Elements of Renal Function - McCormick Flashcards
Characteristics of cortical nephrons
Short loops of Henle
Surrounded by peritubular capillaries
Characteristics of Juxtamedullary nephrons
Long loops of Henle
Long efferent arterioles are divided into specialized peritubular capillaries - the vasa recta
Functions to concentrate urine
Venous drainage of kidney
Interlobular v
Arcuate v
Interlobar v
Renal v
What is in charge of filtration?
Glomerular capillaries
High hydrostatic pressure - 60mmHg
What is in charge of reabsorption?
Peritubular capillaries
Lower hydrostatic pressure - 13mmHg
Large amts of water and solute reabsorbed
Which portion of the kidney receives the most amount of blood?
Cortex - 4-5 L
Outer medulla - .7-1 L
Inner medulla - .2-.25 L
What two places do sympathetic neurons synapse on? What is effect?
- Smooth muscle - afferent arteriolar constriction
2. Granular cells - in afferent arterioles causing renin secretion
4 Basic processes of urine formation?
Glomerular filtration - Bowman’s
Tubular Reabsorption - lumen to peritubular cap
Tubular Secretion - peritubular back to lumen
Excretion
How to calculate urinary excretion?
Amount filtered - amount reabsorbed + amount secreted
If excretion rate is higher than filtration rate?
Tubular secretion must have occurred
And vice versa
Filtration rate
Of any freely filtered substance
GFR x plasma concentration of substance
Clearance
The volume of plasma from which a substance is completely removed (cleared) by the kidneys in a given period of time
-how effectively the kidneys remove a substance from the bloodstream and excrete it in the urine
Varies
How do you calculate the clearance of a substance?
Cx = Ux x V / Px
What are the requirements if a compound is used to estimate GFR?
Freely filtered
Not secreted, reabsorbed, produced or degraded by the kidneys
Ex. inulin
What is good for monitoring of long term GFR
Pcreatinine
Inversely proportional to GFR
A BUN/Cr ratio of > 20/1 indicates?
Preranal
-reduced to renal perfusion due to hypovolemia
BUN reabsorption is increased, sitting around longer so more of it gets taken up
BUN/Cr ratio of 10-20/1 indicates?
Normal range or post renal problem
ex. obstruction
BUN/Cr ratio of < 10/1 indicates?
Intrarenal problems
Renal damage causes reduced reabsorption of BUN
Advantages of using Cystatin C as a marker of GFR?
Continuously made by nucleated cells
Freely filtered
NOT dependent on muscle mass like creatinine
PAH clearance estimates?
Estimates renal plasma flow
Filtration fraction
The part of renal plasma flow (RPF) that is filtered/diverted into the tubule
Changes with ultrafiltration pressure
Normally ~ 20%
How to calculate filtration fraction?
FF = GFR/RPF
What happens with an increased FF?
The oncotic pressure of the efferent arteriole increases, facilitating reabsorption of tubular fluid
