L8 Flashcards
what is a Na channel of tight absorptive epithelia
ENaC
what blocks ENaC
why is it not TTX
amiloride
it is not sensitive to TTX like other Na channels (because ENaC isn’t voltage gated)
Tight absorptive epithelia
A. express SGLT1.
B. express ENaC.
C. express SGLT2.
D. express NHE3.
B
explain how glucose gets from the lumen to the interstitial fluid
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
what is the common principles for glucose movement through the apical and basolateral membranes in leaky epithelium
Secondary active (Na+ coupled) uptake through apical membrane (uphill)
Facilitated diffusion through
basolateral membrane
(downhill)
describe glucose transport in the proximal tubule
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
describe how Na gets through a tight absorptive epithelial cell
through a Na channel in the apical membrane (facilitated diffusion)
and out of the cell vis Na K ATPase
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.
D
what is the important solute involved in absorption
Na
what is the important solute involved in secretion
Cl
what are the electrical properties of secretory epithelia
leaky for water secretion
tight (e.g. K+ secretion in cortical duct)
how does ion transport effect water secretion in a secretory epithelial cell
actively secrete Cl- ions (because of the electrogenic process)
Na+ and water follows passively
secretion of isosmotic NaCl solution
what are the apical membrane properties of secretory epithelia
high permeability to Cl- due to the presence of Cl channels
Cl- channels need to be activated to open
what are the 2 types of epithelial Cl channels
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+
what is the hydraulic conductivity properties of secretory epithelia
Hydraulic conductivity is high which causes the secretion of isosmotic NaCl solution
how does hormonal/nervous control effect secretory epithelia
it is under precise control with low basal rates of secretion increased by nervous or hormonal
control as required
what are some examples of secretory epithelia
Exocrine glands
Small & Large intestine
Respiratory epithelium
Reproductive tract
what are some examples of exocrine glands that have secretory epithelia
Sweat glands
Salivary glands
Pancreas
Liver
what contains secretory epithelia in the reproductive tract
Male - epididymis
Female - vagina, uterus
and fallopian tubes
all of the organs that possess secretory epithelia have functions that involve mucus. what is Cl effect on that mucus
less Cl causes the mucus to become thick which causes infections
what is the physiological function of secretory epithelia in the GI tract
contains exocrine glands and intestinal epithelium which secretes enzymes for the digestion of food
what drives water secretion
Cl
Ion transport sets up osmotic gradient for water transport
what is the physiological function of secretory epithelia in the respiratory epithelium
Keeps surface moistened to maintain mucociliary
clearance
what is the physiological function of secretory epithelia in the reproductive tract
Male - maturation of sperm
Female - survival and fertilisation of gamete
what is the physiological function of secretory epithelia in the sweat gland
thermoregulation
describe the electrogenic Cl secretion of a secretory epithelial cell
NKCC
are the principles driving transport the same in
absorptive and secretory epithelia
yes
what are the common functional concepts in absorptive and secretory epithelia
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
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.
B
what happens with CF
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
