Renal Circulation

Question 1

What is the equation for Renal Plasma Flow

Answer 1

RPF= RBF x (1-Hct)

Question 2

What is the equation for Filtration fraction?

Answer 2

FF= Glomerular Filtration Rate/ Renal Plasma Flow

Question 3

How much of the CO do the kidneys receive?

Answer 3

~20-25% of CO

Question 4

What are the two major factors that generate filtrate?

Answer 4

1. Hydraulic pressure in glomerular capillaries

2. Renal blood flow rate

Question 5

What other factors contribute to filtrate formation?

Answer 5

Hydraulic pressure
Renal blood flow rate
Minor- Blood oncotic pressure
Filtration coefficient (how easily you can move fluid across: characteristics of vessel, SA)

Question 6

What is the equation for blood flow?

Answer 6

Flow (Q)= Pressure Change/Resistance

Question 7

What factors influence resistance in the vessels?

Answer 7

1. Length of blood vessels
2. Radii of blood vessels (MAJOR factor)
3. Blood viscosity

Question 8

What are the effects of vasoconstriction?

Answer 8

Decreased flow
pressure up stream increases
downstream pressure decreases

Question 9

B/c of the presence of of both pre- and post- glomerular capillary sphincters:

• Glomerular capillary pressure is much (greater/less) than in most capillaries elsewhere in the body.
• Peritubular capillary pressure is (higher/lower) than in most capillaries elsewhere in the body

Answer 9

1. greater
2. lower
   These pressure differences facilitate formation of filtrate in glomeruli and reabsorption of fluid from peritubular capillaries.

Question 10

What are three factors that promote renal constriction?

Answer 10

1. Sympathetic n (catechoamines)
2. Angiotensin II
3. Endothelin

Question 11

What are 5 factors that promote renal constriction?

Answer 11

1. PGE2
2. PGI2
3. NO
4. Bradykinin
5. Dopamine

Question 12

What effect do sympathetic nerve fibers have?

Answer 12

They activate alpha 1 receptors on afferent and efferent arterioles –> vasoconstriction

Question 13

How would SNS activation affect on RBF and GFR?

Answer 13

Decrease RBF and GFR

Question 14

What effect does Angiotensin II have?

Answer 14

Potent vasoconstrictor
Affects both AA and EA
Greater effect on the efferent arteriole

Question 15

How would Angiotensin II affect RBF and GFR?

Answer 15

Decrease RBF and Inc. GRF

Question 16

Levels of ATII release influences the relative effects so…..
At low levels of ATII which vessel is influenced more?
At high levels of ATII?

Answer 16

At low levels: both AA and EA constrict, then EA> AA, –> inc. GFR

At high levels, both AA and EA constrict, then EA dec. GFR

Question 17

What effect does Prostaglandins (PGE2 and PGI2) have?

Answer 17

Vasodilate both vessels

Question 18

Activation of SNS and ATII also activates renal PG production, explain why. (also how it relates to Advil)

Answer 18

PG activation is a safety mechanism- vasodilates vessels deep in the kidney to maintain blood flow

Question 19

What effect does Dopamine have on the kidneys (and other organs) at:

1. Low doses
2. High doses

Answer 19

1. At low doses:; dilates renal, cerebral, cardiac and splanchic arterioles
   constricts skeletal and cutaneous arterioles
2. At high doses: vasoconstricts renal arterioles

Question 20

What is autoregulation?

Answer 20

system in place that limits changes in kidney function due to changing systemic BP. (protects glomerulus from systemic pressure)

Question 21

What primarily controls autoregulation?

Answer 21

The Afferent arteriole.
Theories: Myogenic: physical stretch is detected, open sm. muscle Ca channels –> vasoconstriction
Tubuloglomerular: macula densa senses

Question 22

Net flow across vessel wall depends on:

Answer 22

1. Hydrostatic Pressure on each side
2. Oncotic Pressure on each side
3. Filtration coefficient of the vessel wall.

Question 23

Why are NSAIDS toxic to kidneys?

Answer 23

They suppress PG production, can have too much vasoconstriction (PG is protective of kidney blood flow)