2 RBF and GFR

Question 1

Kidneys receive _________ (fraction) of cardiac output.

Answer 1

1/4 - High flow not needed for metabolism - Needed to support filtration (20% of plasma is filtered)

Question 2

__% of plasma is filtered.

Answer 2

20

Question 3

______ liters of filtrate formed per day.

Answer 3

180

Question 4

FF = _______

Answer 4

GFR/RPF

Question 5

RBF (constant) = _______

Answer 5

1.1 L/min

Question 6

RPF (formula) = ________

Answer 6

(1 - Hct)RBF Normal values: (1 - 0.45)(1.1 L/min) = 605 ml/min

Question 7

Normal GFR = _______

Answer 7

125 ml

Question 8

Normal FF = _________

Answer 8

GFR/ RPF 125 ml / 605 ml = 0.2 = 20%

Question 9

What are the vasoconstrictors that regulate RBF and what is their effect on RBF?

Answer 9

• Sympathetic nerves (A1 receptors; decrease RBF and GFR) -Molecules: Angiotensin II, ADH, ATP, and endothelin (decrease RBF and GFR) - Ang II constricts both the afferent and efferent, but the efferent arteriole is more sensitive

Question 10

What are the vasodilators that regulate RBF and what is their effect on RBF?

Answer 10

Atrial natriuretic peptide (ANP), glucocorticoids, NO, Prostaglandins (PGE2, PGI2) -Increase RBF and GFR

Question 11

How is autoregulation related to blood flow and GFR?

Answer 11

It maintains a constant blood flow and GFR at different arterial pressures

Question 12

What can override autoregulation?

Answer 12

large increases in sympathetic tone

Question 13

During severe blood loss how are RBF and GFR affected?

Answer 13

they both decrease (hypotension)

Question 14

Throughout what arterial blood pressure range is blood flow regulated (constant)?

Answer 14

80-180 mmHg

Question 15

What are the 2 mechanisms for autoregulation?

Answer 15

Myogenic mechanism - Intrinsic to VSMC (vascular SM cells) ; contract in response to stretch

Tubuloglomerular feedback (“flow dependent”) - Increasing GFR increases NaCl delivery to LOH; sensed by the macula densa which causes the resistance of the afferent arteriole (Ra) to increase thereby decreasing BF and GFR

Question 16

the signal affects RBF and GFR mainly by changing the resistnace of the __________ arteriole.

Answer 16

afferent

Question 17

Purpose of tubuloglomerular feedback

Answer 17

Maintains constancy of salt load delivered o distal tubule

Question 18

Protein _______ normally pass the filter in significant quantities.

Answer 18

does not

Question 19

All small-MW solutes that are not protein-bound appear in the filtrate in _________ concentrations as in blood plasma.

Answer 19

the same

Question 20

The fluid in Bowman’s capsule is essentially a ___________ filtrate of blood plasma.

Answer 20

protein-free

Question 21

All the composition of plasma and glomerular filtrate will be the same except _________. It will be much higher in the _________.

Answer 21

protein; plasma

Question 22

Put these in order of the route of the filtrate: basal lamina, fenestrae, filtration slits (between pedicels)

Answer 22

fenestrae, basal lamina, filtration slits

Question 23

Glomerular filter: substances are separated by ________ and ________.

Answer 23

Size (MW 7000 - can pass, 70,000 - can’t pass)

Electrical charge (basal lamina and slits are coated with negative charges –> proteins (-) are repelled)

Question 24

In the glomerular filter: the main barriers to proteins are ________ and ________.

Answer 24

basal lamina (-); filtration slits (-)

Question 25

Write out the starling equation: GFR = ?

Answer 25

GFR = Kf[(Pgc - Pbc) - (πgc- πbc)]

where Kf = filtration coefficient

the rest = the net filtration pressure (NFP)

Note: πbc is ~0 b/c proteins don’t pass into bowman’s capsule

Question 26

Kf is the filtration produced by each ______ of _________ pressure

Answer 26

mmHg net filtration pressure

Question 27

Kf for glomerular capillaries versus Kf for capilllaries of skin and muscle?

Answer 27

the Kf for glomerular capillaries is 50-100 times greater than that for capillaries in skin and muscle

Question 28

Kf can be altered by __________ cells. What affect?

Answer 28

Mesangial, all reduces Kf

Question 29

Use Kf to calculate GFR

GFR = Kf x NFP

Answer 29

Example:

GFR = 15 ml/min/mmHg x 8 mmHg

= 120 ml/min

Question 30

What is the main effect of the Pgc on GFR?

Answer 30

driving force of GFR

Question 31

What is the effect of Pbc on GFR??

Answer 31

Pbc = back pressure in bowman’s capsule –> retards GFR

Question 32

What is the effect of πgc (oncotic pressure of glomerular cap bed)?

Answer 32

Retards GFR (proteins are unable to cross barrier –> higher concentration in glomerular cap –> pressure towards the higher protein conc.)

Question 33

What are the average pressures for Pgc, Pbc, IIgc, Iibc, and Kf?

Answer 33

Pgc = 45 mmHg Pbc = 10 mmHg Iibc = ~0 IIgc = 26 mmHg Kf = 14 ml/min/mmHg

Question 34

How does increased Ra affect Pgc and RBF?

Answer 34

It deccreases Pgc (less afferent = less blood in capillary) It decreases RBF (less flow)

Question 35

How does increased Re affect Pgc and RBF?

Answer 35

It increases Pgc (like a traffic jam that builds up at the capillary) RBF decreases (any increase in resistance will decrease RBF)

Question 36

If there is equal increases in Ra AND Re, how will this affect Pgc and RBF?

Answer 36

Pgc will be unaffected (no net difference b/c the two resistances cancel out) The RBF will be severely decreased (lots of resistance)

Question 37

Name the direct determinants of GFR that, when increased, increase GFR

Answer 37

Kf (glomerular surface area) and Pgc (?renal arterial pressure, ?Ra, ?Re)

Question 38

Name the direct determinants of GFR that, when increased, decrease GFR

Answer 38

Pbc (intratubular pressure b/c obstruction)

IIgc (systemic-plasma oncotic pressure –> sets IIgc at beginning of glomerular capillaries, ?Renal plasma flow –> increased rise of Iigc along glomerular capillaries)