Regulation of Extracellular Sodium and H2O Flashcards
loss or gain in ECF sodium cause ___ changes in ECF volume compared to sodium concentration
greater changes because sodium is major osmotic substance in ECF and ECF is in osmotic equilibrium with larger compartment, cells
eat salty fluid
water flow from cells to ECF
incr osmolarity of cellular compartment to equilibrate
incr [NaCl] < incr ECF volume
flow of water from cells
to ECF –> effect on ECF and ICF volume?
because ICF 2x larger than ECF, flow of water from cells changes ECF more quickly (no change in cell osmolarity only change in ECF volume)
with a 10% addition of salt mass to ECF how does ECF volume and ECF sodium concentration change and compare to ICF
ECF volume incr 6.7%
ICF volume decr 3.3%
final ECF sodium concentration incr 3.3% (half the change in volume)
Due to the two-fold greater volume of the ICF over the ECF compartment, gains (or losses) of sodium from the ECF result in ___
Therefore, sensors of sodium regulation monitor changes to ___ not ___
two-fold greater changes in ECF volume than they do in ECF sodium concentration
changes to ECF volume (blood pressure) not sodium concentration (mean arterial pressure)
mechanism of how a decrease in MAP increases plasma aldosterone
1) loss of ECF Na+
2) shift water from ECF to cells
3) decr ECF volume, decr MAP
4) incr baroreceptor reflexes (arterial + intrarenal)
5) incr renin, incr angiotensin II
6) incr aldosterone synth/secretion in adrenal cortex
7) incr Na+ reabs in distal tubule and collecting duct
8) incr Na+ in ECF
Mechanism of ADH release with severe sweating
1) Severe sweating
2) decr ECF volume, decr LA filling pressure, incr baroreceptor flex to hypothalamus,
3) incr ECF osmolarity, incr activ of hypothalamic osmoreceptors
4) incr activ of ADH neurons, incr release of ADH from post pituitary, incr water reabs in DT/CD, more water into ECF
which is more important change in ECF volume or ECF osmolarity
change in ECF volume because affects LA filling pressure and atrial distension is better indicator of circulating volume
How does severe sweating affect ECF osmolarity
normal sweat = HYPOTONIC
so lose hypotonic fluid and ECF becomes hypertonic
What happens acutely with severe diarrhea
1) initial isotonic loss of 3 L ECF volume
2) incr activ of low volume path (LA filling pressure, baroreceptors)
3) incr ADH secretion
What happens when treat acute diarrhea with fluids?
1) ingest 2L of pure fluid so still ECF deficit of 1 L
2) activate volume stim for incr ADH secretion
3) and replace with pure not isotonic
4) inhib osmotic pathway for ADH secretion –> decr ADH levels fall
IF ECF volume is constant ~15L how does changes in ECF osmolarity affect ADH levels
IF normal osmolarity, how does changes in ECF volume affect ADH
1) ADH incr linearly
2) ADH constant except when ECF volume falls severely
acute diarrhea = ECF volume decr, massive ADH secretion
after drink 2L of water, volume change is less so no stim for ADH
decr osmolarity after 2L, inhibitory to osmotic pathway and ADH low, urine excretion high
ECF water regulation is primary an osmoregulatory system with an emergency low volume override
this means
incr osmolarity with hypovolemia >10% VOLUME LOSS, incr ADH
therefore, circulation is DEFENDED AT ALL CONSTS WITH SEVERE HYPOVOLEMIA
Effect of ANP
1) incr ECF volume
2) incr atria distention
3) release ANP granules
4) incr urine output
Key effects of ANP
1) decr secretion and effect of ADH on tubules
2) blocks aldosterone synthesis and action on tubules
3) incr GFR
4) incr water and Na+ excretion
