Renal - Physiology (Basic Concepts)

Question 1

What percentage of total body weight (kg) is total body water (L) versus nonwater mass?

Answer 1

60% total body water (L); 40% nonwater mass

Question 2

Of total body water, what portion is extracellular versus intracellular fluid?

Answer 2

1/3 extracellular fluid; 2/3 intracellular fluid

Question 3

What are the main extracellular fluid compartments? What portion of extracellular fluid is each?

Answer 3

Plasma volume - 1/4; Interstitial volume - 3/4

Question 4

What is the major intracellular ion?

Answer 4

K+; Think: “HIKIN’ = HIgh K INtracellular”

Question 5

What is the way to remember the % of body weight that applies to total body water, extracellular fluid, and intracellular fluid?

Answer 5

60-40-20 rule (% of body weight): 60% total body water, 40% ICF, 20% ECF

Question 6

How is extracellular volume measured? How is plasma volume measured?

Answer 6

Extracellular volume measured by inulin; Plasma volume measured by radiolabeled albumin

Question 7

What is the osmolarity (of plasma)?

Answer 7

290 mOsm/L

Question 8

According to what 2 properties does the glomerular filtration barrier manage filtration?

Answer 8

Responsible for filtration of plasma according to size and net charge

Question 9

What are the components of the glomerular filtration barrier? Where applicable, relate a component’s purpose to the overall function of the glomerular filtration barrier.

Answer 9

Composed of: (1) Fenestrated capillary endothelium (size barrier) (2) Fused basement membrane with heparan sulfate (negative charge barrier) (3) Epithelial layer consisting of podocyte foot processes

Question 10

Which component of the glomerular filtration barrier acts to filter plasma according to size?

Answer 10

Fenestrated capillary endothelium (size barrier)

Question 11

Which component of the glomerular filtration barrier acts to filter plasma according to charge?

Answer 11

Fused basement membrane with heparan sulfate (negative charge barrier)

Question 12

What is lost in nephrotic syndrome? What are 4 associated consequences?

Answer 12

The charge barrier (of the glomerular filtration barrier) is lost in nephrotic syndrome, resulting in albuminuria, hypoproteinemia, generalized edema, and hyperlipidemia

Question 13

What is renal clearance? Define it in both words and as a formula.

Answer 13

Cx = UxV/Px = volume of plasma from which the substance is completely cleared per unit time; (Note: Cx = clearance of X [mL/min], Ux = urine concentration of X (mg/mL), Px = plasma concentration of X, V = urine flow rate)

Question 14

Give the fate of the substance x in the following scenarios: (1) Cx < GFR (2) Cx > GFR (3) Cx = GFR.

Answer 14

(1) Net tubular reabsorption of X (2) Net tubular secretion of X (3) No net secretion or reabsorption

Question 15

What can be used to (accurately) calculate glomerular filtration rate (GFR), and why?

Answer 15

Inulin clearance can be used to calculate GFR because it is freely filtered and is neither reabsorbed nor secreted

Question 16

What is the limitation of creatinine in terms of measuring GFR?

Answer 16

Creatinine clearance is an approximate measure of GFR. Slightly overestimates GFR because creatinine is moderately secreted by the renal tubules

Question 17

What is a normal GFR?

Answer 17

100 mL/min

Question 18

What is the clearance equation that equals GFR? What is another equation that can be used to define GFR?

Answer 18

GFR = U inulin x V/P inulin = C inulin; GFR = Kf [(Pgc - Pbs) - (PIgc - PIbs)] (Note: gc = glomerular capillary, bs = Bowman’s space, PI = mathematical pi, P = hydrostatic pressure, PI = oncotic pressure).

Question 19

Again, what is the (Starling’s force) equation used to define GFR? Which component of this equation is normally zero?

Answer 19

GFR = Kf [(Pgc - Pbs) - (PIgc - PIbs)] (Note: gc = glomerular capillary, bs = Bowman’s space, PI = mathematical pi, P = hydrostatic pressure, PI = oncotic pressure); PIbs normally equals zero

Question 20

What defines the stages of chronic kidney disease?

Answer 20

Incremental reductions in GFR define the stages of chronic kidney disease

Question 21

What can be used to estimate effective renal plasma flow, and why?

Answer 21

ERPF can be estimated using PAH clearance because it is both filtered and actively secreted in the proximal tubule. All PAH entering the kidney is excreted.

Question 22

What is the clearance equation that equals effective renal plasma flow?

Answer 22

ERPF = U pah x V/ P pah = C pah

Question 23

How does renal blood flow relate to renal plasma flow?

Answer 23

RBF = RPF/(1-Hct)

Question 24

How well does ERPF estimate true RPF?

Answer 24

ERPF underestimates true RPF by ~10%.

Question 25

What is the equation for filtration fraction (FF)? What is a normal FF?

Answer 25

FF = GRF/RPF; 20%

Question 26

What is the equation for filtered load?

Answer 26

Filtered load = GFR x plasma concentration

Question 27

With what can GFR be estimated?

Answer 27

GFR can be estimated with creatinine clearance

Question 28

With what is RPF best estimated?

Answer 28

RPF is best estimated with PAH clearance

Question 29

Create a visual labeling the following: (1) Proximal convoluted tubule (2) Parietal layer of glomerular capsule (3) Afferent arteriole (4) Juxtaglomerular cells (5) Efferent arteriole.

Answer 29

See p. 481 in First Aid for visual

Question 30

Which renal arteriole do prostaglandins affect? What are their effects on RPF, GFR, and FF? What blocks their effects?

Answer 30

Prostaglandins dilate afferent arteriole (increase RPF, increase GFR, so FF remains constant); NSAIDs

Question 31

Which renal arteriole does Angiotensin II preferentially affect? What are its effects on RPF, GFR, and FF? What blocks its effects?

Answer 31

Angiotensin II preferentially constricts efferent arteriole (decrease RPF, increased GFR, so FF increases); ACE inhibitor

Question 32

What do NSAIDs versus ACE inhibitors block?

Answer 32

NSAIDs block prostaglandins (which dilate afferent arteriole to increase RPF, decrease GFR, so FF remains constant); ACE inhibitors block Angiotensin II (which preferentially constricts efferent arteriole to decrease RPF, increase GFR, so FF increases)

Question 33

What is the effect of afferent arteriole constriction on: (1) RPF (2) GFR (3) FF (GFR/RPF)?

Answer 33

(1) Decrease (2) Decrease (3) NC

Question 34

What is the effect of efferent arteriole constriction on: (1) RPF (2) GFR (3) FF (GFR/RPF)?

Answer 34

(1) Decrease (2) Increase (3) Increase

Question 35

What is the effect of increased plasma protein concentration on: (1) RPF (2) GFR (3) FF (GFR/RPF)?

Answer 35

(1) NC (2) Decrease (3) Decrease

Question 36

What is the effect of decreased plasma protein concentration on: (1) RPF (2) GFR (3) FF (GFR/RPF)?

Answer 36

(1) NC (2) Increase (3) Increase

Question 37

What is the effect of constriction of ureter on: (1) RPF (2) GFR (3) FF (GFR/RPF)?

Answer 37

(1) NC (2) Decreased (3) Decreased

Question 38

Again, what is the equation for filtered load? What is the equation for excretion rate?

Answer 38

Filtered load = GFR x Px; Excretion rate = V x Ux

Question 39

How is reabsorption versus secretion calculated/defined?

Answer 39

Reabsorption = filtered - excreted; Secretion = excreted - filtered

Question 40

What is the fate of glucose at a normal plasma level (once filtered into the renal tubules)? What is the mechanism by which this occurs?

Answer 40

Glucose at a normal plasma level is completely reabsorbed in proximal tubule by Na+/glucose cotransport

Question 41

What is the plasma glucose level threshold at which glucosuria begins? What is the level at which all transporters are fully saturated (Tm)?

Answer 41

At plasma glucose of ~160 mg/dL, glucosuria begins (threshold); At 350 mg/dL, all transporters are fully saturated (Tm)

Question 42

For what condition is glucosuria an important clinical clue?

Answer 42

Diabetes mellitus

Question 43

What renal/urinary change does normal pregnancy cause, and why?

Answer 43

Normal pregnancy reduces reabsorption of glucose and amino acids in the proximal tubule, leading to glucosuria and aminoaciduria

Question 44

What happens to amino acids in the renal tubule, where, and via what mechanism?

Answer 44

Sodium-dependent transporters in the proximal tubule reabsorb amino acids

Question 45

What kind of disorder is Hartnup's disease? What and where does it affect mechanistically?

Answer 45

Autosomal recessive disorder; Deficiency of neutral amino acid (e.g., tryptophan) transporters in proximal renal tubular cells and on enterocytes

Question 46

What percentage of total body weight are each of the following fluid compartments: (1) Total body water (2) Extracellular fluid (3) Intracellular fluid (4) Plasma volume (5) Interstitial volume.

Answer 46

(1) 60% (2) 20% (3) 40% (4) 5% (5) 15%

Question 47

What effects does Hartnup disease have?

Answer 47

Leads to neutral aminoaciduria and decreased absorption from gut --> results in pellagra-like symptoms

Question 48

How is Hartnup disease treated?

Answer 48

Treat with high-protein diet and nicotinic acid