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DEN 7101S Human Structure and Function II > Exam 3 Britton Renal Physiology II > Flashcards

Exam 3 Britton Renal Physiology II Flashcards

1
Q

Movement of solutes and H2O is via either ____ or ____

A

Paracellular transport or transcellular transport

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2
Q

What is paracellular transport?

A

Between cells and across tight junctions

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3
Q

What is transcellular transport?

A

Across both the luminal (apical) and the basolateral membrane

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4
Q

What primarily provides the driving force for solute movement?

A

Na+/K+-ATPase pump in the basolateral membrane

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5
Q

What are some mechanisms by which substances move across membranes for reabsorption or secretion?

A
  • Diffusion
  • Active transport (pumps)
  • Facilitated diffusion
  • Co-transport
  • Counter transport (exchangers)
  • Osmosis
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6
Q

Reabsorption can be ____ or ____

A

Active or passive

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7
Q

The mechanisms for reabsorption involve transporters where?

A

In the membranes of the nephron

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8
Q

Reabsorption depends mostly on ____

A

Active transport

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9
Q

Active transport of Na+ from tubule to blood creates a ____

A

Transepithelial electrical gradient

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10
Q

What is the transepithelial electrical gradient?

A
  • Active transport of Na+ from tubule into blood
  • Anions follow Na+ out of lumen
  • Water leaves tubule via osmosis
  • K+ reabsorption is due to solvent drag
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11
Q

____ is a hallmark of proximal tubular function

A

Isosmotic reabsorption

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12
Q

During isosmotic reabsorption, ____ and ____ are coupled to each other and are ____ to each other

A

Solute and H2O; Proportional

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13
Q

Glucose reabsorption in the proximal tubule requires what transporters?

A
  • Na+/K+ ATPase pump
  • SGLT2
  • GLUT2
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14
Q

What is SGLT2?

A

Sodium glucose co-Transporter 2

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15
Q

____ establishes the concentration gradient for Na+

A

Na+/K+ ATPase pump

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16
Q

Normally, ___ of filtered glucose is reabsorbed

A

100%

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17
Q

The SGLT2 and GLUT2 mechanism in the _____ is responsible for ___ of glucose reabsorption. The remaining ____ is reabsorbed in the ____ involving SGLT1 and GLUT1

A

Early proximal tubule; 90%; 10%; Late proximal tubule

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18
Q

Where is SGLT2 located on the proximal tubule?

A

Apical membrane

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19
Q

Where is Na+/K+ ATPase pump located on the proximal tubule?

A

Basolateral membrane

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20
Q

Where is the GLUT2 transporter located on the proximal tubule?

A

Basolateral membrane

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21
Q

____ enables glucose to leave the cell down a concentration gradient

A

GLUT2

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22
Q

____ transports Na+ and glucose into the cell simultaneously

A

SGLT2

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23
Q

As plasma glucose increases, the filtered load will increase ____

A

Linearly

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24
Q

When the plasma concentration of glucose is less than 200 mg/dL, ____ is reabsorbed

A

All filtered glucose

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25
Q

When the plasma concentration of glucose is less than 200 mg/dL, why is reabsorption = filtration?

A

Because SGLT2 transporters are plentiful

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26
Q

When the plasma concentration of glucose is greater than 200 mg/dL, what happens?

A

Some of the filtered glucose is not reabsorbed, since the number of SGLT2 transporters is limited

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27
Q

At P>350 mg/dL, what happens? (glucose)

A

SGLT2 transporters are completely saturated and thus reabsorption levels off at maximal value (transport maximum)T

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28
Q

True or false: For glucose, when [P] < 200 mg/dL, all filtered glucose is reabsorbed and none is excreted

A

True

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29
Q

For glucose, when [P] > 200 mg/dL, the SGLT2 carriers are near ____. Glucose that is not reabsorbed is ____

A

Saturation; excreted

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30
Q

What is renal threshold for glucose?

A

[P]glucose at which glucose is first excreted in the urine (glucosuria)

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31
Q

At [P] glucose > 350 mg/dL, Tm is reached and SGLT carriers are ____. Glucose excretion in urine _____

A

Fully saturated; Now increases linearly

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32
Q

Excess glucose in diabetes: Tm occurs as ___ are saturated. Excess glucose in nephron tubule will ____. What symptoms will the patient experience?

A

SGLT; Osmotically hold water; Excess urination and thirst

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33
Q

What is splay?

A

Where reabsorption is approaching saturation but is not fully saturated

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34
Q

Of all functions of the kidney, ____ is the most important

A

Reabsorption of Na+

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35
Q

Na+ is the major cation of the ____

A

ECF compartment

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36
Q

What occurs during positive Na+ balance?

A

Hypernatremia

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37
Q

What is hypernatremia?

A

Abnormal increase of blood Na+

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38
Q

Hypernatremia can be caused by:

A

Hormonal imbalances

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39
Q

Describe what happens during hypernatremia

A
  • Increased Na+ content in ECF
  • Increased ECF volume (termed ECF volume expansion, attracts more water)
  • Increased blood volume and MAP
  • May be edema in the limbs
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40
Q

What happens in negative Na+ balance?

A

Hyponatremia

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41
Q

What is hyponatremia?

A

An abnormal decrease of blood Na+

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42
Q

Describe what happens during hyponatremia

A
  • Decreased Na+ content in ECF
  • Decreased ECF volume (ECF volume contraction)
  • Decreased blood volume and MAP
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43
Q

What diseases/situations can lead to hyponatremia?

A
  • Sweating
  • Vomiting
  • Diarrhea
  • Diuretics
  • Diabetes
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44
Q

___% of the filtered load of Na+ is subsequently reabsorbed in various segments throughout the nephron. ___% is excreted

A

99%; 1%

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45
Q

What % of Na+ is reabsorbed in the proximal tubule?

A

~65%

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46
Q

What % of Na+ is reabsorbed in the thick limb of the ascending loop of Henle?

A

~25%

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47
Q

What % of Na+ is reabsorbed in the early distal tubule?

A

5-10%

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48
Q

What % of Na+ is reabsorbed in the principal cells of the late distal tubule and collecting duct?

A

1-5%

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49
Q

In the early proximal tubule, Na+ is co-transported with:

A
  • Glucose
  • Amino acids
  • Phosphate
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50
Q

In the early proximal tubule, Na+ is exchanged for:

A

H+ (via Na+/H+ exchanger)

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51
Q

Na+ co-transporters and exchangers are located on what surface of the PT cell?

A

Apical

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52
Q

On which membrane is the Na+/K+ ATPase located? (early PT)

A

Basolateral

53
Q

The late proximal tubule allows for additional Na+ movement across the membrane through what mechanism?

A

Cl- gradient (paracellular transport)

54
Q

In the proximal tubule, ____ reabsorption is always linked to Na+ reabsorption. This mechanism is described as ____

A

H2O; isosmotic

55
Q

How is Na+ reabsorbed in the thick ascending limb of LoH?

A

Via the Na+-K+-2Cl- co-transporter (NKCC) on apical membrane

56
Q

NKCC is inhibited by:

A

Loop diuretics

57
Q

How is Na+ reabsorbed in the early distal tubule?

A

Via the NaCl co-transporter (NCC) on the apical membrane

58
Q

NCC is inhibited by:

A

Thiazide diuretics

59
Q

How is Na+ reabsorbed in the principal cells of the late DT and collecting duct?

A
  • Via epithelial Na+ channels (EnaC) on the apical membrane
  • Na+ diffuses through these channels down its electrochemical gradient
60
Q

The nephron Na+ reabsorption at the late DT and collecting duct is regulated by what hormone?

A

Aldosterone

61
Q

ENaC are inhibited by:

A

K+-sparing diuretics

62
Q

What mechanisms regulate renal Na+?

A
  • Sympathetic nerve activity
  • Atrial Natriuretic peptide (ANP)
  • Starling forces in peritubular capillaries
  • Renin-angiotensin-aldosterone system
63
Q

Describe how sympathetic nerve activity regulates renal Na+

A
  • Decreased MAP activates the baroreceptor mechanism
  • Causes vasoconstriction of afferent arterioles
  • Leads to decreased GFR and increased Na+ reabsorption in PT
64
Q

Describe how atrial natriuretic peptide (ANP) regulates renal Na+

A
  • Increase in ECF volume
  • ANP secreted by atria
  • Vasodilation of afferent arterioles and vasoconstriction of efferent arterioles
  • Increases GFR, decreases Na+ reabsorption
65
Q

ANP secretion leads to ____ Na+ reabsorption

A

Decreased

66
Q

Sympathetic nerve activity leads to ____ Na+ reabsorption

A

Increased

67
Q

Increase in ECF volume leads to ____ Na+ reabsorption in the PT

A

Decreased

68
Q

Decrease in ECF volume leads to ____ reabsorption in the PT

A

Increased

69
Q

RAAS system is activated in response to:

A

Decreased MAP (decreased renal perfusion pressure)

70
Q

Na+ reabsorption is governed by what 2 hormones?

A
  • Angiotensin II
  • Aldosterone
71
Q

Angiotensin II stimulates Na+ reabsorption in the ___ via ___

A

PT; Na+-H+ exchange

72
Q

Aldosterone stimulates Na+ reabsorption in the ____

A

Late DT and collecting duct

73
Q

The actions of Angiotensin II cause:

A

Increased total body Na+, total body H2O, and vascular tone

74
Q

Aldosterone is a steroid hormone secreted by:

A

Zona glomerulosa of the adrenal cortex

75
Q

Aldosterone release is stimulated by:

A

Angiotensin II

76
Q
  • Aldosterone is delivered to the ____ via the circulation and diffuses into cells across the ____
  • Aldosterone transfers to the ____, where it stimulates the synthesis of mRNA involved in Na+ reabsorption, including ____ and ___
A
  • Principal cells; Basolateral cell membrane
  • Nucleus; ENaC and Na+/K+ pump
77
Q

What is the function of the principal cells in the late distal tubule and collecting duct?

A
  • Reabsorb Na+ from tubular filtrate
  • Secrete K+ into the filtrate
    (thus aldosterone causes increased Na+ reabsorption and H2O)
77
Q

____ increases K+ secretion

A

Aldosterone

78
Q

How much K+ is reabsorbed in the proximal convoluted tubule?

A

67%

79
Q

How much K+ is reabsorbed in the thick ascending limb of LoH?

A

20%

80
Q

What is responsible for fine tuning K+ excretion that occurs when dietary K+ varies?

A
  • Distal tubule
  • Collecting duct
81
Q

True or false: Principal cells in the DT reabsorb K+

A

False - secretes K+

82
Q

____ reabsorb K+ in the DT and CD

A

alpha-intercalated cells (also H+ secretion)

83
Q

What are the 4 renal effects of aldosterone?

A
  • Decreased Na+ excretion in urine
  • Decreased Cl- excretion in urine
  • Increased K+ excretion in urine
  • Increased NH4+ excretion in urine
84
Q

A number of sensors detect changes in the blood volume or plasma Na+ concentrations, such as:

A
  • Carotid baroreceptors
  • Juxtaglomerular cells (intrarenal baroreceptirs)
  • Macula densa
  • Stretch receptors in atria (ANP release)
85
Q

The release of renin ultimately leads to ____ production, increased ____ reabsorption and ____ retention

A

ANG II; Na+; H2O

86
Q

H2O reabsorption occurs mainly in the ____. Reabsorption is by ____

A

Proximal tubule; osmosis

87
Q

What are the different segments of the loop of Henle? What are these segments responsible for?

A
  • Thin descending limb, thin and thick ascending limb
  • Responsible for countercurrent multiplication
88
Q

Countercurrent multiplication is essential for:

A

The concentration and dilution of urine

89
Q

Where does H2O reabsorption occur?

A

In the descending limb of the LoH and at the collecting duct via aquaporins in the membrane

90
Q

The structure of the ___ and associated ____ create a countercurrent multiplier system

A

LoH and vasa recta

91
Q

In the countercurrent multiplier system, where does the term countercurrent come from?

A

The fact that the descending and ascending limbs of the LoH are next to each other and their fluid flows in opposite directions

92
Q

In the countercurrent multiplier system, where does the term multiplier come from?

A

Due to the action of solute pumps that increase (multiply) the concentrations of urea and Na+ deep in the medulla

93
Q

There is ____ osmolality as you go deeper into the medulla

A

Increased

94
Q

In the countercurrent multiplier system:
____ concentrates the filtrate
____ dilutes the filtrate

A

Descending loop; Ascending loop

95
Q

Is the descending loop permeable to water?

A

Yes, aquaporin channels are present and is impermeable to Na+ and Cl-

96
Q

Is the ascending loop permeable to water?

A

No, but transporters such as NKCC are present for reabsorption

97
Q

Anti Diuretic Hormone (ADH) is secreted from ____

A

Pituitary gland

98
Q

What stimuli cause the release of ADH?

A
  • Osmoreceptors
  • Baroreceptors
  • ANG II
99
Q

What are the two major effects of ADH?

A
  • Arteriole constriction in the peripheral circulation – reduces blood flow to the kidney
  • Causes epithelial cells that line the nephron collecting duct to insert aquaporins into the apical cell membrane

INCREASES water reabsorption into the blood

100
Q

Actions of ADH in the Kidney

A
  • ADH acts via V2 receptor
  • Causes aquaporins to be inserted into the apical membrane of principal cells
  • dramatically increases the reabsorption of H2O to the blood
101
Q

Cardiovascular: ADH vascular receptor is ____

A

V1

102
Q

What is the action of ADH in the cardiovascular system?

A

Potent vasoconstrictor and increases blood pressure

103
Q

What is the effect of ADH on water reabsorption in the collecting duct?

A
  • Without ADH, the late DT and CD are impermeable to water
  • With ADH release, AQP-2 channels are present. Late DT and CD become permeable to H2O
104
Q

What are the critical roles of phosphate in the body?

A
  • Constituent of bone
  • Urinary buffer for H+ (acid base balance)
105
Q

What regulates blood phosphate concentration?

A

Kidneys

106
Q

Where is phosphate localized primarily in?

A
  • Bone matrix
  • ICF
  • ECF
107
Q

In the ICF, phosphate is a component of:

A
  • Nucleotides
  • High energy molecules (ATP)
  • Metabolic intermediates
108
Q

In the ECF, phosphate is present in its ____ form and serves as a ____ for H+. ~10% phosphate in plasma is ____

A

Inorganic; buffer; Protein bound

109
Q

Phosphate not bound to plasma proteins is ____

A

Filtered

110
Q

What % of phosphate is reabsorbed?

A

85% (70% in the PCT, 15% in the proximal straight tubule)

111
Q

Phosphate reabsorption is via what transporter in the nephron membrane?

A

Na+-phosphate cotransporter

112
Q

True or false: Phosphate reabsorption is saturable and therefore exhibits a Tm

A

True (when Tm is reached, any phosphate not reabsorbed will be excreted)

113
Q

What % of phosphate is excreted?

A

15%

114
Q

The high level of excretion of phosphate (15%) is important because:

A

Unreabsorbed phosphate is a urinary buffer for H+ (titratable acid)

115
Q

What regulated phosphate reabsorption in the PT?

A

Parathyroid hormone

116
Q

Parathyroid hormone ____ Na+/phosphate co-transport which ____ the Tm for phosphate reabsorption

A

Inhibits; decreases

117
Q

99% of the body’s Ca2+ is contained in ____. 1% is present in ____ and ____

A

Bone; ICF and ECF

118
Q

What is the total [Ca2+] in plasma?

A

10 mg/dL

119
Q

Of the total plasma Ca2+:
____ is bound to plasma proteins
____ is bound to other anions such as phosphate and citrate
____ is in the free, ionized form

A

40%; 10%; 50%

120
Q

Can Ca2+ bound to plasma proteins be filtered across glomerular capillaries?

A

No - therefore only 60% plasma Ca2+ is filtered

121
Q

What % of filtered Ca2+ is reabsorbed?

A

> 99%

122
Q

Renal handling of Ca2+
____ is reabsorbed in the PT
____ is reabsorbed in the TAL
____ is reabsorbed in the DT

A

67%; 25%; 8%

123
Q

Plasma [Ca2+] is regulated by ____

A

Parathyroid hormone

124
Q

____ stimulates Ca2+ reabsorption at the DT

A

Parathyroid hormone

125
Q

____ plasma Mg2+ is filtered
____ Mg2+ reabsorbed

A

80%; 95%

126
Q

____ Mg2+ reabsorbed in the PT
____ Mg2+ reabsorbed in the DT
____ Mg2+ reabsorbed in the TAL

A

30%; 5%; 60%

127
Q

What is Mg2+ reabsorption driven by?

A

The potential difference generated by NKCC

128
Q

What is the major site of Mg2+ reabsorption?

A

Thick ascending limb of LoH

DEN 7101S Human Structure and Function II (21 decks)

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