Renal 3. Gfr And Rbf 2

Front 1

What do the overall kidney processes do?

Back 1

Determines the composition of urine

Front 2

4 kidney processes:

Back 2

1. Filtration
2. Reabsorption
3. Secretion
4. Excretion

Front 3

What are the forces that govern filtration by glomerular capillaries?

Back 3

Starling's forces

Front 4

Glomerular hydrostatic pressure:

Back 4

60 all along its length

Front 5

Glomerular oncotic pressure:

Back 5

32 mm Hg

Front 6

Bowman's space hydrostatic pressure:

Back 6

18 mm Hg

Front 7

Bowman's space oncotic pressure:

Back 7

not there; no protein filtered

Front 8

4 common factors that can alter the GFR:

Back 8

1. Increased G-cap filtration coefficient - increases GFR
2. Increased G-cap hydrostatic pressure - increases GFR
3. Increased gcap oncotic pressure - decreases GFR
4. Increased Bowman's space hydrostatic pressure - decreases GFR

Front 9

What does gcap oncotic pressure start out as at the beginning of the glomerulus?

Back 9

28 mm Hg - same as in systemic capillaries

Front 10

What is the final gcap oncotic pressure at the end of the glomerular capillary?

Back 10

36 mm Hg

Front 11

Why does gcap oncotic pressure increase so much as fluid moves through it?

Back 11

B/c fluid is filtered and so the concentration of plasma protein increases.

Front 12

What happens to the change in oncotic gcap pressure if the filtration fraction is increased?

Back 12

The increase in gcap oncotic pressure goes from 28 to 40 mm Hg and plateaus.

Front 13

What happens to the change in oncotic gcap pressure if the filtration fraction is decreased?

Back 13

Oncotic pressure in gcap does not increase as much - only to about 32 instead of 36

Front 14

What is an important effect of the increase in gcap oncotic pressure along the length of it?

Back 14

It decreases the net filtration pressure.

Front 15

What is the normal difference between the forces out and in at the gcap?

Back 15

Forces out = 60
Forces in = 46
Net force out = 14 mm Hg

Front 16

What is the filtration fraction equal to?

Back 16

GFR/RPF

Front 17

What happens to gcap oncotic pressure as you move along the length of the gcap?

Back 17

It increases from 28 to 36

Front 18

What happens to the increase in gcap oncotic pressure if you increase the filtration fraction?

Back 18

Filtering more means the gcap oncotic pressure increases more for example from 28 to 40

Front 19

What happens to the increase in gcap oncotic pressure if you decrease the filtration fraction?

Back 19

It increases less; from 28 to only 32

Front 20

What is filtration equilibrium?
What causes it?

Back 20

When NFP = 0 due to the increase in gcap oncotic pressure; caused by a decreased renal plasma flow (RPF) which increases FF and gcap oncotic pressure faster.

Front 21

What is filtration disequilibrium? What causes it?

Back 21

When NFP always stays positive even to the end of the gcap; Caused by high RPF, which causes gcap oncotic pressure to increase less quickly.

Front 22

What will GFR change in; filtration equilibrium or disequilibrium?

Back 22

Equilibrium

Front 23

What is the concept that is the basis for quantifying renal function?

Back 23

Mass balance

Front 24

For the body what does dietary fluid intake equal?

Back 24

-Excretion in urine and feces
-Insensible loss (sweat/breath)

Front 25

What does renal arterial input equal?

Back 25

-Renal venous output
plus
-Urine output
plus
-Lymphatic output

Front 26

What is the mass balance equation for the kidney?

Back 26

Filtration+secretion = Reabsorbed+Excreted

Front 27

What is Inulin?

Back 27

An exogenous substance that is freely filtered, not reabsorbed, and not secreted.

Front 28

So what is inulin used for?

Back 28

measuring the GFR which corresponds to clearance of inulin

Front 29

Formula for GFR based on inulin clearance:

Back 29

(UF x U(inulin)
GFR = ---------------
P(inulin)

Front 30

If the urine flowrate is 1 ml/min, and you collect a urine sample that is 125 mg/dl in inulin, and you gave the plasma 1 mg/ml inulin, what is the GFR?

Back 30

GFR = 1x125/1 = 125ml/min

Front 31

Define Clearance:

Back 31

the volume of plasma from which a substance has been removed and excreted into the urine per unit of time

Front 32

units of clearance

Back 32

vol / time

Front 33

How do you calculate the clearance of a substance X?

Back 33

Urine flowrate x Urine conc X
-----------------------------
Plasma conc X

Front 34

What endogenous substance can be used as a marker of GFR?

Back 34

Creatinine

Front 35

How is GFR estimated clinically?

Back 35

By considering urine flowrate and creatinine conc to be constant, then taking the inverse of plasma creatinine.

Front 36

So what is the clinical index for % normal creatinine?

Back 36

100/plasma creatinine

Front 37

Why isn't the creatinine index such a good estimate of GFR?

Back 37

Because it is not exactly produced at the same rate in everyone, and it is slightly secreted.

Front 38

What happens to the serum concentration of creatinine if you decrease GFR by 50%? Why?

Back 38

Serum levels rise by 2X over several days because the kidneys are filtering and excreting only half as much creatinine.

Front 39

What happens to the urinary excretion rate initially after a 50% drop in GFR?

Back 39

It decreases by 50%

Front 40

What happens to the urinary excretion rate of creatinine over the next few days after GFR reduction?

Back 40

It will rise back to normal to regain the balance between creatinine production and excretion.

Front 41

What if the GFR is maintained at 50% reduction?

Back 41

Plasma creatinine levels will increase and remain elevated at the same level once kidney excretion equals production.

Front 42

What will happen to plasma creatinine levels if GFR falls to 1/8 its normal rate, and maintained?

Back 42

Plasma levels will increase 8X

Front 43

So what can you say about creatinine excretion rate always?

Back 43

It always equals the rate of creatinine production, despite reductions in GFR. At the expense of increased plasma levels.

Front 44

What is the relationship between GFR and plasma creatinine concentration?

Back 44

As GFR decreases, plasma concentration increases inversely proportionally.

Front 45

What substances will be affect most by a decreased GFR and thus accumulate in the plasma?

Back 45

Urea and creatinine

Front 46

What substances will be affect less by a decreased GFR and thus accumulate in the plasma later at more severely decreased GFRs?

Back 46

-Phosphate
-Urate
-H+ ions

Front 47

What substances plasma levels will be maintained virtually constant even with severe decreases in GFR?

Back 47

Sodium and chloride

Front 48

So what are the best substances for identifying a case of chronic renal failure?

Back 48

Creatinine or urea - because they will be abnormal soonest.

Front 49

What are 2 clinical estimates of the GFR that are better than creatinine?

Back 49

-Cockroft-Gault formula
-MDRD (modific. of diet in renal disease)

Front 50

What is PAH clearance used to measure?

Back 50

Renal plasma flow

Front 51

What makes PAH a good marker for renal plasma flow?

Back 51

The fact that it is completely cleared from the plasma.

Front 52

How does the kidney treat PAH?

Back 52

-Freely filtered
-Rest is secreted
-None is reabsorbed

Front 53

How do you calculate renal PAH clearance?

Back 53

(Urine vol)(Urine PAH)
----------------------
Plasma PAH

Front 54

Is ALL PAH removed from the plasma?

Back 54

Well no, .001 mg/ml stays in the renal vein; but it's still the best estimate of RPF.

Front 55

Why can't you use creatinine to estimate RPF?

Back 55

Because the GFR is only about 20% of total renal plasma flow.

Front 56

What is the extraction ratio of PAH?

Back 56

The difference between renal arterial PAH and renal venous PAH divided by arterial PAH.

Front 57

How do you calculate renal plasma flow based on PAH clearane?

Back 57

Clearance of PAH
RPF = ---------------------
PAH extraction ratio

Front 58

Why must you take into account the extraction ratio for PAH?

Back 58

Because not all PAH is extracted from the plasma, and if you didn't you would underestimate RPF.

Front 59

How can you use RPF to calculate renal bloodflow?

Back 59

RPF
RBf = ------
1-Hct

Front 60

What are the 2 types of GFR and RBF regulation?

Back 60

1. Acute regulation
2. Chronic regulation

Front 61

What is the timeframe over which acute regulation of GFR/RBF occurs?

Back 61

Seconds to minutes

Front 62

What is the timeframe over which chronic regulation of GFR/RBF occurs?

Back 62

Minutes to days

Front 63

What does Acute regulation respond to?

Back 63

Transient changes in arterial blood pressure

Front 64

What IS acute regulation?

Back 64

Autoregulation

Front 65

What does Chronic regulation respond to?

Back 65

Changes in neural or hormonal input to the kidney

Front 66

What types of neural or hormonal input stimulates chronic regulation of GFR and RBF?

Back 66

Ang II
NE
Renal nerves

Front 67

What happens to GFR and RBF in the short-term as arterial pressure increases? Why?

Back 67

They remain fairly constant up to a point; because urine output increases in proportion to MAP to bring it back down to normal.

Front 68

What are the 2 mechanisms of GFR and RBF autoregulation?

Back 68

1. Myogenic mechanism
2. Tubuloglomerular feedback

Front 69

What is the myogenic autoregulation mechanism?

Back 69

Stretch of vessels during increased arterial pressure stimulates contraction, increases vasc resistance, and maintains constant RBF & GFR.

Front 70

What is the Tubuloglomerular feedback mechanism?

Back 70

When renal perfusion pressure is high, more fluid is filtered; more NaCl passes the macula densa cells; they detect the increase and elicit an increase in vascular resistance.

Front 71

What are macula densa cells? Where are they?

Back 71

Specialized cells in the distal tubule near the afferent arteriole

Front 72

What results from macula densa cells detecting increased NaCl?

Back 72

Constriction of the afferent arteriole to decrease renal bloodflow.

Front 73

What is the tubuloglomerular response to a decreased renal perfusion pressure?

Back 73

1. Decreased pressure
2. Decreased filtration
3. Decreased NaCl detected by macula densa
4. Decreased afferent arteriole resistance
5. Increased renal perfusion

Front 74

What are 3 hormones/autocoids that decrease the GFR?

Back 74

-Norepi
-Epi
-Endothelin

Front 75

How does angiotensin II affect the GFR?

Back 75

It can go either way; it acts on both the afferent and efferent arterioles.

Front 76

What does Ang II preferentially act on?

Back 76

The efferent arteriole - causes vasoconstriction and thus reduces renal bloodflow and increases gcap hydrostatic pressure.

Front 77

Under what circumstances is Ang II normally elevated?

Back 77

Those where blood pressure needs to be raised, so the GFR would be decreased to promote fluid retention.

Front 78

So what is Ang II's normal effect on the GFR?

Back 78

It prevents a decrease in the GFR while the efferent constriction allows for increased Na reabsorption.

Front 79

What are 2 hormones/autocoids that increase the GFR?

Back 79

-Endothelial-derived Nitric oxide
-Prostaglandins