Exam3Lec3ProximalTubule/Concentration&Dilution

Question 1

What is the primary mechanism for potassium movement and sodium reabsorption?

Answer 1

the 3Na+/2K+ ATPASE

2K+ pumped into ICF inside cells
3Na+ pumped out of cell into interstium

Question 2

Na+ reabsorption and reabsorption of other soulutes (and isomotic reabsorption of water) is quantitively greatest where?

Answer 2

In the proximal tubule

Question 3

2/3 of filtrate is reabsorbed where?

Answer 3

Proximal Tubule

Question 4

What are the percentages of the filtered load reabsorbed for Na+ for each compartment?

Answer 4

Question 5

What is TF/p?

Answer 5

concenctration of a substance in the tubular fluid compated to its concentration in plasma

Question 6

In the PT why is the BC TF/plasma 1.0 from Inulin to AA?

Answer 6

At the beginning of the proximal tubule (Bowman’s space), the TF/P ratio for all freely filtered substances is 1.0; because no reabsorption or secretion has yet occurred, the solute concentrations in tubular fluid equal their concentrations in plasma.

Becuase just filtration is ocurring here

Question 7

Why is the BC TF/plamsa for protein nearly 0?

Answer 7

Its almost 0 because if the “shield” for glomerular filtration, protein canlt get through

Question 8

Why is Na+, Free Ca2+, and Osm all 1 in both the BC (early) and for Late PT TF/plasma?

Answer 8

Because we have isotonic reabsorption occuring here so no change in osm. Reabsorption is not only water, but also Na+, K+ reabsorb proportionally to water.

isosmotic reabsorption

water and ions being reabsorbed equally
1 in bc tf/plasms 1 in late pt tf plasma

Question 9

Why is inulin 3.0 at the Late PT/plasma?

Answer 9

D/t the properties of inulin. It is not metabolised, reabs, secretd. etc. This means that there is water reabsorption occuring and high concentration of inulin within the late pt because it doenst move.

[TF/P]inulin rises steadily along the proximal tubule because inulin, once filtered, is not reabsorbed; [TF/P]inulin rises because as water is reabsorbed and inulin is left behind in the lumen, the tubular fluid inulin concentration increases.

Question 10

Why is Glucose, AA, and protein all 0 at late PT TF/plasma?

Answer 10

Because sodium absorption is driven by Na+K+ ATPase

Because reabsorption of glucose, amino acids, and protein is proportionately greater than water reabsorption causing concentration of solute in tubular fluid to decr below that in plasma

Question 11

What type of transporters, pumps, or exchangers do you see in the Lumen (apical side) in the proximal tubule

Answer 11

1. Sodium dependent co-transporters: Na+/Glu, Na+/HPO4-/SO4-, Na+/AA
2. Sodium Hydrogen Exchanger: leads to bicarb reabsoption

H+ binds to bicarb to maintian pH

Question 12

What type of transporters, pumps, or exchangers do you see in the capillary (basal membrane) side of the proximal tubule

Answer 12

Na+/K+ pump

Question 13

How is Glucose reabsorbed in the proximal tubule?

Answer 13

1. Lumen: Driven by the Na+ gradient, gluc comes in using transporter SGLT1
2. Basal membrane: Glucose leaves lumen/apical membrane with GLUT2 carrier

1 is an active process, bc it depends on Sodium
2 is passive, just facilitating diffusion

Question 14

What does each graph represent in regards to the reabsoprtion of glucose?

Answer 14

1. Glucose filtered
2. Gluocose excreted
3. Glucose reabsorbed

excreted=filtered-reabsorbed

Question 15

What substance does each slope represent?

Answer 15

1. Inulin
2. Cl-
3. Na+/osmolariy
4. HCO3-
5. Glucose/amino acids

Question 16

NaCl reabsorption in the ;late PCT

Na+ reabsorption in the late PCT occurs mostly with which ion?

Answer 16

Cl-

Question 17

Both Na+ and Cl– cross the late PCT by what two pathways?

Answer 17

• by transcellular (2/3 of the time) and paracellular (1/3 of the time) pathways.

Question 18

Is water passively or actively reabsorbed in the PCT? Via which pathway(s)? Due to what?

Answer 18

Water is passively reabsorbed via transcellular and paracellular pathways due to the osmotic gradient established by transport of NaCl.

water follows solute

• Additional solute (e.g., Ca2+) is carried along via solvent drag.

Question 19

Proximal Tubule Summary. Fill in the blank
1. ____ of salts and water reabsorbed
2. All glucose and a.a.____
3. Reabsorption is____
* PT Osmolality is ____ at the beginning & the end

Answer 19

1. 2/3 of salts and water reabsorbed (67%)
2. All glucose and a.a. are reabsorbed
3. Reabsorption is isotonic
   * PT Osmolality is isotonic at the beginning & the end

Question 20

Does sodium reabsortion occur at the thin descending and thin ascending limb?

Answer 20

NO

Question 21

In the thin descending limb of the loop of henle what is the permeability for
1. solutes
2. Water

Answer 21

1. Low permeability to solutes (no sodium reabs)
2. High permeability to water

not perm to solute

Question 22

Which compartment in the nephrom accounts for 25% of Na+ reabsorption?

Answer 22

Thick ascending limb

Question 23

The thick ascending limb of henle (TAL) can also be called what?

Answer 23

Diluting segment ( this is because we see a decr in osm because we are removing lots of solutes therefore diluting it. Dilution is NOT bc of water impermeability)

Question 24

In the thick ascending limb of the loop of henle what is the permeability for
1. solutes
2. Water

Answer 24

1. High permeablity for soulutes: Special carriers co-transport ions from tubule to interstitium for reabsorbtion
2. impermeable to H2O

water cannot leave or come in
special carriers to transport Na+, K_m 2Cl- at the same time, found ONLY in thick ascendig limb

Question 25

Which structures are responsible for the counter current multiplication and why is it essential?

Answer 25

The loop of Henle comprises three segments: the thin descending limb, the thin ascending limb, and the thick ascending limb. Together, the three segments are responsible for countercurrent multiplication, which is essential for the concentration and dilution of urine.

Question 26

What is the counter current multiplier factor?

Answer 26

More NaCl is reabsorbed into the interstitial fluid and this increases the activity of the Na+-K+-2Cl− cotransporter of the thick ascending limb, thereby enhancing countercurrent multiplication and the size of the corticopapillary osmotic gradient. ## Footnote This is where NaCl is dumped into the interstium increasing osmolarity of interstium, thefore more Na reabsob

Question 27

What is responsible for counter current exchange?

Answer 27

Vasa recta ## Footnote The vasa recta are capillaries that serve the medulla and papilla of the kidney. The vasa recta follow the same course as the loop of Henle and have the same hairpin (U) shape.

Question 28

What is counter current exchanger responsible for?

Answer 28

Countercurrent exchange is a purely passive process that helps maintain the gradient ## Footnote Countercurrent multiplication, as described, is an active process that establishes the corti- copapillary osmotic gradient

Question 29

Explain how the counter current exchanger can help maintain the gradient

Answer 29

They are freely permeable to small solutes and water. Blood flow through the vasa recta is slow, and solutes and water can move in and out, allowing for efficient countercurrent exchange

Question 30

All of our hormone system in our body tries to regulate what segments of the nephron?

Answer 30

The distal convoluted tubule (5%) and the cortical collecing duct (3%) (we reguate this 8% of reabsorption to keep us alive)

Question 31

How does the distal convoluted tubule contribute to the counter current multiplier?

Answer 31

You see the osm decr even further (150-> 60) because we only have NaCl cotransporter and it's still impermeable to H20. The osm decr b/c solutes are still leaving, "Dilution" is still occuring

Question 32

What type of exchangers, pumps, or co-transporters do we have in the lumen and capillary side of the early distal tubule?

Answer 32

Lumen: NaCL co-transporter Capilar side: Na+K+ pump

Question 33

What are the 2 segments of the collecting duct?

Answer 33

Cortical Collecting duct (CCD): near cortex Medullary Collecting duct (MCD): near medulla ## Footnote have slightly diff properties

Question 34

What are the 2 cell types in the cortical collecting duct and name what they each secrete and reabsorb

Answer 34

Principal cells: secretes K+ and reabsorbs Na+ Intercalated cells: secrete Acid/Base equivalents and reabsorbe K+ | cortical coll=closer to cortex/top

Question 35

ADH ____ tubular permeability to water

Answer 35

increases

Question 36

Which segment of the nephron is the site of ADH/vasopression action?

Answer 36

The collecting duct

Question 37

What is the result of binding the ADH to the basolateral membrane of principal cells?

Answer 37

Insertion of water channels (aquaporin-2) into the apical membrane

Question 38

Is the baslolateral side of the principal cell of the late distal tubule and collecting duct water permeable? Why or why not?

Answer 38

It is always water permeable b/c water channels are always expressed on the basolateral side (ADH/vasopressin side)

Question 39

In the absence of ADH what occurs to the water channels?

Answer 39

The water channels are recycled and the apical membrane is again impermeable to water

Question 40

Is the lumen (facing tubular fluid) of the principal cell of the late distal tubule and collecting duct water permeable? Why or why not?

Answer 40

It is impermeable and has low water concentration b.c no water channels are constituvely being expressed on apical membrane.

Question 41

Explain how AQP2 can become activated in the principal cell of the later distal tubule and collecting duct

Answer 41

1. ADH binds to the receptor coupled with Gs protein. Adenyl cyclase is activated and this leads to the activation of PKA 2. PKA phosphorylates AQP2 (usually free floating and has water in it) and it will transport from cytoplasm into apical membrane and exocytosize. 3. This makes the WHOLE tubule H2O permeable

Question 42

Explain what is occuring in the 1. Cortex 2. Outer Medulla 3. Inner medulla 4. inner medulla in regard to the mechanism of urea recycliing

Answer 42

1. Cortex: ADH incr H2O permeability 2. Outer Medulla: Increase in [TF] urea 3. Inner medulla: ADH incr H2O permeability and urea trasnport occurs (UT1). 4. Urea then rapidly diffuses from tubuilar fluid into interstitial fluid of inner medullla ## Footnote urea is reab back into interstitium instead of being excreted

Question 43

Summary of ADH Actions on the kidneys 1. ____ permeability of water for the entire collecting duct 2. ____ permeability of urine of Medullary CD 3. ____ vasa recta blood flow 4. ____ expression of the Na/K/2Cl transporter in the Thick Ascending limb

Answer 43

1. **Incr** permeability of water for the entire collecting duct 2. **Incr** permeability of urine of Medullary CD 3. **Decr** vasa recta blood flow 4. **Incr** expression of the Na/K/2Cl transporter in the Thick Ascending limb

Question 44

How do we generate and maintain the high meduallr interstitial osmolality? (5 points)

Answer 44

1. Reabsorption of Na+ and Cl- in the thick acscending limb (diluting segment) 2. Low flow thru vasa recta 3. Counter current multiplication 4. Counter current exchange b/w descending and ascending vasa recta 5. Importance of urea to maintain the osmorality

Question 45

If you can explain this graph, you gucci

Answer 45

Question 46

True or False: Most of the filtrate is absorbed in the thick ascending limb of the loop of henle

Answer 46

False

Question 47

True or False: Fluid leaving the proximal tubule is isosmotic to plasma

Answer 47

True

Question 48

True or False: Renal medullary hyperosmolality is primarily dependent on passive mechanisms

Answer 48

False ## Footnote dependent on active Na/K/2Cl reabsopb

Question 49

True or False: Most reabsorption in the renal tubule is directly or indirectly dependent on Na/K ATPase

Answer 49

True

Question 50

True or False: ADH incr water absorption in most parts of the renal tubule

Answer 50

False ## Footnote only in collecting duct