Costanzo Renal Physiology: Renal clearance, blood flow, and GFR Flashcards
(32 cards)
What is renal clearance?
The volume of plasma cleared of a substance per unit time.
What are the unit for renal clearance?
mL/min or mL/24hr
What is the equation for renal clearance?
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)
What proportion of cardiac output does the kidney receive?
25%
What factors are directly proportional to renal blood flow?
The pressure difference between renal artery and renal vein
What factor is renal blood flow inversely proportional to?
RBF is inversely proportional to the resistance of the renal vasculature.
What mediates renal vasoconstriction?
The sympathetic nervous system and angiotensin II.
What is special about low concentration aniotensin II?
It preferentially constricts the efferent arterioles leading thus protecting the GFR.
What is the effect of angiotensin converting enzyme (ACE) inhibitors?
Decreased angiotensin II and thus dilating efferent arterioles and reducing GFR.
What is the effect of vasodilation on RBF?
Vasodilation increases RBF
What are the factors which cause renal vasodilation?
(1) PGE2
(2) PGI2
(3) dopamine
(4) bradykinin
(5) nitric oxide.
How is a constant rate of RBF maintained?
If arterial pressure changes then the renal vascular resistance changes
Within what range does RBF remain constant?
Between 80-200 mm Hg
What are the two mechanisms for autoregulation of RBF?
Myogenic mechanisms and Tubuloglomerular feedback.
What is the myogenic mechanism of RBF regulation?
Renal afferent arterioles contract in response to stretch.
What is the tubularglomerular feedback mechanism of RBF regulation?
increased renal arterial pressure leads to increased fluid load on the macula densa which causes constriction of nearby blood vessels.
How is renal plasma flow measured and why is it measured like this?
By the clearance of para-aminohippuric acid (PAH) because PAH is both filtered and secreted by the kidney.
What is the equation for effective renal plasma flow?
RPF = C(PAH) = U(PAH)/[Ppah]
What is the equation for measurement of RBF?
RBF = RPF/(1-Hct)
What is used to measure Glomerular filtration rate and why is it used?
Insulin is used to measure GFR because it is filtered but neither secreted or reabsorbed by the kidney.
What is the equation for GFR?
GFR = Uinsulin/[Pinsulin]
What two substances are used to monitor GFR andy why are they used?
Blood urea nitrogen (BUN) and serum Creatinine. Both increase in the serum when GFR is decreased.
What is prerenal azotemia and what is its effect on BUN and creatinine?
Prerenal azotemia is hypovolemia that increases serum BUN more so than cratinine thus raising the BUN : Creatinine ratio.
What happens to the GFR with aging?
The GFR decreased with age although the creatinine remains the same because of decreased muscle mass.
