1. 1. Digestion
Digestion of Carbohydrates
• It is the breakdown &
degradation of polysaccharides &
oligosaccharides into their
simplest units (Monosaccharides)

2. Classification of Carbohydrates
3
1
Digestible Do not need
digestion
2
Non-Digestible
Starch
Monosaccharides
Glycogen
Cellulose Pentoses
Lactose Hexoses
Sucrose

3. The
Digestive
System

4. PH 6.4 – 6.9. Activated
by Cl-, digests starch to Acidic PH of stomach (1-2) is
dextrins, maltose & unsuitable for salivary
isomaltose amylase
4.
-
(Activated by Cl ).
3. Brush border (Intestinal juice,
Succus Entericus) containing:
Maltase, Lactase & Sucrase

5. Carbohydrate Digestion in Small Intestine
• Salivary amylase stops working in acidic
stomach (if pH  4.5)
• 50% of dietary starch digested before it
reaches small intestine
• Brush border enzymes act upon
oligosaccharides, maltose, sucrose & lactose
• lactose indigestible after age 4 in most
humans (due to lack of lactase)

6. Carbohydrate Digestion
in Small Intestine

7. & Isomaltose

9. 2. Absorption
Monosaccharides Absorption
• Pentoses are absorbed by facilitated diffusion then
excreted through the kidney
• Fructose is absorbed by facilitated diffusion then
converted to glucose inside the cell
• Sodium-glucose transport proteins (SGLT) in
membrane help absorption of glucose & galactose

10. Pentoses absorbed
by Passive Diffusion
According
concentration
gradient
Hexoses absorbed
by Active Transport
Against
concentration
gradient
Absorption of Pentoses & Hexoses

12. Types of Transport Carriers

13. Monosaccharides Absorption
Liver

14. GLUT1 in RBCs membrane is Facilitated Diffusion

15. Digestion of Lactose
(Lactase)

16. Lactose Intolerance
• Some individuals (90% of adult blacks & Orientals)
have a defect in lactase enzyme
• Undigested lactose (osmotically active compound)
passes to the bowel (large intestine), acted upon by
bacteria of large intestine producing short chain fatty
acids & CO2 gas, leading to:
1. Abdominal distention (cramping)
2. Abdominal pain
3. Nausea
4. Bloating
5. Watery diarrhea

18. Lactase deficiency

19. Fate of Absorbed Glucose
• Glucose enter Liver & Brain by Passive
diffusion
• Glucose enter other tissues (skeletal muscle,
adipose tissue, etc…) by Active transport
• Active transport is enhanced by Insulin

24. Utilization of Glucose
Anabolic
Reactions Catabolic
Reactions
1) Storage in the form of
Glycogen (Glycogenesis)
2) Storage in the form of Lipid
1) Glycolysis
(Lipogenesis) 2) Kreb’s Cycle
3) Synthesis of sugar alcohols 3) Pentose Shunt
and amino sugars
4) Formation of
4) Interconversion between
monosaccharides
Uronic acids