For School Students

1. Prepared by: Richa Khatiwada

2. Digestion : Process of breaking down of food into simpler compounds.

3.  Mechanical Digestion
 Chewing, also known as mastication, crumbles the carbohydrate
foods into smaller and smaller pieces to form bolus.
 Chemical Digestion
 Salivary glands in oral cavity secrets saliva.
 Saliva contains enzyme salivary amylase/ptyalin.
 Salivary amylase hydrolyses starch into maltose and dextrin at pH
of 6.8 to 7.
 Only about 5% starch are broken down in mouth.

4.  Mechanical Digestion
 The strong peristaltic contractions of the stomach mix the carbohydrates
into the more uniform mixture of chyme.
 Chemical Digestion
 The action of ptyalin continues only inside bolus.
 About 30-40% of dietary starch is digested before bolus is broken down
and acidified.
 The action of ptyalin is blocked by acidic nature of stomach(pH 1.5).
 Further breakdown of carbohydrates takes place when the chyme is passed
down to the small intestine.

5.  Mechanical Digestion
 There is no mechanical digestion in small intestine.
 Chemical Digestion
 The pancreas releases pancreatic juice through a duct.
 Pancreatic juice contains the enzyme, pancreatic amylase.
 Enzymes are also secreted by the intestinal cells that line the
villi.

6. Hydrolyze oligo- and polysaccharides into
monosaccharide as follow:
o Starch pancreatic amylase Maltose + Isomaltose
o Maltose maltase Glucose +Glucose
o Isomaltose isomaltase Glucose + Dextrin
o Dextrin dextrinase Glucose
o Sucrose sucrase Glucose + Fructose
o Lactose lactase Glucose + Galactose

7.  Certain carbohydrate like cellulose are undigested by human
due to lack of enzymes like cellulase.
 But ,it provides fibers for absorption of water into the large
intestine ,expand the muscle walls and trigger the muscle
contractions for egestion.
 Cure for constipation.

8.  Digested food from
alimentary canal to
blood stream.
 Monosaccharide is absorbed
in small intestine.
 Sodium Glucose Transport
Protein(SGLT) in membrane
helps absorb glucose and
galactose.
 Fructose absorbed is
converted to glucose inside
cell.