Digestion and Absorption of Carbohydrates

MBBS students

1. DIGESTION AND ABSORPTION
OF CARBOHYDRATES
By: Dr. Sohil Takodara

2. Biomedical importance
•Glucose- Main carbohydrate
•Major source of energy
•Important Compounds(2,3 BPG,NADPH,GAG)
•Defective Metabolism( DM,Galactosemia,
Hemolytic Anaemia, Glycogen Storage Disease)

3. We eat food containing carbohydrates

4. DIETARY CARBOHYDRATES
•Starch- Cereals, Wheat,Rice,Potato
•Lactose-Milk Sugar
•Sucrose- Cane Sugar
•Glycogen- Animal meat
•Fructose, Maltose- Fruits and Malt

5. DIGESTION :
• Dietary carbohydrates mainly consist of the
polysaccharides.

• Other CHO in the diet are sucrose, lactose,
maltose & glucose ( from fruits & honey).

6. •Cooking helps in breaking of glycosidic linkages
in polysaccharides & thus makes the digestive
process easier.
•Liquid foods like milk, soups etc. escape digestion
in mouth as they are swallowed but solid food
stuffs are masticated & digestion of solid
carbohydrates starts in mouth.
•Food digestion in mouth is for short time, as they
are swallowed into stomach.

7. Digestion in mouth:
Starch Salivary amylase Limit dextrins
maltose
Glycogen Cl
-
pH 6.7 isomaltose
•Salivary amylase or α-amylase (ptyalin) requires
chloride ion for activation & optimum pH of 6.7
(6.6-6.8).
•It hydrolyzes the α1-4 glycosidic linkages in starch
& glycogen into smaller molecules dextrins,
maltose, isomaltose & maltotriose.

8. Digestion in stomach:
•No enzymes present in stomach for further
digestion.
•Acidic pH in the stomach (pH -2) inhibits the
action of salivary amylase.

9. Digestion in intestine:
Pancreatic Juice
Pancreatic
amylase
Intestinal Juice
Maltose Maltase Glucose + Glucose
Isomaltose Glucose + Glucose
Isomaltase
Maltose,
Isomaltose,
Sucrose,
Lactose
Starch,
Glycogen,
Limit Dextrin

10. Sucrose Glucose + Fructose
Lactose Glucose + Galactose
sucrase
lactase

11. Summery

12. MOUTH
STOMACH
PANCREAS
INTESTINE
DIET -- CARBOHYDRATES
POLYSACCHARIDES MONO/DISACCHARIDES
MALTOSE,ISO MALTOSE,SUCROSE,LACTOSE
GLUCOSE, FRUCTOSE, GALACTOSE
LIMIT DEXTRIN, MONO/DISACCHARIDES
NO DIGESTION
A B S O R P T I O N
SALIVARY
AMYLASE
PANCREATIC
AMYLASE
DISACCHRID
ASES
INACTIVE
ENZME

13. ABSORPTION :
• Monosaccharides are the products of digestion
of dietary carbohydrates.
• Only monosaccharides are almost entirely
absorbed from the intestine ( jejunum)

14. Two mechanisms are responsible for the absorption
of monosaccharides.
I.Active transport against concentration
gradient. ( SGLT)

II.Facilitated transport with concentration
gradient. ( GLUT)

15. II. Facilitated transport :
( Sodium independent for glucose & other
monoaccharides.) (GLUT)
•This is mediated by a family of atleast 5-6 glucose
transporters in the cell membrane designated
GLUT-1 to GLUT -5
•These glucose transporters show significant
homology in their primary sequence but display
a tissue specific pattern of expression.

16. Glucose Transporters
Facilitated transport
mediated by a family of
at least five known
glucose transporters
GLUT 1, 2, 3, 4, 5.

17. GLUCOSE TRANSPORTERS
TYPES SITE PROPERTIES
GluT1
GluT2
GluT3
GluT4
GluT5
RBC, Brain, Kidney ,
Colon, Retina.
Serosal surface of
enterocytes, Liver , β-
cells of pancreas.
Neurons, Brain.
Skeletal, Heart muscle
adipocytes
Small intestine , Testis,
Sperm
Glucose uptake
Affinity, Glucose uptake in
liver, sensor in β-cells
Affinity, Glucose into brain
cells
Insulin mediated uptake
(DM)??
Fructose transporter

19. Sodium Dependent GLUT ( SGLT)

20. Oral rehydration therapy is widely considered to be
the best treatment for dehydration caused by diarrohea
and vomiting.
Significance of including sodium chloride along
with glucose in the oral rehydration solution
----
* The basis for oral rehydration is the
cotransport of Na
+
with glucose as they travel
across the intestinal cell .

21. WHO / UNICEF ORS solution contains
Reduced osmolarity ORS grams/litre
Sodium chloride 2.6
Anhydrous Glucose 13.5
Potassium chloride 1.5
Trisodium citrate, dihydrate2.9

22. LACTOSE INTOLERANCE:
- Due to lactase deficiency, intolerance to lactose
(milk sugar ) occurs .

Sensitivity to milk & milk products (milk allergy )

is due to sensitivity to ß – lactoglobulin.

23. Signs & symptoms – nausea, abdominal cramps,
diarrhea, bloating & flatulance .
• Lactose cannot be completely digested , absorbed
in the small intestine.
• Accumulation of undigested lactose in the large
intestine, leading on to fermentation of the sugar
by intestinal bacteria, resulting in production
of gas & other toxic products that cause irritation
to the intestine.

24. Types of lactase deficiency:
1. Inherited or congenital lactase deficiency:
- Rare, symptoms of intolerance develop soon
after birth.
- Feeding of lactose - free diet results in the
disappearance of symptoms.
2. Secondary low - lactase activity:
- as a consequence to intestinal diseases such
as tropical sprue, coeliac disease, kwashiorkor,
gastroenteritis & colitis.

25. 3. Primary low- lactase activity :
- Gradual decline in the lactase activity in susceptible

individuals as the age advances owing to the
reduction of the expression of the enzyme.
DISACCHARIDURIA - in excretion of disaccharides
due to disaccharidases deficiency.
MONOSACCHARIDE MALABSORPTION – defect in
SGLT-1 transporter mechanism.
SUCROSE , ISOMALTASE INTOLERANCE –
inherited coexisting deficiency of the disaccharidases ,
sucrase & isomaltase .

26. Sulphonylurias (Tolbutamide) Anti
Diabetic ( Increase Insulin Sensitivity)