Sodium Balance and Transport Flashcards
Where in the nephron does the hormonal fine tuning of Na+ reabsorption happen?
The collecting duct.
The PT and medullary thick ascending limb are going to reabsorb the vast majority of it no matter what.
In the first 3rd of the proximal tubule (PT), sodium is preferentially reabsorbed with which solutes?
Exchange with H+, and cotransport with glucose and amino acids.
(Bicarb happens further along, and Cl- not as much in the PT)
Where in the PT is most Cl- reabsorbed?
How does absorption in the early PT contrast from that in late PT?
More Cl- absorbed in the late PT.
Early PT: paracellular.
Late PT: transcellular
Review: What ion channel is the major player in Na+ reabsorption in the thick ascending limb?
What drug inhibits this?
NKCC2
Furosemide.
Review: What ion channel is the major player in Na+ reabsorption in the DCT?
What drugs inhibits this?
Na+/Cl- cotransporter.
Thiazide diuretics inhibit this.
Review: What molecule is the major player in Na+ reabsorption in the collecting duct?
What’s a drug inhibits this?
ENaC
Amelioride inhibits it.
How does Cl- reabsorption vary between areas of the collecting tubule with Principal Cells and areas with Intercalated Cells?
It’s paracellular between Principals Cells.
Intercalated cells have Cl-/HCO3- exchangers that bring Cl- in transcellularly.
4 responses to low effective circulating volume?
Activation of RAAS.
Sympathetic activation (including increased Na+ reabsorption).
Vasopressin release.
Shutting of atrial natriuretic peptide (ANP).
If GFR goes up, does enough Na+ get absorbed?
Yes… the Na+ absorption goes up to compensate.
“glomerulotubular balance”
How is “glomerulotubular balance” achieved?
Basically through pressure changes - with greater GFR, less hydrostatic pressure and more osmolality remains in the efferent arteriole / vasa recta, facilitating absorption.
What effect does AVP have on the thick ascending limb?
It stimulates NKCC2 (the opposite effect of a loop diuretic).
What affect does hypercalcemia have on the thick ascending limb?
High Ca++ hits CaSR (Ca++ sensing receptor)… inhibits NKCC2 (acting like a loop diuretic).
What effects do prostaglandins have on ENaC?
Thus what side effect can NSAIDs have?
Prostaglandins inhibit ENaC.
NSAIDs can thus increase ENaC activity, and in rare cases, cause edema/hyponatremia.
2 things that must be true for you to call something hypovolemia?
Low total body Na+.
Decreased effective circulating blood volume.
3 types of clinical finding seen in hypovolemia?
Orthostasis.
Reduced skin turgor.
Reduced organ perfusion / shock.
(Other things too… like reduced JVP)
