Glomerular Filtration Rate and its Regulation

Question 1

Glomerular Filtration Rate (GFR)

Answer 1

The amount of glomerular ultrafiltrate formed each minute and an indicator of kidney function

Question 2

How is GFR expressed in cats?

Answer 2

ml/min/kg

Question 3

What may be the first and only clinical sign of kidney disease?

Answer 3

A fall in the GFR

Question 4

What can GFR measurement tell?

Answer 4

A key significance in patients that are in early stage of renal failure that non-azotemic (no significant increase in BUN or creatinine)

Question 5

Nephron and GFR reduction

Answer 5

Functioning nephrons reduced to half, but GFR reduces by 25% because the remaining nephrons compensate

Question 6

How does a substance have to be to measure GFR?

Answer 6

Must be freely filtered through the glomeruli
Neither secreted nor reabsorbed by the tubules
Nontoxic
Not metabolized by the body

Question 7

Renal plasma clearance

Answer 7

The volume of plasma from which a substance is completely removed by the kidney in a given amount of time (usually minutes)

Question 8

What is the result of substance that appears in urine per unit of time result?

Answer 8

The the renal filtering of a certain number of ml of plasma that contained this amount
mL/ min

Question 9

How do you measure the plasma level of a substance?

Answer 9

By measuring the amount of that substance that’s secreted

Question 10

What substance meets the GFR criteria?

Answer 10

Inulin- a polymer of fructose, molecular weight of 5200, injected into the body

Question 11

GFR calculation for inulin

Answer 11

GFR= Urine inulin x volume / plasma inulin

Question 12

What happens if a substance is filtered and reabsorbed but not secreted and what is the formula?

Answer 12

The plasma clearance rate is always less than the GFR
This cannot be used because it calculate the GFR incorrectly
Ex; glucose

Question 13

What happens if a substance is filtered, not reabsorbed but secreted?

Answer 13

The plasma clearance rate is always greater than the GFR (hydrogen ion)– also can’t be used

Question 14

How is kidney function usually assessed in a clinical setting?

Answer 14

By measuring the plasma creatinine concentration

Question 15

Creatinine

Answer 15

A breakdown product of creatine phosphate in the muscle and produced at a fairly constant rate by the body

Question 16

How is creatinine processed?

Answer 16

Freely filterable
No reabsorbed
Small amount secreted into the tubular lumen

Question 17

Why aren’t blood creatinine levels a good indicator of early stages of chronic kidney disease?

Answer 17

Because significant increase in blood creatinine only occurs following significant nephron loss

Question 18

What gives you a better GFR estimation for renal function?

Answer 18

Blood creatinine, urine creatinine and urine flow rate does

Question 19

SDMA

Answer 19

Serum levels of Symmetrc dimethylarginine
Correlates well in cats and dogs (detects kidney problems)

Question 20

How is SDMA better than Creatinine?

Answer 20

An increase of SDMA levels occur earlier than an increase in creatinine in kidney disease
Increase has been detected when as little as 25% loss of renal function has occurred

Question 21

How would a blockage in the nephron affect the Bowman’s capsule hydrostatic pressure and the GFR?

Answer 21

Tubular obstruction –> increased Bowman’s capsule hydrostatic pressure –> decease in GFR

Question 22

How would loss of water in patient suffering from diarrhea affect the plasma-colloidal oncotic pressure and GFR?

Answer 22

Loss of water due to diarrhea–> increase in plasma colloid osmotic pressure –> decrease in GFR

Question 23

How do the changes in glomerular hydrostatic pressure affect regulation of GFR?

Answer 23

Primary means for physiological regulation of GFR
Increase = increase in GFR
Decrease = decrease in GFR

Question 24

Intrinsic myogenic mechanism to maintain constant GFR rate (increased blood pressure)

Answer 24

1/ physiology increases blood pressure
2/ myogenic constrictor response in afferent arterioles
3/ contraction of the vascular smooth muscle within seconds
4/ attenuation of transmission of increased arterial pressure to the glomerular capillaries
5/ helps prevent excessive increases in renal blood flow and GFR when arterial pressure increases

Question 25

Intrinsic myogenic mechanism to maintain constant GFR rate (decreased blood pressure)

Answer 25

1/ physiology fall in blood pressure
2/ reduced blood flow to the glomerulus
3/ myogenic vasodilator response in afferent arterioles
4/ transient increase in the blood flow to the glomerular capillaries despite the fall in blood pressure

Question 26

Intrinsic tubuloglomerular feedback mechanism to maintain a constant GFR rate

Answer 26

1/ increased blood pressure
2/ increase in GFR
3/ increased flow rate in the tubule
4/ decreased absorption of NaCl
5/ increased concentration of Na and Cl in the mecula densa
6/ increased ATP and adenosine release
7/ vasoconstriction of afferent arteriole and decreased blood pressure

Question 27

What do the mechanisms do?

Answer 27

Keep the GFR constant under physiological conditions