Digestion And Absorption Of Carbohydrate

DIGESTION AND ABSORPTION OF CARBOHYDRATE

Q. 1 The absorption of glucose from the gut into intestinal mucosal cells is coupled to Na+,K+ ATPase.  In  contrast,  the  movement  of  glucose from the intestinal epithelial cells into the submucosal bloodstream occurs
through  passive  transport.  Given  these  facts, which of the following statements can be true at one time or another?
 A Levels of plasma glucose are approximately equal
to levels in the cytosol of intestinal epithelial cells
 B Free glucose levels in the lumen of the intestine can never be higher than levels in intestinal cells
 C Plasma glucose levels are much higher than intestinal cell cytosolic levels of glucose
 D Levels  of  glucose  in  the  intestinal  lumen  are always higher than those in the cytosol of intestinal epithelial cells
Q. 1 The absorption of glucose from the gut into intestinal mucosal cells is coupled to Na+,K+ ATPase.  In  contrast,  the  movement  of  glucose from the intestinal epithelial cells into the submucosal bloodstream occurs
through  passive  transport.  Given  these  facts, which of the following statements can be true at one time or another?
 A Levels of plasma glucose are approximately equal
to levels in the cytosol of intestinal epithelial cells
 B Free glucose levels in the lumen of the intestine can never be higher than levels in intestinal cells
 C Plasma glucose levels are much higher than intestinal cell cytosolic levels of glucose
 D Levels  of  glucose  in  the  intestinal  lumen  are always higher than those in the cytosol of intestinal epithelial cells
Ans. B

Explanation:

The plasma membranes of intestinal epithelial cells contain a sodium gradient that drives the active transport of glucose. The rate and amount of glucose transported depend upon the sodium gradient maintained across the plasma membrane. Sodium ions entering the cell in the company of glucose are pumped out again by Na+,K+-ATPase. Once in the cytosol of the intestinal cell, the glucose moves across the cell and diffuses out of the cell into the interstitial fluid of the submucosa and then into the plasma of the capillaries underlying the intestinal epithelium. This occurs for the following reason: while glucose is maintained in blood plasma at an approximately constant level, it is always slowly moving out of the plasma into the cells of tissue that use it. Given that the diffusion from the intestinal cells into the plasma is passive, the intestinal cells and the plasma try to maintain an equilibrium. Thus, plasma glucose levels are always approximately equal to or slightly less than levels in the intestinal cells. Due to the passive maintenance of this equilibrium, it is highly unlikely that the concentration of glucose in the plasma can get much higher than that in the intestinal cell cytosol. It is also unlikely that the levels of glucose in other tissues of the body (for example, muscle) will have any bearing on those found in the intestinal cells


Q. 2

Which of the following requires co-transport with sodium for its absorption in the GI tract?

 A

Glucose

 B

Aminoacids

 C

Galactose

 D

All of the above

Q. 2

Which of the following requires co-transport with sodium for its absorption in the GI tract?

 A

Glucose

 B

Aminoacids

 C

Galactose

 D

All of the above

Ans. D

Explanation:

Glucose and galactose: The transport of most hexoses is dependent on Na+ in the intestinal lumen; a high concentration of Na+on the mucosal surface of the cells facilitates and a low concentration inhibits sugar influx into the epithelial cells. This is because glucose and Na+ share the same co-transporter, or symport, the sodium-dependent glucose transporter (SGLT, Na+-glucose transporter).

Amino acids: At least seven different transport systems transport amino acids into enterocytes. Five of these requires Na+ and co-transport amino acids and Na+ in a fashion similar to that of Na+ and glucose.
 
Ref: Ganong’s Review of Medical Physiology, 23rd Edition, Page 453

 


Q. 3

Which of the following occurs along with glucose transport into a cell:

 A

Sodium symport

 B

Sodium anteport

 C

Potassium transport

 D

Amino acid transport

Q. 3

Which of the following occurs along with glucose transport into a cell:

 A

Sodium symport

 B

Sodium anteport

 C

Potassium transport

 D

Amino acid transport

Ans. A

Explanation:

A i.e. Sodium symport

Glucose and Na+ share the same Co-transporter (or symport) – the sodium dependent glucose transporter: (SGLT – sodium glucose co- transporter)Q.

Sodium dependent glucose transporter (symport)

– Since the intracellular Nat concentration is low in intestinal & renal cells, Nat moves into the cells along its concentration gradient.

Glucose moves with the Na+ & released into the cell.

–  The Na+ is then transported to lateral intercellular spaces & the glucose is transported by GLUT-2 into the interstitium & then into capillaries.

– This is an example of secondary active transport i.e. the energy for glucose transport is provided by the active transport of Na+ out of cells.

Also know: Glucose mechanism also transport glactoseQ. Fructose utilizes different mechanism, it is transported by facilitated diffusionQ.

Glucose is incorporated in ORS to facilitate Na* absorptionQ.



Q. 4

The function of glucose in ORS –

 A

Increase Na+ absorption by co-transport

 B

Gives sweet taste of ORS

 C

Increase Na+-K+ pump activity

 D

b and c

Q. 4

The function of glucose in ORS –

 A

Increase Na+ absorption by co-transport

 B

Gives sweet taste of ORS

 C

Increase Na+-K+ pump activity

 D

b and c

Ans. A

Explanation:

Ans. is ‘a’ i.e., Increase Na+ absorption by co transport


Q. 5

Ion which promotes glucose absorption in the gut region:           

September 2007

 A

CI ‑

 B

K+

 C

Na+

 D

Ca2+

Q. 5

Ion which promotes glucose absorption in the gut region:           

September 2007

 A

CI ‑

 B

K+

 C

Na+

 D

Ca2+

Ans. C

Explanation:

Ans. C: Na+

Glucose enters cells by facilitated diffusion or, in the intestine and kidneys, by secondary active transport with Na+. In muscle, fat, and some other tissues, insulin facilitates glucose entry into cells by increasing the number of glucose transporters in the cell membranes.

The glucose transporters that are responsible for facilitated diffusion of glucose across cell membranes are a family of closely related proteins that cross the cell membrane 12 times and have their amino and carboxyl terminals inside the cell. They differ from and have no homology with the sodium-dependent glucose transporters, SGLT 1 and SGLT 2, responsible for the secondary active transport of glucose out of the intestine, although the SGLTs also have 12 transmembrane domains. Particularly in transmembrane helical segments 3, 5, 7, and 11, the amino acids of the facilitative transporters appear to surround channels that glucose can enter. Presumably, conformation then changes and glucose is released inside the cell.


Q. 6

Salivary amylase is activated by:           

March 2007

 A

Sodium Ion

 B

Chlorine Ion

 C

Potassium Ion

 D

Bicarbonate Ion

Q. 6

Salivary amylase is activated by:           

March 2007

 A

Sodium Ion

 B

Chlorine Ion

 C

Potassium Ion

 D

Bicarbonate Ion

Ans. B

Explanation:

Ans. B: Chlorine Ion

Salivary Amylase break large, insoluble starch molecules into soluble starches (amythrodextrin, achrodestrin and ultimately maltose.

Ptyalin acts on linear alpha (1,4) glycosidic linkages.

Optimum conditions for ptyalin

  • Optimum pH – 5.6 -6.9
  • Human body temperature-37 degrees Celsius
  • Presence of certain anions and activators:

Chlorine and bromine – most effective

– Iodine – less effective

– Sulfate and phosphate

– least effective



Q. 7

In ORS, the effect of glucose on sodium absorption is:

September 2005

 A

Increase in sodium absorption

 B

Decrease in sodium absorption

 C

Variable effect on sodium absorption

 D

No effect on sodium absorption

Q. 7

In ORS, the effect of glucose on sodium absorption is:

September 2005

 A

Increase in sodium absorption

 B

Decrease in sodium absorption

 C

Variable effect on sodium absorption

 D

No effect on sodium absorption

Ans. A

Explanation:

Ans. A: Increase in sodium absorption

Oral fluid therapy is based on the observation that glucose given orally enhances the intestinal absorption of salt and water, and is capable of correcting the electrolyte and water deficit.


Q. 8

Glucose diffusion in RBC by ‑

 A

GLUT I

 B

GLUT 2

 C

GLUT 3

 D

GLUT 4

Q. 8

Glucose diffusion in RBC by ‑

 A

GLUT I

 B

GLUT 2

 C

GLUT 3

 D

GLUT 4

Ans. A

Explanation:

Ans. is ‘a’ i.e., GLUT 1



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