The document summarizes the digestion and absorption of carbohydrates. Carbohydrate digestion begins in the mouth where salivary amylase breaks down starches. Digestion pauses in the stomach but continues in the small intestine where pancreatic amylase and intestinal enzymes break carbohydrates down into monosaccharides like glucose and fructose. These monosaccharides are then absorbed into the bloodstream via facilitated diffusion or active transport using glucose transporters. Undigested carbohydrates like cellulose provide fiber in the diet. Lactose intolerance and sucrase deficiency can occur if enzymes that break down lactose or sucrose are deficient.

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2. Ashok Katta
The major source of carbohydrate is found
in plants.
Dietary carbohydrate principally consist
of…
Polysaccharides :- Starch, glycogen & cellulose.
Disaccharides :- Sucrose and Maltose.
Monosaccharides :- glucose and fructose.
Monosaccharides does not need digestion.
Digestion of Carbohydrates

3. Ashok Katta
Salivary gland:
Salivary juice
Stomach :
Gastric juice
Intestine:
Intestinal juice
Liver:
Hepatic juice
Pancreas:
Pancreatic juice Intestine:
Absorption
Ashok Katta

4. Mouth
Salivary
α-amylase
Stomach
No
enzymes
Pancreas
Intestine
Digestion of Carbohydrates
(Overview)
Ashok Katta

5. Ashok Katta
Digestion of carbohydrate starts at the mouth.
In mouth, food undergoes mastication.
During mastication, food comes in contact with
saliva(secreted by salivary gland).
Saliva contain salivary amylase (ptyalin).
Action of salivary amylase-
It requires Cl- ion for activation and PH 6.7.
The enzyme hydrolyzes α-(1-4) glycosidic bonds at
random deep inside polysaccharide (starch, glycogen).
Producing dextrins, maltose, maltotriose, glucose.
Digestion in Mouth

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Glycogen molecule
Dextrin
(oligosaccharide)
Maltotriose Maltose Isomaltose
α-Amylase
α-1-4 bond
Branching point (α-1-6 bond)

7. Ashok Katta
Digestion of carbohydrate temporarily stops in
the stomach.
The action of salivary amylase stops in stomah
because of high acidity of stomach.
No carbohydrate splitting enzymes available in
gastric juice.
Digestion in Stomach

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Further digestion of carbohydrate occurs in small
intestine by pancreatic enzymes.
Food bolus reaches the small intestine from
stomach where it meets the pancreatic juice.
Pancreatic juice contain enzyme called pancreatic
amylase(amylopsin) similar to S. amylase.
There are two phase of intestinal digestion….
Digestion due to pancreatic amylase
Digestion due to intestinal brush border enzyme.
Digestion in Intestine

9. Ashok Katta
Action of pancreatic amylase-
It hydrolyzes the dextrins to mixture of maltose,
isomaltose, limit dextrin.
Dextrin
(oligosaccharide)
Maltotriose Maltose Isomaltose
α-Amylase
Limit dextrin

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Action of intestinal brush border enzyme-
These enzymes are responsible for final digestion
of carbohydrate.
The enzymes & their reactions are as follows……
Maltose
Maltase
Glucose Glucose
Isomaltose
Isomaltase
Glucose Glucose
Sucrose
Sucrase
Glucose Fructose
Lactase
Lactase
Glucose Galactose
Limit dextrin
Dextrinase
Glucose Maltose Maltotriose

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Digestion of
Carbohydrates
Maltose
Maltase
Glucose
Lactose
Dietary Carbohydrates
Polysaccharides Disaccharides Monosaccharides
Dextrins
Dextrins
Sucrose
Fructose Galactose
Sucrase Lactase
Salivary
α-amylase
Pancreatic
α-amylase

12. Ashok Katta
Why cellulose is not digested by humans?
Cellulose is polysaccharide found in plants.
It contain β- (1-4) glycosidic bond in its
structure.
Humans cannot synthesize the enzyme which
can break β glycosidic bond.
So, cellulose is not digested by humans.
But, although is not digested it is one of the
imp component in the diet.
Because, undigested cellulose provide bulk os
fibre in the diet.
Fibre helps in intestinal motility & as a stool
softer.

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ABSORPTION OF CARBOHYDRATES
The end product of carbohydrate digestion are…
Glucose
Fructose
galactose
These are readily absorbed through the
intestinal mucosal cells into the blood stream.
Two mechanism are responsible for the
absorption of these sugars….
Facilitated transport, with conc gradient..
Active transport, against conc. gradient.

14. Ashok Katta
Facilitated transport.
This is depends on the conc. of sugar across the
intestinal lumen and mucosal cells.
All the monosaccharide are absorbed o some
extent by facilitated diffusion.

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Active Transport.
The transport of glucose and Galactose across
the brush boarder of mucosal cells occur by
active transport.
It is an energy requiring process that requires
transport protein and presence of sodium ions.
A sodium dependent glucose transporter (SGLT-
1) binds both glucose and sodium at separate
sites and transports them into the cell.
The sodium transport down conc. gradient &
glucose transported against conc. gradient.
This process is called cotransport or symport.
The energy for this reaction is provided by ATP
linked to sodium pump.

16. ATP
ADP + Pi
Na+ - K+
Pump
Sodium -
Potassium -
Monosaccharides
Intestinal
epithelium
Brush
Border
To
capillaries
Absorption of Carbohydrates
Ashok Katta

17. Ashok Katta
Glucose Transporters
Several glucose transporter (GLUT-1 to 7) have
been identified in various tissues.
GLUT- 1 Brain, Kidney, placenta, RBC Uptake of glucose
GLUT- 2
Liver, pancreatic β- cell, small
intestine, Kidney
Rapid uptake & release
of glucose
GLUT- 3 Brain, Kidney, placenta Uptake of glucose
GLUT- 4
Heart, skeletal muscle, adipose
tissue
Insulin stimulated
uptake of glucose
GLUT- 5 Small intestine Absorption of glucose
SGLT-1 Small intestine and kidney
Active uptake &
reabsorption of glucose

18. Lactose intolerance
This is condition, in which there is deficiency of the
enzyme Lactase.
The enzyme which hydrolyse lactose to glucose and
galactose.
Due this, lactose gets accumulates in the gut where it
is a substrate for bacterial fermentation in the large
intestine with production of H2 & CO2 gases and low
molecular weight acids, like acetic acid, propionic acid
& butyric acids which are osmotically active.
Abdominal cramps & flatulence results from the
accumulation of gases and osmotically active products
draw water from intestinal cells into lumen resulting in
diarrhea and dehydration.
Disorders of
Digestion & Absorption of Carbohydrates

19. Sucrase deficiency
This is condition,
There is inherited deficiency of the enzyme Sucrase.
The enzyme which hydrolyse Sucrose to glucose and
fructose.
Symptoms occur in early childhood
These symptoms are same as lactose intolerance.

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