GFR, RBF, and clearance Flashcards
What is the renal definition of filtration?
Movement of ultrafiltrate of plasma into Bowman’s space
What is the general equation for excretion?
Excretion = Filtration - reabsorption + secretion
What is the normal volume of glomerular filtration per minute and per day?
120 mL/min or 180 L/day
What is the is the filtration fraction?
GFR/RPF
What is the equation for GFR?
Kf x net filtration pressure
What are the autoregulation mechanisms of renal blood flow?
Myogenic response
Tubuloglomerular feedback
What is the myogenic response in renal autoregulation?
Stretch receptors activated to cause vasoconstriction
What is the function of the macula dense?
Responds to increased Na and Cl levels to trigger tubuloglomerular feedback
What are the two end results of tubuloglomerular feedback?
Decreased renin release
Vasoconstriction
What is the direct action of SyNS stimulation in the kidney?
Acts on alpha-1 receptors to constrict afferent arterioles, decreasing GFR
What is the mechanism of SyNS constriction of efferent arterioles?
SyNS stimulates beta-1 receptors on granular cells to increase renin release; angiotensin II causes efferent vasoconstriction
What stimulates renal prostaglandin synthesis?
Increased SyNS
Increased angiotensin II
What is the role of renal prostaglandins?
Modulating effect on the vasoconstriction caused by SyNS and angiotensin II
What stimulates release of ANP and BNP?
Increased blood volume
What stimulates NP production in the kidney?
Increased blood volume
Vasoactive hormones
What is the definition of clearance?
Volume of plasma which contains the substance excreted per given time
What is the equation for clearance?
Cx = (Ux x V)/Px
Excreted = urinary concentration x urine flow
What are the properties of inulin in the kidneys?
Freely filtered
Not reabsorbed or secreted
What are the properties of creatinine in the kidneys?
Freely filtered
Not reabsorbed
Slightly secreted
What are the properties of PAH in the kidneys?
Freely filtered
Actively secreted
Not reabsorbed
What is the equation of RBF?
RBF = RPF x [1/(1-hematocrit)]
What is the equation for net transport?
Net transport = filtered load - rate of excretion
What is indicated by a positive net transport?
Filtered load > rate of excretion
substance is reabsorbed
What is indicated by a net transport equal to zero?
Substance is freely filtered
It is not reabsorbed or secreted
What is indicated by a negative net transport?
Rate of excretion > filtered load
Substance is freely filtered and secreted
What is likely for a substance whose clearance is higher than the clearance of inulin?
Substance is likely freely filtered and secreted
What is likely for a substance whose clearance is less than the clearance of inulin?
It is likely filtered and partially reabsorbed
What does a clearance of 0 indicate about a substance?
It is either not filtered, or filtered and entirely absorbed
What is indicated about a substance whose clearance is equal to the clearance of PAH?
It is filtered and entirely secreted
What is the effect of decreased GFR on BUN?
BUN will increase
What are the properties of BUN in the kidney?
Freely filtered
About 50% reabsorbed
How is BUN affected by ADH?
Increased ADH will increase BUN reabsorption
What is the affect on plasma creatinine and BUN if GFR is reduced by half?
Both plasma concentrations will double
