Elements of Renal Function

Question 1

How does the kidney microcirculation compare to the circulation network associated with the kidney nephron and collecting duct system?

Answer 1

Microcirculation is a distinct and separate network, it runs in parallel with network associated with kidney nephron and collecting duct system

Question 2

Microcirculation consists of 2 capillary networks in ________. Compare the 2 in terms of hydrostatic pressure

Answer 2

Series

Glomerular capillaries - high in hydrostatic pressure (60)

Peritubular capillaries - low in hydrostatic pressure (13)

Question 3

Compare blood flow through the renal cortex vs medulla

Answer 3

Rate and perfusion in kidney is high in renal cortex and low in inner medulla

[with impaired kidney function get decreased cortex perfusion with physiological consequences]

Question 4

3 major functions of sympathetics in increasing systemic BP

Answer 4

Vasoconstriction via alpha-1 adrenoceptors

RAAS system via beta-1 receptors on JG cells

Na/K ATPase increased Na reabsorption via alpha-1 adrenoceptors on tubular epithelial cells

Question 5

Equation for renal clearance

Answer 5

(U[x] x V)/P[x]

Or clearance = excretion rate/plasma concentration of x

Question 6

Filtered load equation

Answer 6

Filtered load of x = P[x] x GFR

Question 7

How is urinary excretion amount calculated using amount filtered, reabsorbed, and secreted?

Answer 7

Amount filtered - amount reabsorbed + amount secreted

Question 8

What variables are involved in degree of renal excretion of a compound?

Answer 8

GFR
Plasma concentration
Urine concentration
Urine flow rate (V)

Question 9

What 4 criteria must be met for GFR to be directly proportional to renal clearance?

Answer 9

Substance is freely filterable in glomeruli

Substance is neither reabsorbed nor secreted by renal tubules

Substance is not synthesized, broken down, or accumulated by the kidney

Substance is physiologically inert

Question 10

Primary difference between clearance of inulin and creatinine as measures of GFR

Answer 10

Creatinine is more commonly used bc it is made endogenously, while inulin must be infused

[note that cystatin may also be used which is produced endogenously and has inverse relationship to GFR]

Question 11

How does GFR compare to plasma concentrations of BUN or creatinine?

Answer 11

Inverse relationship

Question 12

Elevations in BUN are often a result of a ______ in GFR

Answer 12

Decreae

[occurs in high protein diet, hypovolemia, etc.]

Question 13

BUN/creatinine ratio associated with pre-renal problem

Answer 13

BUN:CR of greater than 20:1

BUN reabsorption is increased and disproprotionately elevated relative to creatinine in serum

Examples: hypovolemia, dehydration, reduced renal perfusion, high protein diet

Question 14

BUN/Cr ratio associated with intrarenal problem

Answer 14

BUN:Cr of less than 10:1

Renal disease reduces BUN reabsorption, thereby decreasing plasma levels and lowering the ratio

Example: liver disease, low protein diet (vegetariean)

Question 15

BUN/Cr ratio associated with post-renal problem

Answer 15

BUN:Cr of 10-20:1 (normal)

Question 16

Equation for filtration fraction

Answer 16

FF = GFR/RBF

FF is about 20% of renal plasma flow, changes with ultrafiltration pressure which is influenced by BP.

Question 17

What happens to oncotic pressure in efferent arterioles and oncotic pressure in peritubular capillaries as FF increases?

Answer 17

Both increase, bc more and more filtration is occurring, facilitating reabsorption + secretion of tubular fluid

Question 18

Effects of severe hemorrhage or renal artery stenosis on GFR, FF, and oncotic pressure

Answer 18

GFR increases to maintain homeostasis –> filtration fraction increases –> oncotic pressure increases