Lecture 10- Regulation Of Sodium Balance Flashcards
What determines the size of the extracellular fluid volume
Sodium balance
What determines the amount of sodium excreted
GFR controls the filtered sodium which controls excreted sodium
Glomerulotubular balance
System where the rate of sodium resorption increases and decreases with increases and decreases in GFR
How does the glomerulotubular balance work?
Couple of hypothesis:
Possible link between organic solutes and sodium i.e. Increased GFR results in increased organic solutes and therefor increased sodium resorption
Peritubular capillary starling forces
Describe how starling forces influence fluid and sodium flow among the peritubular capillaries
Increased GFR leads to less water leaving glomerular capillaries and entering peritubular capillaries. This increases oncotic pressure and decreases hydrostatic pressure in peritubular capillaries. This makes fluid (and therefore sodium) enter the interstitium and peritubular capillaries.
Action of aldosterone
Released from adrenal glands
Increases Na resorption in distal tubule and collecting duct
Mechanism of aldosterone
Combines with a cystolic receptor and forms a complex.
This complex is translocated to the nucleus and activates mRNA
The mRNA codes for possible formation of a protein that increases permeability of luminal border to sodium, an increased quantity of Na/K ATPase, or an increased amount of ATP for the ATPase
How is aldosterone release regulated
Low sodium
Increased potassium
Increased plasma angiotensin II
ACTH
increases aldosterone release
Describe the renin-angiotensin-aldosterone system
Angiotensinogen is released from the liver and converted into angiotensin I using renin
Angiotensin I is converted into angiotensin II and III using enzyme from the lungs.
Angiotensin II induces aldosterone production from the renal gland
What regulates renin release?
Afferent arteriole baroreceptors detect ECF volume
Macula densa detects decreased NaCl
Sympathetic nervous system increases renin release by decreasing renal blood flow
Atrial natriuretic peptide
Released from atria in response to increased ECF volume
Increases Na excretion by increasing GFR, inhibiting Na resorption, and inhibiting renin/aldosterone
Mainly responds to increased sodium or volume load rather than regulating balance under normal conditions
How does lasix (furosemide) work
It is a loop diuretic
Inhibits sodium reabsorption in thick ascending limb
So more sodium is delivered to distal tubule and the urine is not diluted
Less sodium is transported to medulla, so the concentration gradient is reduced and less water is reabsorbed in the collecting duct
End result is diuresis and natriuresis
How does thiazides work
Inhibits Na-Cl cotransporter in distal tubule
More sodium and water is delivered to collecting ducts and diuresis/natriuresis occurs
How does potassium-sparing diuretics work
Examples= amiloride and spironolactone
Blocks sodium channels preventing reabsorption of sodium (amiloride)
Blocks aldosterone receptor (spironolactone)
