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Renal I > Regulation of Sodium and Water Balance > Flashcards

Regulation of Sodium and Water Balance Flashcards

1
Q

Main substances exerting osmotic pressure in compartments:

• cells: ?
• interstitial fluid: ?
plasma: ?

A

K+

Na+

protein (usually albumin)

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2
Q

What two electrolytes are particularly abundant in the ECF?

A

Na+

Cl-

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3
Q

What electrolytes are particularly abundant in the ICF?

A

K+

Pi

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4
Q

What determines the distribution of body water?

A

Osmotic pressure

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5
Q

Water & Na balance are regulated independently by specific pathways designed to prevent large changes in plasma osmolality. What happens as a result of…

­ increased total body Na+ content –>

A

H2O osmosis from cells, renal H2O retention –> increased­ extracellular fluid volume.

Thus, increased Na+ in the body expands extracellular fluid volume and effective circulating volume.

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6
Q

How is plasma Na+ balance (and therefore osmolarity) regulated?

A

primarily by changes in water balance

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7
Q

•Total Body Na+ content = ?

A

•Total Body Na+ content = dietary Na+ intake - urinary Na+ excretion

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8
Q

•Dietary Na+ intake is not regulated in humans. How do we control body Na+ content?

A

the kidneys control body Na+ content by adjusting urinary excretion

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9
Q

What activates retention and excretion of Na+?

A

Increased ECF volume activates mechanisms that increase Na+ excretion.

Decreased ECF volume causes Na+ to be stored.

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10
Q

Where is the bulk of Na+ reabsorption done in the kidney?

A

Proximal Tubule, loop of henle

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11
Q

Where is the fine tuning of the Na+ reabsorption handled?

A

At the distal nephron

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12
Q

What are the major functions of the early proximal tubule?

A

Isosmotic reabsorption of solute and water

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13
Q

What are the early proximal tubule cellular mechanisms?

A

Na +-glucose, Na+-amino acid, Na +-phosphate cotransport

Na +-H +exchange

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14
Q

What hormones act at the early proximal tubule?

A

PTH inhibits Na +-phosphate cotransport

Angiotensin II stimulates Na +-H +exchange

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15
Q

What are the diuretics associated with the early proximal tubule?

A

Osmotic diuretics

Carbonic anhydrase inhibitors

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16
Q

What are the major functions of the late proximal tubule?

A

Isosmotic reabsorption of solute and water

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17
Q

What are the cellular mechanisms of the late proximal tubule?

A

NaCl reabsorption driven by Cl −gradient

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18
Q

What hormones act at the late proximal tubule? diuretics?

A

none.

Osmotic diuretics

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19
Q

What are the major functions of the thick ascending limb of the loop of henle?

A

Reabsorption of NaCl without water; Dilution of tubular fluid ;Single effect of countercurrent multiplication; Reabsorption of Ca 2+ and Mg 2+ driven by lumen-positive potential

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20
Q

What are the cellular mechanisms of the thick ascending loop of henle?

A

Na +-K +-2Cl− cotransport

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21
Q

What hormones act at the thick ascending limb of the loop of henle?

A

ADH stimulates Na +-K +-2Cl−cotransport

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22
Q

What diuretics act at the thick ascending limb of the loop of henle?

A

Loop diuretics

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23
Q

What is the major function of the early distal tubule?

A

Reabsorption of NaCl without water

Dilution of tubular fluid

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24
Q

What are the cellular mechanisms of the early distal tubule?

A

Na +-Cl −cotransport

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25
Q

What hormones act at the early distal tubule?

A

PTH stimulates Ca 2+reabsorption

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26
Q

What diuretics act at the early distal tubule?

A

Thiazide diuretics

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27
Q

What is the function of the Late Distal Tubule and Collecting Ducts (principal cells)

A

Reabsorption of NaCl

Variable water reabsorption

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28
Q

What are the cellular mechanisms of the late distal tubule and collecting ducts (principle cells)

A

Na +channels (ENaC)

K + channels

AQP2 water channels

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29
Q

What hormones act on the Late Distal Tubule and Collecting Ducts (principal cells)?

A

Aldosterone stimulates Na +reabsorption and K+ secretion

ANP inhibits Na+ reabsorption in collecting duct

30
Q

What diuretics act on the Late Distal Tubule and Collecting Ducts (principal cells)

A

K +-sparing diuretics

31
Q

What is the function of the Late Distal Tubule and Collecting Ducts (α-intercalated cells)?

A

Reabsorption of K +

Secretion of H +

32
Q

What are the cellular mechanisms associated with the Late Distal Tubule and Collecting Ducts (α-intercalated cells)

A

H +-K +ATPase

H + ATPase

33
Q

What hormones act at the Late Distal Tubule and Collecting Ducts (α-intercalated cells)?

A

Aldosterone simulates H+ secretion

34
Q

What diuretic actions happen at the Late Distal Tubule and Collecting Ducts (α-intercalated cells)?

A

K +-sparing diuretics

35
Q

In the early proximal convoluted tubule what is the one countertransport and what does it drive?

A

•Na+-H+ is the one countertransport and drives HCO3- resorption

36
Q

In the early proximal convoluted tubule, how are glucose, AA’s, and HCO3- transported?

A

secondary active transport

37
Q

By the end of the early PCT nearly all of what five compounds has been reabsorbed?

A

•At the end of the early proximal convoluted tubule all glucose, 85% of filtered HCO3-, and most phosphate, lactate, and citrate is reabsorbed

38
Q

The diffusion of Cl- in the late proximal convoluted tubule generates what?

A

a lumen-positive potential difference

39
Q

What is the major regulatory mechanism of the proximal tubule?

A

glomerotubular balance

40
Q

What does glomerotubular balance do? How does it accomplish this?

A

By enacting changes to the filtration fraction and Starling forces (πc) this maintains a constant fractional reabsorption and keeps the balance between filtration and reabsorption

41
Q

What hormone regulates the Na+ reabsorption in the principle cells of the late distal tubule and collecting duct?

A

Aldosterone

42
Q

Water reabsorption in the late distal tubule and collecting duct is variable. How is it controlled?

A

ADH/AVP

43
Q

Where is aldosterone secreted?

A

Zona glomerulosa of the adrenal cortex

44
Q

How does aldosterone act on principle cells?

A

It diffuses into the cell and induces the synthesis of mRNA for proteins involved with Na+ transport.

45
Q

What do K+ sparing diuretics do in principle cells?

A

interfere with Na+ reabsorption

46
Q

What factors promote Na+ reabsorption?

(3)

A

–Activation of renal sympathetic nerves
–Activation of renin/angiotensin system
–Secretion of aldosterone

47
Q

•Factors that promote Na+ excretion:
(3)

A

–Release of atrial, brain natriuretic peptides (ANP, BNP)
–Release of urodilatin
–Intrarenal prostaglandins

48
Q

What factors promote renin secretion?

(3)

A

Sympathetic stimulation

Tubuloglomerular feedback

Intrarenal baroreceptor (wall of afferent arteriole)

49
Q

What causes renal sympathetic stimulation? How does this lead to renin secretion?

A

•due to fall in perfusion pressure through the cardiopulmonary baroreceptors: directly stimulates renin secretion via β1 receptor activation in the JG apparatus

50
Q

How do internal receptors stimulate renin secretion?

A

•Intrarenal baroreceptor (wall of afferent arteriole): afferent arteriolar vasoconstriction –> decreased pressure at granular cells –> increased­ renin secretion

51
Q

What leads to TGF ramping up renin secretion?

A

decreased NaCl delivery to macula densa –> ­ increased renin secretion

52
Q

What effect do loop diuretics have on renin secretion?

A

since effective circulating volume drops due to the diuretics, renin secretion is increased

53
Q

What six things does Ang II stimulate?

A
  1. •Systemic arteriolar constriction
  2. •Renal arteriolar constriction: efferent > afferent.
  3. •Na+ reabsorption: PCT (via ↑ Na-H exchanger activity) > TAL, CCD (can result in a contraction alkalosis
  4. •Thirst
  5. •ADH secretion from posterior pituitary
  6. •Aldosterone secretion from adrenal cortex
54
Q

What are the renal effects of Ang II

A
55
Q

Outline the Response of renin/angiotensin mechanism to decreased ECF volume

A
56
Q

What three things does aldosterone do in the late distal convoluted tubule and collecting duct (principle cells)?

A
  • Stimulates sodium reabsorption
  • Stimulates potassium secretion
  • Stimulates H+ secretion (↑ H +-ATPase activity in intercalated cells of CCD)
57
Q

•What would happen to K & H excretion in a patient with hyperaldosteronism?

A

excretion of both would increase

58
Q

What are 6 actions of ANP?

A
  1. •ANP increases GFR: Afferent arteriolar dilation, efferent arteriolar constriction
  2. •ANP inhibits Na+ reabsorption in medullary collecting duct
  3. •ANP suppresses renin secretion
  4. •ANP suppresses aldosterone secretion
  5. •ANP is a systemic vasodilator
  6. •ANP suppresses AVP secretion, actions
59
Q

Outline the ANP response to increased ECF volume

A
60
Q

Where, and due to what, is urodilatin secreted?

A

•Secreted by DCT, collecting duct in response to increased arterial pressure and ECF volume

61
Q

What does Urodilatin do? What does it specifically not do?

A
  • Urodilatin suppresses Na+ and water reabsorption by medullary collecting duct
  • Unlike ANP and BNP, urodilatin has no effect on systemic circulation
62
Q

What effect do intrarenal prostaglandins (PGE2) have on Na+ in the kidney? How do they effect this?

A

They increase Na+ excretion

By…
•Increase GFR by dilating renal arterioles
•Suppress Na+ reabsorption in thick ascending limb, cortical collecting duct-

63
Q

What are the (3) actions of ADH?

A
  1. increases permeability of late distal tubule and collecting duct to water (via the insertion of aquaporins)
  2. Increases the activity of na+-K+-2Cl- cotransporter
  3. Increases urea permeability in the inner medullary collecting ducts
64
Q

Where is AVP synthesized?

A

Hypothalamus

65
Q

What are the two major stimuli for ADH release?

A

Hyperosmolality

Volume depletion

66
Q

Which are more important - hypothalamic osmoreceptors or hepatic osmoreceptors?

A

hypothalamic

67
Q

What are the sensors of plasma osmolarity? How do they effect change?

What is affected?

A

hypothalamic receptors

ADH and thirst

Urine osmolarity and water intake are affected

68
Q

What sensors regulate volume?

A

Macula densa

afferent arterioles

atria

carotid sinus

69
Q

What do the volume regulating sensors sense?

A

Adequate tissue perfusion

70
Q

How do the volume regulating sensors enact change? What does this lead to?

A

RAAS; ANP; NE ADH

Urinary sodium; Thirst

71
Q

What are the 6 neurohumoral factors controlling Na+ reabsorption?

A
  1. •sympathetic activity,
  2. angiotensin II,
  3. aldosterone,
  4. ANP,
  5. BNP,
  6. urodilatin
72
Q

What factors control AVP secretion?

A

Osmolality

Blood pressure

Renal I (11 decks)

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