Epithelial Transport of Glucose

Question 1

what is the primary role of epithelial tissues?

Answer 1

to form continuous sheets that act as protective or secretory barriers between environments

Question 2

what structure do epithelial cells rest on?

Answer 2

bm

Question 3

why do epithelial cells have high turnover?

Answer 3

due to high mechanical stress and exposure

Question 4

what are the two major types of epithelia?

Answer 4

covering/lining epithelium and glandular epithelium

Question 5

what distinguishes simple, stratified, and pseudo-stratified epithelia?

Answer 5

the number of cell layers and contact with the BM

Question 6

what is the function of squamous epithelial cells?

Answer 6

diffusion

Question 7

what is the function of cuboidal epithelial cells

Answer 7

secretion and absorption

Question 8

what do tight junctions do?

Answer 8

act as barriers and fences, limiting paracellular movement and maintaining membrane polarity

Question 9

what protein components form tight junctions?

Answer 9

claudins and occludins

Question 10

what does the Na+/K+ ATPase do?

Answer 10

pumps 3 NA+ out and 2 K+ in, maintaining Na+ gradient

Question 11

which transporter moves glucose and Na+ across the apical membrane?

Answer 11

SGLT

Question 12

which transporter facilitates glucose exit on the basolateral side?

Answer 12

GLUT transporter

Question 13

what causes glucose/galactose malabsorption syndrome?

Answer 13

mutation in the SGLT1 gene

Question 14

what is glucosuria?

Answer 14

glucose in the urine due to saturation of SGLT transporters

Question 15

what is the renal threshold for glucose?

Answer 15

~200 mg/dL plasma glucose

Question 16

why is epthelial polarity important for transepithelial transport?

Answer 16

it allows specific transporters to be localised to apical or basolateral domains, directing transport direction

Question 17

how do tight junctions contribute to maintaining cell polarity?

Answer 17

they prevent lateral diffusion of proteins/lipids between membrane domains

Question 18

why does glucose exit via GLUT and not SGLT on the basolateral side?

Answer 18

because GLUT facilitates passive diffusion down the glucose gradient

Question 19

how does ORT utilise epithelial transport mechanisms?

Answer 19

it uses SGLT to enhance Na+ and glucose uptake, promoting water reabsorption via osmotic gradients

Question 20

why does glucose/galactose malabsorption cause diarrhoea?

Answer 20

unabsorbed sugars create an osmotic gradient that pulls water into the gut

Question 21

what does the pump-leak hypothesis explain?

Answer 21

continuous Na+/K+ ATPase activity due to ongoing Na+ and K+ leakage across membranes

Question 22

why does glucosuria happen in diabetes mellitus?

Answer 22

blood glucose exceeds renal threshold, overwhelming SGLT capacity in the kidney

Question 23

how does the structure of transitional epithelium support its function?

Answer 23

its ability to change shape allows stretching, ideal for the bladder

Question 24

how do electrochemical gradients drive transcellular transport?

Answer 24

they determine the direction and energy requirement of ion and solute movement

Question 25

why does tight junction resistance increase distally in the GGI tract and nephron?

Answer 25

to create stronger barriers where finer regulation of solute movement is needed

Question 26

epithelial cells rest on a ___ membrane, which provides structural support

Answer 26

basement

Question 27

simple epithelium has a ___ layer of cells and is suited for diffusion and absorption

Answer 27

single

Question 28

tight junctions are formed by ___ and ___ proteins

Answer 28

claudin; occludin

Question 29

the ___ membrane of epithelial cells faces the lumen and is involved in absorption/secretion

Answer 29

apical

Question 30

the ___ membrane contacts blood vessels and is key for exchange and signalling

Answer 30

basolateral

Question 31

paracellular transport moves substances ___ epithelial cells via tight junctions

Answer 31

between

Question 32

SGLT on the apical membrane uses the ___ gradient to transport glucose

Answer 32

Na+

Question 33

the Na+/K+ ATPase consumes ATP to pump out ___ and bring in ___

Answer 33

3 Na+; 2 K+

Question 34

ORT enhances rehydration by promoting Na+ and glucose absorption via ___

Answer 34

SGLT

Question 35

glucose/galactose malabsorption syndrome is caused by a mutation in the ___ gene

Answer 35

SGLT1

Question 36

in the kidney, glucose is reabsorbed by ___ transporters in the proximal tubule

Answer 36

SGLT

Question 37

glucosuria occurs when plasma glucose exceeds the ___, overwhelming SGLT capacity

Answer 37

renal threshold

Question 38

___ epithelium appears multilayered but all cells touch the basement memebrane

Answer 38

pseudostratified

Question 39

the transport of ions across epithelia alters ___, driving water reabsorption

Answer 39

osmolarity

Question 40

ion movement is often coupled with counter-ions to maintain ___

Answer 40

electroneutrality