SM_196a: Sodium Balance and Control of Extracellular Fluid Volume

Question 1

BP = ___ * ___

Answer 1

BP = CO * TPR

Question 2

You would have to have a _____ loss of water to affect BP because _____

Answer 2

You would have to have an extreme loss of water to affect BP because only a tiny fraction of water is in the extracellular fluid

Question 3

When you take in a lot of Na⁺, extracellular osmolality _____, so you _____ and _____

Answer 3

When you take in a lot of Na⁺, extracellular osmolality increases, so you drink more water and decrease water secretion

Question 4

Disorders involving excess total body Na⁺ include _____ and _____

Answer 4

Disorders involving excess total body Na⁺​ include hypertension and edema

Question 5

Disorders involving deficit of total body Na⁺ include _____

Answer 5

Disorders involving deficit of total body Na⁺​ include hypotension

Question 6

Describe the difference between osmoregulation and volume regulation

Answer 6

Question 7

Most Na⁺ is reabsorbed in the _____ and then the _____

Answer 7

Most Na⁺ is reabsorbed in the proximal tubule and then the thick ascending limb of loop of Henle

Question 8

Decreasing ECF volume _____ renal perfusion, which _____ GFR

Answer 8

Decreasing ECF volume decreases renal perfusion, which decreases GFR

Question 9

If GFR decreases, physiological compensation involves _____ and _____

Answer 9

If GFR decreases, physiological compensation involves restoration of GFR and decreased urinary Na⁺ secretion

Question 10

Describe physiological responses to volume depletion

Answer 10

Physiological responses to volume depletion

• Stimulation of volume sensors
• Increased renal sympathetic activity
• Decreased right atrial stretch
• Decreased RBF / GFR
• Decreased solute delivery to macula densa
• Actions of angiotesin II

Question 11

Increased renal sympathetic activity in response to volume depletion involves _____ and _____

Answer 11

Increased renal sympathetic activity in response to volume depletion involves renin release (beta-1 adrenergic) and increased proximal Na⁺ transport (alpha-1 adrenergic)

Question 12

Decreased right atrial stretch in response to volume depletion involves _____ and _____

Answer 12

Decreased right atrial stretch in response to volume depletion involves decreased ANF released and decreased inhibition of collecting duct Na⁺ transport

Question 13

Decreased RBF/GFR in response to volume depletion includes _____, _____, and _____

Answer 13

Decreased RBF/GFR in response to volume depletion includes angiotensin II mediated constriction of efferent arteriole, increased oncotic pressure in peritubular capillaries, and increased driving force for tubular reabsorption (glomerulotubular balance)

Question 14

Decreased solute delivery to macula densa in response to volume depletion involves _____ and _____

Answer 14

Decreased solute delivery to macula densa in response to volume depletion involves stimulation of renin release and dampening of tubuloglomerular feedback (attenuated afferent arteriole vasoconstriction)

Question 15

Angiotensin II in response to volume depletion involves _____, _____, and _____

Answer 15

Angiotensin II in response to volume depletion involves efferent arteriole vasoconstriction, increased proximal Na⁺ reabsorption by stimulation of Na⁺/H⁺ exchanger, and stimulation of adrenal aldosterone secretion and increased collecting duct Na⁺ reabsorption

Question 16

Describe regulation of GFR in volume depletion

Answer 16

Regulation of GFR in volume depletion

1. RBF falls in volume depletion
2. Hydrostatic pressure falls
3. GFR falls
4. NaCl delivery to macula densa falls
5. Tubuloglomerular feedback dampened and renin release triggered
6. Afferent arteriole vasodilates and efferent arteriole vasoconstricts

Question 17

In volume depletion, net filtration ______, and driving force for reabsorption is ______ in peritubular capillaries

Answer 17

In volume depletion, net filtration increased, and driving force for reabsorption is enhanced in peritubular capillaries

(oncotic pressure rises to a level higher than it was before)

Question 18

Describe glucocorticoid-remediable aldosteronism

Answer 18

Glucocorticoid-remediable aldosteronism

• Autosomal dominant
• Early onset
• Severe HTN (strokes, suppressible by glucocorticoids)
• Unequal crossing over event leads to chimeric gene between Aldo synthetase and 11-beta-hydroxylase
• Aldosterone elevated without control

Question 19

In glucocorticoid-remediable aldosteronism, _____ is markedly elevated, but _____ can be used to treat via feedback inhibition

Answer 19

In glucocorticoid-remediable aldosteronism, aldosterone markedly elevated, but ACTH can be used to treat via feedback inhibition

Question 20

Describe apparent mineralocorticoid excess

Answer 20

Apparent mineralocorticoid excess

• Autosomal recessive
• Mutations in 11-beta-hydroxysteroid dehydrogenase -> cannot convert cortisol to less active cortisol -> more cortisol acts on the receptor
• Plasma aldosterone unmeasurable
• Treat by blocking Na⁺ reabsorption and interfering with interaction of cortisol with receptor

Question 21

Describe Liddle syndrome

Answer 21

Liddle syndrome

• Autosomal dominant
• Leads to stroke
• Activating mutations in ENaC -> increased Na⁺ reabsorption -> HTN
• Plasma aldosterone unmeasurable

Question 22

Describe pseudohypoaldosteronism I

Answer 22

Pseudohypoaldosteronism I

• Loss of function mutations in ENaC -> decreased Na⁺ -> hypotension

Question 23

_____ is the opposite of Liddle syndrome

Answer 23

Pseudohypoaldosteronism I is the opposite of Liddle syndrome

Question 24

Describe Bartter syndrome

Answer 24

Bartter syndrome

• Loss of function mutations in NKCC2, ROMK, CLCNKB, or Barttin
• Cl^- low (Cl^- lost)

Question 25

Describe Gitelman syndrome

Answer 25

Gitelman syndrome

• Loss of function mutation in NCCT
• Mimics chronic treatment with thiazide
• Conditions favoring reabsorption of Na⁺ limit reabsorption of Ca²⁺