GFR, RBF, and clearance

Question 1

What is the renal definition of filtration?

Answer 1

Movement of ultrafiltrate of plasma into Bowman’s space

Question 2

What is the general equation for excretion?

Answer 2

Excretion = Filtration - reabsorption + secretion

Question 3

What is the normal volume of glomerular filtration per minute and per day?

Answer 3

120 mL/min or 180 L/day

Question 4

What is the is the filtration fraction?

Answer 4

GFR/RPF

Question 5

What is the equation for GFR?

Answer 5

Kf x net filtration pressure

Question 6

What are the autoregulation mechanisms of renal blood flow?

Answer 6

Myogenic response
Tubuloglomerular feedback

Question 7

What is the myogenic response in renal autoregulation?

Answer 7

Stretch receptors activated to cause vasoconstriction

Question 8

What is the function of the macula dense?

Answer 8

Responds to increased Na and Cl levels to trigger tubuloglomerular feedback

Question 9

What are the two end results of tubuloglomerular feedback?

Answer 9

Decreased renin release
Vasoconstriction

Question 10

What is the direct action of SyNS stimulation in the kidney?

Answer 10

Acts on alpha-1 receptors to constrict afferent arterioles, decreasing GFR

Question 11

What is the mechanism of SyNS constriction of efferent arterioles?

Answer 11

SyNS stimulates beta-1 receptors on granular cells to increase renin release; angiotensin II causes efferent vasoconstriction

Question 12

What stimulates renal prostaglandin synthesis?

Answer 12

Increased SyNS
Increased angiotensin II

Question 13

What is the role of renal prostaglandins?

Answer 13

Modulating effect on the vasoconstriction caused by SyNS and angiotensin II

Question 14

What stimulates release of ANP and BNP?

Answer 14

Increased blood volume

Question 15

What stimulates NP production in the kidney?

Answer 15

Increased blood volume
Vasoactive hormones

Question 16

What is the definition of clearance?

Answer 16

Volume of plasma which contains the substance excreted per given time

Question 17

What is the equation for clearance?

Answer 17

Cx = (Ux x V)/Px
Excreted = urinary concentration x urine flow

Question 18

What are the properties of inulin in the kidneys?

Answer 18

Freely filtered
Not reabsorbed or secreted

Question 19

What are the properties of creatinine in the kidneys?

Answer 19

Freely filtered
Not reabsorbed
Slightly secreted

Question 20

What are the properties of PAH in the kidneys?

Answer 20

Freely filtered
Actively secreted
Not reabsorbed

Question 21

What is the equation of RBF?

Answer 21

RBF = RPF x [1/(1-hematocrit)]

Question 22

What is the equation for net transport?

Answer 22

Net transport = filtered load - rate of excretion

Question 23

What is indicated by a positive net transport?

Answer 23

Filtered load > rate of excretion
substance is reabsorbed

Question 24

What is indicated by a net transport equal to zero?

Answer 24

Substance is freely filtered
It is not reabsorbed or secreted

Question 25

What is indicated by a negative net transport?

Answer 25

Rate of excretion > filtered load Substance is freely filtered and secreted

Question 26

What is likely for a substance whose clearance is higher than the clearance of inulin?

Answer 26

Substance is likely freely filtered and secreted

Question 27

What is likely for a substance whose clearance is less than the clearance of inulin?

Answer 27

It is likely filtered and partially reabsorbed

Question 28

What does a clearance of 0 indicate about a substance?

Answer 28

It is either not filtered, or filtered and entirely absorbed

Question 29

What is indicated about a substance whose clearance is equal to the clearance of PAH?

Answer 29

It is filtered and entirely secreted

Question 30

What is the effect of decreased GFR on BUN?

Answer 30

BUN will increase

Question 31

What are the properties of BUN in the kidney?

Answer 31

Freely filtered About 50% reabsorbed

Question 32

How is BUN affected by ADH?

Answer 32

Increased ADH will increase BUN reabsorption

Question 33

What is the affect on plasma creatinine and BUN if GFR is reduced by half?

Answer 33

Both plasma concentrations will double