Cellular Processes [Glucose Absorption]

Question 1

2 functions of tight junctions

Answer 1

Barrier to restrict the movement of substances through intercellular space.
Fence to prevent membrane proteins from diffusing in the plane of the lipid bilayer.

Question 2

Proximal paracellular transport (type of epithelium, electrical, strands, transport, examples)

Answer 2

Leaky epithelium.
Low electrical resistance.
Low number of strands.
Bulk transport.
Duodenum, proximal tuble.

Absorb goodies in epithelium first.

Question 3

Distal transcellular transport (type of epithelium, electrical, strands, transport, examples)

Answer 3

Tight epithelium.
High electrical resistance.
High number of strands.
Hormonally controlled.
Colon, collect duct.

Absorb more selective bits in GI tract.

Question 4

What is paracellular transport governed by?

Answer 4

Laws of diffusion and tightness of junctions.

Question 5

How does transcellular transport work?

Answer 5

Primary and secondary transport used with passive diffusion.

Question 6

What steps need to be considered for trans epithelial transport?

Answer 6

Entry and exit steps
Electrochemical gradient
Electroneutrality (passive or active entry /exit step
Osmosis

Question 7

What is electroneutrality?

Answer 7

Movement of a positive or negative ions will attract a counter ion

Question 8

Step 2 of Glucose Absorption

Answer 8

Na/K pump sets up ion gradients (primary, antiporter)

Question 9

Step 3 of Glucose Absorption

Answer 9

The sodium glucose symporters SGLT uses energy of the Na+ gradient to actively accumulate glucose above its conc gradient (secondary)

Question 10

Step 4 of Glucose Absorption

Answer 10

Facilitative glucose transporter GLUT mediates glucose exit across the basolateral membrane via passive diffusion down its gradient.

Question 11

Step 5 of Glucose Absorption

Answer 11

Na+ taken up via the sodium-glucose symporter and exits via the basolateral Na/K pump (pump leak).

Question 12

Step 6 of Glucose Absorption

Answer 12

The transport of Na+ and glucose across the epithelium induces paracellular Cl- and water fluxes. Isotonic fluid absorption.

Question 13

What is oral rehydration therapy?

Answer 13

Give a solution of sugar, salt and water to dehydrated babies suffering from diahorrea. This uses the bodies ability to use glucose to absorb more Na+, Cl- and H2O.

Question 14

WHAT is glucose/galactose malabsorption syndrome?

Answer 14

Caused by a mutation in the SGLT (step 3). Results in accumulation of glucose and galactose in the lumen of the small intestine. This produces an osmotic imbalance which attracts water = diahorrea.

Question 15

How is an osmotic imbalance created in glucose/galactose malabsorption syndrome?

Answer 15

The lumen is morality is increased as a starch molecule is broken down into smaller glucose molecules. H2O moves from blood to lumen.

Question 16

How to treat glucose/galactose malabsorption syndrome.

Answer 16

Remove glucose and galactose from the diet. Switch to fructose as a source of carbs. This uses a facilitative transporter GLUT5 which replaces steps 3 and 4.

Question 17

What does the kidney do to glucose and how does it work?

Answer 17

Glucose is filtered in the plasma then needs to be reabsorbed so it doesn’t appear in the urine. V similar to intestine except glucose provided by kidney filtrate.

Question 18

Glucosuria

Answer 18

Accumulation of glucose in the urine. Occurs if transport max of SGLT protein is exceeded (too much glucose). Common cause is diabetes.

Question 19

What is the renal threshold?

Answer 19

Reflects the transport max of SGLT. Glucose appears in the urine once it is reached.