Dr. Dhiraj J. Trivedi presenting Lecture on Carbohydrate metabolism for medical students.
Professor, SDM College of Medical Sciences, Dharwad, Karnataka, India
3. Breaking down of complex macromolecules to
simple, absorbable and assimilable molecules.
Digestion –
Digestion apparatus –
MOUTH STOMACH SMALL INTESTINE LARGE INTESTINE
Let us recall
8. Digestion in Intestinal Lumen
Pancreatic Amylase
Pancreatic Amylase – From pancreas
Acts on cooked or uncooked Starch or glycogen
Hydrolyses α 1—4 and α 1—6 Glycosidic bonds
Exocarbohydrase
Product -- Maltose, Isomaltose , Trisaccharides
Activator – Chloride ion, Alkaline pH
Limit dextrin, Oligosaccharides – digested by glycosidase
Starch / Glycogen
Limit dextrin, O S,
Maltose, Isomaltose
H2O
Cl
Pancreatic
Amylase
9. Starch
Amylo dextrin
Erythro dextrin
Achro dextrin
Malto triose
Maltose & Isomaltose
Hydrolysis
Blue colour
Purple blue colour
Red Colour
No Colour
No Colour
No Colour
Colour with Iodine
Hydrolytic products
of starch
10. Digestion in small intestine
Main digestion takes place in
the small intestine
by pancreatic amylase, Dextrimax &
disaccharidases
Starch / Glycogen
Digestion is completed
by pancreatic amylase
because food stays for a looong time.
11. Disaccharidases
Present in the brush border epithelium
of intestinal mucosal cells
They act on disaccharides
Different disaccharidases are
1. Maltase – act on maltose
2. Isomaltase – act on Isomaltose
3. Sucrase – digest sucrose
4. Lactase – hydrolyses lactose
5. Di and Trisaccharidases
12. Digestion in Intestinal Lumen
Maltase & Isomaltase
Maltose (1—4)
Glucose + Glucose
H2O
Intestinal
Maltase
Isomaltose (1—6)
Glucose + Glucose
H2O
Intestinal
Isomaltase
Hydrolysis of α 1 – 4 linkage
from straight chain
Hydrolysis of α 1 – 6 linkage
present at branch point
13. Digestion in Intestinal Lumen
Lactase & Sucrase
Lactose
Glucose + Galactose
H2O
Intestinal
Lactase
Sucrose
Glucose + Fructose
H2O
Intestinal
Sucrase
Hydrolysis of β 1 – 4 linkage Hydrolysis of α1 – β2 linkage
Di and Trisaccharides
Glucose
14. End product of Digestion
Glucose --- (80%)
Fructose
Galactose
Non digestible carbohydrates
Dietary fiber
Cellulose, Hemicellulose
Pectin, Inulin
Due to lack of enzymes
15. In short
Site Digestive
juice
pH Source Enzyme Substrate End product
Mouth Saliva 6.8 Salivary gland S Amylase
(ptylin)
Starch /
Glycogen
Dextrins
Duodenum Pancreatic
juice
7.5 –
8.3
Pancreas P Amylase
(Amylopsin)
Starch /
Glycogen
Dextrins,
Oligosaccharides
Small
Intestine
Intestinal
juice
7.5 –
8.0
Intestinal - EC
brush border
Dextrimax
Maltase
Isomaltase
Lactase
Sucrase
Di –Tri
saccharidase
Dextin
Maltose
Isomaltose
Lactose
Sucrose
Di & Tri
saccharides
Glucose,
Fructose,
Galactose
Undigested carbohydrates – food fibers
21. GLUT type Km value of Glucose Tissue
distribution
Significance of
distribution
1, 3, 5 Low Brain, RBC Use only glucose
2 High Liver, Intestine,
Kidney, Panaceas
Handling high
glucose load
4 Intermediate Heart & Skeletal
muscle, Adipose
Insulin dependent
Types of glucose transporters
23. Lactose Intolerance
o Commonest Disaccharidase deficiency
o Either complete absence of Lactase
o Or low concentration of Lactase (non inducible enzyme)
24. •Develops over a time
•No congenital absence of lactase
•But low enzyme synthesis and
precipitate in adult
•Very common in Asian population
•There is intolerance to milk and
dairy products
Primary lactase deficiency
Fine/
good
OK
Oh ! NO
25. Secondary lactase deficiency
Occurs because of mucosal damage or from
medications resulting from certain
gastrointestinal diseases
Exposure of gastrointesinal parasites like
Giardia lamblia [giardiasis].
Production of lactase disturbed
Temporary lactose intolerance
Another form is due to lactose over load
26. Clinical manifestations
*Osmotic effect
Form of abdominal cramps, distensions,
diarrhea, constipation, flatulence
upon ingestion of milk or dairy products
Dislike towards milk and milk product
27. Biochemical basis of the disease
Undigested lactose in lumen is acted upon by intestinal
bacteria and forms CO2, H2, and 2-C and 3-C
compounds which remain undigested
CO2 and H2 causes Distension and flatulence
Lactose + 2C & 3C are somatically active
They withdraw water from intestinal mucosal cell
and cause osmotic diarrhea or constipation because
of undigested milk