Sodium Balace and Diuretics Flashcards
Amount of Na+ excreted/day
100mEq/mL
Water follows _____ only in the _______ _____
Salt! Proximal tubule!
Coupled reabsorption.
Sodium cotransport coupling
Utilising the concentration gradient to perform secondary active transport of other molecules.
Na+ absorption over the early proximal tubule (3)
Overall absorption
Apical
- SGLT - cotransport of glucose
- NHE - antiport of H+
Basolateral
- Na+ pump
Active reabsorption of glucose in the proximal tubule
Apical 2ndary active with Na+, passive transport across the basolateral membrane (GLUT)
Starling forces into the capillary
Drive fluid movement from the interstitial space.
Greatest contribution from the colloid osmotic (oncotic) pressure of the peritubular blood.
Na+ absorption in the late proximal tubule
Apical:
- NHE
Basolateral
- Na/K ATPase
Paracellular
- Driven by transepithelial [Cl-] gradient (higher in lumen, want to flow to blood, sodium follows)
Na+ in the ascending loop of henle (25%)
Apical
- NKCC: Na, K, Cl cotransporter
Basolateral
- Na/K ATPase
Furosemide (loop diuretic)
Inhibits NKCC in the loop of henle to inhibit sodium reabsorption to favour higher urine volume.
Na+ absorption in the early distal tubule (5%)
Apical:
- NCC (Na, Cl cotransporter)
Basolateral:
- Na/K ATPase
Thiazide diuretics
Inhibits NCC in distale tubule
Decreases Na reabsorption
Na absorption in the late distal tubule and the collecting duct (3%)
Apical:
- ENaC (constituitively open Na+ channel)
Basolateral:
- Na/K ATPase
K+ sparing diuretics
Acts on ENaC (inhibitory) to decrease Na reabsorption, subsequently K secretion decreases.
in late distal tubule and collecting duct
Increase in sodium on blood pressure
Osmolarity increases in blood, renal system adjusts within an hour by retaining water. Water retention decreases osmolarity but increases blood volume, blood pressure.
Higher blood pressure indicates more sodium must be excreted.
4 systems in controlling Na+ excretion
SNS, ANP, πc, Renin-angiotensin- aldosterone.
SNS in sodium excretion
Stimulated by change (-) in EFV, modulates afferent arteriolar resistance to change GFR, amount of fluid passing through then determines the amount of sodium available for secretion.
Colloid osmotic pressure in sodium excretion
Isoosmotic reabsorption in the proximal tubule.
If EFV goes up, πc goes down due to concentration dilution, causes lower driving force across to the peritubular capillary, increased sodium secretion.
Renin-angiotensin-aldosterone
Favours sodium reabsorption
ANP
Favours sodium excretion
Angiotensin II effect
On kidneys (indirect) - adrenal gland secretes aldosterone, triggers kidneys
On pituitary - secretion of ADH
Renin origin, stimulated by ____
Released by juxtaglomelular cells, released directly into renal circulation
Stimulated by low pressure in the afferent arteriole, a decrease in EFV.
Decreased EFV, decreased Na, want to absorb more sodium
Angiotensin II effect on kidneys
Acts of AT1 receptors of tubular epithelial cells, increases transport protein activity, increases reabsorption. (N/KA, NHE, NBC)
Aldosterone effect on kidneys
Increases ENaC activity in the collecting duct
Increases expression of ENaC and Na/K ATPase genes
Increases sodium reabsorption.
ANP secretion
From the heart in response to volume expansion (high blood volume, high Na concentration)
Acts antagonistically to the RAA system
