Renal System 3 Flashcards
What is renal clearance?
Measure the ability of the kidney to extract any given molecule from the blood and eliminate it from the body
How well can the kidney filter substances to get rid of them?
What is the unit of renal clearance?
ml/min (it should be mass/min) EXAM!!
it is a virtual volume: because you can’t identify a specific cleared volume
If you clear 1g/1000ml every hr -> you would clear 200 ml every hour -> because 5g : 5 —> 1000 ml :5 = 200 ml
Renal clearance depends on:
GFR (ml/min), at which fluid moves from the blood into Bowman’s capsule
When is the clearance of a substance considered equal to GFR?
1) when it is freely filtered (isoosmotic on both sides of the filtration barrier
2) not reabsorbed, not secreted -> amount filtered = amount excreted
The formula for Renal clearance? EXAM!!
U V over P
U = concentration of a substance in urine (urine sample)
V = Volume of urine (urine sample)
P = concentration of a substance in blood plasma (blood sample)
Cx = Ux * V / P = ml plasma / min
What substance was used initially to determine GFR?
!!! it is freely filtered, not reabsorbed, not secreted -> only excreted !!!111
Inulin
Why can we use creatinine as GFR, even though 0.3 g is secreted per day?
Because we exactly know the value of 0.3 g per day, we know that the clearance of creatinine exceeds GFR by 20% (0.3g p day)
What is the estimated creatinine level if the kidney doesn’t work properly?
If the GFR (glomerular filtration rate) is low, the kidney doesn’t filtrate enough -> creatinine level in the plasma would be higher than it should be
Example: What needs to be checked before dosing of aminoglycosides ?
GFR, beacause aminoglycosides are used to treat serious infection but it can damage the kidneys when it is too high
aminoglycosides are cleared by the kidneys -> have to make sure the kidneys work properly
What is PAH how does it pass the Bowman´s capsule?
PAH - para amino hippuric acid
-some of it gets freely filtered
-no reabsorption
-anything that is not filtered, passes the efferent arteriole -> and gets secreted into Bowman´s space to urine by 100%
What was PAH used for? EXAM !!!!
to determine renal plasma flow (RPF)
because 100% gets excreted
Clearance of PAH = renal plasma flow (RPF)
RPF / (1 - hematocrit) = RBF (renal blood flow)
What is Micturition?
Emptying the bladder
-partly controlled voluntarily
-the involuntary part is controlled by autonomous NS
-> Parasaympathetic: Let it flow
-> Sympathetic: No, don’t go
What muscle types does the bladder consist of?
Detrusor (smooth) - relaxes and allows the bladder to fill, and contract when you urinate
Internal urethral sphincter (smooth) - involuntary - it opens
External urethral sphincter (skeletal) - voluntary -> you tell to relax, open
How are the muscles controlled?
By neurotransmitters
For micturition and contraction:
Detrusor -> Parasympathetic: Acetylcholine/musacrinic receptor
(muscarinic receptor because smooth muscle)
Internal sphincter -> Sympathetic: NE/alpha receptor
External sphincter -> Sympathetic: Acetylcholine/nicotinic receptor
(nicotinic because skeletal muscle)
