HSF 4 - Unit 1 Physiology: Clearance, RBF, GFR, CDT

Question 1

what is the definition of GFR? what is it driven by?

Answer 1

the rate at which filtrate is formed by both kidneys per minute; passive process driven by NFP particularly high Pgc

Question 2

what is the equation for GFR?

Answer 2

Kf = [(Pgc-Pbs) - (Pigc-Pibs)]

Question 3

what is Kf in GFR?

Answer 3

permeability glomerular capillary (hydraulic conductivity * surface area)

Question 4

how do we push filtration in the glomerulus? how is this different than other areas of the body?

Answer 4

higher hydrostatic pressure along the glomerular capillary bed; others have a pressure that facilitates exchange instead of only filtration by crossing the capillary oncotic pressure

Question 5

what is the equation for clearance?

Answer 5

= urinary excretion ([U] * [UV])/[P]

Question 6

what does clearance represent?

Answer 6

how much of a substance can be removed from a a certain amount of plasma volume in a given amount of time

Question 7

why is inulin a good indicator of renal clearance?

Answer 7

non-toxic, infusible, freely filterable by the kidney, not reabsorbed, secreted, metabolized, synthesized or stored in any way and unable to alter the GFR so is equal to GFR

Question 8

what is the process of using inulin to measure GFR?

Answer 8

infuse a substance into the patient, achieve steady plasma concentration, collect urine and blood, collect clearance

Question 9

why is creatinine a good indicatory of renal clearance?

Answer 9

a metabolite produced by creatinine phosphate metabolism so no infusion is needed, rate of production should be constant and thus equal to the rate of excretion, freely filterable by the kidney, some secretion (10%) but balanced with the measurement error

Question 10

what is the process of using creatinine to measure GFR?

Answer 10

collect blood, measure creatinine, use prediction equation

Question 11

how is plasma creatinine related to GFR?

Answer 11

inversely proportional

Question 12

what GFR is considered normal? CKD stage 4? failure?

Answer 12

90-130; 30-15; <15

Question 13

what is the GFR of both kidneys?

Answer 13

120 ml/min

180 L/day

Question 14

what is the plasma volume?

Answer 14

3 L *filtered 60 times per day

Question 15

what is the daily urine volume?

Answer 15

1-2 L/day

Question 16

how much of the GFR is reabsorbed?

Answer 16

99%

Question 17

what is the cardiac output? how much does the kidney get?

Answer 17

5-6 L/min; RBF/CO = 20%

1000-1200 ml/min

Question 18

how large are the kidneys? how does this compare with blood flow?

Answer 18

300 g; 3.5 ml/min/g (<0.5% bodyweight); more than brain and sk. m

Question 19

what is the filtration fraction equation? what is FF?

Answer 19

% plasma filtered into the renal tubules, FF = GFR/Renal Plasma Flow; 125 mL/600 mL/min (hematocrit is 50% of 1200 mL for cardiac output value) = 20% filtered

Question 20

why is PAH a good marker for RPF?

Answer 20

majority of injected gets excreted, freely filtered (10 mg/min) and highly secreted into the nephron (50 mg/min)

Question 21

what is the RPF equation?

Answer 21

RPF = [U] * UV / [P]

Question 22

what is the major controller of GFR in terms of blood vessels?

Answer 22

afferent arterioles, causes a decrease of GFR, Pgc, and RPF

Question 23

what happens when you constrict efferent arterioles?

Answer 23

Pgc incresaes, RPF declines and stabilizes GFR

Question 24

what 2 mechanisms does the kidney use to protect RBF and GFR from changes in the MAP

Answer 24

neuroendocrinne and intrinsic autoregulation

Question 25

what is neuroendocrine regulation composed of?

Answer 25

vasoconstriction versus dilators

Question 26

what happens with intrinsic autoregulation?

Answer 26

occurs independent of renal nerves, circulating hormones, and metabolism; myogenic control and tubuloglomerular feedback from the JGA

Question 27

NE/Epi neuroendocrine influencer effects

Answer 27

constriction of AA, decreases RBF, happens with pain, stress, exercise, and hemorrhage

Question 28

AngII and ADH/AVP neuroendocrine influencer effects

Answer 28

constriction of EA, decreases RBF, countered in AA via NO and PG

Question 29

ATP/Adenosine neuroendocrine influencer effects

Answer 29

constriction of AA, decreases RBF, released by macula densa during high tubular flow

Question 30

NO neuroendocrine influencer effects

Answer 30

dilation of AA and EA, increases RBF, happens with shear stress, helps keep GFR constant despite constrictors

Question 31

Renal PGs neuroendocrine influencer effects

Answer 31

dilation of AA, increases RBF, helps keep GFR constant despite constriction

Question 32

ANP neuroendocrine influencer effects

Answer 32

dilation of AA and constriction of EA, first increases and second decreases RBF, high atrial pressure constriction to the EA is less than dilation to the AA

Question 33

what is the myogenic mechanism of autoregulation?

Answer 33

with increases in the arterial BP, arterial walls stretch in the afferent arteriole, and this is sensed by stretch receptors, which triggers opening of VGCC, increasing the influx of Ca from ECF to vascular SM cells, causing contraction of these cells, causing vasoconstriction to minimize the change of afferent arteriole blood flow to minimize changes in GFR

Question 34

what is the sequence of events with TGF when you decrease tubule flow?

Answer 34

decreased NaCl to the macula densa, decreasing depolarization and Ca2+ influx at the macula densa, increasing renin release to increase AngII, resulting in EA constriction and thus an increase inn GFR and Pgc to increase tubular flow

Question 35

what is the sequence of events with TGF when you increase tubule flow?

Answer 35

increased NaCl to the macula densa, increasing depolarization and Ca2+ influx at the macula densa, decreasing renin release to inhibit AngII and increase adenosine, resulting in AA constriction and EA dilation and thus a decrease in GFR and Pgc to decrease tubular flow