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Physio II > Tubular Reabsorption & Secretion(A)- Exam 3 > Flashcards

Tubular Reabsorption & Secretion(A)- Exam 3 Flashcards

1
Q

What does clearance tell us?

A

Tells us how many mls of plasma is completely cleared of a substance.

Ex. 10mls/min- tells us in every minute 10 mls of plasma is completely cleared of that given substance

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2
Q

Excretion Equation

A

Excretion = Filtration - Reabsorption + Secretion

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3
Q

Where does filtration occur?

A

Glomerulus

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4
Q

Where does reabsorption and secretion occur?

A

Proximal tubule
Loop of Henle
Distal Tubule
Collecting Tubule

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5
Q

Filtration Rate Equation

A

GFR x Plasma concentration

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6
Q

Glucose concentration

A

1 g/L

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7
Q

Describe the filtration of glucose

A

Freely filtered

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8
Q

Normal GFR

A

125 mls/min; 180 L/day

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9
Q

% Filtered Load Reabsorbed: Glucose

A

100%

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10
Q

% Filtered Load Reabsorbed: Bicarb

A

> 99.9%

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11
Q

% Filtered Load Reabsorbed: Sodium

A

99.4%

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12
Q

% Filtered Load Reabsorbed: Chloride

A

99.1%

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13
Q

% Filtered Load Reabsorbed: Potassium

A

87.8%

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14
Q

% Filtered Load Reabsorbed: Urea

A

50%

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15
Q

% Filtered Load Reabsorbed: Creatinine

A

0%

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16
Q

How do the kidneys have independent control over exertion rate?

A

By changing appropriate reabsorption rate

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17
Q

What are the 4 distinct movements for water and solutes?

A
  1. Tubular lumen to tubular cells
  2. Tubular lumen to tubular interstitial space
  3. Interior of cells into tubular interstitial space
  4. Interstitial space into peritubular capillary
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18
Q

What drives fluid movement from interstitial space into peritubular capillary?

A

Capillary filtration forces (Bulk flow)

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19
Q

What is bulk flow?

A

Net movement into the capillaries

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20
Q

What type of gradient does water follow?

A

Osmotic gradient

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21
Q

What is the major driving force moving substances from lumen of tubule to interstitial spaces?

A

Diffusion

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22
Q

What is the transcellular path?

A

From tubular lumen into tubular cells

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23
Q

What is the Paracellular path?

A

from tubular lumen into tubular interstitial spaces

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24
Q

How does permeability at junctions compare to permeability of substances directly into tubular cells?

A

Permeability at the junction is lower ( see size of the arrow in slide 6 diagram)

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25
Q

Rank the permeabilities of bulk flow, paracellular path, and transcellular path.

A

Bulk flow (most permeable) > Transcellular Path > Paracellular path (least permeable)

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26
Q

What types of mechanisms does tubular reabsorption involve?

A

Both active and passive mechanisms

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27
Q

What are the 5 types of tubular reabsorption movements?

A
  1. Primary active transport
  2. Secondary active transport: Co-transport
  3. Secondary active transport: Counter-transport
  4. Pinocytosis (requires energy)
  5. Passive
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28
Q

What ATPase pumps use primary active transport?

A

Na/K
H/K
Hydrogen (secretion only)
Calcium

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29
Q

What pumps use secondary active transport: co-transport?

A

Sodium-glucose

Sodium-amino acid

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30
Q

What pumps use secondary active transport: counter-transport?

A

Sodium-hydrogen

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31
Q

What uses pinocytosis? Describe.

A

proteins; once in cell broken down to component amino acids and amino acids reabsorbed

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32
Q

What does pinocytosis require?

A

Energy

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33
Q

What is pinocytosis?

A

the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane

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34
Q

What uses passive methods for reabsoprtion?

A

Water (osmotic gradient)

Bulk flow into peritubular capillaries

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35
Q

What is the membrane potential within the tubular epithelial cells (created by Na/K pump)?

A

-70 mV

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36
Q

What is the membrane potential within the tubular lumen?

A

-3mV

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37
Q

Where is the brush border found?

A

Luminal membrane of the proximal tubule

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38
Q

What is sodium actively transported?

A

Sodium is pumped out of tubular cells into the interstitial spaces.

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39
Q

Where is potassium actively pumped?

A

Pumped into tubular cells (Na/K pump; countertransport)

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40
Q

Where are the Na/K ATPase pumps found?

A

Basolateral sides of the tubular epithelial cells

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41
Q

Where does sodium follow the concentration gradient?

A
  1. Tubular lumen into tubular cells

2. From interstitial space into capillary

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42
Q

What type of gradient does sodium follow when passively diffusing from lumen to cells?

A

Diffusion down concentration AND electrical gradient

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43
Q

Brush border of proximal tubule luminal membrane creates what surface area increase for diffusion?

A

20x increase

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44
Q

What also enhances sodium reabsorption?

A

Carrier proteins through luminal membrane

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45
Q

What type of carrier proteins enhance sodium reabsorption?

A

Co-transport and counter-transport proteins

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46
Q

What moves along with sodium from interstitial fluid into peritubular capillary?

A

Water

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47
Q

How fast does sodium move from interstitial fluid into peritubular capillary?

A

Very Quickly!

48
Q

How is glucose reabsorbed? (What mechanism)

A

Co-transport mechanism

49
Q

What is glucose reabsorption tied to?

A

Sodium gradient from tubular lumen to interior of tubular cells

50
Q

How efficient glucose reabsorption?

A

So efficient that is usually removes all filtered glucose

51
Q

What are the two luminal transporters for glucose reabsorption?

A

SGLT2 and SGLT1

52
Q

What percent of glucose is reabsorbed by SGLT2?

A

90%

53
Q

What percent of glucose is reabsorbed by SGLT1?

A

10%

54
Q

Where is glucose reabsorbed by SGLT2?

A

Early part of the proximal tubule

55
Q

Where is glucose reabsorbed by SGLT1?

A

Late part of proximal tubule

56
Q

What are the 4 transporters of glucose reabsorption?

A

SGLT1 (luminal)
SGLT2 (luminal)
GLUT1 (basolateral)
GLUT2 (basolateral)

57
Q

What are the two basolateral transporters by glucose reabsorption?

A

GLUT1

GLUT2

58
Q

What type of transport do the two basolateral glucose transporters use?

A

Passive facilitated transport down glucose concentration gradient

59
Q

Where is GLUT2 vs GLUT1 used a a glucose transporter?

A

GLUT1 in the later stages

GLUT2 in the early stages of the proximal tubules

60
Q

Where does bulk flow move glucose?

A

from interstitial spaces into the peritubular capillaries

61
Q

How is glucose reabsorbed?

A
  1. Co-transport (sodium)
  2. Two luminal transporters (SGLT1, SGLT2)
  3. Two basolateral transporters (GLUT1, GLUT2)
  4. Bulk flow
62
Q

How are amino acids reabsorbed?

A
  1. Co-transport (sodium)
  2. Luminal co-transporter pumps
  3. Diffusion
  4. Bulk flow
63
Q

Amino acid co-transport mechanism is tied to what?

A

Sodium gradient from tubular lumen to interior of tubular cells

64
Q

How efficient is the co-transport mechanism of amino acid reabsorption?

A

So efficient that it usually removes all filtered amino acids

65
Q

Where does the luminal co-transporter system pump amino acids?

A

Into the cells

66
Q

Where do amino acids undergo diffusion?

A

Diffuse out of the cells into the interstitial spaces

67
Q

Where do amino acids undergo bulk flow?

A

Bulk flow moves the amino acids form interstitial space into peritubular capillaries

68
Q

How does hydrogen secretion occur?

A

Counter-transport (sodium gradient)

Sodium-hydrogen exchanger

69
Q

What is the hydrogen counter-transport mechanism tied to?

A

Sodium gradient from tubular lumen to the interior of the cell

70
Q

Where is the sodium-hydrogen exchanger located?

A

Brush border of the luminal membrane

71
Q

What is a transport maximum?

A

Max amt of solute that can be reabsorbed (transport max transport)

72
Q

When does the transport maximum occur?

A

Occurs when tubular load exceed transport capacity of carrier proteins

73
Q

Tubular load

A

amount of solute delivered to tubule

74
Q

Glucose Tmax

A

375 mg/min

75
Q

Glucose filtered load

A

GFR x [GFR]= 125 mls/min x 1 ml/mg = 125 mg/min

76
Q

What is the threshold concentration of glucose?

A

250 mg/dl; concentration where glucose first appears in the urine

77
Q

Why is the threshold concentration less than Tmax?

A

each individual nephron is different; chart represents action of both kidneys so Tmax reached when ALL nephrons have reached their max

78
Q

Amino Acid Transport Max

A

1.5 mM/min

79
Q

Plasma protein Transport Max

A

30mg/min

80
Q

Creatinine Transport Max

A

16 mg/min

81
Q

Para-aminohipuuric acid Transport Max

A

80 mg/min

82
Q

What are the two excretion rates?

A
  1. Before secretion Tmax is reached; the amount excreted is the sum of amt filtered and amt secreted (steepest slope of excretion curve)
  2. After secretion Tmax is reached rate of excretion parallels filtration rate (slow of excretion curve matches slop of filtration curve)
83
Q

Which solute may not show maximum rate of transport?

A

Solute reabsorbed passively and some actively reabsorbed solute

84
Q

What does the rate of gradient-time transport depend on?

A

Electrochemical gradient
Membrane permeability for solute
Time fluid containing solute remains in tubule

85
Q

How does transport rate relate to tubular flow rate?

A

Inversely

86
Q

What is the transport max for sodium in the proximal tubules?

A

Does not show a transport max in the proximal tubule, even though it is actively reabsorbed

87
Q

How does the capacity of the Na-K ATPase compare to net sodium reabsorption in the proximal tubule?

A

Capacity > Rate of net sodium reabsorption

In the proximal tubule

88
Q

Does sodium leak back into the tubular lumen in the proximal tubule?

A

Yes, a significant amt of transported sodium leaks back

89
Q

What does sodium “leak back” in the proximal tubule depend on?

A

Permeability of tight junctions between cells

Forces controlling bulk flow of water and solute into peritubular capillaries

90
Q

As plasma concentration of sodium increases, what happens to sodium concentration in the proximal tubule and sodium reabsorption in proximal tubule?

A

Sodium concentration in prox tubule increases

Sodium reabsorption increases

91
Q

A decrease in tubular flow rate will do what to sodium reabsorption in proximal tubule?

A

increase sodium reabsorption

92
Q

What is the sodium tubular max transport in the distal tubule?

A

Classic tubular max transport

93
Q

How does the capacity of Na-K ATPase compare to net sodium reabsorption in the distal tubule?

A

Capacity does not exceed rate of net sodium reabsorption.

94
Q

How much “leak back” of sodium is there into the tubular lumen in the distal tubule? Why?

A

Minimal leak back; tighter, less permeable junctions couple transport of much smaller amt of sodium

95
Q

What does aldosterone do?

A

Increases Tmax level in distal tubule

96
Q

What drives the passive reabsorption of water?

A

Osmotic differences created by the movement of solute (mainly sodium) from tubular lumen to the tubular interstitial space

97
Q

What affects passive reabsorption of water?

A

Cellular permeability (cell membranes and tight junctions)

98
Q

Increased permeability does what to reabsorption and water excretion?

A

Increased reabsorption

Decreased water excretion

99
Q

What is the permeability of the proximal tubule?

A

Highly permeable

100
Q

Why is the solute gradient in the proximal tubule minimal?

A

Rapid movement

101
Q

Solvent drag

A

water carries significant amount of sodium, chloride, potassium, calcium, magnesium because of high permeability

102
Q

What is the permeability in the loop of henle (ascending loop)?

A

Low permeability

103
Q

Describe the movement of water in the loop of henle.

A

Little movement of water even though there is a large osmotic gradient

104
Q

What is the permeability in the distal tubule/collecting tubules/collecting ducts?

A

Variable permeability

105
Q

What does cellular permeability in the distal tubule/collecting tubule/ and collecting ducts dpeend on?

A

Presence of ADH

106
Q

Permeability is ___________related to ADH.

A

directly

107
Q

What does changing water permeabiliy in the distal tubule/collecting tubules/ collecting ducts affect?

A

Only affects amount of water reabsorbed, not the amount of solute due to low solute permeability

108
Q

What pulls chloride ions into the cell?

A

Sodium diffusion into cells creates electrical gradient that pulls negative chloride ions into the cell

109
Q

What concentrates chloride, creating a concentration gradient into the cell?

A

Movement of water into cells

110
Q

How is chloride reabsorbed?

A

Diffusion (electrical gradient - Na; concentration gradient - water)
Co-transport mechanism with sodium across the luminal membrane

111
Q

What membrane is the co-transport mechanism of Cl and sodium?

A

Luminal membrane

112
Q

What concentrates urea?

A

Movement of water into the cell

113
Q

What is more permeable: water or urea?

A

Water

114
Q

What contains specific passive urea transports which facilitates reabsorption?

A

Inner medullary collecting duct

115
Q

What percent of filtered urea is reabsorbed?

A

50%

Physio II (14 decks)

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