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Renal Module > Costanzo Renal Physiology: Renal clearance, blood flow, and GFR > Flashcards

Costanzo Renal Physiology: Renal clearance, blood flow, and GFR Flashcards

1
Q

What is renal clearance?

A

The volume of plasma cleared of a substance per unit time.

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2
Q

What are the unit for renal clearance?

A

mL/min or mL/24hr

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3
Q

What is the equation for renal clearance?

A

C = U(V)/P

C = clearance (mL/min or mL/24hr)
U = urine concentration (mg/mL)
V = urine volume/time (mL/min)
P = plasma concentration (mg/mL)
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4
Q

What proportion of cardiac output does the kidney receive?

A

25%

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5
Q

What factors are directly proportional to renal blood flow?

A

The pressure difference between renal artery and renal vein

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6
Q

What factor is renal blood flow inversely proportional to?

A

RBF is inversely proportional to the resistance of the renal vasculature.

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7
Q

What mediates renal vasoconstriction?

A

The sympathetic nervous system and angiotensin II.

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8
Q

What is special about low concentration aniotensin II?

A

It preferentially constricts the efferent arterioles leading thus protecting the GFR.

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9
Q

What is the effect of angiotensin converting enzyme (ACE) inhibitors?

A

Decreased angiotensin II and thus dilating efferent arterioles and reducing GFR.

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10
Q

What is the effect of vasodilation on RBF?

A

Vasodilation increases RBF

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11
Q

What are the factors which cause renal vasodilation?

A

(1) PGE2
(2) PGI2
(3) dopamine
(4) bradykinin
(5) nitric oxide.

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12
Q

How is a constant rate of RBF maintained?

A

If arterial pressure changes then the renal vascular resistance changes

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13
Q

Within what range does RBF remain constant?

A

Between 80-200 mm Hg

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14
Q

What are the two mechanisms for autoregulation of RBF?

A

Myogenic mechanisms and Tubuloglomerular feedback.

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15
Q

What is the myogenic mechanism of RBF regulation?

A

Renal afferent arterioles contract in response to stretch.

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16
Q

What is the tubularglomerular feedback mechanism of RBF regulation?

A

increased renal arterial pressure leads to increased fluid load on the macula densa which causes constriction of nearby blood vessels.

17
Q

How is renal plasma flow measured and why is it measured like this?

A

By the clearance of para-aminohippuric acid (PAH) because PAH is both filtered and secreted by the kidney.

18
Q

What is the equation for effective renal plasma flow?

A

RPF = C(PAH) = U(PAH)/[Ppah]

19
Q

What is the equation for measurement of RBF?

A

RBF = RPF/(1-Hct)

20
Q

What is used to measure Glomerular filtration rate and why is it used?

A

Insulin is used to measure GFR because it is filtered but neither secreted or reabsorbed by the kidney.

21
Q

What is the equation for GFR?

A

GFR = Uinsulin/[Pinsulin]

22
Q

What two substances are used to monitor GFR andy why are they used?

A

Blood urea nitrogen (BUN) and serum Creatinine. Both increase in the serum when GFR is decreased.

23
Q

What is prerenal azotemia and what is its effect on BUN and creatinine?

A

Prerenal azotemia is hypovolemia that increases serum BUN more so than cratinine thus raising the BUN : Creatinine ratio.

24
Q

What happens to the GFR with aging?

A

The GFR decreased with age although the creatinine remains the same because of decreased muscle mass.

25
Q

What is the filtration fraction?

A

Filtration fraction is the fraction of RPF that is filtered across the glomeruli.
filtration fraction = GFR/RPF

26
Q

What is the normal filtration fraction?

A

About .20 or 20%

27
Q

What is the result of increased filtration fraction?

A

increased protein concentration in the peritubular blood leading to increased reabsorption from in the proximal tubule.

28
Q

What is the result of a decreased filtration fraction?

A

decreased protein concentration in the peritubular blood leading decreased reabsorption in the proximal tubule.

29
Q

What is the driving force behind glomerular filtration?

A

net ultrafiltration pressure (starlings forces) which always forces fluid out of the capillaries.

30
Q

What is starlings equation?

A

GFR = Kf [ (Pgc-Pbs) - (Cgc - Cbs) ]

Kf is the filtration coefficient (related to glomerular barrier.)
P is hydrostatic pressure
C is colloid osmotic pressure

31
Q

What prevents negatively charged plasma proteins from being filtered?

A

Anionic glycoprotein line the barrier of the glomerular filtration slits and prevent negative proteins from leaving.

32
Q

Why is bowman’s space oncotic pressure normally zero?

A

because very little protein is normally filtered by the glomerulus.

Renal Module (17 decks)

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