Lecture 14 -- Review questions Flashcards
in which part of the nephron does glomerular filtration occur?
glomerulus
what is the overall purpose of tubular reabsorption?
reclaiming what the body needs to keep
in which part of the nephron does most reabsorption occur (essential solutes, electrolytes, water)?
PCT
which part of the nephron usually reabsorbs the most water and sodium?
PCT
what is meant by tubular secretion?
process of selectively moving substances from the blood into the filtrate
what is the difference b/n paracellular and trans cellular transport routes across tubule cells?
paracellular – substances cross tubule cells by passing the gap b/n them
transcellular – substances cross tubule cells by directly passing thru them
which structures must the substances inside the renal tubule cross if they want to be reabsorbed by the peritubular capillaries?
lumen –> apical membrane –> cytosol in tubule cell –> basolateral membrane –> interstitial fluid –> endothelial cell of capillary –> blood in peri tubular capillary
what does Tm stand for? When is the Tm reached?
Tm = transport maximum == max rate of reabsorption
Tm is reached when transporters are saturated
which factor limits the amount of solute the renal tubule can reabsorb and, thus, the Tm?
of transport proteins
(limited number of transport proteins –> limit the amount of solute that the renal tubule can reabsorb)
which pumps generate a strong concentration gradient for sodium reabsorption in the renal tubule?
where is it located (apical or basolateral membrane)?
Na+/K+ pumps
located in basolateral membrane on the side facing interstitial fluid
in which renal tubule segment is sodium reabsorbed with other solutes?
PCT
what does Na+/H+ anti porter (Na+/H+ exchanger-3) do in the renal tubule?
does it transport Na+ out or toward the tubule cell?
In which segment?
transports Na+ from filtrate into PCT
transports H+ from PCT out into filtrate
anti porter is located on apical membrane of PCT facing filtrate
which hormone stimulates the proximal tubule Na-H anti porter?
angiotensin-II
what do the Na+/K+ pumps do?
does it transport Na+ into the interstitial fluid or into inside the tubule cell?
how about K+?
generate strong [] gradient for Na+ reabsorption
transports Na+ out of tubule cell into interstitial fluid
transports K+ into tubule cell from interstitial fluid
what does SGLT stand for?
in which renal tubule segment can you find it?
what is its function?
Na+/glucose transporters
PCT
bring Na+ from filtrate into PCT with other solutes like glucose and amino acids
which segment of the nephron loop is permeable to water?
descending limb
which segment of the nephron loop is impermeable to water?
ascending limb
which segment of the nephron loop is permeable to solutes?
ascending limb
which segment of the nephron loop is impermeable to solutes?
descending limb
why is the ascending limb of the nephron loop considered “the diluting segment of the nephron?”
solutes leave the filtrate at the ascending limb –> tubular fluid becomes diluted
how many ions of potassium and chloride are cotransported with sodium in the thick ascending loop of Henle?
1 Na+
1 K+
2 Cl-
are all cotransported together
what does Na+/K+/2 Cl- cotransporter do? (direction of ion movement)
moves ions out of the filtrate and into the blood
in which type of kidney tubule are the Na+ - K+ - 2 Cl- symptorters (NKCC2) found?
thick ascending loop of Henle
what is the function of the Na+ - Cl- cotransporters? (direction of ions movement)
where are they located?
moves Na+ and Cl- from urine back into DCT
where are the principal cells in the renal tubule, and what is their primary function? (ions reabsorbed and secreted)
which hormone controls these processes?
located in the cortical collecting duct
adjust [electrolyte] by:
- reabsorbing Na+ and H2O
- secreting K+
aldosterone
where are the type A intercalated cells located in the renal tubule, and what are 2 of their primary functions?
(ions reabsorbed and secreted)
located in the DCT
pH homeostasis (acid-base regulation)
- reabsorbing K+
- secreting H+
how does the medullary portion of the collecting duct contribute to the hyper osmotic medullary interstitial fluid =
which solute diffuses from the CD and contributes to the medullary osmotic gradient?
reabsorbing urea
which hormone controls water reabsorption and, therefore, urine concentration in the CD?
ADH
which 2 factors allow the kidney to produce concentrated (hypertonic) urine?
medullary osmotic gradient:
- ISF of renal medulla has a high osmolarity - >
water gets reabsorbed and causes the urine to be more concentrated
ADH acting on DCT and CD:
- more aquaporins in DCT and CD –>
greater water permeability in DCT and CD –> more water gets reabsorbed and causes the urine to be more concentrated
to produce concentrated urine, do you need to reabsorb more or less water?
you need to reabsorb more water
water leaves urine –> urine is more concentrated
where can you find more concentrated interstitial fluid, deep in the medulla or the cortex?
deep in the medulla
which 3 mechanisms help with creating and/or maintaining the medullar osmotic gradient?
(1) countercurrent multiplier
(2) recycling of urea
(3) countercurrent exchanger
where does the countercurrent multiplier occur?
nephron loops of juxtamedullary nephrons
why is the countercurrent multiplier system called a “multiplier”?
it multiplies the osmolarity deep in the medulla
by recapturing salt and returning it to the deep medullary tissue
what does “countercurrent” mean regarding the countercurrent multiplier system?
filtrate flows in opposite direction (countercurrent) thru 2 adjacent parallel sections of a nephron loop
Figure 1 – in this part of the nephron, water is drawn from the tubular fluid thru aquaporins, following an osmotic gradient created by which ion?
Na+
in which segment of the nephron loop is the tubular fluid more concentrated in solutes?
bottom of the nephron loop
Figure 2 – why are sodium ions leaving the filtrate at this point of the nephron loop and not before?
[NaCl] is the highest at this point
what is responsible for increasing the interstitial fluid’s osmolarity of the medulla: pumping sodium outside the tubule or water?
pumping sodium outside the tubule
what is the difference b/n countercurrent exchange and countercurrent multiplier?
countercurrent multiplier – creates the medullary gradient (causes medulla to have a much higher osmolarity)
countercurrent exchange – preserves the medullary gradient
what are the purposes of the countercurrent exchange?
(1) prevent rapid removal of salt from the medullary interstitial space
(2) removing reabsorbed water
what is the difference b/n obligatory vs. facultative water reabsorption?
obligatory – water is “obliged” by osmosis to follow solutes that have been reabsorbed
facultative – water is reabsorbed according to body’s needs –> regulated by hormones
in which segments of the renal tubule does obligatory water reabsorption take place?
and facultative?
85% of water reabsorption –> PCT and descending limb of loop of Henle
15% of water reabsorption –> DCT and CD
which parts of the renal tubule are considered aldosterone-sensitive?
distal nephron:
late DCT
connecting tubule
collecting duct
