Renal Physiology Part 2 Flashcards Preview

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Flashcards in Renal Physiology Part 2 Deck (62)
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-kidney guards filtration carefully
-accomplished by the glomerulus being situated between 2 arteriolar beds
-vascular tone in these 2 beds protects the delicate glomerular architecture at times of high blood pressure and preserves GFR at times of low systemic blood pressure


You can control GFR by

adjusting resistance of afferent and efferent arterioles


Afferent arteriolar constriction

-greater pressure drop upstream of glomerular capillaries
-Pgc falls, which lowers GFR
-renal blood flow falls due to increased resistance
-want to protect again hyperperfusion; high pressure


Efferent arteriolar constriction

-pooling of blood in glomerular capillaries
-increased Pgc increase GFR
-renal blood flow decreased
-want to protect against hypo perfusion; low pressure


In a patient with hypertension secondary to renal artery stenosis, treatment with an ACE inhibitor will

-decrease BP, RBF, and intraglomerular pressure below normal due to the stenosis.
-although auto regulation normally maintains glomerular pressure/GFR by increasing efferent arteriolar constriction, an ACE inhibitor decreases formation of angiotensin II and blunts this response with a net effect of lowered GFR


Moderate efferent arteriolar constriction

-increased Pgc
-increased GFR
-decreased RBF


Effects of Sympathetic stimulation

-invoked in any situation which results in hypo perfusion of the renal vasculature bed
-constriction of afferent and, to a lesser extent, efferent arterioles: decreased RBF, GFR--diverts the renal fraction to vital organs
-increased renin secretion by granular cells
-angiotensin II thus produced restores blood pressure (systemic vasoconstriction)
-angiotensin II promotes arteriolar constriction (efferent > afferent): raises bp, may stabilize GFR (moderate ang II)
-stimulates Na+ reabsorption in proximal tubule, thick ascending limb of Henle's loop, distal convoluted tubule, collecting duct


Renal prostaglandins

-dampen vasoconstriction by angiotensin II and sympathetic activity


high doses of chronic use of NSAIDS

-block prostaglandin production and may have a deleterious effect on renal function


Renal Clearance

-volume of plasma form which a substance is completely removed (cleared) by the kidneys in a given time period
-units are volume/time, e.g. ml/min, l/hr, etc
-describes how effectively the kidneys remove a substance form the bloodstream and excrete it into the urine.
-different substances have different clearances


Clearance of substance X=

concentration of X in urine x urine volume/concentration of X in plasma


Creatinine clearance approximates




-long term monitoring of GFR
-inversely proportional to GFR
-in reality, inverse relationship isn't perfect: differences in lean muscle mass among patients; compensatory increased proximal tubule secretion
-useful for long-term monitoring of renal function


Theoretically, if GFR falls to 50% of normal, Pcreatinine

-should increase 2x over a few days
-e.g. if a patient has a plasma creatinine of 1 mg/dL and a creatinine clearance (GFR) which drops from 100 ml/min to 50 ml/min, then the expectation is that their plasma creatinine will rise to approximately 2 mg/dL over several days


BUN/creatinine ratio >20/1

-prerenal problem
-BUN reabsorption is increased
-BUN is disproportionately elevated relative to creatinine in serum
-reduced renal perfusion due to hypovolemia


BUN/creatinine ratio 10-20/1

-normal range or postern
-normal range; can also be postern disease (obstruction)
-BUN reabsorption within normal limits


BUN/creatinine ratio

-intrarenal problem
-renal damage causes reduced reabsorption of BUN and a lower BUN:Cr ratio


BUN and creatinine are both

-freely filtered by glomerulus, however urea reabsorbed by the tubules can be regulated (inquired or decreased) whereas creatinine reabsorption remains the same (minimal reabsorption)


Filtration Fraction (FF)

-fraction of total renal plasma flow which is filtered through glomerular membrane
-the proportion of fluid reaching the kidneys which passes into the renal tubules
-normally, approximately 20%


In renal artery stenosis or severe hemorrhage,

-blood flow (RPF) to kidney is reduced, so increased filtration fraction
-a higher proportion of that flow reaching the kidney must be passed into the renal tubules in order to perform the normal tasks of the kidney in balancing fluid and electrolytes in the body and maintain homeostasis
-this higher proportion of the total blood flow being passed into the tubules results in a higher filtration fraction
-i.e. the kidneys have to do more work with the fluid they are receiving
-reflected in a higher FF


Glomerular Filtration

-filtration of plasma from glomerular capillaries into Bowman's capsule


Filtered load of a substance x=

GFR x Px


Tubular reabsorption

-transferral of substances from tubular lumen to peritubular capillaries


Tubular secretion

-transferral of substances from peritubular capillaries to tubular lumen



-voiding of substances in the urine


urinary excretion=

amount filtered - amount reabsorbed OR amount filtered + amount secreted
-product of urine flow rate x concentration of substance in the urine


Tubular reabsorption=

glomerular filtration - urinary excretion


net rate of reabsorption or secretion of a substance=

difference between glomerular filtration and urinary excretion (assuming substance is not produced or metabolized by the kidneys)


If excretion

net reabsorption occurred


If excretion > filtration

net secretion occurred