Elements of Renal Function

Question 1

Cortical nephrons

Answer 1

short LOH

surrounded by peritubular capillaries (low pressure)

Question 2

Juxtamedullary nephrons

Answer 2

long LOH
long efferent arterioles are divided into vasa recta
function to concentration urine

Question 3

Prerenal hyovolemia

Answer 3

BUN is reabsorbed by PCT to help bring water back in
Cre cannot be brought back in
>20/1 ratio
indicates reduced renal perfusion

Question 4

10-20/1 ratio

Answer 4

Normal ratio, BUN reabs WNL

Question 5

<10/1

Answer 5

Intrarenal

renal damage causes reduced reabsorption of BUN and a lower BUN:Cr ratio

Question 6

Cystatin C

Answer 6

similar to creatinine, used to estimate GFR
Elevated in plasma when GFR declines
not affected by muscle mass, age, or gender

Question 7

PAH

Answer 7

freely filtered, avidly re-secreted by proximal tubule

completely cleared from plasma of peritubular capillaries when Plasma PAH conc is low

gives you an estimate the renal plasma flow

Question 8

forces affecting glomerular filtration

Answer 8

1) conductivity of membrane (how porous is it)
2) surface area for filtration (think aging or disease)
these two create the ultrafiltration coefficient (Kf)
3) Capillary Ultrafiltration pressure

Question 9

Mechanisms for altering GFR

Answer 9

alter Kf (mesangial cell contraction)
alter Puf (changes in Pgc)
Change Pgc (renal arterial BP, afferent arteriole resistance, efferent resistance)

Question 10

afferent arteriolar constriction

Answer 10

greater pressure drop upstream of capillaires
Pgc falls 
decreases GFR
decreased renal blood flow 
increased resorption

Question 11

Efferent arteriolar constriction

Answer 11

pooling of blood in the capillaries
increased Pgc
increases GFR (for a while)
decreased renal blood flow
increases resorption in peritubular capillaries
**RAAS
autoregulatory protective mechanism in response to hypovolemia

Question 12

SNS stimulation on renal function

Answer 12

constriction of afferent and efferent—>Dec RBF, dec GFR

renin from granular cells—>Ang II—>PG release–>efferent VC—>stabilize GFR

increases Na reabs—>increase blood volume—>increase BP

Question 13

tubuloglomerular feedback

Answer 13

autoregulation of GFR by rate of fluid NaCl delivery to macula densa
inc NaCl in distal tubule (i.e. inc GFR)—>MD tells JG—>constriction of afferent arteriole—>Decrease GFR

one mechanism of autoregulation that prevents exs fluid loss during times of elevated BP

Question 14

glomerular filtration

Answer 14

filtration of plasma from glomerular cap into Bowman’s

Question 15

Tubular reabsorption

Answer 15

transferral of substances from tubular lument to peritubular capillaries

Question 16

tubular secretion

Answer 16

transfer of substances from peritubular capillaries to tubular lumen

Question 17

Excretion

Answer 17

voiding of substances in the urine

Question 18

Reabsorption vs. Secretion rates

Answer 18

if excretionfiltration, then net secretion has occured

Question 19

Creatinine use in estimating GFR

Answer 19

Normally cre production=cre excretion
and increase in Pcre=decreased GFR
(i.e. if you decrease GFR by 1/4, then Pcre increases by 4x)

not perfect (vary by differences in muscle mass

useful for LONG TERM MONITORING of renal function

Question 20

filtration fraction

Answer 20

FF=GFR/RPF

how much of the renal blood flow that is filtered into the tubule

normally about 20%

changes with ultrafiltration pressure
if you increase FF too much, oncotic pressure increases in the peritubular capillaries which increases reabs

Question 21

Myogenic autoregulation

Answer 21

increased BP—>increase Ca2+ into smooth muscle causing decreased capillary pressure and therefore decreased GFR

One mechanism of autoregulation that prevents extreme fluid loss during times of mildly elevated BP