Berne and Levy Ch. 32 Elements of Renal Function

Question 1

Properties of molecules that are freely filtered

Answer 1

Radius smaller than 20A, neutral

Question 2

Properties of unfiltered molecules

Answer 2

Radius larger than 42A, negative

Question 3

Properties of variously filtered molecules

Answer 3

Radius between 20-42A

Question 4

Filtration fraction

Answer 4

GFR/RPF (usually 15-20%)

Question 5

For any given molecular radius, __________ molecules are more readily filtered than __________ molecules

Answer 5

cationic; anionic

Question 6

What is the only Starling force that favors filtration?

Answer 6

Pgc (glomerular capillary hydrostatic pressure)

Question 7

What two forces oppose filtration?

Answer 7

Pbc and glomerular oncotic pressure

Question 8

Ultrafiltration pressure at afferent end

Answer 8

17mmHg

Question 9

ultrafiltration pressure at efferent end

Answer 9

8mmHg

Question 10

What happens to Pgc along the length of the capillary?

Answer 10

DECREASES slightly (due to resistance to flow)

Question 11

What happens to glomerular capillary oncotic pressure (pi gc) along the length of the capillary?

Answer 11

INCREASES (water is filtered out so protein conc increases in the capillary)

Question 12

What is Kf?

Answer 12

ultrafiltration coefficient = the product of the intrinsic permeability of the glomerular capillary and the glomerular surface area available for filtration

Question 13

Why is the rate of glomerular filtration so much greater in glomerular capillaries than in systemic capillaries?

Answer 13

the Kf is 100x greater in glomerular capillaries

Pgc is 2x greater as hydrostatic pressure in systemic caps

Question 14

What happens to GFR with an INCREASE in afferent arteriole resistance?

Answer 14

decreases (because Pgc decreases)

Question 15

What happens to GFR with a DECREASE in afferent arteriole resistance?

Answer 15

increases (Pgc increases)

Question 16

What happens to GFR with an INCREASE in efferent arteriole resistance?

Answer 16

increases (Pgc increases)

Question 17

What happens to GFR with a DECREASE in efferent arteriole resistance?

Answer 17

decreases (Pgc decreases)

Question 18

Increase blood pressure has a transient ________ on Pgc and GFR

Answer 18

increase

Question 19

What two mechanisms are responsible for autoregulation of RBF and GFR?

Answer 19

1) Myogenic mechanism

2) Tubuloglomerular feedback

Question 20

What is the myogenic mechanism of autoregulation?

Answer 20

tendency of smooth muscle to contract when stretched (renal afferent arteriole constricts when stretched by high blood pressure)

Question 21

What is the tubuloglomerular feedback mechanism in autoregulation?

Answer 21

concentration of NaCl is sensed by macular densa of JGA and converted into signals that affect afferent arteriolar resistance and GFR

When more NaCl is sensed (higher GFR), macula densa cells release ATP and adenosine which causes vasoconstriction of afferent arteriole (decrease flow)

Question 22

Macula densa releases ___ as a vasodilator, attenuating tubuloglomerular feedback and ____________ enhancing it

Answer 22

NO; angiotensin II

Question 23

When does autoregulation fail?

Answer 23

arterial pressures less than 90mmHg and in the presence of certain hormones/symp nerve activity

Question 24

How do catecholamines (ep and norep) affect GFR?

Answer 24

act on alpha 1 receptors to vasoconstrict; DECREASE GFR

think, don’t need to pee when scared

Question 25

What effect does angiotensin II have on GFR?

Answer 25

DECREASES it; vasoconstricts arteries

Question 26

What two molecules counteract sympathetic vasoconstriction?

Answer 26

Prostaglandins (during hemorrhage) and NO (and Bradykinin via NO)

Question 27

What effect does adenosine have on renal flow and why is it special?

Answer 27

VASOCONSTRICTS (normally vasodilates systemically)