Renal Phys

Question 1

What’s the 60/40/20 rule?

Answer 1

Total body water is 60% of body weight (42L).
ICF is 40% of body weight. (28L)
ECF is 20% of body weight. (14L)

Question 2

What portion of total body weight is intravascular/total blood volume?

Answer 2

7% (~5L)

Question 3

How is the ECF divided between plasma and interstitial fluid?

Answer 3

plasma is 25% of ECF (3L)

interstitial fluid is 75% of ECF (11L)

Question 4

Does total body fluid increase or decrease with age?

Answer 4

Decreases (from 75% in neonate to 50% in old age)

Question 5

Do adult men or women have a higher total body fluid volume %?

Answer 5

Men; women have more fat and therefore less water

Question 6

What’s the average osmolarity of body fluids? Do ICF and ECF have the same?

Answer 6

~300mOsm/L; ECF and ICF have about the same osmolarity but solute composition is different

Question 7

What’s a normal GFR?

Answer 7

125mL/min

Question 8

What percentage of the CO perfuses the kidneys?

Answer 8

20%

Question 9

What ion determines the ECF volume?

Answer 9

Na

Question 10

If the ECF volume expands, how does the kidney respond to correct it?

Answer 10

increase output of sodium and water in the urine by decreasing reabsorption

Question 11

What does it mean to be in sodium balance?

Answer 11

dietary intake and urinary output are equal

Question 12

Are the following causes of edema via increased hydrostatic or decreased oncotic pressures? congestive heart failure, liver disease, nephrotic syndrome, pulmonary edema

Answer 12

CHF, pulm edema - inc hydrostatic

liver, kidney - dec oncotic

Question 13

In the renal handling formula, Excretion =

Answer 13

Filtration - Reabsorption + Secretion

Question 14

What happens to sodium in the proximal tubule?

Answer 14

about 66% is reabsorbed isosmostically with water

Question 15

What percentage of filtered sodium is reabsorbed in the loop of Henle?

Answer 15

25%

Question 16

The ascending limb of the loop of Henle is impermeable to water and resorbs solutes in excess of water. This dilutes the tubular fluid to what approximate osmolarity?

Answer 16

~100mOsm/L

Question 17

Why is it important that water not be reabsorbed in the loop of Henle?

Answer 17

allows urine to be diluted in relation to plasma; sets up the concentration gradient in the medulla that allows for urine concentrating when volume depleted

Question 18

What happens with sodium and water in the distal tubule?

Answer 18

~6% Na reabsorbed in early distal tubule; late distal tubule regulated by aldosterone
early distal tubule impermeable to water and helps dilute tubular fluid further; late distal tubule controlled by ADH

Question 19

Why is the functioning of the collecting duct important?

Answer 19

sensitive to ADH and travels through the medulla allowing the kidney to reabsorb water to defend against ECF contraction

Question 20

What fraction of plasma is filtered to form the ultra filtrate? How is this determined?

Answer 20

20%; ration of GFR/RPF (RPF = renal plasma flow)

Question 21

How frequently is the entire ECF of a 70kg adult seen by the kidney?

Answer 21

entire ECF is filtered every 2 hours

Question 22

How can GFR be approximated using lab values?

Answer 22

GFR = Cin (clearance of inulin) = UV/P
U - conc in urine
V - urine flow rate
P - plasma conc

Question 23

How can the fractional excretion of water be estimated?

Answer 23

V/GFR = Pin / Uin

creatinine is a good surrogate for inulin

Question 24

How is the fractional excretion of any substance estimated?

Answer 24

FEx = (UxPcreat) / (UcreatPx)

Question 25

What is the constitutive reabsorption of potassium and where does it occur?

Answer 25

67% in proximal tubule, 20% in loop of henle

Question 26

What will the fractional excretion of potassium be in a low-K diet? high-K diet?

Answer 26

low-K - dec secretion and inc reabsorption leading to <1% excretion
high-K diet - inc secretion and dec reabsorption leading to FE as high as 110%

Question 27

What hormone increases potassium secretion in late distal tubule?

Answer 27

aldosterone

Question 28

What’s the effect of alkalosis and acidosis on potassium handling?

Answer 28

alkalosis increases potassium secretion

acidosis decreases potassium secretion

Question 29

What’s the effect of diuretics acting earlier in the nephron on potassium handling in the late nephron?

Answer 29

Blocking early sodium reabsorption increases the amount of sodium seen by the distal tubule and causes an increase in potassium secretion there, leading to increased risk of hypokalemia

Question 30

Name the important transporters in the talH.

Answer 30

luminal - Na-K-2Cl

basolateral - efflux of Cl, K; Na/K ATPase

Question 31

What type of potential difference exists across the talH epithelium? What does this drive reabsorption of?

Answer 31

lumenal positive potential difference; drives Ca and Mg reabsorption

Question 32

The talH is responsible for creating the concentration gradient in the interstitium of the medulla. What’s the maximum osmolarity achieved at the bottom?

Answer 32

~1200mOsm/L, which is 4x the osmolarity of the plasma