Renal 5: Tubular Functions Along Nephron Flashcards
In the proximal nephron, there is high/low volume, high/low gradient pumping of solutes and water.
high, low
How much of a filtered load is typically reabsorbed in the proximal nephron?
2/3
What is the primary mechanism for reabsorption int he proximal tubule
Na+, K+, ATPase in basolateral membrane
What transporters exist in the apical membrane in the first half of the proximal tubule?
Na+/H+ antiporter : couples entry of Na+ with extrusion of H+ (H+ secretion also leads to sodium bicarb reabsorption)
Na+/Glucose symporter (SGLT2)
What transporters exist in the basolateral membrane in the first half of the proximal tubule?
Na+/K+ ATPase.
HCO3- transporter,
Glucose transporter (GLUT2)
How is Na+ mainly reabsorbed in the second half of the proximal tubule?
With Cl- both transcellular and paracellularly
What transporters exist in the apical membrane in the second half of the proximal tubule?
Parallel
Na+/H+ Antiporters
Cl-/anion antiporters
SGLT1 Na/glucose symporter (difference is 2Na per 1 glucose)
What happens to the H+ and anion in the tubular fluid of the second half of the proximal tubule?
Combine and reenter the cell
What transporters exist in the basolateral membrane in the second half of the proximal tubule?
Na+/K+ ATPase- Na+leaves cell and enters blood
K+/Cl- symporter- Cl- leaves cell and enters blood
GLUT1 glucose transporter
In what part of the proximal tubule is the Na/K ATPase located?
basolateral membrane, both halves
In what part of the proximal tubule is the SGLT2 located?
apical membrane, first half
In what part of the proximal tubule is the GLUT1 located?
basolateral membrane, 2nd half
In what part of the proximal tubule is the Na/H antiporter located?
apical membrane, both halves
In what part of the proximal tubule is the anion/Cl- antiporter located?
apical membrane, 2nd half
In what part of the proximal tubule is the K+/Cl- symporter located?
basolateral membrane, 2nd half
In what part of the proximal tubule is the SGLT2 symporter located?
apical membrane, 1st half
In what part of the proximal tubule is the GLUT2 transporter located?
basolateral membrane, 1st half
In what part of the proximal tubule is the HCO3- transporter located?
basolateral membrane, 1st half
Isosmotic Reabsorption
water reabsorption occurs in equal proportion wiht reabsorbed solutes
How is the driving force for osmotic reabsorption of water across the proximal tubule established?
Via transport of solutes into lateral interceullar space, causing the osmolality of this compartment to increase
How does the movement of solutes across the proximal tubule membranes affect osmosis?
It increases osmolarity on the basolateral side, favoring water transport to that side.
What is an important consequence of osmotic water flow in the proximal tubule regarding potassium and calcium ions?
They are entrained in the reabsorbed fluid and thereby reabsorbed by the process of solvent drag.
How much of filtered protein is reabsorbed in the proximal tubule?
100%
What are the 2 causes of complete protein reabsorption in the proximal tubule?
enzymatic degradation of proteins to amino acids
encapsulation of proteins by pinocytic processes
What causes proteinuria?
saturation of the transport process results in protein appearing in the urine.
What happens to organic cations and anions in the proximal tubule?
actively secreted.
What effect does cimetidine have on procainamide plasma concentration?
Increases (vice versa as well)
Why is drug toxicity a danger for the cations of cimetidine and procainamide?
They elevate the plasma concentration of each other
In the distal nephron, the kind of pumping that occurs is low/high volume and low/high gradient.
low, high
What fraction of filtered loads is typically reabsorbed in the distal nephron?
1/3
What conditions indicate the urine/plasma osmolality ration in the distal nephron being < 1
low ADH, dilute pale urine
What conditions indicate the urine/plasma osmolality ratio in the distal nephron being >1
high ADH, concentrated dark urine
Is the tubular lumen potential in the distal nephron strong or weak? What does this mean in regards to tight junctions there?
strong(-40 mV), tight junctions don’t leak
What is reabsorbed in the thin descending limb of the loop of Henle?
water
What is reabsorbed in the thin ascending limb of the loop of Henle?
Na+ and Cl-
What is not reabsorbed in the thin descending limb of the loop of Henle?
Na+ and Cl-
What is not reabsorbed in the thin ascending limb of the loop of Henle?
water
What is the prime mover in the loop of Henle?
Na+/K+ ATPase
What channels are on the apical membrane in the thick ascending loop of henle?
K+ channel (ROMK)
1Na+-1K+-2Cl- Symporter (NKCC2)
Na+/H+ Antiport
What channels are on the basolateral membrane in the thick ascending loop of henle?
Cl- Channel (C1CNKB)
Na/K ATPase
K+/Cl- Symporter
What is Bartter’s syndrome caused by?
mutation in channels of ascending loop of henle?
What channels are located in the early segment of the distal tubule?
apical: Na/Cl symporter
basolateral: Na/K ATPase, Cl channel
what channels are located in principle cells of the distal tubule?
Apical: Na channels inward, K channels outward
Basolateral: Na/K ATPase, K channel outward
What channels are located in intercalated cells of the distal tubule?
apical: H+ ATP pump, H/K ATPase
Basolateral: Cl-/ HCO3- channel (out)
What happens to salt and water reabsorption and the RAA system when extracellular volume decreases?
v ECV –> ^RAA system –> ^AT-II –> ^H2O, Na+, H+, Cl- reabsorption in proxmal tubule
What happens to salt and water reabsorption and the RAA system when extracellular volume increases?
^ ECV –> v RAA system –> v AT-II –> v H2O, Na+, H+, Cl- reabsorption
How does aldosterone regulate salt and water reabsorption
^ AT-II or ^ plasma K+ => ^ Aldosterone => ^ reabsorption of Na+ and Cl- in thick ascending loop of Henle, distal tubule, and collecting duct
What is the effect of atrial natriuretic peptide on the following? natriuresis total peripheral resistance Na+ reabsorption ADH
increase
decrease
decrease
decrease
How does ANP and Urodilatin regulate salt and water reabsorption
^ ECFV or ^ Blood Volume => atrial stretch => ^ ANP => ^ natriuresis => v total peripheral resistance and v reabsorption of Na+, Cl- and v ADH
What happens to sympathetic nervous activity and Na+ reabsorption with decreased ECV?
v ECV => ^ symp. activity => ^ NE and E => ^ Na+ and Cl- reabsorption in proximal and distal nephron
What happens to Na+ reabsorption with increased dopamine?
decreased
What happens to dopamine activity and Na+ reabsorption with increased ECV?
^ ECV => ^ dopamine => v Na+ and Cl- reabsorption in PT
How does increased GFR affect Na+ reabsorption?
^ GFR => ^ filtered load of glucose and AAs => ^ H2O and Na+ reabsorption in PT
What happens to Na+ reabsorption with increased antidiuretic hormone?
Nothing. Reabsorbs water in collecting duct with no effect on Na+/Cl- excertion
What happens to peritubular cap reabsorption when glomerular cap filtration increases?
Increases
What is meant by glomerulotubular balance?
Despite variations in GFR, a constant fraction of Na+ and H2O are still reabsorbed from the proximal tubule.
What are the 3 routes of water transport across the proximal tubule?
- solutes and water reabsorbed across apical membrane
And then 2 paths: - solute and water cross the lateral cell membrane.
- remainder enters interstitial space and flows into capillary.
