha – amylase , secreted mainly by the parotid glands . This enzyme hydrolyses amylase , secreted mainly by the parotid glands . This enzyme hydrolyses starch in to the disaccharide maltose &other small polymers of glucose starch in to the disaccharide maltose &other small polymers of glucose that contain 304 glucose molecules , but the food remaine in the mouth that contain 304 glucose molecules , but the food remaine in the mouth only a short time &probably not more than 5%of all starch that eaten will only a short time &probably not more than 5%of all starch that eaten will become hydrolized by the time the food is swallowed .become hydrolized by the time the food is swallowed .

Digestion continues in stomach for as long as one hour befor the food Digestion continues in stomach for as long as one hour befor the food become mixed with stomach secretion , then the activity of salivary become mixed with stomach secretion , then the activity of salivary amylase is blocked by the acid pf gastric secretion because it is inactive amylase is blocked by the acid pf gastric secretion because it is inactive once as the PHof the medium falls below 4, nevertheless, on the average once as the PHof the medium falls below 4, nevertheless, on the average 30- 30%of the starch will be hydrolysed mainly to maltose.30- 30%of the starch will be hydrolysed mainly to maltose.

2- digestion of CHO in the S.I.2- digestion of CHO in the S.I.

A- BY PANCREATIC AMYLASE :pancreatic secretion contain large A- BY PANCREATIC AMYLASE :pancreatic secretion contain large quantity of alpha amylase that is identical in it is function with salivary quantity of alpha amylase that is identical in it is function with salivary amylase , within 15 – 30 minutes after chyme empties in to the duodenum amylase , within 15 – 30 minutes after chyme empties in to the duodenum &mixed with pancreatic juice , virtually all the starch are digested .in &mixed with pancreatic juice , virtually all the starch are digested .in general . The starch are converted in to maltose &other small glucose general . The starch are converted in to maltose &other small glucose polymers .polymers .

B- BY INTESTINAL EPITHELIAL ENZYMES hydrolyses of disacch. B- BY INTESTINAL EPITHELIAL ENZYMES hydrolyses of disacch. &small glucose polymers in to monosach.:&small glucose polymers in to monosach.:

The enterocytes lining the villi of S.I contain 4 enzymes lactase , sucrase , The enterocytes lining the villi of S.I contain 4 enzymes lactase , sucrase , maltase, &alpha dextrinase which are able for splitting the disaccharides maltase, &alpha dextrinase which are able for splitting the disaccharides lactose , succarose, maltose as well as small glucose polymers in to their lactose , succarose, maltose as well as small glucose polymers in to their constituant monosaccharides , these enzymes are located in the constituant monosaccharides , these enzymes are located in the membrabe of microvilli brush border of the enterocytes . They are membrabe of microvilli brush border of the enterocytes . They are digested as ehey become in contact with these membranedigested as ehey become in contact with these membrane

Lactose splitted in to galactose &glucose Lactose splitted in to galactose &glucose

Succarose fractose &glucose Succarose fractose &glucose

Maltose & small polymers → glucose moleculessMaltose & small polymers → glucose moleculess

DDigestion of proteins :igestion of proteins :1- in stomach :1- in stomach :Pepsine the important peptic enzyme of the stomach , it is Pepsine the important peptic enzyme of the stomach , it is most active at PH 2-3 &inactive at PH above 5 for this most active at PH 2-3 &inactive at PH above 5 for this enzyme to cause any digestive action on protein the stomach enzyme to cause any digestive action on protein the stomach juice must be acidic , Hcl secreted by the parietal cell at PH juice must be acidic , Hcl secreted by the parietal cell at PH about 8 but it mixed with the stomach contents &with about 8 but it mixed with the stomach contents &with secretion of other glandular cells of stomach , the PH ranges secretion of other glandular cells of stomach , the PH ranges from 2-3 .one of the important pepsine digestion is its ability to from 2-3 .one of the important pepsine digestion is its ability to digest collagen which is the major constituent of the digest collagen which is the major constituent of the intracellular connective tissue of meat , therefore ,digestive intracellular connective tissue of meat , therefore ,digestive enzyme of GIT pentrate meat &digest the cellular enzyme of GIT pentrate meat &digest the cellular protein ,pepsine usually providing 10-20%of the total protein protein ,pepsine usually providing 10-20%of the total protein digestion .digestion .

2- digestion of proteins by pancreatic secretion :Most protein digestion occure in the upper S.I.under the influence of proteolytic enzyme of pancreatic secretion , when the proteins leave stomach , they are mainly proteoses, peptones &large poly peptides . Trypsine &chymotrypsine split protein molecules in to small poly peptides , carboxypolypeptides cleave the indivisual amino acids from the carboxyl end of the polypeptides . Elastase digestt elastin fiber that hold meat together , only small percentage of protein are digested to amino acoids by pancreatic juice , most remaine as di or tri peptides &some even larger

Digestion of peptides by peptidase in the enterocytes:Digestion of peptides by peptidase in the enterocytes:The last digestion of ptroteins is achieved by the enterocytes The last digestion of ptroteins is achieved by the enterocytes that line the villi of S.I.mainly in the duodenum &jujenum, that line the villi of S.I.mainly in the duodenum &jujenum, these cells have a brush border that consist microvilli these cells have a brush border that consist microvilli projecting from the surface of each cell, in the cell membrane projecting from the surface of each cell, in the cell membrane of each microvilli are multiple peptidase that protrude through of each microvilli are multiple peptidase that protrude through the membrane to the exterior , where they come in contact the membrane to the exterior , where they come in contact with intestinal fluid 2 types of peptidase enzymes are with intestinal fluid 2 types of peptidase enzymes are especially important , aminpoly peptidase &several especially important , aminpoly peptidase &several dipeptidase , they splitting the remainder larger polypeptides dipeptidase , they splitting the remainder larger polypeptides into tri &di peptides are transported through the microvilli into tri &di peptides are transported through the microvilli membrane to the interior of the enterocytemembrane to the interior of the enterocyteFinally inside enterocyts are other peptidases that are specific Finally inside enterocyts are other peptidases that are specific for the remaining linkage between amino acids within minutes for the remaining linkage between amino acids within minutes all the last di &tripeptides are digested to single amino acids all the last di &tripeptides are digested to single amino acids

Digestion of fat :Digestion of fat :A small amount of of triglycerides digested in the stomach by lingual A small amount of of triglycerides digested in the stomach by lingual lipase that is secreted by limgual glands in the mouth &swallwed lipase that is secreted by limgual glands in the mouth &swallwed with saliva , the amount of digestion is less than 10%, essentially all with saliva , the amount of digestion is less than 10%, essentially all fat digestion occure in the S.I.fat digestion occure in the S.I.Emulsification of fat by bile acid &lecithen :Emulsification of fat by bile acid &lecithen :Emulsification of faty mean breaking of fat globules in to small sizes Emulsification of faty mean breaking of fat globules in to small sizes so that the water soluble enzyme can act on the surface of the so that the water soluble enzyme can act on the surface of the globule , emulsification achieved partially by agitation in the globule , emulsification achieved partially by agitation in the stomach with products of stomach digestion , but mainly by the stomach with products of stomach digestion , but mainly by the influence of bile . Both of bile salt & lecithin are important for influence of bile . Both of bile salt & lecithin are important for emulsification emulsification Bile salt & lecithin molecules are highly soluble in fat , therefore,the Bile salt & lecithin molecules are highly soluble in fat , therefore,the fat soluble portion of bile salt molecule dissolve in the surface layer fat soluble portion of bile salt molecule dissolve in the surface layer of the fat globule &other portion soluble in the surrounding fluid , of the fat globule &other portion soluble in the surrounding fluid , this effect greatly decrease the surface tension of fat & make the fat this effect greatly decrease the surface tension of fat & make the fat globule readily fragmentable by agitation in the S.I .globule readily fragmentable by agitation in the S.I .DIGESTION OF TRIGLYCERIDE BY PANCREATIC LIPASEDIGESTION OF TRIGLYCERIDE BY PANCREATIC LIPASE : :The most important enzyme for digestion of triglycerides (neutral fat) The most important enzyme for digestion of triglycerides (neutral fat) is pancreatic lipase enough to digest all triglycerides the enterocyte is pancreatic lipase enough to digest all triglycerides the enterocyte of small intestine contain small quantity of enteric lipase but it is of small intestine contain small quantity of enteric lipase but it is usually unimportant . Most of triglycerides of diet are split into free usually unimportant . Most of triglycerides of diet are split into free fatty acids & 2 monoglyceride fatty acids & 2 monoglyceride

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ROLE OF BILE SALT IN ACCELERATING FAT DIGESTION : ROLE OF BILE SALT IN ACCELERATING FAT DIGESTION :

During triglyceride digestion , monoglycerides& free fatty acids are During triglyceride digestion , monoglycerides& free fatty acids are formed they become dissolved in the central fatty portion of the formed they become dissolved in the central fatty portion of the micells which cause reducing the concentration of these end micells which cause reducing the concentration of these end products of digestion in the vicinity of the fat globule &digestion products of digestion in the vicinity of the fat globule &digestion process can proceed.process can proceed.

The bile salt micells also act as transport medium to carry The bile salt micells also act as transport medium to carry monoglycerids &free fatty acids to the brush border of intestinal monoglycerids &free fatty acids to the brush border of intestinal epithelial cells &they are absorbed , on delivery of these end epithelial cells &they are absorbed , on delivery of these end products bile salts are again released back in to chyme &used again products bile salts are again released back in to chyme &used again &again. &again.