Digestion in stomach:
The chief organic molecules in food that are digested in the stomach are the proteins (native) and short chain simple lipids. The cells of the mucosal wall produce the gastric juice and it consists of the following enzymes apart from HCI and mucin.
- Pepsin- proteolytic enzyme(endopeptidase)
- Renin – milk curdling enzyme (Calf and infants of humans)
- Gastric lipase – acts on simple lipids. Pepsin acts on native protein molecules of food in the lumen of the stomach converting it into proteoses, peptones and polypeptides.
proteoses, peptones and polypeptieds.
In Infants & calf, where the chief source of food is milk, renin is an additional enzyme which helps in curdling of milk protein casein and later this curdled casein is digested by the action of pepsin and converted to proteoses, peptones and polypeptides.
proteoses, peptones and polypeptides.
Digestion in small Intestine:
Two types of juices are secreted into the intestinal lumen namely the pancreatic juice and intestinal juice. Both there juices possesses enzymes digesting all types of complex organic molecules namely carbohydrates, proteins, lipids & nucleic acids. The digestion by these enzyme in the small intestine proceeds as follows:
Carbohydrates:
Polysaccharides starch (plant source) and glycogen (animal source) are acted upon by pancreatic amylase (amylopsin) in the small intestinal lumen and converted to a pool of maltose, a disaccharide.
The disaccharides, in the intestinal lumen namely maltose (obtained from digestion of polysaccharides or direct source); sucrose and Lactose (from diet) are acted upon disaccharide digesting (disaccharases) enzyme into a pool of monosaccharides, glucose, Fructose and galactose.
Proteins:
The proteins reaching the small intestinal lumen are in the form of native proteins, proteoses, peptones and polypeptides. They are acted upon by following enzymes.
Thus resulting in a final pool of absorbable amino acids.
Lipids:
The Lipids are first emulsified by bile salts in the intestinal lumen. The emulsified lipids are then worked upon by the pancreatic lipase to a pool of glycerol, fatty acids and monoglycerides.
Fattyacids, monoglycerides
Nucleic acids:
Nucleases from the pancreas” acts upon the RNA & DNA nucleic acids breaking them into nucleotides and these nucleotides are later acted upon by nucleotidases & nucleosidases of the intestinal juice.
deoxyribose sugar; ribose sugar; nucleic acid bases.
