Glomerular Filtration/Quantifying Renal Function (45)

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Review glomerular filtration.

1

Review effect of change in relative arteriolar resistance.

2

Which renal arteriole constricts more upon sympathetic activation?

afferent arteriole

Which renal arteriole constricts more upon exposure to angiotensin 2?

efferent arteriole

Filtration fraction =

GFR/RPF

What percentage of the renal plasma flow is filtered?

20%

What term describes the ability to maintain renal blood flow and glomerular filtration rate within narrow limits in the face of fluctuating MAP?

autoregulation; a

What are the 2 mechanisms of autoregulation?

myogenic mechanism

tubulo-glomerular feedback

Considering the myogenic response, what happens to vascular resistance if blood pressure increases?

vascular resistance increases

*maintains constant flow

Describe afferent arteriolar response to change in tension (transmural pressure) and its effects on GFR and RPF.

stretch-activated cation channels

depolarization

Ca influx

vascular smooth muscle contraction

increased afferent arteriolar resistance

decreased GFR, decreased RPF

Name the 3 components of tubulo-glomerular feedback.

signal

mediators

effectors

Describe the signal of the tubulo-glomerular feedback mechanism.

macula densa detects flow rate (NaCl concentration in tubular fluid)

Give an example of a mediator of the tubulo-glomerular feedback mechanism.

adenosine

What is the action of the effector in the tubulo-glomerular feedback mechanism?

contraction of afferent arteriolar smooth muscle

Review tubulo-glomerular feedback.

3

Describe TGF in the case of increased GFR.

NKCC2 senses influx of Na, Cl

ATP released and converted to adenosine

adenosine binds receptor on afferent arteriole

[Ca]i increases

contraction of afferent vascular smooth muscle

Why is renin inhibited by the tubulo-glomerular feedback in case of increased GFR?

renin would promote unwanted water retention

Review regulation of RPF and GFR.

b

Describe TGF in the case of decreased GFR.

macula densa senses decreases in Na, Cl

NOS released

NO stimulates prostaglandin production

prostaglandin binds to Gs on afferent arteriole

increased RPF, GFR, renin

Do glucocorticoids promote vasoconstriction or vasodilation?

vasoconstriction

How do glucocorticoids promote vasoconstriction?

potentiate vasoconstriction action of norepinephrine

What is renal clearance?

the volume of plasma rendered free of a substance per unit time

Renal clearance ratio =

amount of substance in urine/concentration of substance in arterial plasma

Renal clearance =

(urine concentration of substance x urine flow)/arterial plasma concentration of substance

What are the units (general) of renal clearance?

volume/time

Review suitable substance for estimation of GFR.

z

What is the purpose of renal clearance?

measure GFR

Name a very suitable substance for estimation of GFR.

inulin

Derive the equation for GFR using inulin.

rate of inulin filtration = rate of inulin excretion

volume of plasma cleared = glomerular filtration rate

GFR = (urine concentration of inulin x urine flow)/renal plasma concentration of inulin

What ion transporter is found on macula densa cells?

NKCC2

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