Phsyiology 5 Renal Handling of Sodium Flashcards
Glomerulotubular Balance
the porximal tubule usually reabsorbs a constant fraction (65%) of the filtered load of Na and water. CONSTANT FRACTIONAL REABSORPTION
How do changed in GFR or plasma Na levels change filtered load of sodium
If we increase filtration we get mor ein the tubule and 65% of that gets absorbed. If we are filtering more than a larger amount gets absorbed (always 65% of what is filtered- gets absorbed in teh proximal tubule) Parallel changes in the filtered load of sodium resulting in changes in Na and water excretion ( Na reabsoption is LOAD DEPENDENT)
what is the fractional reabsorption of sodium in the loop of henle
20% (Note: variable depending on if its cortical or juxtamedullary- cortical is shorter and wont absorb as much )
What is the fractional reabsorption of sodium in the distal nephron
15%
Why is Na reabsorption “load dependent”
1.) Proportional changes in the filtered load of solutes that are coupled to Na reabsorption (eg: more Cl-, glucose, phosphate, and amino acids) 2.) Changes in GFR (filtration fraction) cause parallel changes in plasma oncotic pressure (plasma proteins become more concentrated becase we are filtering more) which influences the reabsorptive capacity of the peritubular capillaries
load dependent Na movement: Increases in filtered sodim
increases in the amount of Na reabsorbed (eventhough its still the same %) and the amount left in the tubule is greater (because there was more filtered) leading to increased Na excretion
load dependent Na movement: Decreases in filtered sodim
decreases the actual amount of Na reabsorbed (same %) and the amount left in the tubule will be less (because there was less to start) leading to decreased Na excretion
why is load dependent Na movement important
Buffers moment to moment changes in GFR to ensure constant fractional reabsorption of sodium (think of it like autoregulation for sodium)
what is the fractional reabsorption of sodium in the collecting ducts
5% - highly variable depending on volume status, flow, and ALDOSERONE LEVELS
What percentage of filtered sodium normally gets excreted?
0.6% (varies with dietary intake) Reabsorb about 99.4% of the filtered load of sodium
relationship between sodium excretiona and intake at steady state
urinary Na excretion = Na intake
what is the most abundant solute in the ultrafiltrate
Sodium
What drives the intracellular Na gradient for Na coupled cotransport
Na-K-ATPase. Na reabsorption is coupled to the reabsorption of almost all other solutes and water (reduction in Na reabsorption decreases the reabsorption of almost all other solutes)
Water reabsorption
Water follows solute movement if isotonic proportions (you move as much water as solute - ex: of you move from a hypotonic solution it will stay hypotonic because you have moved the same amount of solute as water)
what do we mean when we say water follows soulute in isotonic proportions
We move equal amounts of solute and water (because water follows solute) Ex: if we were moving out of a hypertonic solution the solution would remain hypertonic because we have moved equal amounts of solute and water)
Sodium Reabsorption in the Prximal tubule
1.) Na-K-ATPase 2.) Uniport (passive via Na channels) 3.) Na-H counter transport (Na-H exchanged) 4.) Co-transport: Na- glucose (SGLT) 2Na-Phosphate, Na-Aminoacid)
NaCl coupled transport: Cl-OH
Parallel operation of the Na-H and Cl-OH exchangers = net effect of absorption of NaCl from the tubular lumen and secretion of water
NaCl coupled transport: Cl-formate
net effect of reabsorbing NaCl and recycling formate throuh the formation of the nonionized form in the tubular lumne that is allowed to diffuse back into the cell to start the cycke again (also seen with lactate, urea, and other weak organic acids
Cl driven Na reabsorption
other anions are reabsorbed with NA preferentially in the early proximal tubule so the tubular lumen [Cl] increases and a favorable concentration gradient developsfor the reabsorption of Cl. Cl moves down its gradient and Na moves wiith it (and water) accounts fo r30% of Na reabsorption in distal proximal tubule
Tonicity of the fluid leaving the proximal tubule
ISOTONIC- the concntration of Na doesn’t change (65% of the filtered Na and water is reabsorbed)
Reabsorption in the Proximal Tubule
1.) 65% of Na and water 2.) Most of the glucose, HCO3-, AAs, and phosphate, increase in [Cl] due to the reabsorption of other anions
Reabsorption in the decending limb of the loop of henle
Descending limb of the loop of henle is permeable to water and IMPERMEABLE To solutes = water leaves (gets reabsorbed) and tubular fluid osmolarity increases
Reabsorption in the ascending limb
the thin ascending limb is IMPERMEABLE to water but permeable to solutes = passive diffusion of NaCl (out- into the medillary interstitium to help the decending loop draw mor ewater out) and urea (in) Tubular fluid becomes progressively more dilute
Reabsorption of NaCl in the thick ascending limb
IMPERMEABLE to water. Na-K-2Cl pump (Na absorbed down its gradient abd brings K and 2Cl with it ) Net NaCl absorption. K gets gets recycled and creates a lumen positive potential that promotes the reabsorption of Na, Ca, and Mg via the paracellular route. Fluid becomes more dilute (becomes hypotonic)
NaCl reabsorption in the thick ascending limb (what stimulates it, what inhibits it)
Stimulated by aldosterone and ADH. Inhibited by loop diuretics. Stimulation and inhibition of the Na-K-2Cl pump
Where do loop diuretics work
Block the reabsorption of solute by inhibiting the Na-K-2Cl pump - If you do not reabsorb Na it will stay in the tubule and get excreted in the urine
Reabsorption in the early distal tubule
IMPEREABLE to water at all times and Na and Cl are reabsorbed (tubular fultrate continuesto become more hypotonic. Na-Cl cotransporter in the luminal membrane that can be blocked by thiazide diuretics. The distal tubule is IMPORTANT IN CA REABSORPTION)
The diluting segment (what is included, what is its function)
Thin ascending limb, thick ascending limb, distal tubule. Creates and osmotic gradient that sets us up to reabsorb water
Reabsorption in the principle cells (collecting ducts)
1.) Na and K channels (passive movement) 2.) NaK-ATPase (Na reabsorbtion is coupled to K secretion) Rapid Na entry procuces a lumen negative potential that promotes the secretion of K and Cl reabsorption (via paracellular pathway)
Role of aldosteromne in priciple cells
1.) Increase Na reabsorption 2.) Increase K secretion 3.) Increase Cl- reabsorption 4.) Increase H secretion
Reabsorption fo NaCl in the medullary capillary ducts
Medullary collecting duct functions parallel to the cortical collecting tubule. 1.) Aldosterone sensitive (Na and Cl reabsorption, K and H secretion) 2.) ADH sensitive (reabsorption of free water) 3.) ANP, BNP and urodilin sensitive (inhibit Na reabsorption and inhibit water reabsorption)
Coupling NaCl reabsorption with reabsorption and secretion of water and other solutes
1.) Direct carrier coupling between Na and other solutes 2.) WATER FOLLOWS THE REABORPTION OF WATER BY OSMOSIS 3.) Reabsorption of Na and water generates favorable concentration gradients for passive reabsorption of other solutes (Cl, urea, K) 4.) in collecting ducts Na reabsorption approximately = to (H +K secretion) + Cl reabsorption 5.) Blocking Na reabsorption results in diuresis (water stays in teh system and you pee it out) 6.) If Na reabsorptio is blocked almost all renal reabsorption ceases
General: Na movement in the proximal tubule
Na coupled co transport (Na-Solutes; Na-H), Cl dirvien Na reabsorption
General: Na movement in the loop of henle
passive diffusion and Na-K-2Cl
General: Na movement in the distal tubule
Na-Cl co transport
General: Na movement in the collecting ducts
Na channels
