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Physiology > Exam3Lec3ProximalTubule/Concentration&Dilution > Flashcards

Exam3Lec3ProximalTubule/Concentration&Dilution Flashcards

1
Q

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

A

the 3Na+/2K+ ATPASE

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

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2
Q

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

A

In the proximal tubule

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3
Q

2/3 of filtrate is reabsorbed where?

A

Proximal Tubule

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4
Q

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

A
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5
Q

What is TF/p?

A

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

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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

Why is inulin 3.0 at the Late PT/plasma?

A

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.

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10
Q

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

A

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

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11
Q

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

A
  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

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12
Q

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

A

Na+/K+ pump

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13
Q

How is Glucose reabsorbed in the proximal tubule?

A
  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

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14
Q

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

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

excreted=filtered-reabsorbed

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15
Q

What substance does each slope represent?

A
  1. Inulin
  2. Cl-
  3. Na+/osmolariy
  4. HCO3-
  5. Glucose/amino acids
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16
Q

NaCl reabsorption in the ;late PCT

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

A

Cl-

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17
Q

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

A
  • by transcellular (2/3 of the time) and paracellular (1/3 of the time) pathways.
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18
Q

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

A

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.
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19
Q

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

A
  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
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20
Q

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

A

NO

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21
Q

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

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

not perm to solute

22
Q

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

A

Thick ascending limb

23
Q

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

A

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)

24
Q

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

A
  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

25
Q

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

A

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.

26
Q

What is the counter current multiplier factor?

A

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.

This is where NaCl is dumped into the interstium increasing osmolarity of interstium, thefore more Na reabsob

27
Q

What is responsible for counter current exchange?

A

Vasa recta

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.

28
Q

What is counter current exchanger responsible for?

A

Countercurrent exchange is a purely passive process that helps maintain the gradient

Countercurrent multiplication, as described, is an active process that establishes the corti- copapillary osmotic gradient

29
Q

Explain how the counter current exchanger can help maintain the gradient

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

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

33
Q

What are the 2 segments of the collecting duct?

A

Cortical Collecting duct (CCD): near cortex
Medullary Collecting duct (MCD): near medulla

have slightly diff properties

34
Q

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

A

Principal cells: secretes K+ and reabsorbs Na+
Intercalated cells: secrete Acid/Base equivalents and reabsorbe K+

cortical coll=closer to cortex/top

35
Q

ADH ____ tubular permeability to water

A

increases

36
Q

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

A

The collecting duct

37
Q

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

A

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

38
Q

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

A

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

39
Q

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

A

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

40
Q

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

A

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

41
Q

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

A
  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
42
Q

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

A
  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

urea is reab back into interstitium instead of being excreted

43
Q

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

A
  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
44
Q

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

A
  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
45
Q

If you can explain this graph, you gucci

numbers in () refer to the volume of filtrate in m/min remaining to be reabsorbed
A
46
Q

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

A

False

47
Q

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

A

True

48
Q

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

A

False

dependent on active Na/K/2Cl reabsopb

49
Q

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

A

True

50
Q

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

A

False

only in collecting duct

Physiology (22 decks)

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