Phsyiology 5 Renal Handling of Sodium

Question 1

Glomerulotubular Balance

Answer 1

the porximal tubule usually reabsorbs a constant fraction (65%) of the filtered load of Na and water. CONSTANT FRACTIONAL REABSORPTION

Question 2

How do changed in GFR or plasma Na levels change filtered load of sodium

Answer 2

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)

Question 3

what is the fractional reabsorption of sodium in the loop of henle

Answer 3

20% (Note: variable depending on if its cortical or juxtamedullary- cortical is shorter and wont absorb as much )

Question 4

What is the fractional reabsorption of sodium in the distal nephron

Answer 4

15%

Question 5

Why is Na reabsorption “load dependent”

Answer 5

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

Question 6

load dependent Na movement: Increases in filtered sodim

Answer 6

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

Question 7

load dependent Na movement: Decreases in filtered sodim

Answer 7

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

Question 8

why is load dependent Na movement important

Answer 8

Buffers moment to moment changes in GFR to ensure constant fractional reabsorption of sodium (think of it like autoregulation for sodium)

Question 9

what is the fractional reabsorption of sodium in the collecting ducts

Answer 9

5% - highly variable depending on volume status, flow, and ALDOSERONE LEVELS

Question 10

What percentage of filtered sodium normally gets excreted?

Answer 10

0.6% (varies with dietary intake) Reabsorb about 99.4% of the filtered load of sodium

Question 11

relationship between sodium excretiona and intake at steady state

Answer 11

urinary Na excretion = Na intake

Question 12

what is the most abundant solute in the ultrafiltrate

Answer 12

Sodium

Question 13

What drives the intracellular Na gradient for Na coupled cotransport

Answer 13

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)

Question 14

Water reabsorption

Answer 14

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)

Question 15

what do we mean when we say water follows soulute in isotonic proportions

Answer 15

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)

Question 16

Sodium Reabsorption in the Prximal tubule

Answer 16

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)

Question 17

NaCl coupled transport: Cl-OH

Answer 17

Parallel operation of the Na-H and Cl-OH exchangers = net effect of absorption of NaCl from the tubular lumen and secretion of water

Question 18

NaCl coupled transport: Cl-formate

Answer 18

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

Question 19

Cl driven Na reabsorption

Answer 19

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

Question 20

Tonicity of the fluid leaving the proximal tubule

Answer 20

ISOTONIC- the concntration of Na doesn’t change (65% of the filtered Na and water is reabsorbed)

Question 21

Reabsorption in the Proximal Tubule

Answer 21

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

Question 22

Reabsorption in the decending limb of the loop of henle

Answer 22

Descending limb of the loop of henle is permeable to water and IMPERMEABLE To solutes = water leaves (gets reabsorbed) and tubular fluid osmolarity increases

Question 23

Reabsorption in the ascending limb

Answer 23

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

Question 24

Reabsorption of NaCl in the thick ascending limb

Answer 24

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)

Question 25

NaCl reabsorption in the thick ascending limb (what stimulates it, what inhibits it)

Answer 25

Stimulated by aldosterone and ADH. Inhibited by loop diuretics. Stimulation and inhibition of the Na-K-2Cl pump

Question 26

Where do loop diuretics work

Answer 26

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

Question 27

Reabsorption in the early distal tubule

Answer 27

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)

Question 28

The diluting segment (what is included, what is its function)

Answer 28

Thin ascending limb, thick ascending limb, distal tubule. Creates and osmotic gradient that sets us up to reabsorb water

Question 29

Reabsorption in the principle cells (collecting ducts)

Answer 29

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)

Question 30

Role of aldosteromne in priciple cells

Answer 30

1.) Increase Na reabsorption 2.) Increase K secretion 3.) Increase Cl- reabsorption 4.) Increase H secretion

Question 31

Reabsorption fo NaCl in the medullary capillary ducts

Answer 31

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)

Question 32

Coupling NaCl reabsorption with reabsorption and secretion of water and other solutes

Answer 32

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

Question 33

General: Na movement in the proximal tubule

Answer 33

Na coupled co transport (Na-Solutes; Na-H), Cl dirvien Na reabsorption

Question 34

General: Na movement in the loop of henle

Answer 34

passive diffusion and Na-K-2Cl

Question 35

General: Na movement in the distal tubule

Answer 35

Na-Cl co transport

Question 36

General: Na movement in the collecting ducts

Answer 36

Na channels