Renal Basics Flashcards
75% of gluconeogenesis occurs in the liver
25% of gluconeogenesis occurs in the ______
kidneys
Renal plasma flow rate
amount of plasma that passes through kidneys per minute
~600 mL/min
Total blood flow through kidneys per minute
~1000 mL/min
Macula densa
cells located at junction of afferent and efferent arterioles
sense changes in sodium concentration
- can cause vasodilation
- renin release control from juxtroglomerular cells
Mesangium
specialized sm muscle cells that regulate bloodflow in the kidney
Molecules up to what size are freely filtered into Bowman’s space?
< 7,000 D
Molecules up to what size will be completed excluded from filtration into Bowman’s space?
> 70,000
What is the approximate size of albumin?
66,000 D
*some escapes into Bowman’s space and is lost in the urine
Is albumin lost into the urine?
yes, some
MW = 66,000 D
some filtered up to 70,000 D
Charge of glomerulus basement membrane
negative
+ charges more easily filtered into Bowman’s space
- charges less easily filtered into Bowman’s space
Normal values for:
Pgc (glomerular capillary)
Pbs (Bowman’s space)
πgc
πbs
Pgc = 60
Pbs = 15 (because backing up to filtrate)
πgc = 29
πbs = 0 (unless pathologic albumin filtration)
Normal GFR
in mL/min
125 mL/min
Effect of NE on renal arteries and GFR
constricts both afferent and efferent arterioles
overall decrease in GFR due to decreased blood flow
Effect of angiotensin II on renal arteries and GFR
preferentially constricts efferent arteriole
increased GFR
Effect of prostaglandins on renal arteries and GFR
dilation of afferent
increased GFR
How do COX inhibitors affect renal arteries?
decrease PG synthesis
decreased afferent dilation
increased afferent vasoconstriction
Peritubular capillaries arise from…
efferent arterioles
What is the equation used to calculate GFR?
GFR x [Xp] = UFR x [Xu]
[Xp] = concentration of X in plasma
UFR = urine filtration/formation rate
[Xu] = concentration of X in urine
In what clinical circumstance is creatinine clearance absolutely a poor test choice?
catabolic state
serum creatinine is not stable
2 reasons why, even when you do the test perfectly, measuring a 24 hr creatinine collection is not a good test
10-40% of creatinine is secreted (not filtered)
(and we want to measure GFR–glomerular FILTRATION rate)
creatinine is synthesized at variable rates depending on moment to moment metabolic changes
How can 24 hr urine creatinine collection be misleading in early stages of decreased GFR?
creatinine is secreted
this occurs after filtration
since creatinine is secreted out of the kidney instead of filtered out, this is not a good test
