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PHSL 233 > L8 > Flashcards

L8 Flashcards

1
Q

what is a Na channel of tight absorptive epithelia

A

ENaC

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2
Q

what blocks ENaC

why is it not TTX

A

amiloride

it is not sensitive to TTX like other Na channels (because ENaC isn’t voltage gated)

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3
Q

Tight absorptive epithelia

A. express SGLT1.

B. express ENaC.

C. express SGLT2.

D. express NHE3.

A

B

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4
Q

explain how glucose gets from the lumen to the interstitial fluid

A

SGLT brings Na and glucose into the cell

Na K ATPase gets Na from inside to outside of the cell

We need K channels because of the function of Na K ATPase

K will start to build up in the cell which will affect Na K ATPase

That is why we have K channels in the basolateral membrane so that K can move down its conc gradient

That has one passive and one active so that we are able to transport Na

For glucose it is the opposite, this is because it has to do with differing concentrations

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5
Q

what is the common principles for glucose movement through the apical and basolateral membranes in leaky epithelium

A 
Secondary active (Na+
coupled) uptake through
apical membrane (uphill)

Facilitated diffusion through
basolateral membrane
(downhill)

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6
Q

describe glucose transport in the proximal tubule

A

in the early prox. tubule
SGLT2 re-absorbs 90% of
the filtered glucose, whereas

in the late prox. tubule
SGLT1 is the main glucose
transporter

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7
Q

describe how Na gets through a tight absorptive epithelial cell

A

through a Na channel in the apical membrane (facilitated diffusion)

and out of the cell vis Na K ATPase

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8
Q

Glucose is

A. absorbed at the basolateral membrane in a
sodium dependent manner.

B. absorbed entirely via facilitated diffusion.

C. secreted.

D. transported against its gradient at the apical
membrane.

A

D

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9
Q

what is the important solute involved in absorption

A

Na

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10
Q

what is the important solute involved in secretion

A

Cl

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11
Q

what are the electrical properties of secretory epithelia

A

leaky for water secretion

tight (e.g. K+ secretion in cortical duct)

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12
Q

how does ion transport effect water secretion in a secretory epithelial cell

A

actively secrete Cl- ions (because of the electrogenic process)

Na+ and water follows passively

secretion of isosmotic NaCl solution

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13
Q

what are the apical membrane properties of secretory epithelia

A

high permeability to Cl- due to the presence of Cl channels

Cl- channels need to be activated to open

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14
Q

what are the 2 types of epithelial Cl channels

A

cAMP-activated Cl- channel
this is Cystic Fibrosis Transmembrane conductance Regulator (CFTR)

Ca2+-activated Cl- channel (TMEM16A)
this is activated by an increase in intracellular Ca2+

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15
Q

what is the hydraulic conductivity properties of secretory epithelia

A

Hydraulic conductivity is high which causes the secretion of isosmotic NaCl solution

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16
Q

how does hormonal/nervous control effect secretory epithelia

A

it is under precise control with low basal rates of secretion increased by nervous or hormonal
control as required

17
Q

what are some examples of secretory epithelia

A

Exocrine glands
Small & Large intestine
Respiratory epithelium
Reproductive tract

18
Q

what are some examples of exocrine glands that have secretory epithelia

A

Sweat glands
Salivary glands
Pancreas
Liver

19
Q

what contains secretory epithelia in the reproductive tract

A

Male - epididymis

Female - vagina, uterus
and fallopian tubes

20
Q

all of the organs that possess secretory epithelia have functions that involve mucus. what is Cl effect on that mucus

A

less Cl causes the mucus to become thick which causes infections

21
Q

what is the physiological function of secretory epithelia in the GI tract

A

contains exocrine glands and intestinal epithelium which secretes enzymes for the digestion of food

22
Q

what drives water secretion

A

Cl

Ion transport sets up osmotic gradient for water transport

23
Q

what is the physiological function of secretory epithelia in the respiratory epithelium

A

Keeps surface moistened to maintain mucociliary

clearance

24
Q

what is the physiological function of secretory epithelia in the reproductive tract

A

Male - maturation of sperm

Female - survival and fertilisation of gamete

25
Q

what is the physiological function of secretory epithelia in the sweat gland

A

thermoregulation

26
Q

describe the electrogenic Cl secretion of a secretory epithelial cell

A

NKCC

27
Q

are the principles driving transport the same in

absorptive and secretory epithelia

A

yes

28
Q

what are the common functional concepts in absorptive and secretory epithelia

A

Electrochemical gradients determine
transport of charged solutes (e.g. ions)

‘Two membranes’ (different transporters)

Combination of active (uphill)
and passive (downhill) transport for each ion/solute to cross the epithelium
29
Q

Water secretion

A. takes only place in the kidney.

B. is mainly facilitated by chloride ions.

C. is mainly facilitated by sodium ions.

D. requires glucose absorption.

A

B

30
Q

what happens with CF

A

Cl secretion is impaired

there is a mutation in CFTR which decreases Cl secretion which decreases water secretion which contributes to viscous (thick mucus in various organs

PHSL 233 (31 decks)

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