6-lipase which attaks the primary ester bond of triacyglycerol the result of lipase action on triacyglycerol is the formation of mixture of diacyglycerol , monoacyglycerol, glycerol and fatty acids
7- cholesterol esterase :catalyses the hydrolyzing of cholesterol ester to cholesterol and fatty acids
8-Ribonuclease : catalyses the hydrolyzing of RNA( ribonucleic acid) to nucleotides make up its composition
9- Deoxyribonuclease: which works on DNA (deoxyribonucleic acid)causing the digestion of DNA.
10-Phosphplipase: hydrolyzes the ester bond in the 2 position of phospholipids
Digestion in intestine
The intestinal juice secretion contains digestive enzymes which complete the digestion processes done by the stomach and pancrease these enzymes are
:
1- Amino peptidase:which is an exopeptidase attacking peptide bond next to n –terminal amino acids of poly peptides and oligopeptides
2- Disaccharidase:which are specific enzyme catalyzing the hydrolysis of disaccharid to monosaccharide
3- Phosphotase :which removes phosphate from certain organic phosphate such as hexose phosphate ,and glycerol phosphate
4- Poly nucleotidase :which split nucleic acids into nucleotides
5- Nucleotidase :catalyze the phsphorolysis of nucleotides to give the nitrogen base plus pentose phosphate
6- Phospholipids :that attacks the phospholipids to produce glycerol ,fatty acids , phosphoric acids and bases such as choline
Final product of digestion:
The final results of the action of digestive enzymes described are to reduce the component of the diet to forms that can be absorbed and assimilated. These end products of digestion are the following:
1-Monosaccharides: which mainly glucose, come from digestion of carbohydrates
2- Amino acids : which are the end products of the digestion of carbohydrates
3-Monoglycerol,glycerol,and fatty acids :are the final major products of digestion of lipids
4-Purins, perimidines, nucleotides, and pentose (ribose and deoxy ribose)are the end products of nucleic acids digestion
5-Fibers (cellulose and lignin)of the diet which can not be digested by mammalian enzymes they make up the bulk of the residues from digestion .fiber performs an important function in adding bulk to the diet help in the processes of digestion
Absorption from gastrointestinal tract:
The small intestine is the main digestive and absorptive organ .about 90% of the ingested food stuffs are absorbed in the course of passage through the small intestine and water is absorbed act the some time considerably more water is absorbed after the foods stuffs pass in to large intestine so that the contain were fluid in the small intestine gradually become more solid in the colon there are 2 pathways for the transport of material absorbed by the intestine
1-Hepatic portal vein:
Which lead directly to the liver transporting the water soluble nutrients.
2-lymphatic vessels :
Which lead directly to the blood by way of thoracic duct and transporting the lipid soluble nutrients.
There is little absorption from the stomach although considerable gastric absorption of ethanol is possible .
Absorption of carbohydrate:
The end product of carbohydrate digestion are the monosaccharides such as fructose ,mannose ,galactose,and pentose 2 mechanisms are responsible for the absorption of
Monosaccharides active transport against the concentration gradient end simpl diffusion active transport mechanism depends on a carrier binds both glucose and sodium (na+) at separate sites and that transport them both through the plasma membrane of intestinal cell it is envisaged that both glucose and (Na+)are released into the cytisol ,allowing the carrier to take up more cargo the (Na+)is the transported down its concentration gradient and at the same time causes the carrier to transport glucose against its concentration gradient the free energy required for this active transport is obtained from the hydrolysis of ATP linked to sodium that expels(Na+)from the cell in exchange for K+.
Absorption of lipid:
The bile salts from micelles consisting of colloidal particles with a polar exterior exposed to water and a non polar interior these micelles provide the vehicle for the transport of the lipids from the intestine lumen to epithelial cell where absorption occurs micelles participated in the absorption of free fatty acids monoacylglycerols, cholesterol, and fat soluble vitamins (A, D, E,and K)after fatty acids and 2- monoacylglycerols, are take up by the intestinal epithelium and are converted to triacylglycerols by the mucosal cell dietary lipid is released into the lymph from the intestine as chylomicrons . chylomicrons which are made up of lipids and proteins represented one from of circulation of lipoprotein the content of the chylomicrons are then delivered to tissues short and medium chain fatty acids which are present in food in only small amounts are absorbed into the portal blood and delivered to the liver as free fatty acids by pass the lipoprotein path way for intestinal absorption and this property can be used to advantage in human therapeutics.
Absorption of amino acids:
Under normal circumstances the dietary protein are almost completely digested to their constituent amino acids and these end products of protein digestion are then rapidly absorbed from the intestine into the portal blood some of hydrolysis of dipeptides is completed in the intestinal wall before the released into the hepatic portal vein newborn infants are able to take up some proteins without prior digestion immunoglobulin’s of A type (IGA)from colostrum of maternal milk are absorbed intact providing the newborn with passive immunity the newborn loses the ability to take up intact immunoglobulin’s about 2 days postpartum.