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Renal Exam 1 > Transport Mechanisms 1 > Flashcards

Transport Mechanisms 1 Flashcards

1
Q

plasma is filtered by the glomerulus into

A
  • bowman’s space
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2
Q

what lines the lumen of the nephron

A
  • polarized epithelial cells
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3
Q

what is the transcellular pathway

A
  • transport through tubular epithelial cells across apical and basolateral membrane
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4
Q

what is the paracellular pathway

A
  • transport between tubular epithelial cells
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5
Q

in the trans cellular pathway, solutes require what

A
  • tranporters
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6
Q

in the transcellular pathway, water moves along osmotic gradients through

A
  • aquaporins
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7
Q

in the paracellular pathway, solutes require what

A
  • leaky epithelia
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8
Q

where are the leaky epithelias located

A
  • proximal tubule

- descending limb of LOH

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9
Q

where are the tight epithelias located

A
  • ascending limb of LOH
  • distal tubule
  • collecting duct
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10
Q

the proximal tubule receives ultra filtrate that is

A
  • isosmolar with plasma
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11
Q

what does the proximal tubule reabsorb

A
  • 67% NaCL
  • 67% water
  • all glucose
  • all amino acids
  • most bicarb
  • 67% K+
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12
Q

what constitutes the majority of the total solute of the tubular fluid

A
  • Na+ and Cl-
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13
Q

how does Na+ get through the glomerulus

A
  • freely filtered
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14
Q

where is the Na/K ATPase located

purpose

A
  • in the basolateral membrane of literally all cells in all portions of the nephron
  • keeps Na low inside the epithelial cell and in interstitial fluid so it can move out of the tubular membrane and into the epithelial cell and get reabsorbed
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15
Q

what transporters are located on the lumen of the PCT

A
  • Na/Cl cotransporter
  • Na/glucose cotransporter
  • Na/amino acid cotransporter
  • Na/H+ exchanger
  • aquaporin 1
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16
Q

what transporters are located on the basolateral membrane of the PCT

A
  • Na/K ATPase
  • glucose transporters
  • amino acid transporters
  • Na/HCO3 cotransporters
  • aquaporin 1
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17
Q

what is the concentration of Na+ inside the epithelial cell

why

what is the importance of this

What happens to hydrogen?

A
  • low
  • due to the basolateral Na/K ATPase
  • drives the reabsorption of sodium into the epithelial cell along with glucose and amino acids.

H+ pumped out of the cell and into the tubular lumen.

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18
Q

amino acid reabsorption in the proximal tubule. How much reabsorbed?

on which membranes

A
  • 99% reabsorbed
  • secondary active transport on lumen membrane
  • facilitated diffusion on basolateral membrane
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19
Q

glucose is freely filtered where

A
  • at the glomerulus
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20
Q

glucose reabsorption by the proximal tubules

A
  • 100% reabsorbed
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21
Q

what glucose transporters are located on the lumen membrane of the PCT

by what mechanism

what are the numbers of glucose transporters on the lumen membrane of the PCT

A
  • sodium dependent glucose transporter (SGLUT)
  • secondary active transport
  • finite number
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22
Q

what glucose transporters are located on the basolateral membrane

by what mechanism

A
  • glucose transporter (not using sodium)

- via facilitated diffusion

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23
Q

plasma glucose in uncontrolled diabetes

result

A
  • plasma glucose concentration rises
  • elevated plasma glucose = elevated ultra filtrate glucose
  • transport maximum of SGLT is exceeded
  • glucose appears in the urine
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24
Q

what is the capacity of the SGLUT transporters in the lumen

A
  • 180 mg/dL
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25
Q

what happens when excess glucose remains in the PCT

A
  • excess glucose in urine
  • water retain due to osmotic action of unabsorbed glucose
  • high urine flow
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26
Q

plasma glucose after a meal in uncontrolled diabetics

A

> 180 mg/dl

27
Q

big symptom of diabetes

A
  • thirst and excessive drinking
28
Q

carbonic anhydrase enzyme is located where

A
  • brush border

- cytoplasmic face

29
Q

reclaiming filtered bicarb mechanism in PCT

A
  • filtered HCO3 exposed to acidic tubular lumen due ot Na/H exhcnager
  • HCO3 + H2O -> H2CO3
  • brush border carbonic anhydrase catalyzes conversion of H2CO3 -> H2O and CO2
  • H2O and CO2 diffuse across luminal membrane
  • cytoplasmic carbonic anhydrase converts CO2 + H2O -> H2CO3
  • H2CO3 breaks down into H+ and HCO3-
  • Na/HCO3 symporter
30
Q

role of Na/HCO3 symporter

how many of each one

A
  • transports 3 HCO3 and 1 Na across basolateral membrane and into peritubular capillaries
31
Q

mechanism for generation of new bicarbonate from glutamine

A
  • glutamine metabolism by epithelial cells
  • transport into epithelial cell by Na/AA cotransporter
  • breaks down into HCO3 and NH4
  • HCO3 transporter across basolateral membrane by Na/HCO3 symporter
  • NH4 secreted into tubular fluid by Na/H+ exchanger
32
Q

how is K+ reabsorbs in the PCT

A
  • 80% by solvent drag
33
Q

solvent drag of K+

A
  • water flowing through paracellular route pulls K+ along with it
34
Q

how much urea is reabsorbed in the PCT

A
  • about 50%
35
Q

what does H2O reabsorption in the early PCT do the urea

A
  • concentrates
36
Q

urea moves out of PCT lumen by

A
  • diffusion along concentration gradient

- tubules are permeable to urea

37
Q

comparison of water permeability to urea permeability

A
  • urea permeability is slower than water
38
Q

what happens to urea if GFR decreases

why

A
  • it increases
  • decreased flow rate gives more time for urea to be reabsorbed
  • increased urea there plasma BUN increases
39
Q

what is the definition of secretion into the proximal tubule

A
  • from peritubular capillary into tubular lumen
40
Q

what is secreted into the PCT

mechanism

A
  • end products of metabolism
  • pollutants
  • drugs
  • nonspecific transporters
41
Q

which drugs can compete for the same transporter on the PCT

A
  • cimetidine and procainamide
42
Q

what creates a hyper osmotic medullary interstitium

A
  • countercurrent multiplication
43
Q

the proximal tubules reabsorb

A
  • salt and water together
44
Q

which limb of the LOH is leaky

result

A
  • descending limb

- permeable to H2O and slightly to NaCl

45
Q

is there active transport in the descending limb of LOH

A
  • no
46
Q

ascending limb of LOH

what is reabsorbed

A
  • impermeable to H2O

- reabsorbs Na, Cl, K

47
Q

what transporter is located in the ascending limb of the LOH

role

A
  • Na/K/2Cl transporter

- brings those solutes into the epithelial cell

48
Q

what in the ascending limb allows K+ secretion into the tubular lumen

importance

A
  • lumenal ROMK (renal outer medullary) channel

- tubular K+ helps drive Na/K/2Cl transporter

49
Q

what is the osmolarity of the late proximal tubule

A
  • 300 mOsm
50
Q

what is the osmolarity of the bend of the LOH

A
  • 1200 mOsm
51
Q

what is the osmolarity of the early distal tubule

A
  • 100 mOSM
52
Q

what is the osmolarity of the outer medulla

A
  • 300-600 mOsm
53
Q

what is the osmolarity of the inner medulla

A
  • 600-1200 mOsm
54
Q

what is a condition where you would have the absence of ADH

A
  • full hydration
55
Q

result of absence of ADH

A
  • late distal tubule and collecting duct impermeable to water
  • excretion of a large volume of dilute urine
56
Q

what is a condition where you would have ADH present

A
  • dehydration
57
Q

result of ADH present

A
  • late distal tubule and collecting duct permeable to water

- excretion of small volume of concentrated urine

58
Q

what is the urea cycle in response to ADH

A
  • ADH stimulates insertion of urea transporter making the medullary collecting duct permeable to urea
  • urea diffuses out into the interstitium and increases the osmotic gradient
59
Q

result of low protein diet on urea

result on osmotic gradient and urine

A
  • low urea
  • decreased osmotic gradient
  • inability to form concentrated urine

END PRODUCT OF PROTEIN METABOLISM IS UREA

60
Q

effect of long loops of henle on osmotic gradient and concentration of urine

A
  • larger osmotic gradient

- more concentrated urine

61
Q

effect of short loops of henle on osmotic gradient and concentration of urine

A
  • smaller osmotic gradient

- less concentrated urine

62
Q

result of high rates of flow on osmotic gradient and concentration of urine

A
  • prevents complete equilibrium and NaCl trapping in medulla

- prevents full hyper osmotic concentration

63
Q

role of the vasa recta

A
  • prevents destruction/dissipation of longitudinal osmotic gradients in medullary interstitium

Renal Exam 1 (24 decks)

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