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Renal 1 > Renal Transport Mechanisms > Flashcards

Renal Transport Mechanisms Flashcards

1
Q

Na+ and H2O percentage reabsorption in:

  • proximal convoluted tubule
  • proximal straight tubule
  • thick ascending limb
  • distal convoluted tubule
  • collecting duct
  • bladder
A 
PCT: 70% h20 , 60-70% Na
PST: none
Thick LOH: 25% Na, no H20
DCT: 5% Na, H2O variable
Collecting Duct- 3% Na, H20 variable 
Bladder- 1% Na, H20 variable
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2
Q

PCT reabsorption for:

  • glucose
  • amino acid
  • urea
  • H2O, Na, Cl, K

What is main transporter?
What is special feature of PCT?

A

Glucose: 100%
Amino acids: 100%
Urea: 50%
others: 67%

Na/K ATPase in basolateral membrane

*Freely permeable to water

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3
Q

Transcellular vs paracellular diffusion and pathway

A

Transcellular- through the cell membrane
Through luminal membrane-> cytosol-> basolateral membrane of tubule cell-> interstitial fluid -> endothelium of peritubular capillaries

Paracellular- between cells

  • between tubule cells
  • tight junctions, but can be leaky and ions can get through (Ca, Mg, K)
  • into PCT
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4
Q

Four ways to transport

A

1) ATPase
- only in basolateral membrane
- Na/K (Na out, K in)

2) Cotransporter
- ions move in same direction

3) Countertransporter
- ions move in opposite direction

4) Channel
- water channel, sodium channel, potassium channel

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5
Q

Sodium Reabsorption (4)

A
  • most abundant cation in filtrate
  • 80% of energy used for active transport for reabsorption
  • active via transcellular route
  • can occur sodium ion leak channels
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6
Q

Transport Na (3 steps)

A

1) Na+ diffuses across luminal membrane (apical) via Na/K ATPase pump
2) Na+ diffuse across basolateral membrane
3) Na H20 reabsorved from interstitial fluid into peritubular capillaries by ultrafiltration (passive)

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7
Q

Na+/H+ Exchange

  • effects
  • significance
A

-important for reabsorption for Na, Cl, and HCo3

  • sodium reabsorption
  • bicarbonate reclamation
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8
Q

Issues with Na+/H+ exchange (2)

5 step process of H+ ad HCO3

A
  • H+ outside=acidic
  • presence of carbonic anhydrase

1) Lumen: H+ + HCO3=> H2CO3
2) H2CO3 converted into CO2 + H2O via carbonic anhydrase
3) CO2 diffused into tubule cell cytosol (transcellular) + H2O => H2CO3 via carbonic anhydrase (splits into H and HCO3)
4) HCO3 into interstitial fluid then into blood
5) H+ recycles and helps process over again in lumen

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9
Q

Chloride Reabsorption

- mechanism

A
  • PCT: H2O> Cl- reabsorbed more
    • more Cl- in in tubule
  • Drives Chloride movement passively=> paracellular pathway (down conc gradient)
  • chloride reclamation
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10
Q 
Paracellular Route (H2O)
- examples
A
  • depends on presence/absence of tight junction
  • thin descending limb : not a lot of tight junction => paracellular water movement occur freely
  • Thick ascending limb and Collecting duct : lots of tight junction => no paracellular water movement
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11
Q

Transcellular Route (H20)

A

Aquaporins 1- Proximal Tubule, endothelia

Aquaporin 2- collecting duct , under control of ADH

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12
Q

Water Reabsorption in:

  • Proximal Tubule
  • Loop of Henle
  • Distal Tubule
  • Late distal tubule and CD

state %, mechanism, and hormones

A

PT: 67% , passive, no hormones

LoH: 15%, DESCENDING LIMB ONLY, passive, no hormone

Distal Tubule: no water reabsorption, no hormone

-Late distal tubule and CD: 8-17, passive, AVP, ANP, BNP

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13
Q

Glucose Transport

  • location
  • percentage
A

Proximal Convoluted Tubule

2 Sodium coupled Glucose Transporter

1) SGLT2- 90% of reabsorption
- high capacity
- low affinity
- S1, S2

2) SGLT1- 10% of reabsorption
- low capacity
- high affinity
- S3

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14
Q

Diabetes effect with SGLT2 inhibition

A

with SGLT 2 inhibition

  • reduced blood glucose levels=> less glucose resorption
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15
Q

Transport Maximum for Glucose

A

Tm= 375 mg/min (typically 200mg/dl)

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16
Q

Descending Loop of Henle reabsorption

- what can get filtered

A 
H2O permeable (25%)
NaCl IMPERMEABLE

increase solute= increase tubular fluid concentration => osmolarity increase( hyperosmolar)

-passive

17
Q

Thin and thick ascending loop reabsorption

A

WATER IMPERMEABLE

- 75% of particles that enter are reabsorbed

18
Q

Na K 2Cl cotransporter

A

ALL INTO loop of henle
1 NA
1 K
2 Cl

19
Q

Countercurrent Multiplier (7 steps)

A

1) Fluid enter tubule
- Active transport Na, Cl, K into medullar interstitial fluid increases osmolarity

2) water moves out of descending limb by osmosis
3) iso-osmotic state in descending limb ; osmotic difference in descending and ascending limb

4) more fluid enter tubule, push fluid through bulk fow
- active transport of Na, Cl, K into medullary interstitial fluid increases osmolarity

5) water moves out of descending limb by osmosis
6) iso-osmotic state in descending; osmotic difference btw ascending and descending limbs
7) continuous process=> osmotic gradient

20
Q

Distal tubule Reabsorption

  • normally reabsorbs
  • water
  • at DCT what is % of originally components
A

Water IMPERMEABLE

5-8% of filtered sodium chloride

at DCT
about 10% of NaCl and 25% of water originally remains

21
Q

Collecting Ducts

  • hormones
  • if no ADH, what happens
A
  • Aldosterone for NA
  • ADH for water
  • PTH for Ca2+
  • no ADH= water IMPERMEABLE
  • no Na leave body in urine
22
Q

Aldosterone goal

-location

A
  • on thick segment of LOH, DCT, CD (cortical)
  • retain NaCl and water
  • urine volume reduced
  • elevated K concentration

-increase Na+ reabsorption and K+ secretion

23
Q

Salt Reabsorption in:

  • Proximal Tubule
  • Loop of Henle
  • Distal Tubule
  • Late distal tubule and CD

state %, mechanism, and hormones

A

PT: 67, Na/H antiporter, SGLT2, angiotensin II, NE, EPI, Dopamine

LOH: 25, N/k 1cl symporter, na/h antiporter, aldosterone, angiotensin II

Distal:5, NaCL symporter, aldosterone, angiotensin II

Late distal tubule and collecting duct: 3, Na channel, aldosterone, anp, bnp, angiotensin II

24
Q 
Inhibiting Transporters (3)
mechanism of action
effect
A

1) Thiazide Diuretics
Mode of Action: Inhibits the reabsorption of Na+ & Cl in the cortical diluting segment of DCT.
-increase Ca2+ reabsorption in the distal tubule. - Natriuresis and decrease blood volume and pressure.

2) Loop Diuretics (Furosemide)
Mechanism of Action: Inhibits Na-K-2Cl co-transporter in thick ascending limb of loop of Henle.
-decrease reabsorption of Na+ , K+ & Cl-
- Diuresis— increased urine output

3) K + Sparing Spironolactone
Mechanism of Action: Aldosterone-dependent potassium sparing
diuretics.
Inhibits Na+ /K+ exchange in distal tubule and collecting duct.
-Promotes K+ retention and Na+ and water loss. -Hypotensive effect

25
Q

Water Deficit on Urine Concentration

A

ADH secretion->increase h2o permeability in tubule-> increase osmolarity in medullary

  • gradient higher osmolarity in lower medulla
    (100 at distal and collecting tubule)
  • small volume of concentrated urine
  • reabsorbed h20 pick up by peritubular capillaried and conserved for body
26
Q

Water Excess on urine concentration

A

no ADH secretion=> water IMPERMEABLE-> fluid entering distal tubule hypotonic

Net result= large volume of diluted urine, get rid of excess h20
- no h2o reabsorbed in distal portion of nephron

Renal 1 (8 decks)

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