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VET 409: Renal > Glomerulus, RBF, GFR > Flashcards

Glomerulus, RBF, GFR Flashcards

1
Q

ultrafiltrate

A

fluid that passes from capillaries into pores; contains nutrients, waste, small peptides, unbound/partially bound ions

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2
Q

layers of selective permeability

A
  1. glomerular pores
  2. basement membrane
  3. slit diaphragms
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3
Q

glomerular pores

A

openings in the endothelium that restrict molecule filtration by size and charge

negatively charged - prevent filtration of negatively charged ions/proteins

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4
Q

slit diaphragms

A

filtered openings between podocyte foot processes

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5
Q

renal blood flow (RBF)

A

the volume of blood delivered to the kidneys per unit time

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6
Q

glomerular filtration rate (GFR)

A

rate at which blood is filtered each minute

depends on hydraulic permeability + pore surface area (Kf), and net filtration pressure (NFP)

GFR = Kf x NFP

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7
Q

net filtration pressure (NFP)

A

forces favoring filtration - forces opposing filtration

NFP = P(GC) - [pi(GC) + P(BC)]

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8
Q

forces favoring filtration

A

P(GC): hydrostatic pressure in capillary
pi(BC): oncotic pressure in Bowman’s space – equals ZERO in health

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9
Q

forces opposing filtration

A

P(BC): hydrostatic pressure in bowman’s space
pi(GC): oncotic pressure in capillary

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10
Q

what does it mean if NFP = 0

A

only filtration is occurring (forces favoring filtration = forces opposing filtration)

NO reabsorption or secretion

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11
Q

what does it mean if NFP < 0

A

filtration AND reabsorption
(forces opposing filtration > favoring filtration)

do NOT want this to occur in the glomerulus

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12
Q

does NFP change along the length of the capillary

A

yes - NFP decreases along the length of the capillary

as solutes exit the capillary, P(GC) decreases –> LESS FAVORING FORCES

as solutes exit, proteins in the capillary become more concentrated causing pi(GC) to increase –> MORE OPPOSING FORCES

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13
Q

renal clearance (Cx)

A

volume of plasma that is cleared of a substance in a unit time (mL/min)

Cx = (Ux x V) / Px

Ux: urine concentration of X
V: urine flow
Px: plasma concentration of X

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14
Q

what does it mean if Cx = GFR

A

filtration only

(clearance from plasma = clearance from urine)

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15
Q

what does it mean if Cx > GFR

A

filtration and secretion

(more is cleared from the urine than is filtered at the glomerulus, must be coming from secretion)

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16
Q

what does it mean if Cx < GFR

A

filtration and reabsorption

(less is cleared from the urine than is filtered at the glomerulus, must be getting reabsorbed into the blood)

17
Q

filtration fraction

A

proportion of plasma that reaches the kidneys that gets filtered by the glomerulus (ratio of GFR to RPF)

FF = 0.2 = 20% in healthy animals

18
Q

relationship between GFR and FF

A

Increase GFR = Increase FF
Decrease GFR = Decrease FF

**ONLY if RPF stays the same

19
Q

relationship between RPF and FF

A

Increase RPF = Decrease FF
Decrease FF = Increase RPF

OVERRIDES GFR because changes in radius are to the 4th power

20
Q

renal plasma flow (RPF)

A

volume of plasma flowing through the kidneys per unit time (mL/min)

RPF = RBF x (1 - HCT)

21
Q

what does RPF depend on

A

capillary resistance

Resistance = 1/r^4
RPF = delta P / R

SMALL changes in radius = LARGE changes in resistance = LARGE changes in RPF

vasoconstriction = decrease radius = increase resistance = decrease RPF = increase FF

vasodilation = increase radius = decrease resistance = increase RPF = decrease FF

22
Q

what are the main sites of resistance in the kidneys

A

afferent and efferent arterioles

23
Q

effect of vasoconstriction: afferent arteriole

A

DECREASE:
- RBF
- P(GC)
- GFR - minor

INCREASE:
- FF - minor

24
Q

effect of vasoconstriction:
efferent arteriole

A

DECREASE:
- RBF

INCREASE:
- P(GC)
- GFR - minor
- FF

25
Q

effect of vasoconstriction: both arterioles

A

DECREASE:
- RBF
- P(GC) - minor
- GFR - minor

26
Q

regulatory mechanisms of renal blood flow

A
  1. intrinsic: myogenic, tubuloglomerular feedback
  2. extrinsic: neural, hormonal
27
Q

intrinsic regulation of renal blood flow

A

autoregulatory
maintains constant RBF and GFR even when BP changes within a certain range (80-180 mmHg)

occurs mainly at AFFERENT arterioles

28
Q

myogenic regulation

A

smooth muscles in capillary walls respond to changes in BP

Inc. BP –> stretches smooth muscle –> Ca signaling –> vasoconstriction –> decreases RBF

Dec. BP –> no SM stretch –> vasodilation –> increases RBF

29
Q

tubuloglomerular feedback

A

juxtaglomerular apparatus uses paracrine signaling to respond to changes in NaCl concentration in distal convoluted tubule

High NaCl –> JG cells release vasoactive substance –> vasoconstriction –> decrease RBF

Low NaCl –> JG cells release vasoactive substance –> vasodilation –> increase RBF

30
Q

neural regulation

A

sympathetic nervous system responds to drops in BP

Dec. BP –> inc. sympathetic tone –> releases NE –> binds to a1 receptors on afferent > efferent arterioles –> vasoconstriction –> dec. RBF

31
Q

hormonal regulation

A

JG cells release renin in response to low BP sensed by macula densa cells –> becomes angiotensin I/II –> binds to efferent then afferent arterioles –> vasoconstriction –> dec. RBF

32
Q

ways of measuring GFR

A
  1. inulin
  2. creatine
  3. p-Aminohippurate
33
Q

inulin

A

exogenous substance that has constant free plasma concentration, is freely filtered by kidneys, and is not reabsorbed or secreted

allows for direct measuring of GFR b/c rate of appearance in kidney = rate of filtration

34
Q

how to calculate inulin clearance

A

V(plasma) = volume of plasma cleared of inulin per min

inulin is filtered only so clearance (V(plasma)) = GFR

V(plasma) = [urine concentration x urine flow] / plasma concentration

35
Q

creatine

A

endogenous metabolite that is not reabsorbed, secreted, or metabolized by the kidney

GFR = [urine concentration x urine flow] / plasma concentration

36
Q

p-Aminohippurate

A

completely cleared from plasma through filtration and secretion from peritubular capillaries into proximal tubules

37
Q

how to calculate pAH clearance

A

filtration and secretion –> clearance > GFR

Clearance = urine concentration x urine flow / plasma concentration

Clearance = RPF

VET 409: Renal (21 decks)

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