Epithelial Transport of Glucose

Question 1

What effects transepithelial transport

Answer 1

Combining different types of transport proteins

Question 2

Epithelial tissues
- Consist of cells arranged in ______ sheets in either ___ or ____ layers
- Cells sit on a _____ membrane
- Form the _____ between the body’s organs or between the ___ and _____ environment
- Subject to physical breakdown and ____ … therefore undergo ____ and rapid renewal process

Answer 2

Epithelial tissues
- Consist of cells arranged in CONTINUOUS sheets in either SINGLE or MULTIPLE layers
- Cells sit on a BASEMENT membrane
- Form the BOUNDARY between the body’s organs or between the BODY and EXTERNAL environment
- Subject to physical breakdown and INJURY… therefore undergo CONSTANT and rapid renewal process

Question 3

What are epithelial cells separated from the neighbours by

Answer 3

Lateral intercellular space

Question 4

How are epithelial cell held together

Answer 4

Their luminal edges by tight junctions

Question 5

What type of junction is composed of thin bands that encircle the cell and make contact with thin bands from adjacent cells

Answer 5

Tight junctions

Question 6

Appearance of freeze fracture tight junctions

Answer 6

Interlocking network of ridges in the PM

Question 7

Why tight junctions act as a barrier and a fence

Answer 7

To separate the epithelial cells into 2 distinct membrane domains

Question 8

Name the 2 distinct membrane domains

Answer 8

1. Apical (luminal or mucosal)
2. Basolateral

Question 9

Tight junctions act as a barrier or a fence when “they restrict the movement of subst. through the intercellular space between cells”

Answer 9

Tight junctions act as a BARRIER

Question 10

Tight junctions act as a barrier or a fence when “they prevent membrane proteins from diffusing in the plane of the lipid bilayer”

Answer 10

Tight junctions act as a FENCE

Question 11

What membrane domain faces the lumen of the organ/body cavity

Answer 11

Apical (luminal or mucosal)

Question 12

The basolateral membrane…

Answer 12

Adheres to the adjacent basement membrane and interfaces with the blood

Question 13

Why do we need the distinct membrane domains

Answer 13

So different transport proteins can be inserted into either the apical or basolateral membrane

Question 14

True or false, “transport can occur via the paracellular OR transcellular pathway OR both”

Answer 14

TRUE

Question 15

What laws is paracellular transport governed by

Answer 15

Laws of diffusion and tightness of junctions

Question 16

True or false, “the electrical resistance to ion flow through tight junctions can’t be measured”

Answer 16

FALSE… electrical resistance to ion flow through tight junctions CAN be measured

Question 17

What happens to number of tight junction strands holding the cell together if there’s higher electrical resistance to ion flow

Answer 17

Greater number of tight junction strands holding the cell together

Question 18

Epithelial tissues functional classifications

Answer 18

1. Leaky epithelium = paracellular transport dominates
2. Tight epithelium = transcellular transport dominates

Question 19

What changes in proximal to distal direction in GI tract and kidney

Answer 19

Tight junction resistance

Question 20

Features of the proximal direction

Answer 20

• Leaky epithelium
  
  • Low electrical resistance
  • Low # of strands
  • Bulk transport (paracellular)
    e.g duodenum/proximal tubule

Question 21

Features of the distal direction

Answer 21

• Tight epithelium
  
  • High electrical resistance
  • High # of strands
  • Hormonally controlled (transcellular)
    e.g. colon/collect duct

Question 22

What is transcellular transport

Answer 22

Epithelial cells use 1o and 2o active transport often in combination with passive diffusion through ion channels to produce transport across the epithelial tissues

Question 23

Transcellular transport can either be

Answer 23

• Absorption = transport from lumen to blood
• Secretion = transport from blood to lumen

Question 24

4 areas transepithelial transport is broken down into

Answer 24

1. Entry and exit steps
2. Electrochemical gradient
3. Electroneutrality
4. Osmosis

Question 25

What area of transepithelial transport "the entry step for absorption is the apical but for secretion is the basolateral membrane"

Answer 25

Entry and exit steps

Question 26

The electrochemical gradient area of transepithelial transport does…

Answer 26

Entry or exit step passive or active

Question 27

What area of transepithelial transport "movement of a positive or negative ion will attract a counter ion"

Answer 27

Electroneutrality

Question 28

Osmosis area of transepithelial transport does…

Answer 28

The net movement of ions will establish a difference in osmolarity that will cause water to flow by osmosis

Question 29

What do epithelial cells use to mediate either secretion or absorption

Answer 29

Different collections of transporters and channels

Question 30

Step 1 of glucose absorption

Answer 30

Tight junctions divide cells into apical and basolateral membrane domains

Question 31

Step 2 of glucose absorption

Answer 31

Na-pump sets up ion gradients

Question 32

Step 3 of glucose absorption

Answer 32

The sodium glucose symporter (SGLT) uses the energy of the Na gradient to actively accumulate glucose above its conc. gradient

Question 33

Step 4 of glucose absorption

Answer 33

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

Question 34

Step 5 of glucose absorption

Answer 34

Na take up via the glucose exits via the basolateral Na-pump

Question 35

Step 6 of glucose absorption

Answer 35

The transport of Na and glucose across the epithelium induces paracellular Cl and water influxes

Question 36

The ability of glucose to enhance the absorption of Na+ and Cl- and water is exploited in…

Answer 36

Oral rehydration therapy

Question 37

What causes glucose-galactose malabsorption syndrome

Answer 37

A mutation to the glucose symporter in the small intestine means that sugar is retained in the intestine lumen

Question 38

What is induced due to the associated increase in lumen osmolarity

Answer 38

Induces a water efflux

Question 39

The increased water flow produces

Answer 39

Pronounced diarrhea

Question 40

What is the treatment for glucose-galactose malabsorption

Answer 40

- Remove glucose and galactose from diet - Use fructose as source of carbohydrate

Question 41

What utilises a facilitative transporter (GLUT5) that is specific for fructose

Answer 41

Therapy for glucose-galactose malabsorption

Question 42

What fructose uses to exit across the basolateral membrane

Answer 42

GLUT2

Question 43

In the kidney ____ in the ____ is filtered and needs to be _____ or it will appear in the ___

Answer 43

In the kidney GLUCOSE in the PLASMA is filtered and needs to be REABSORBED or it will appear in the URINE

Question 44

Name for when glucose is in the urine

Answer 44

Glucosuria

Question 45

What is the most common cause in diabetes mellitis as insulin activity is deficient and blood sugar too high (over 200mg/mL)

Answer 45

Glucosuria - glucose in the urine

Question 46

What happens to glucose symporter in diabetes

Answer 46

Can not absorb glucose fast enough and glucose appears in the urine

Question 47

What happens to urine if glucose absorption is impaired or the transporter is saturated

Answer 47

Glucose will appear in the urine

Question 48

Glucose in urine - transporter kinetics - All filtered ____ is reabsorbed until the ___ threshold is reached - Once the renal ____ is reached ____ appears in the ____

Answer 48

Glucose in urine - transporter kinetics - All filtered GLUCOSE is reabsorbed until the RENAL threshold is reached - Once the renal THRESHOLD is reached GLUCOSE appears in the URINE

Question 49

What does renal threshold reflect

Answer 49

Transport maximum of SGLT (sodium-glucose linked transporters)