1. GASTROINTESTINAL PHYSIOLOGY Chapter-II (DIGESTION and ABSORPTION)
Ass. Prof. Dr. Emre Hamurtekin
EMU Faculty of Pharmacy

2. INTRODUCTION CARBOHYDRATES PROTEINS NUCLEIC ACIDS LIPIDS
VITAMINS & MINERALS

3. CARBOHYDRATES The principal dietary carbohydrates are:
Polysaccharides (Starches)
Amylopectin***
Amylose
Disaccharides (lactose & sucrose)
Monosaccharides (fructose & glucose)
Salivary and pancreatic α-amylases hydrolyze 1:4 α bonds.
The end products of α-amylase digestion are:
Maltose
Maltotriose
α- limit dextrin
Glucose oligomers
Oligosaccharidases are located in the brush border of small intestinal epithelial cells.
Isomaltase is responsible for hydrolysis of 1:6 α bonds

4. CARBOHYDRATES Sucrase Sucrose Lactase Lactose glucose fructose glucose
galactose
Lactase
Lactose

5. CARBOHYDRATES
SGLT-1 transports glucose & galactose into the intestinal epithelial cell.
Transport of glucose and galactose is dependent on Na in the intestinal lumen.
Fructose absorption is independent of Na; it is transported by facilitated diffusion.
GLUT 5 and GLUT 2 is responsible for the absorption of fructose.

6. PROTEINS Protein digestion begins in the stomach (pepsins).
Pepsins are secreted as proenzymes and activated by gastric acid.
Pepsinogen I
Pepsinogen II
Products of peptic digestion are polypeptides.

7. PROTEINS
Polypeptides are further digested in the small intestine by pancreatic and intestinal proteolytic enzymes.
Endopeptidases:
Trypsin
Chymotrypsin
Elastase
Exopeptidases:
Carboxypeptidase A
Carboxypeptidase B

8. PROTEINS

9. PROTEINS

10. PROTEINS Brush border of the intestinal mucosal cell:
Aminopeptidases
Carboxypeptidases
Endopeptidases
Dipeptidases
Intracellular peptidases hydrolyzes some di-and tripeptides that enters into the intestinal epithelium.

11. PROTEINS
At least seven different transport systems transport a.a. into enterocytes.
Five of them cotransport a.a. and Na.
Two of them are Na independent.
Di- and tripeptides are transported into enterocytes by PepT1 system (requires H).
A.a absorption is rapid in duodenum and jejunum.

12. NUCLEIC ACIDS nucleotides nucleosides phosphoric acid sugars
Pancreatic nucleases
nucleotides
Intestinal enzymes
nucleosides
phosphoric acid
blood
purine / pyrimidine
bases
sugars
active transport

13. LIPIDS
Most of the fat digestion begins in the duodenum (pancreatic lipase*)
The products are:
FFA
2-monoglycerides
Pancreatic lipase acts on emulsified fats and activitiy is facilitated by colipase

15. LIPIDS
Steatorrhea:
Fatty, bulky stool because of the impaired digestion and absorption of the fat.
Mostly due to the lipase deficiency,
Gastric acid hypersecretion & defective reabsorption of bile salts are the other causes.
Malabsorption of fat-soluble vitamins results.

16. LIPIDS
Transport of lipids into the enterocytes occurs mainly by passive diffusion, but also carriers may be involved.
no modification
active transport
FFA
FA < C atoms FA
ENTEROCYTE
BLOOD
esterified
FA > C atoms
Chylomicrons TG +
ChE
LYMPHATIC
CIRCULATION
Chylomicrons
exocytosis

17. VITAMINS Fat-soluble vitamins: Vitamin A, D, E and K
Most vitamins
absorbed
Esterase
Upper small intestine
Incorporation into micelles
Vit B12
Absorption
Ileum

18. VITAMINS Vit B12 and folate absorption are Na-independent.
Remaining water-soluble vitamins
Thiamin
Riboflavin
Niacin
Pyridoxine
Pantothenate
Biotin
Ascorbic acid
Na cotransporters

19. THE END