L2 RBF and GFR

Question 1

How much of CO does the kidney receive? Why?

Answer 1

25% of CO goes to kideys, 20% of plasma is filtered.

FF = GFR / RPF

Question 2

How is Renal blood flow RBF regulated?

Answer 2

1. Vasoconstriction: Decreases RBF and GFR
   * Sympathetic stimulation: constriction via a-1 receptors

• usually countered by prostaglandins
• very high SNS will overpower the prostaglandins (e.g. during severs blood loss)
• Vasoconstrictors: Angiotensin II (AII), ADH ( vasopressin), ATP, endothelin
• AII contstricts efferent arteriole more than afferent
  2. Vasodilators: Increases RBF and GFR
• ANP (like anti aldosterone), glucocorticoids, NO, prostaglandins
  3. Autoregulations: two mechanisms maintain blood flow from pressure changes between 80-180
• Myogenic mechanism:
• intrinsic to smooth muscle, contracts in response to stretch
• Tubuloglomerular feedback
• Macula Densa sense increase flow, signal afferent arteriole to contract and reduce RBF

Question 3

What are the layers of the glomerular filter?

Answer 3

1. fenestra
2. basal lamina
3. filtration slits (between pedicles)

Question 4

How is permeability of the G filter affected by solute size and charge?

Answer 4

Larger molecules and negatively charged molecules filter less (positive molecules filter more easily because the basal lamina is negatively charged)

Question 5

How can the permeability (filtration) of a protein be increased?

Answer 5

By adding a molecule with a positive charge to it.

Question 6

How is GFR determined?

Answer 6

GFR = Kf*(Pgc-Pbc-πgc)

Pgc is the main driving force, pressure in the capillaries promotes movement of solutes into bowmans capsule

NFP = (Pgc-Pbc-πgc)

Question 7

How can Kf be altered?

Answer 7

AII causes mesangial cells contract, creating more resistance to filtration.