Lecture 14 -- Review questions

Question 1

in which part of the nephron does glomerular filtration occur?

Answer 1

glomerulus

Question 2

what is the overall purpose of tubular reabsorption?

Answer 2

reclaiming what the body needs to keep

Question 3

in which part of the nephron does most reabsorption occur (essential solutes, electrolytes, water)?

Answer 3

PCT

Question 4

which part of the nephron usually reabsorbs the most water and sodium?

Answer 4

PCT

Question 5

what is meant by tubular secretion?

Answer 5

process of selectively moving substances from the blood into the filtrate

Question 6

what is the difference b/n paracellular and trans cellular transport routes across tubule cells?

Answer 6

paracellular – substances cross tubule cells by passing the gap b/n them

transcellular – substances cross tubule cells by directly passing thru them

Question 7

which structures must the substances inside the renal tubule cross if they want to be reabsorbed by the peritubular capillaries?

Answer 7

lumen –> apical membrane –> cytosol in tubule cell –> basolateral membrane –> interstitial fluid –> endothelial cell of capillary –> blood in peri tubular capillary

Question 8

what does Tm stand for? When is the Tm reached?

Answer 8

Tm = transport maximum == max rate of reabsorption

Tm is reached when transporters are saturated

Question 9

which factor limits the amount of solute the renal tubule can reabsorb and, thus, the Tm?

Answer 9

of transport proteins

(limited number of transport proteins –> limit the amount of solute that the renal tubule can reabsorb)

Question 10

which pumps generate a strong concentration gradient for sodium reabsorption in the renal tubule?

where is it located (apical or basolateral membrane)?

Answer 10

Na+/K+ pumps

located in basolateral membrane on the side facing interstitial fluid

Question 11

in which renal tubule segment is sodium reabsorbed with other solutes?

Answer 11

PCT

Question 12

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?

Answer 12

transports Na+ from filtrate into PCT
transports H+ from PCT out into filtrate

anti porter is located on apical membrane of PCT facing filtrate

Question 13

which hormone stimulates the proximal tubule Na-H anti porter?

Answer 13

angiotensin-II

Question 14

what do the Na+/K+ pumps do?

does it transport Na+ into the interstitial fluid or into inside the tubule cell?

how about K+?

Answer 14

generate strong [] gradient for Na+ reabsorption

transports Na+ out of tubule cell into interstitial fluid

transports K+ into tubule cell from interstitial fluid

Question 15

what does SGLT stand for?

in which renal tubule segment can you find it?

what is its function?

Answer 15

Na+/glucose transporters

PCT

bring Na+ from filtrate into PCT with other solutes like glucose and amino acids

Question 16

which segment of the nephron loop is permeable to water?

Answer 16

descending limb

Question 17

which segment of the nephron loop is impermeable to water?

Answer 17

ascending limb

Question 18

which segment of the nephron loop is permeable to solutes?

Answer 18

ascending limb

Question 19

which segment of the nephron loop is impermeable to solutes?

Answer 19

descending limb

Question 20

why is the ascending limb of the nephron loop considered “the diluting segment of the nephron?”

Answer 20

solutes leave the filtrate at the ascending limb –> tubular fluid becomes diluted

Question 21

how many ions of potassium and chloride are cotransported with sodium in the thick ascending loop of Henle?

Answer 21

1 Na+
1 K+
2 Cl-

are all cotransported together

Question 22

what does Na+/K+/2 Cl- cotransporter do? (direction of ion movement)

Answer 22

moves ions out of the filtrate and into the blood

Question 23

in which type of kidney tubule are the Na+ - K+ - 2 Cl- symptorters (NKCC2) found?

Answer 23

thick ascending loop of Henle

Question 24

what is the function of the Na+ - Cl- cotransporters? (direction of ions movement)

where are they located?

Answer 24

moves Na+ and Cl- from urine back into DCT

Question 25

where are the principal cells in the renal tubule, and what is their primary function? (ions reabsorbed and secreted) which hormone controls these processes?

Answer 25

located in the cortical collecting duct adjust [electrolyte] by: - reabsorbing Na+ and H2O - secreting K+ aldosterone

Question 26

where are the type A intercalated cells located in the renal tubule, and what are 2 of their primary functions? (ions reabsorbed and secreted)

Answer 26

located in the DCT pH homeostasis (acid-base regulation) - reabsorbing K+ - secreting H+

Question 27

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?

Answer 27

reabsorbing urea

Question 28

which hormone controls water reabsorption and, therefore, urine concentration in the CD?

Answer 28

ADH

Question 29

which 2 factors allow the kidney to produce concentrated (hypertonic) urine?

Answer 29

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

Question 30

to produce concentrated urine, do you need to reabsorb more or less water?

Answer 30

you need to reabsorb more water water leaves urine --> urine is more concentrated

Question 31

where can you find more concentrated interstitial fluid, deep in the medulla or the cortex?

Answer 31

deep in the medulla

Question 32

which 3 mechanisms help with creating and/or maintaining the medullar osmotic gradient?

Answer 32

(1) countercurrent multiplier (2) recycling of urea (3) countercurrent exchanger

Question 33

where does the countercurrent multiplier occur?

Answer 33

nephron loops of juxtamedullary nephrons

Question 34

why is the countercurrent multiplier system called a "multiplier"?

Answer 34

it multiplies the osmolarity deep in the medulla by recapturing salt and returning it to the deep medullary tissue

Question 35

what does "countercurrent" mean regarding the countercurrent multiplier system?

Answer 35

filtrate flows in opposite direction (countercurrent) thru 2 adjacent parallel sections of a nephron loop

Question 36

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?

Answer 36

Na+

Question 37

in which segment of the nephron loop is the tubular fluid more concentrated in solutes?

Answer 37

bottom of the nephron loop

Question 38

Figure 2 -- why are sodium ions leaving the filtrate at this point of the nephron loop and not before?

Answer 38

[NaCl] is the highest at this point

Question 39

what is responsible for increasing the interstitial fluid's osmolarity of the medulla: pumping sodium outside the tubule or water?

Answer 39

pumping sodium outside the tubule

Question 40

what is the difference b/n countercurrent exchange and countercurrent multiplier?

Answer 40

countercurrent multiplier -- creates the medullary gradient (causes medulla to have a much higher osmolarity) countercurrent exchange -- preserves the medullary gradient

Question 41

what are the purposes of the countercurrent exchange?

Answer 41

(1) prevent rapid removal of salt from the medullary interstitial space (2) removing reabsorbed water

Question 42

what is the difference b/n obligatory vs. facultative water reabsorption?

Answer 42

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

Question 43

in which segments of the renal tubule does obligatory water reabsorption take place? and facultative?

Answer 43

85% of water reabsorption --> PCT and descending limb of loop of Henle 15% of water reabsorption --> DCT and CD

Question 44

which parts of the renal tubule are considered aldosterone-sensitive?

Answer 44

distal nephron: late DCT connecting tubule collecting duct