Renal Physio and Diuretics 1

Question 1

Total body fluids account for

Answer 1

60% of body weight; person weighing 70 kg with approx 42 L of water (ICF 40%, ECF 20%, TBW 60%); IVF = 7% of body weight (5 L with 55% plasma, or 3L; and plasma is approx 25% of ECF; extravascular, or interstitial fluid approx 75% of ECF, or 11L)

Question 2

Solute composition of ICF and ECF is different, but; raipd gains and losses in body weight reflect

Answer 2

solute concentration/osmoliarity of ICF and ECF is essentially the same (300 mOsm/L); osmolality and osmolarity essentially equivalent;
change in TBW and distribution of TBW

Question 3

In 70 kg adult man, what is CO, RBF, RPF, GFR, urine output? What do they maean?

Answer 3

1. CO = 5-6 L per min (approx equivalent to blood volume or 7% of body weight)
2. RBF: 1-1.2 L/min (20% of CO perfuses the kidney)
3. RPF = 600-720 ml/min (55% of RBF is this RPF and 20% of renal plasma flow is filtered in the glomeruli)
4. GFR: 125 ml/min (daily, kidney filters 180 L of plasma daily, more than 10 times the ECF volume)
5. Urine output: 14 L/day

Question 4

Normal kidney function assessed by

Answer 4

ability to increase and decrease urine output in response to volume expansion and volume contraction, respectively

Question 5

____ is the major solute determining

Answer 5

Na (Cl); ECF osmolarity and total amount of Na in ECF determines ECF volume; more Na in ECF results in larger ECF volume (expansion) and less Na in ECF results in smaller ECF volume (contraction)

Question 6

What are volume receptors?

Answer 6

In vasculature, CNS, liver and kidneys (detects increase or decrease of ECF volume; expansion of ECF volume results in compensatory increase in Na and water output in urine, and contraction results in opposite)

Question 7

Severe ECF volume contraction can

Answer 7

induce a decrease in GFR (for ECF volume expansion, won’t see a change in GFR)

Question 8

How can we maintain sodium balance as we restrict how much Na we consume?

Answer 8

1. 250 mEq/day of Na enters, then 250 mEq/day eliminated
2. Down to 90, you have 160 eliminated, meaning 70 extra is eliminated, along with 70 of chloride, or 140 mOsmoles/day; here, to maintain ECF osmolarity constant (280 mOsm/L), need to contract ECF volume by amount equivalent to volume of urine necessary to eliminate excess Na and Cl isoosmotically (or .5L)
3. With decrease in ECF volume and Na amount, kidney increases Na and water reabsorption and decreases amount of Na and water in urine (120/day); now need contraction of ECF volume by approx .2 L to maintain ECF osmolarity constant

Question 9

Edema:

Answer 9

1. Excess accumulation of fluid in interstitial space due to cardiac (CHF and increased hydrostatic pressure), renal (nephrotic syndrome with decreased oncotic pressure), hepatic (decreased oncotic pressure in liver disease), or endocrine dysfunction (hyperaldosteronism)
2. imbalance of hydrostatic and oncotic pressures across capillary wall induces a shift in fluid distribution from intravascular space to extravascular space resulting in isotonic retention of Na and water, and decreased circulating volume
3. Decreased circulating volume decreases renal perfusion pressure, RAA activated, and increases Na retention and maintains edema

Question 10

1. Approx ___ of filtered Na is reabsorbed in

Answer 10

66%; proximal tubule (use leaky epi to have isoosmotic reabsorption of H2O and solutes in proximal tubule; this water and solutes go to circulation through renal vein)

Question 11

2. Approx ____ of filtered Na reabsorbed in

Answer 11

25%; thick ascending loop of Henle; thin and thick ascending limb are impermeable to water (unlike thin descending limb), diluting the tubular fluid and reducing solute concentration/osmolarity of tubular fluid

Question 12

Thick ascending limb of Loop of Henle is

Answer 12

solute transport engine driving and maintaining counter current multiplication of interstitial solute concentration difference or solute concentration gradient going from cortex to medulla surrounding CD

Question 13

Distal tubule reabsorbs

Answer 13

6-8% of filtered Na, and in late distal tubule regulated by circulating levels of aldosterone; early distal impermeable to water, but late distal tubule permeable to water when induced by interaction with ADH

Question 14

FF is; FEwater is

Answer 14

fraction of plasma flowing through glomeruli, which is ultrafiltered to form tubular fluid (ratio of GFR to RPF);
ratio of urine flow rate to GFR (clearance of inulin can estimate GFR), ultimately Pcreat/Ucreat or Pin/Uin

Question 15

Amount of inulin filtered is; amount if inulin excreted in urine is

Answer 15

GFR x Pin; V x Uin; Cin = GFR = Uin x V/Pin

Question 16

FEsolute =

Answer 16

CNa/Ccreat = UNaPcreat/UcreatPNa

Question 17

Water and sodium balance means; in negative and positive water balance; fractional reabsorption is

Answer 17

FEwater = FENa = 1%;
negative water: FEwater < 1% and FENa = 1%;
positive water: FEwater > 5% and no real effect on FENa;
1-FE…

Question 18

For K reabsorption, what remains constant?

Answer 18

67% reabsorbed in proximal tubule and approx 20% reabsorbed in thick ascending limb of loop of Henle (constitutive!!);

Question 19

In low K diet, how much could be excreted? High K diet? What can have effects on secretion?

Answer 19

Low K diet: as low as <1%, with decreased secretion and increased reabsorption of K (distal tubule and cortical collecting duct);
High K diet (increased secretion and decreased reabsorption of K, getting as high as 110%);
1. Aldosterone increases K secretion
2. Alkalosis increases K secretion, acidosis decreases K secretion
3. Diuretic-induced, increase in tubular fluid flow will increase K secretion due to outwardly directed K gradient across luminal membrane

Question 20

At the level of the distal tubule and collecting duct, with more Na reabsorption you have; relationship of Na of K at this level?

Answer 20

increased K secretion, increasing FEK (because of decreased Na reabsorption in the ThAL due to diuretic; more Na to late distal tubule and early collecting duct induces increased secretion of K, increasing risk of hypokalemia;
increase in Na reabsorption functionally linked to increase in K secretion, which increases FEK