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

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

Digestion of CHO: 1- digestion of CHO in month &stomach : When food is chewed, it is mixed with saliva, which contains alpha – amylase, secreted mainly by the parotid glands. This enzyme hydrolyses starch in to the disaccharide maltose &other small polymers of glucose 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 become hydrolized by the time the food is swallowed. Digestion continues in stomach for as long as one hour befor the food become mixed with stomach secretion, then the activity of salivary 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 %of the starch will be hydrolysed mainly to maltose.

2- digestion of CHO in the S.I. A- BY PANCREATIC AMYLASE :pancreatic secretion contain large 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 &mixed with pancreatic juice, virtually all the starch are digested.in general. The starch are converted in to maltose &other small glucose polymers. B- BY INTESTINAL EPITHELIAL ENZYMES hydrolyses of disacch. &small glucose polymers in to monosach.: The enterocytes lining the villi of S.I contain 4 enzymes lactase, sucrase, maltase, &alpha dextrinase which are able for splitting the disaccharides lactose, succarose, maltose as well as small glucose polymers in to their constituant monosaccharides, these enzymes are located in the membrabe of microvilli brush border of the enterocytes. They are digested as ehey become in contact with these membrane Lactose splitted in to galactose &glucose Succarose fractose &glucose Maltose & small polymers → glucose moleculess

D igestion of proteins : 1- in stomach : Pepsine the important peptic enzyme of the stomach, it is most active at PH 2-3 &inactive at PH above 5 for this enzyme to cause any digestive action on protein the stomach juice must be acidic, Hcl secreted by the parietal cell at PH about 8 but it mixed with the stomach contents &with secretion of other glandular cells of stomach, the PH ranges from 2-3.one of the important pepsine digestion is its ability to digest collagen which is the major constituent of the intracellular connective tissue of meat, therefore,digestive enzyme of GIT pentrate meat &digest the cellular protein,pepsine usually providing 10-20%of the total protein 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: The last digestion of ptroteins is achieved by the enterocytes that line the villi of S.I.mainly in the duodenum &jujenum, these cells have a brush border that consist microvilli projecting from the surface of each cell, in the cell membrane of each microvilli are multiple peptidase that protrude through the membrane to the exterior, where they come in contact with intestinal fluid 2 types of peptidase enzymes are especially important, aminpoly peptidase &several dipeptidase, they splitting the remainder larger polypeptides into tri &di peptides are transported through the microvilli membrane to the interior of the enterocyte Finally inside enterocyts are other peptidases that are specific for the remaining linkage between amino acids within minutes all the last di &tripeptides are digested to single amino acids

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

ROLE OF BILE SALT IN ACCELERATING FAT DIGESTION : During triglyceride digestion, monoglycerides& free fatty acids are formed they become dissolved in the central fatty portion of the micells which cause reducing the concentration of these end products of digestion in the vicinity of the fat globule &digestion process can proceed. The bile salt micells also act as transport medium to carry monoglycerids &free fatty acids to the brush border of intestinal epithelial cells &they are absorbed, on delivery of these end products bile salts are again released back in to chyme &used again &again.