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PSL301 > PSL301: Water 3 > Flashcards

PSL301: Water 3 Flashcards

Tubular Function

1
Q

value: normal GFR

A

> 90 mL/min or > 125 L/day

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2
Q

value: normal urine volume

A

0.5L - 2 L per day

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3
Q

why is there such a big difference between filtered volume and excreted volume?

A

> 99% of water & solutes are reabsorbed by the tubules

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4
Q

function of tubules

A
  • reabsorb solutes & water
  • secrete solutes & water
  • maintain homeostasis
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5
Q

when everything is normal, intake…

What is this called?

A

intake = secretion

“steady state”

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6
Q

steady state

A

intake = secretion

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7
Q

when there is a deficit of something, intake…

A

intake > excretion

excretion decreased

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8
Q

when there is an excess of something, intake…

A

intake < excretion

excretion increased

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9
Q

How does the kidneys maintain homeostasis?

A

adjust how much is reabsorbed & secreted

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10
Q

What signals do the tubules receive, and what do they do?

A
  • hormones
  • nerves
  • pH
  • electrolyte concentrations
  • pressure

signals modify reabsorption / excretion to keep body fluid composition normal

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11
Q

Hormone signals to the kidney

A
  • vasopressin / ADH
  • aldosterone
  • ANG II
  • PTH
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12
Q

purpose of ADH

A

water balance

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13
Q

purpose of aldosterone

A

Na & K balance

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14
Q

purpose of ANG II

A

Na & acid-base balance

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15
Q

purpose of PTH

A

Ca++ & phosphate balance

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16
Q

main nephron segments

A
  1. proximal tubule
  2. loop of Henle
  3. distal tubule
  4. collecting duct
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17
Q

the collecting duct is divided into…

A
  1. cortical collecting duct

2. medulla collecting duct

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18
Q

the Loop of Henle is divided into…

A
  1. Thick descending limb
  2. descending limb
  3. ascending limb
  4. thick ascending limb
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19
Q

function of tight junctions at the transporting epithelium

A
  • keep cells attached to each other

- prevent movement between adjacent cells (must pass through epithelial cells)

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20
Q

The basolateral membrane of the epithelium faces the…

A

ECF / blood stream

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21
Q

The apical membrane of the epithelium faces the…

A

lumen of kidney / intestines

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22
Q

____ increases absorptive surface area on the __ side of the proximal tubule

A

brush border microvilli

lumen

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23
Q

Most of the reabsorption occurs in the…

A

proximal tubule

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24
Q

sites of reabsorption

A
  • proximal tubule
  • loop of Henle
  • distal convoluted tubule & collecting duct
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25
Q

Glucose is reabsorbed in the…

A

all glucose is reabsorbed in the proximal tubule

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26
Q

How is K homeostasis maintained?

A

by secretion at the distal convoluted tubule & collecting duct

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27
Q

Most solutes & water homeostasis is controlled by the…

What is the exception?

A

distal convoluted tubule & collecting duct

Glucose, controlled by proximal tubule

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28
Q

What are the things reabsorbed / secreted by the kidneys? (5)

A
  • water
  • Na
  • K
  • glucose
  • bicarb
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29
Q

How do transporting epithelial cells work?

A

Polarized, so have different transport proteins on each side. Solutes must pass through different ones to get to other side.

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30
Q

the Na/K ATPase is located on which membrane?

A

basolateral

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31
Q

the Na/K ATPase is next to…

A

peritubular capillary

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32
Q

what does the Na/K ATPase do?

A

pumps 3 Na out of cell
pumps 2 K into cell

  • makes cell negative
  • make [Na] in cell low
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33
Q

the Na/K ATPase has what effect on Na in the lumen?

A

can enter cell naturally (down electrochemical gradient) @ apical membrane

Na then leaves through Na/K ATPase @ basolateral membrane

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34
Q

What is the purpose of Na movement?

A

Drives the movement of other solutes by cotransporters and antiporters on the apical membrane

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35
Q

cotransporters

A

transport 2 things in the same direction

- movement of 1 thing down the gradient drives movement of other against the gradient

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36
Q

antitransporters

A

transport 2 things in opposite directions

- movement of 1 thing down the gradient drives movement of other against the gradient

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37
Q

movement of water at the proximal tubule

A 
follows Na (moves into capillaries)
- osmotic gradient
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38
Q

absorption & secretion t the proximal tubule is ___ because of the movement of sodium

A

passive

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39
Q

define: secondary active transport

A

an ion can move against the gradient by coupling with another that moves down the gradient

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40
Q

the Na/glu transporter is a(n)…

A

cotransporter

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41
Q

reabsorption of glucose

A
  1. Na/glu cotransporter moves glucose into cell (where it is high concentration)
  2. glucose moves out of cell on basolateral side using GLUT transporter
  3. Na/K ATPase pumps Na out of cell to keep intracellular Na low
42
Q

which ions use sodium co-transport as a method to get through cells?

A
  • glucose
  • phosphate
  • chloride
    …
43
Q

how is paracellular transport achieved (at the renal tubules)?

A
  • through tight junctions
  • selective
  • have pores
  • driven by gradients
  • only some ions (Na, Cl, Ca, Mg…) can get through
44
Q

diuretic drugs block…

A

lumenal Na transporters
- increase Na secretion

specific diuretics target specific transporters

45
Q

common target of diuretics

A
  • loop of Henle
  • distal convoluted tubule
  • collecting duct
46
Q

how does each nephron segment differ?

A
  • type of transport protein
  • leakiness
  • type of hormone receptors present
47
Q

things that will affect leakiness in tubules

A
  • nature of the tight junction

- presence of channels (e.g. aquaporins)

48
Q

Trend of leakiness at the nephron tubules

A

Start off very leaky (proximal tubule)

Get tighter as you go on (collecting duct)

49
Q

proximal tubule is the site of…

A

most reabsorption (Na, Cl, K, bicarb, water)

50
Q

the most important lumenal Na transport protein at the proximal tubule is…

A

NHE3 (sodium-hydrogen exchanger)

51
Q

NHE3 works by…

A

pump Na into the cell

pump H+ out of the cell

52
Q

Purpose of NHE3

A

bicarb reabsorption

53
Q

which cotransporters are only found on the proximal tubule?

A
  • glucose
  • phosphate
  • amino acid
54
Q

the proximal tubule is very leaky -> ____ reabsorption of Na. What does this mean?

A

isotonic

[Na] in lumen is the same as [Na] in plasma due to water moving with Na

55
Q

The thick ascending limb reabsorbs ___% of ___

A

20 - 30%

filtered Na

56
Q

what is the lumenal transport at the thick ascending limb?

A

Na/K/2Cl cotransporter (NKCC2)

57
Q

NKCC2 is inhibited by…

A

furosemide (diuretic)

58
Q

how permeable is the thick ascending limb to water?

A

not at all

59
Q

fluid leaving the thick ascending limb is ____

A

hypotonic

less concentrated than plasma because water in tubule cannot get out

60
Q

What concentrates the medullary interstitium? What is the necessary for?

A

Add salt without water

Necessary for urine concentration

61
Q

the thick ascending limb has a ___ lumen and a ___ ISF

A

dilute

concentrated

62
Q

the distal convoluted tubule reabsorbs ___% of _____

A

5 - 10%

filtered Na and water

63
Q

what is the lumenal Na transporter in the distal convoluted tubule?

A

NCC (sodium chloride cotransporter)

64
Q

NCC is inhibited by which diuretic?

A

thiazides

65
Q

Which is more potent: thiazides or furosemides? Why?

A

furosemide.

thick ascending loop reabsorb more Na than the distal convoluted tubule

66
Q

the distal convoluted tubule is important for…

A

urine dilution

67
Q

when are thiazides used? furosemides?

A

furosemides used when you want a lot of Na+ lost in the urine.
thiazides used when you only want a bit more Na+ lost in the urine.

68
Q

the collecting duct reabsorbs ____% of ____

A

1-3%

filtered Na

69
Q

reabsorption at the collecting duct depends on…

A

body’s needs

70
Q

what is the lumenal transport protein at the collecting duct?

A

ENaC (epithelial sodium channel)

71
Q

the collecting duct has receptors for…

A
  • aldosterone

- vasopressin

72
Q

effect of aldosterone binding to the collecting duct

A

increase Na reabsorption

  • increase amount of Na channels
  • open more Na channels
73
Q

effect of ADH binding to the collecting duct

A

increase water reabsoprtion

- increase aquaporin2

74
Q

Effect of drugs on the collecting duct

A

collecting duct has low capacity, so it is easily affected by drugs

75
Q

why is the collecting duct important?

A
  • can generate large [ ] gradients

- establish final urine composition / concentration

76
Q

the collecting duct is less permeable to ___ than Na. What does this cause?

A

Cl-

Causes lumen to be neg, so K+ will be secreted (down charge gradient)

77
Q

the collecting duct is the site of regulation for the secretion of…

A
  • Na
  • K
  • water
  • ammonium
78
Q

ammonium is secreted to regulate…

A

acid-base balance

79
Q

There are __ transporters for glucose. They are…

A

2

in series: proximal and distal

80
Q

Properties of the proximal glucose transporter

A
  • low affinity

- high capacity

81
Q

Properties of the distal glucose transporter

A
  • high affinity

- low capacity

82
Q

How does the SGLT protein work?

A
  1. Na+ binds
  2. creates a site for glucose
  3. glucose binding changes SGLT conformation
  4. Na+ released, glucose follows
83
Q

what does “high affinity for glucose” mean?

A

can transport glucose even if the glucose gradient is very opposing

84
Q

what is the proximal glucose transporter called?

A

SGLT2

85
Q

what is the distal glucose transporter called?

A

SGLT1

86
Q

How does SGLT1 have a higher affinity for glucose?

A

exchanges 2 Na for 1 glucose

2 Na creates a higher drive into the cell

87
Q

SGLT2 is located…

A

S1 segment of the proximal tubule / early proximal tubule

88
Q

SGLT1 is located…

A

S3 segment of the proximal tubule / late proximal tubule

89
Q

job of SGLT1

A

remove all glucose from the lumen

90
Q

glucose (in) : glucose (out) ratio for SGLT2

A

70:1

91
Q

glucose (in) : glucose (out) ratio for SGLT1

A

5000:1

92
Q

What happens when someone has glucose in the urine with normal blood glucose?

A
  • problem with SGLT2

- no problem as long as they get enough calories

93
Q

___ can be possible treatment for hyperglycemia and diabetes. What effect might this have?

A

SGLT2 inhibitor drugs.

  • lower blood glucose
  • lower weight
94
Q

lumenal Na transport proteins

A
  • Na cotransporters
  • Na antiporters
  • Na channels
95
Q

___ has no large gradients because of ____

A

proximal tubule.

very leaky

96
Q

___ has large gradients because of ____

A

collecting duct.

tight

97
Q

Organic solute transporters are all…

A

proximal

98
Q

water reabsorption is…

A

passive (osmotic gradient)

99
Q

water reabsorption at the proximal tubule

A

follows Na isotonically

100
Q

water reabsorption at the collecting duct

A

dependson the presence of ADH (aquaporin2)

PSL301 (29 decks)

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