Renal Physiology Lecture 1: Control of RBF & GFR

Question 1

What stabilizes RBF and GFR?

Answer 1

autoregulation via ANS

• Renal blood flow (RBF) can be modulated by systemic arterial pressure
  
  • Receives high blood flow
• Renal sympathetic nerves innervate vascular & tubular components of the kidneys
  
  • ANS major contributor to RBF
  • Increased renal nerve activity decreases RBF and GFR → vasoconstriction
• RBF and GFR remain remarkably stable in the face of fluctuations in arterial pressure
  
  • Due to the constant operation of renal autoregulatory mechanisms

Question 2

What is the renal autoregulation comprised of?

Answer 2

• Myogenic response
• Tubuloglomerular feedback mechanism (TGF)

Question 3

Where does renal autoregulation stabilize RBF and GFR?

Answer 3

between 80- 180mmHg held relatively constant

• RBF & GFR fall below 80 mmHg, rise above 180mmHg could risk damage

Question 4

What is the myogenic response?

Answer 4

The myogenic response is the reflex response of the afferent arterioles to changes in blood pressure. Increased blood pressure increases the tension in the vascular wall, and the vascular smooth muscle contracts. Similarly, decreased blood pressure decreases the tension and the smooth muscle relaxes.

• smooth muscle stretches as blood pressure and blood flow increases and stretch ions open and muscle cells polarize causing contraction with ion flow. This increases resistance to blood flow and as a result blood flow downstream to capillaries is reduced, so the hydrostatic pressure is turned back towards normal
• efferent artioles can also impact GFR → Active constriction of efferent artiole causes blood to back up in glom capillaries causing increasing glom hydrostatic pressure and increasing GFR as result. If resistance of efferent is reduced blood can easily flow out of glom capillaries and pressure would not be increased

Question 5

Tubuloglomerular Feedback

Answer 5

• Rate of tubular fluid flow can modulate RBF and thus stabilize GFR
• Macula densa cells located in the wall of the early distal tubule
• Contacts cells in the wall of the afferent arteriole
  
  • Juxtaglomerular cells
  • Secrete renin
• Tubuloglomerular feedback is an adaptive mechanism that links the rate of glomerular filtration to the concentration of salt in the tubule fluid at the macula densa. A high [NaCl] and reabsorption rate at this site causes contraction of the afferent arteriole and a reduction in GFR.
• TGF is local control where rate of fluid flowing through parts can initiate changes in RBF and can stabilize GFR.
• Loop ascends such that late portion and early distal tubule pass between the afferent and efferent arterioles at this point the wall of tubule and arterioles are specialized in this region where they make contact and is called juxtaglomerus apparatus

Question 6

TGF mechanism with increased GFR

Answer 6

Question 7

TGF feedback mechanism with decreased arterial pressure

Answer 7