Control of Sodium and Water Excretion Flashcards
How do baroreceptors affect GFR and Na reabsorption?
Low total-body sodium -> low CV pressure ->activated baroreceptors -> causes decreased GFR and increased sodium reabsorption
Net effect is to decrease Na excretion, retaining Na in the body
How does sweating or diarrhea affect plasma protein concentration?
Fluid loss decreases plasma volume, increasing oncotic pressure
This decreases GFR
How does increased sodium intake affect plasma protein concentration?
Increased plasma volume, causes decreased protein concentration
Results in lower oncotic pressure, and increased GFR
How does hemorrhage affect plasma protein concentration?
Net movement of interstitial fluid to the vascular compartment decreases plasma protein concentration
However, sympathetics are also activated, causing afferent arteriole constriction
Glomerular-capillary pressure fall > oncotic pressure fall results in decreased GFR during hemorrhage
What is glomerulotubular balance?
A change in GFR automatically induces a proportional change in the reabsorption of sodium by the PTs
What is the role of aldosterone?
Stimulates sodium reabsorption mainly in the principal cells of the CD
Controls the reabsorption of about 2% of the filtered load
Increases activity/number of luminal membrane sodium channels and BL membrane Na,K pumps
How does renal interstitial hydrostatic pressure affect sodium and water reabsorption?
Increased RIHP - decreased reabsorption and vice versa
How does Ang II affect sodium reabsorption?
Indirect - increased aldosterone secretion, decreased RIHP
Direct - tubular cells
What is pressure natriuresis?
When renal arterial pressure increases the kidneys show a marked and rapid increase in sodium excretion with only little change in GFR
What are the affects of atrial natriuretic peptide?
Acts on inner medullary CDs to decrease sodium reabsorption
Decreases renin secretion from granular cells
Causes afferent arteriole dilation and efferent arteriole constriction
Dilation of mesangial cells
What is the effect of ADH?
Increase permeability of the cortical and meduallry CDs to water
Increase sodium reabsorption by Cd
Describe osmoreceptor control of ADH secretion.
Hypothalmic cells that secrete ADH receive neural input from hypothalamic and hepatic osmoreceptors
Increase in osmolarity -> stimulates osmoreceptors -> increases ADH secretion
