Sodium and Water

Question 1

draw diagram of body fluid distribution

Answer 1

see notes

Question 2

formula to calculate osmolarity

Answer 2

2[Na+] + glucose/18 + [BUN]/2.8

Question 3

increase in osmolarity triggers….

Answer 3

ADH release and thirst

Question 4

JGA senses what? what happens?

Answer 4

change in Na+ flow rates –> stim RAAS

Question 5

Baroreceptors sense what? what happens?

Answer 5

decreased arterial pressure –> stim adrenergic pressure, stim ADH release

Question 6

Atrial stretch receptors sense what? what happens?

Answer 6

volume expansion –> ANP release

Question 7

Action of angiotensin II (3)

Answer 7

1. direct vasoconstrictor (efferent arteriole)
2. increases Na+ and HCO3- reabsorption in proximal tubule
3. stim aldosterone release

Question 8

Action of aldosterone

Answer 8

1. stimulates Na+ channels in the principal cells (CD)

2. stim H+ secretion in intercalated cells

Question 9

ANP

Answer 9

1. direct vasodilator: lowers BP, afferent arteriolar dilation –> increased GFR
2. stim Na+ excretion

Question 10

what is the response to increased ECV?

Answer 10

Na+ diuresis: increased renal blood flow –> less renin

ANP

Question 11

equation to estimate free water deficit

Answer 11

0.6wt[(Na+/140))-1]

Question 12

rate of correction for a given free water deficit

Answer 12

Estimated water deficit/[(desired change in Na+)x2] = cc/hr

Question 13

correction for hyperosmolar hyponatremia

Answer 13

in hyperglycemia: Na+ falls 1.6-4 mEq/L for every 100mg/dL rise in glucose

Question 14

pseudohyponatremia

Answer 14

when lots of lipids are in the serum, get an artificially inflated total sample volume –> hyponatremia

Question 15

how to calculate water excess

Answer 15

0.6weight(([Na+]-140)/140)

Question 16

when is ADH released? name an exception

Answer 16

when osmolarity increases

except, decreased ECV overrides osmolar control –> sim ADH to maintain BP

Question 17

when do you get low ADH hyponatremia?

Answer 17

1. renal failure - water intake exceeds excretion as GFR falls
2. primary polydipsia - excessive intake exceeds excretion
3. beer potomania/”tea and toast” - take in lots of fluid but not enough osmoles to excrete large volumes of water

Question 18

types of high ADH hyponatremia

Answer 18

1. decreased ECV: volume depletion, diuretics, CHF, etc.
2. reset osmostat
3. SIADH

Question 19

reset osmostat

Answer 19

some pts have a lower ADH set point than normal
no other abnormalities other than low [Na+]
no tx needed

Question 20

causes of euvolemic hyponatremia

Answer 20

1. SIADH
2. hypothyroidism
3. hypoadrenalism

Question 21

osmotic demyelination

Answer 21

stroke-like syndrome of neurological deficits associated with overly rapid correction of hyponatremia

Question 22

V2 antagonists - what do they do, when to use

Answer 22

block ADH action

useful for elevated ADH (SIADH, CHF, cirrhosis)

Question 23

tx for SIADH

Answer 23

fluid restrict asymptomatic pts
hyperosmotic saline for symptomatic or severe
DO NOT GIVE NS

Question 24

how to calculate FENa

Answer 24

FENa= (UnaScr)/(SnaUcr)

Question 25

draw a diagram of the whole nephron!

Answer 25

see notes