GI8 Carbohydrate digestion and absorbtion Flashcards
Define
digestion
the process by which ingested food is converted into a form which can enter the blood or lymph
define absorbtion
the process by which nutrient molecules are transported through the intestinal epithelial cells into the blood or lymph
Name all the dietary carbohydrates you can get + a bit on structure:
• Fibre – mostly cellulose (-1,4, linked glucose)
• Sugars
Disaccharides (sucrose, lactose, maltose)
Monosaccharides (glucose, galactose, fructose)
• Starch
Amylose – linear polymer of glucose containing -1,4 linked glucose: storage
Amylopectin – branched with higher molecular weight containing -1,4 and -1,6 linked glucose: enzyme act on it
Digestion of starch begins with the action of alpha amylase present in ___a___ and ____b___
1) What bond does this amylase hydrolyse?
2) What less obvious types does it not?
3) So what are the products of its action:
a=saliva
b= pancreatic juice
1)Hydrolyse -1,4 links= maltose
2)•Cannot hydrolyse -1,6 links
•Cannot hydrolyse -1,4 links adjacent to branch point or terminal -1,4 links
3) alpha-limit dextrins, maltotriose and maltose
Why does oral retention time in the mouth effect cariogenic potential of a food?
In mouth some bacteria can take up alpha limit dextrins and use as energy source,
oral retention time in the mouth will determine amount of digestion).
Where are carbohydrates digested?
• Mouth: salivary amylase breaks down starch into maltose, maltotriose and -limit dextrins (oral retention time will determine extent of digestion)
• Duodenum: pancreatic -amylase rapidly digests remaining starch to maltose, maltotriose and -limit dextrins
-duodenum and jejunum: Oligosaccharidases complete carbohydrate digestion on the brush border membrane of the duodenum and jejunum
Why aren’t carbohydrates digested in the stomach?
Stomach: acidic pH inhibits -amylase - no further digestion occurs here
List the brush border membrane Oligosaccharidases:
+ what the break down and products:
- Isomaltase (-dextrinase) – hydrolyses -1,6 links
- Maltase – hydrolyses maltose and maltotriose to glucose
- Lactase – hydrolyses lactose to glucose and galactose
- Sucrase – hydrolyses sucrose to glucose and fructose
Starch broken down to _______1_________
maltose and maltotriose acted upon by ___2___ will be broken down into the monomers.
_____3_____ act on a-limit dextrins forming glucose. ___4___ takes up glucose. Whenever glucose is taken up so it ___4.b___
Sucrose broken down into monomers. Fructose enters cells via ___5___
___6___ brakes down lactose. Galactose enters cells via ____7____ (same as ____8____).
1) a-limit dextrins and maltose and maltotriose.
2) maltase
3) Isomaltase
4) SGLT-1
b) Na+
5) GLUT-5.
6) Lactase
7) SGLT1
8) glucose
9) Na+
Glucose and galactose – ______1_____ taken up by a transport protein ‘sodium glucose transporter 1 (SGLT-1)’ in __2-__ membrane.• The electrochemical potential is created by a ___3-___ in the ____4___ membrane
1) actively
2) apical
3) Na+/K+ ATPase
4) baso-lateral
How do glucose , galactose an dfructose exit the epithelial cell into the blood?
2) What type of transport is this?
1) GLUT2
2) facilitated
Fructose enters the intestinal epithelial cell by ____1-____using ___2-___ and exits using GLUT2.
1) facilitated transport
2) GLUT5
The ___1___ entry of glucose and galactose into intestinal epithelial cells is stimulated by the presence of ___2___ in the GI lumen
1) active
2) sodium,
