Lecture 3: Renal Blood Flow

Question 1

What % of cardiac output do the kidneys receive?

Answer 1

25%

Question 2

What % of blood in cortex?

Answer 2

93%

Question 3

What % of blood in outer medulla?

Answer 3

6%

Question 4

What % of blood in inner medulla?

Answer 4

1%

Question 5

RBF is directly proportional to what?

Answer 5

Pressure gradient between renal artery and renal vein

Question 6

RBF inversely proportional to resistance of

Answer 6

Renal vasculature (mainly the arterioles)

Question 7

What is the major mechanism for changing renal blood flow?

Answer 7

Changing arteriolar resistance, which changes filtration in the kidney

Question 8

Vasoconstriction does what to GFR in afferent arterioles?

Answer 8

Decreases GFR

Question 9

Vasoconstriction does what to GFR in efferent arterioles?

Answer 9

Increases GFR

Question 10

Sympathetic nervous system and circulating catecholamines have what receptors?

Answer 10

Alpha 1

Question 11

Alpha 1 receptors are more abundant on what part of the glomerulus?

Answer 11

Afferent arterioles

Question 12

If there is an increase in SNS activity, what happens?

Answer 12

Decrease both RBF and GFR

Question 13

Angiotensin 2 is a

Answer 13

Renal vasoconstrictor

Question 14

Angiotensin 2 affects

Answer 14

Both afferent and efferent arterioles

Question 15

Which part of glomerulus is more sensitive to angiotensin 2?

Answer 15

Efferent arterioles

Question 16

What happens with low levels of angiotensin 2 in the kidneys?

Answer 16

Increase GFR because main effect is on efferent

Question 17

What happens with high levels of angiotensin 2?

Answer 17

Decrease GFR and RBF because both afferent and efferent constricted

Question 18

Dominant effect of atrial natriuretic peptide (ANP)

Answer 18

Dilation of afferent arterioles

Question 19

Effect of atrial natriuretic peptide (ANP) on efferent arterioles

Answer 19

Constriction

Question 20

What happens when ANP is affecting the glomerulus?

Answer 20

Vascular resistance decreases, RBF and GFR increase

Question 21

Where do Prostaglandins E2 and I2 get produced and where do they act?

Answer 21

Produced locally in the kidneys and act locally

Question 22

What do Prostaglandins E2 and I2 do when effecting the glomerulus?

Answer 22

Vasodilation of afferent and efferent arterioles

Question 23

What do Prostaglandins E2 and I2 act in opposition to?

Answer 23

SNS

Question 24

Why do Prostaglandins E2 and I2 vasodilate (what are they trying to prevent)

Answer 24

Trying to protect RBF and protect from renal failure due to vasoconstriction caused by SNS

Question 25

What effect does dopamine have on kidney?

Answer 25

Dilates renal arterioles

Question 26

What condition is dopamine particularly useful in?

Answer 26

Hemorrhage

Question 27

How does Dopamine protect?

Answer 27

Vasodilates to counteract SNS vasoconstriction

Question 28

Renal arterial pressure can vary from

Answer 28

80 - 200 mm Hg

Question 29

How is RBF maintained within the large range that renal arterial pressure can vary from?

Answer 29

1. Vary to resistance of arterioles - more control of afferent arterioles
2. RBF only decreases when renal arterial pressure falls below 80 mm Hg

Question 30

What are the two theories of autoregulation?

Answer 30

1. Myogenic hypothesis
2. Tubuloglomerular feedback hypothesis of autoregulation

Question 31

Explain the myogenic hypothesis

Answer 31

Increased arterial pressure stretches blood vessels, which causes reflex contraction of smooth muscle in blood vessel walls, which increases resistance to RBF

Question 32

How does the myogenic hypothesis maintain RBF?

Answer 32

The increase in arterial pressure is balanced by the increase in resistance of the afferent arteriole, so RBF remains relatively constant (NOT through autonomic nervous system)

Question 33

Explain tubuloglomerular feedback steps

Answer 33

1. Renal arterial pressure increases
2. Both RBF and GFR increase
3. Increase in GFR delivers more solutes and water to macula densa region of early distal tubule
4. Macula densa senses increased load and responds by secreting vasoactive substance to constrict afferent arteriole
5. RBF and GFR return to normal

Question 34

Reasons PAH is gold standard to measure RPF

Answer 34

1. Removed only by the kidneys
2. Both filtered and secreted into proximal tubule
3. Doesn’t alter RPF
4. Not synthesized or degraded by kidneys
5. Almost all PAH enters urine

Question 35

Difference between measuring true and effective RPF?

Answer 35

Effective is more practical than True RPF