L2: RBF and GFR

Question 1

Equation for filtration fraction

Answer 1

FF = GFR/RPF

Question 2

Equation for renal plasma flow

Answer 2

RPF = (1-Hct)RBF

Question 3

What are the vasconstrictors that regulate RBF (increase BP)?

Answer 3

Sympathetic nerves (via alpha1 receptors)
ATII, ADH, ATP, endothelin
*Remember ATII effects can be variable

Question 4

Which arteriole is more sensitive to ATII at low concentrations?

Answer 4

Efferent

Question 5

What are the vasodilators that regulate RBF (decrease BP)?

Answer 5

Atrial natriuretic peptide (ANP)
Glucocorticoids
NO
Prostaglandins

Increase RBF and GFR

Question 6

The kidneys are able to autoregulate blood flow and GFR between what pressure range?

Answer 6

80-180 mmHg

Question 7

What are the 2 mechanisms for autoregulation of RBF and GFR? Describe.

Answer 7

1. Myogenic mechanism: Intrinsic to VSMC; contract in response to stretch
2. Tubuloglomerular feedback: Increasing GFR increases NaCl delivery to LOH; sensed by MD which causes resistance of afferent arteriole to increase, therefore decreasing RBF and GFR (“flow dependent”)

*Both of these change resistance of AFFERENT arteriole

Question 8

What is an average GFR?

Answer 8

120-125 ml/min

Question 9

Describe the fluid in Bowman’s capsule (compared to the plasma).

Answer 9

Protein-free filtrate of blood plasma

proteins do not normally pass; small MW solutes not bound to protein appear in same concentrations as in plasma

Question 10

What is the route of filtrate?

Answer 10

Fenestrate > basal lamina > filtration slits > Bowman’s capsule

Question 11

What are the main filtrate barriers to proteins?

Answer 11

Basal lamina and filtration slits (due to size and charge; slits are negatively charged which repel negatively charged proteins)

Question 12

What is the equation for GFR (long)?

Answer 12

GFR = Kf [(PGC-PBC) - (#GC - #BC)]

*everything other than Kf = NFP
#BC essentially zero (no proteins in BC)

Question 13

Kf for glomerular capillaries is ______ than that for capillaries in skin and muscle.

Answer 13

50-100 times greater

Question 14

What is the driving force of GFR?

Answer 14

PGC = BP in the glomerular capillary

Question 15

If you increase PGC, what happens to the GFR?

Answer 15

Increase GFR

Question 16

What would cause an increase in PGC? What happens to RBF?

Answer 16

Efferent arteriolar resistance (ex: low ATII conc.)

RBF decreases

Question 17

What would cause a decrease in PGC? What happens to RBF?

Answer 17

Afferent arteriolar resistance

RBF decreases

Question 18

What would cause a significant decrease in RBF?

Answer 18

Afferent AND efferent arteriolar resistance (PGC remains the same) (ex: high ATII conc.)

Question 19

Describe NSAIDs effects on the kidneys

Answer 19

• Prostaglandins receive SNS stimulation/high ATII conc. to vasodilate afferent arteriole, reducing vasoconstriction
• NSAIDs INHIBIT THE SYNTHESIS OF PROSTAGLANDINS (Cox-1 and Cox-2)
• Interfere with protective effects of prostaglandins on RBF

Question 20

What is the more useful equation for GFR? What favors absorption and filtration?

Answer 20

GFR = Kf (PGC - PBC - #GC)
Absorption: #GC
Filtration: PGC

Question 21

If Kf is increased, then GFR is _____.

Answer 21

increased

increases glomerular surface area due to relaxation of glomerular mesangial cells

Question 22

If PGC is increased, then GFR is _____.

Answer 22

increased

increased renal arterial pressure, decreased Ra, increased Re

Question 23

If PBC is increased, then GFR is _____.

Answer 23

decreased

Question 24

If #GC is increased, then GFR is _____.

Answer 24

decreased