The undigested food in terms of polysaccharides, starch and glycogen and disaccharides, sucrose & lactose (got from diet), maltose (produced from digestive action of salivary amylase on polysaccharides or those got directly as a food source) are acted upon by the carbohydrates of the pancreas and intestinal juice in the lumen of the intestine.
(i) The polysaccharides starch (plant source) and glycogen (animal source) are acted upon by the pancreatic amylase (or amylopsin) splitting them into a pool of maltose, a disaccharide.
(ii) The final pool of disaccharides produced by the action of polysaccharides (Pancreatic and salivary amylases) or those obtained directly through diet are acted upon by the di- saccharases Sucrase, Lactase and Maltase (disaccharide splitting enzymes) of the intestinal juice in the intestinal lumen as follows,
(a) Sucrose (s) are acted upon by sucrase enzyme and split into a molecule of glucose and a moecule of Fructose each.
(b) Maltose (s) are acted upon by Maltase -enzyme and split into two glucose molecules each.
(c) Lactose (s) are acted upon by Lactase enzyme and split into a molecule of glucose and galactose
Finally resulting in an absorbable pool of monosaccharides in the intestinal lumen. The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralised by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the
- Pancreatic juice – namely trypsin, chymotryr.in and carboxypeptidase.
- ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.
Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carbxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.
The action of the above enzymes on proteins is as follows;
(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
proteoses,peptones,polyhepties
(ii) Carboxypeptidases and amino peptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
Finally, resulting in a pool of amino acids which can be easily absorbed.
