Intro renal Flashcards
all nephrons are composed of _____ epithelium
simple
apical membrane faces the _____
lumen
basolateral membrane faces the _____
ECF
what are the apical membrane and basolateral membrane separated by
tight junctions
another name for tight junctions
zonula occludens
what do renal epithelia never contain
gap junctions
what is paracellular transport
solute moving across epithelium by going around the cells & through tight junctions
what is transcellular transport
solute moving across epithelium by going through the cells (crossing both the apical & basolateral membranes)
why are tight junctions important
they determine permeability
tighter epithelium = _____ TEPD
greater
uniport membrane transporter
facilitated diffusion OR primarily active transport (if ATPase pump)
of a single type of solute
symport (coupled membrane transporter)
secondarily active transport
2 different solute types move in the same direction
antiport (coupled membrane transporter)
secondarily active transport
2 different solute types move in opposite directions
another name for symport
co-transport
another name for antiport
exchanger
3 important renal co-transporters (symports)
SGLT
NKCC
NCC
SGLT function
renal co-transporter
3 isoforms: SGLT1, 2, 3
SGLT1 - requires 2 Na+ to move 1 glucose
SGLT2,3 - require 1 Na+ to move 1 glucose
NKCC function
renal co-transporter
uses Na+ gradient to accumulate Cl- & K+ intracellularly
SGLT location
SGLT1 - in later proximal tubule where [glucose] is lower
SGLT2,3 - in early proximal tubule where [glucose] is high
NKCC location
NKCC1 - on basolateral membrane of non-renal epithelia & non-epithelial cells
NKCC2 - on apical membrane of thick ascending limb
NKCC2 is a target for what
one class of loop diuretic
NCC function
renal co-transporter
NCC location
on apical membrane in early distal tubule cells
NCC is a target for what
a class of diuretics
3 important renal exchangers (antiports)
NHE
AE
OAT
NHE function, and what is it regulated by
Na+ / H+ exchanger
important in acid-base balance
regulated by angiotensin II
NHE location
NHE3 isoform - on apical membrane of proximal tubule
AE function
anion exchanger (Cl- / HCO3- exchanger)
OAT function
organic anion transporter
Na+/K+ ATPase function
responsible for almost all transepithelial transport in the nephron bc it maintains ionic gradients
in the kidney, which ATPase is most protein-mediated reabsorption & secretion coupled to
the basolateral Na+/K+ ATPase
what is TEPD
TransEpithelial Potential Difference
TEPD equation
TEPD = Vb - Va
Vb: voltage across basolateral membrane (membrane potential)
Va: voltage across apical membrane (membrane potential)
in both the basolateral & apical membranes, what is the voltage relative to ground
cytoplasmic side is negative
what is the magnitude of TEPD proportional to
tightness of tight junctions
how does the TEPD look across the nephron
it varies in different segments
why does the magnitude of TEPD influence transepithelial flux
bc ions are charged particles
the 3 basic renal processes
filtration
reabsorption
secretion
general process of Filtration
aka glomerular filtration
plasma is filtered across the glomerular capillary endothelia
-> enters nephron & into the tubular fluid of Bowman’s capsule
-> flows into proximal tubule (forms “pre-urine”)
only occurs at the renal corpuscle
general process of Reabsorption
nephron reabsorbs most of the solutes & water from the tubular fluid/lumen (the main function of the nephron)
general process of Secretion
secretion of ions & solutes (waste) from blood/cells into tubular fluid/lumen
reabsorption & secretion _____ tubular fluid as it flows through the nephron
modify the composition of
is excretion one of the basic renal processes?
no, it is the result of the 3 processes
2 additional renal processes
synthesis
catabolism
what 2 additional renal processes also modify the composition of tubular fluid
synthesis
catabolism
2 examples of solutes synthesized in the nephron
ammonia (synthesized in proximal tubule)
Tamm-Horsfall protein (synthesized in thick ascending limb of Henle)
where does Catabolism occur in the nephron, and what is produced from what
at peptidases in the luminal membrane of the proximal tubule
catabolizes small polypeptides -> forms individual AAs & 2-4 AA peptides
what makes the renal vasculature unique in configuration
has two capillary beds in series = a portal system
glomerular capillaries combine to form another arteriole -> the efferent arteriole
(instead of capillaries coming back together to form the beginning of the venous system like most capillary beds)
what is the glomerular capillary bed surrounded by
afferent & efferent arterioles
what forms the entry/exit to an individual glomerular capillary tuft
entry: a single afferent arteriole
exit: a single efferent arteriole
what primarily impacts filtration of plasma into Bowman’s capsule
the glomerular capillary hydrostatic pressure
filtration coefficient (k) is _____ for fenestrated glomerular capillaries
much greater
greater filtration coefficient = _____ rate of fluid filtration
greater
what is GFR in technical terms
(glomerular filtration rate)
volume of fluid (plasma) filtered from all glomerular capillaries into all Bowman’s capsules of both kidneys / per unit time
normal GFR range
100-125 ml/min
renal disease GFR range
< 60 ml/min
what is GFR in general terms
a measure of kidney function and filtration efficiency
3 factors that can change GFR
filtration coefficient (k) - (area & leakiness of glomerulus)
net filtration pressures
physical changes
arterioles are _____ vessels
resistance
what is the cascade of events if a change in diameter of either a afferent AND/OR efferent arteriole occurs
change in diameter of arteriole
->
resistance to blood flow changes
->
RBF changes
->
net filtration pressure changes
->
GFR changes
if afferent/efferent arteriole(s) increase in resistance = _____ renal blood flow
decreases
if afferent/efferent arteriole(s) decrease in resistance = _____ renal blood flow
increases
what does RBF stand for
renal blood flow
equation for RBF
RBF = delta P / R
concentration of solutes that are “freely filtered” is the same in what two locations
tubular fluid
&
plasma
amount of protein usually in filtrate entering nephron
very little bc protein is NOT filtered
what is the “filtered load”
quantity of given solute that enters nephron from the plasma
(amount of the substance that is filtered across glomeruli / per unit time)
what is the primary determinant of “filtered load” of a solute
the plasma concentration of that solute
plasma concentration and filtered load have what kind of relationship
a direct linear relationship
(if constant GFR)
equation for filtered load (for a solute that is freely filtered)
filtered load of solute = plasma concentration of solute x GFR
freely filtered solutes
univalent ions (such as Na+, K+, Cl-, HCO3-)
sugars
AAs
organic ions
solutes that are NOT freely filtered
proteins
any solutes that bind to proteins (such as divalent ions: Ca2+, PO42-, Mg2+)
concentration =
mol / L
what is the TF/P ratio
tubular fluid : plasma concentration ratio
compares concentration of given solute in tubular fluid to concentration of that solute in plasma
what is TF/P ratio in Bowman’s capsule
1
what does it mean if TF/P ratio < 1
more solute is reabsorbed than water
what does it mean if TF/P ratio > 1
less solute is reabsorbed than water (or solute is secreted)
what membrane is SGLT2 on
apical
what membrane is Na+/K+ ATPase on
basolateral
what membrane is GLUT2 on
basolateral
what happens if glucose is not reabsorbed by the end of the proximal tubule, and why
it will be excreted
bc there are no other glucose transporters expressed in any other segments of the nephron
how much plasma do all total glomeruli filter per day
180 L /day
how much plasma flows through all total glomeruli per day
900 L /day
define Filtration Fraction (FF), and what % of plasma volume is this
proportion of plasma volume flowing through glomerular capillaries that is filtered
~20%
equation for quantity of solute excreted in the urine (E)
E = F - R + S
F: filtered load (quantity filtered)
R: quantity reabsorbed
S: quantity secreted
quantity filtered (filtered load) vs quantity excreted
quantity filtered (quantity in) = [solute in plasma] x GFR
quantity excreted (quantity out) = [solute in urine] x V
what does it mean if
quantity excreted < quantity filtered
net reabsorption of the solute from the lumen of the nephron back into the ECF
what does it mean if
quantity excreted > quantity filtered
net secretion of the solute into the lumen of the nephron (usually from the ECF)
what does it mean if
quantity excreted = quantity filtered
NO net reabsorption or secretion of solute
what makes up the renal corpuscle
Bowman’s capsule
&
its glomerulus
are the glomular capillaries (the glomerulus) part of the nephron
no
main regions of the nephron in order
-Bowman’s capsule
-proximal convoluted tubule (PCT)
-loop of Henle (LoH)
-distal convoluted tubule (DCT)
-collecting duct
