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Renal > Sodium Balance > Flashcards

Sodium Balance Flashcards

1
Q

A chronic positive sodium balance (i.e. net increase in total body sodium) will normally cause which of the following?

a. Suppression of vasopressin secretion
b. An increase in renin secretion
c. Hypernatremia
d. Weight loss

A

a. Suppression of vasopressin secretion
This answer requires information shared during the water balance lecture (see Fig. 9 of that LG). Blood pressure is a major non-osmotic stimulus for vasopressin release by the posterior pituitary gland. Higher blood pressure is associated with attenuation of vasopressin secretion.

b. An increase in renin secretion
Positive Na balance will cause expanded extracellular fluid volume, which will be associated with lower renin secretion. c. Hypernatremia
Changes in Na balance are reflected in ECF volume, not the concentration of Na in plasma (this reflects the state of water balance).
d. Weight loss
Positive Na balance will be associated with ECF volume expansion and weight gain. We assume that positive Na balance evokes thirst and greater water intake to preserve normal ECF osmolality.

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2
Q

Which of the following physiological parameters is NOT affected by the regulation of renal sodium excretion?

a. Plasma volume
b. Interstitial volume
c. Arterial blood pressure
d. Plasma sodium concentration
e. Cardiac output

A

d. Plasma sodium concentration
Regulating renal Na excretion will impact ECF volume, not the concentration of Na in blood. We assume that positive Na balance evokes thirst and greater water intake to preserve normal ECF osmolality.

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3
Q

A 70 year old woman with chronically impaired kidney function develops swollen feet and ankles (edema) and a blood pressure of 180/100 (elevated). Which statement best explains the edema and hypertension?

a. the patient has been standing too much and is overly anxious
b. she has expansion of total body water
c. she has hypoosmolality of extracellular fluid
d. she has increased interstitial fluid and plasma volume
e. her probably has proteinuria that is causing inflammation of peripheral capillary beds

A

d - increased interstitial fluid and plasma volume

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4
Q

Addition of sodium, broadly speaking, triggers what two responses?

A
  1. increased water intake (thirst)

2. water conservation by decreased excretion (ADH)

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5
Q

Why does adding or removing water alone have a minimal effect in the setting of increased sodium load have a minimal effect on total ECF volume?

A

water is distributed throughout the body (i.e. mostly ICF)

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6
Q

What is the sensor for osmoregulation?

A

hypothalamic osmoreceptors

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7
Q

in osmoregulation, what is the sensed variable?

A

plasma osmolality

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8
Q

in osmoregulation, what are the effectors?

A

thirst

ADH

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9
Q

in osmoregulation, what is the controlled variable?

A

water excretion and intake

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10
Q

In volume regulation, what is the sensed variable/

A

effective ECF volume

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11
Q

in volume regulation, what is the sensor?

A

volume sensors, baroreceptors, and macula densa

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12
Q

in volume regulation what is the effector?

A

RAAS
sympathoadrenal
TGF

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13
Q

what is the controlled variable in volume regulation?

A

renal Na excretion

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14
Q

What are the two main determinants of blood pressure that can be controlled to maintain adequate volume?

A

CO (i.e. SV i.e. plasma volume) and vascular resistance

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15
Q

Initially following increased Na intake, what is the response?

A

an increase in ECF volume, followed by proportional increase in urinary Na excretion

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16
Q

Why is the increase in ECF volume transitory in response to an acute increase in Na intake?

A

The rise in ECF volume in this situation occurs because of a transient elevation in plasma osmolality that stimulates thirst (increased water intake) and drives increased renal water reabsorption (reduced water excretion).

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17
Q

How long does the renal response to an abrupt dietary change in Na take?

A

1-2 days

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18
Q

How are abrupt changes in ECF volume detected?

A

changes in body weight

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19
Q

What is the main determinant of sodium excretion?

A

renin system

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20
Q

Where is renin synthesized and secreted?

A

granular cells of the afferent arteriole wall

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21
Q

Beta 1 adrenergic stimulation, input from the macula densa, and prostaglandins can all cause what response?

A

renin secretion to control NA

22
Q

What is the role of AII in Na balance?

A

direct stimulation of Na/H exchange in the PT increases Na reabsorption

indirectly, it also stimulates aldosterone secretion and constricts efferent arteriole , which increase filtration and therefore reabsorption.

23
Q

What inhibits renin release?

A

Angiotensin II via negative feedback loop

24
Q

Which nerves carry volume sensors to the brain?

A

cranial nerves Ix and X to hypothalamus and medulla

25
Q

What is the response to increased stretch due to volume sensation in the atria, ventricles and Pa?

A

selective inhibition of renal sympathetic nerve activity, reducing renin secretion

26
Q

Where are volume sensors located?

A

atria, ventricles and pulmonary artery

27
Q

where are arterial baroreceptors located?

A

carotid arteries and afferent arteriole of the kidney

28
Q

What effect does carotid artery stretch have on Na excretion?

A

increases it

29
Q

What effect does release of ANP have? Where?

A

increased Na excretion rate by blocking IMCD Na reabsorption

30
Q

WHich ion is sensed by the macula densa?

A

chloride

31
Q

What transporter is involved in sensation of chloride flow by the macula densa/

A

Na/K/2Cl

32
Q

WHat effect does a decrease in Cl delivery to the macula densa have?

A

increased renin release by granular cells

33
Q

What are the two mechanisms of sympathoadrenal control of Na reabsorption?

A

a direct effect on the proximal tubule to increase Na/H exchange, and direct stimulation of renin release.

34
Q

In orthostatic hypotension, what can be administered to treat low ECF volume?

A

synthetic mineralocorticoids like fludrocortisone

35
Q

Ingestion of licorice can cause what problem if consumed in large amounts?

A

Glycyrrhetinic acid, a compound found in natural licorice (not the “twizzler” type) has mild mineralocorticoid activity and can cause hypertension with hypokalemia (resembling an aldosterone-secreting tumor) if ingested in large quantities chronically.

36
Q

Define aldosterone escape

A

Chronic administration of aldosterone causes a substantial decrement in urinary Na+ excretion only for a few days, then Na+ excretion becomes normal again (but ECF volume expansion persists).

37
Q

What is the mechanism for aldosterone escape?

A

decreased proximal tubular Na+ reabsorption during ECF volume expansion. The excess filtered Na+ that is not reabsorbed by the proximal tubule overwhelms the reabsorptive capacity of the more distal nephron segments.

38
Q

When is adenosine produced by the macula densa cells?

A

Adenosine is produced by the macula densa cells during periods of high Na+ transport (probably as a by-product of ATP utilization by the Na/K-ATPase).

39
Q

What receptors do adenosine bind to increase vasoconstriction?

A

A1 receptors in afferent arteriole

40
Q

How does adenosine participate in TGF?

A

Adenosine, acting through A1-receptors, may modulate renin secretion and causes vasoconstriction of the afferent arteriole. The latter function may help to limit glomerular filtration when the macula densa senses high Na+ delivery (tubuloglomerular feedback).

41
Q

Define glomerulotubular balance

A

AII constriction of the efferent glomerular arteriole will cause an increase in the filtration fraction and consequently will raise the oncotic pressure (and decrease the hydrostatic pressure) gradient in the peritubular capillaries. This in turn increases the driving force for reabsorption of fluid in the proximal tubule

42
Q

Which of the following inherited disorders in sodium reabsorption are associated with hypertension?

  • Gordon
  • Liddle
  • glucocorticoid remediable aldosteronism
  • apparent mineralocorticoid excess
  • Bartter syndrome
  • Gitelman syndrome
  • pseuhypoaldosteronism I
A
  • Gordon
  • Liddle
  • glucocorticoid remediable aldosteronism
  • apparent mineralocorticoid excess
43
Q

Which of the following inherited disorders in sodium reabsorption are associated with hypotension?

  • Gordon
  • Liddle
  • glucocorticoid remediable aldosteronism
  • apparent mineralocorticoid excess
  • Bartter syndrome
  • Gitelman syndrome
  • pseuhypoaldosteronism I
A
  • Bartter syndrome
  • Gitelman syndrome
  • pseuhypoaldosteronism I
44
Q

In Bartter syndrome, which nephron segment is affected?

A

loop of henle

hypotensive

45
Q

In Gitelman syndrome, which nephron segment is affected?

A

distal convoluted tubule

46
Q

in pseudohypoaldosteronism I, which nephron segment is affected?

A

collecting duct

47
Q

in Gordon syndrome, which nephron segment is affected?

A

distal convoluted tubule

48
Q

in Liddle syndrome, which nephron segment is affected?

A

collecting duct

49
Q

in glucocorticoid remediable aldosteronism, which nephron segment is affected?

A

collecting duct

50
Q

In apparent mineralocorticoid excess, which nephron segment is affected?

A

collecting duct

Renal (28 decks)

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