Renal Hemodynamics

Question 1

GFR

RBF

FF

Answer 1

• GFR - Vol plasma filtered ea minute
• RBF - amount of blood perfusing kidneys ea minute
• FF - GFR/ RBF

Question 2

GFR Equation

Answer 2

• GFR = Kf [(Pgc - Pb) - PIgc - PIb)]
• Kf - how big and how porous the glomerular membrane is (mesangial cells; when relaxed Kf inc and when contract KF dec)
• Pgc - systemic BP
• PIgc - as water exits the protein conc in glomerular capillary inc until reach filtration equilibrium point
• Pb and PIb - negligible (because relatively constant); SO… GFR = Kf (Pgc - PIgc)

Question 3

2 Forms of Intrinsic Autoregulation

Answer 3

2- Myogenic autoregulation

- Inc arterial wall tension (if inc BP) --> act L-type Ca++ channels --> constriction to dec perfusion
- Mainly in afferent arteriole

1- Macula Densa / Tubuloglomerular Feedback

- Macula densa cells sense inc flow by inc Cl- conc --> more ATP hydrolysis --> inc adenosine --> bind type 1 receptors --> vasoconstriction of afferent arteriole
- No clear mechanism for low flow state

Question 4

What is the overall goal of autoregulation?

Answer 4

maintain GFR and RBF despite varying systemic BP

Mainly thru changes in afferent arteriole resistance (but may have efferent constriction if really low vol)

Question 5

RAAS v Prostglandins in Autoregulation

Answer 5

-Renin –> Angio- II –> constricts both afferent an efferent arteriole

• Prostglandins
  
  • Maintain flow in high angio-II state by dilating arteriole afferent (opposes angio-II)
  • **Does not happen if using aspirin or NSAIDs (afferent remains constricted to dec GFR and RBF)

Question 6

What happens when you constrict afferent arteriole v efferent arteriole?

Answer 6

• If constrict afferent arteriole … dec GFR/dec RBF … FF same
• If constrict efferent arteriole …inc GFR/dec RBF … FF inc

Question 7

What happens when you dilate afferent arteriole v efferent arteriole?

Answer 7

• If dilate afferent arteriole… inc GFR/inc RBF … FF same
• If dilate efferent arteriole … dec GFR / inc RBF … FF dec

Question 8

How does symp NS contribute to autoregulation?

Answer 8

• Not as important in everyday autoregulation - normally implicated in severe situations like shock
• If artery clipped in kidney transplant, new kidney has no symp NS stimulation and is still able to auto-regulate
• Vasoconstrict via alpha receptors to dec GFR
• Also inc renin release