Digestion and absorption of carbohydrates for Medical School

BIOCHEMISTRY

1. Digestion and Absorption of
Carbohydrate
V.S.RAVIKIRAN, MSc.

2. V.S.RAVIKIRAN, MSc.,
Department of Biochemistry,
ASRAM Medical college,
Eluru-534005.AP, India.
[email protected]

3. Digestion and Absorption
of Carbohydrate

4. Digestion and Absorption of
Carbohydrate
- Most digestible dietary
carbohydrate is starch.
- The starch digestion begins in
the mouth by salivary amylase.
- But fully digestion of starch
occurs in the small intestines.

5. 5
Carbohydrate Digestion and
Absorption
•Mouth
–Salivary amylase begins digestion of starch
•Small intestine
–Pancreatic amylase completes starch digestion
–Brush border enzymes digest disaccharides
•End products of carbohydrate digestion
–Glucose, fructose, galactose
–Absorbed into bloodstream
•Fibers are not digested, excreted in feces

6. 6
Simple Sugars:Mono and Disaccharides
•Monosaccharides – single sugar unit
–Glucose
•Found in fruits, vegetables, honey
•“blood sugar” – used for energy
–Fructose
•“fruit sugar”
•Found in fruits, honey, corn syrup
–Galactose
•Found as part of lactose in milk

7. 7

8. 8
•Disaccharides – two linked sugar
units
–Sucrose: glucose + fructose
•“table sugar”
•Made from sugar cane and sugar beets
–Lactose: glucose + galactose
•“milk sugar”
•Found in milk and dairy products
–Maltose: glucose + glucose
•Found in germinating cereal grains
•Product of starch breakdown

9. NUTRITION and GI DISORDERS
LACTOSE INTOLERANCE
CAUSES:
•Inability to digest lactose, caused by a shortage of lactase
•Symptoms: nausea, cramps, bloating, gas, and diarrhea
•TREATMENT
•Don’t eat dairy products! Or eat less, and more processed types (ex.
Yogurt vs. milk )

10. - Starch is digested to oligosaccharides (3-8 glucose
residues), disaccharide maltose, and glucose.

11. SF Biology II 11
Carbohydrate (CHO) Digestion

12. SF Biology II 12

13. starch
oligosaccharidesglucose
pancreatic amylase
Brush border
enzymes
Intestinal lumen
Intestinal
epithelial
cells
blood
glucoseglucose

14. Glucose is absorbed by:
- sodium-dependent glucose transporter
(SGLT).
- solvent drag

16. Carbohydrate digestion and absorption
In lumen
•Starch  maltose + maltriose + α-
limit dextrins
–Amylase
At brush-border
•Maltose/maltriose  glucose
–Glucoamylase (maltase)
–Sucrase-isomaltase
•α-limit dextrins  glucose
–Sucrase-isomaltase
•Sucrose  glucose + fructose
–Sucrase-isomaltase
•Lactose  glucose + galactose
–Lactase
SGLT-1
• Na
+
coupled
(Na/K ATPase for
gradient)
• D-hexoses w/
pyranose ring
apical basolateral
GLUT-5
• Fructose absorption
• Jejunum
• Facilitated diffusion
GLUT-2

17. Transporter Present in Properties
Glu T1 RBC, brain, kidney, colon,
retina, placenta
Glucose uptake in most of cells
Glu T2 Serosal surface of intestinal
cells, liver, beta cell pancreas
Low affinity; glucose uptake in
liver ; glucose sensor in beta cells
Glu T3 Neurons, brain High affinity; glucose into brain
cells
Glu T4 Skeletal, heart, muscle, adipose
tissue
Insulin mediated glucose uptake
Glu T5 Small intestine, testis, sperms,
kidney
Fructose transporter; poor ability
to transport glucose
Glu T7 Liver endoplasmic reticulumGlucose from ER to cytosol

18. SF Biology II 18
CHO Digestion — Summary
•Polysaccharides to disaccharides (gut amylases)
•Disaccharides to monosaccharides (brush border)
–Glucose, galactose enter cells by
energy-dependent secondary active transport
•i.e. ‘piggy-back on Na
+
gradient (active)

19. SF Biology II 19
Carbohydrate Absorption
•Glucose, galactose enter capillaries down concentration
gradient
•Fructose enters capillaries via passive carrier mediated
transport

20. THE END
THANKS FOR YOUR
ATTENTION