Physiology 3 (easy) Flashcards
Normal GFR
125ml/min
Major determinant of GFR
Glomerular capillary fluid blood pressure
Extrinsic regulation of GFR
Sympathetic control via baroreceptor reflex
Intrinsic regulation of GFR (autoregulation)
- Myogenic mechanism
- Tubuloglomerular feedback mechanism
Does vasoconstriction or vasodilation increase GFR?
Vasodilation
What is the myogenic mechanism
If vascular smooth muscle is stretched, (i.e. arterial pressure is increased), it constricts thus constricting the arteriols
What is the tubuloglomerular feedback mechanism?
If GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles
What is the plasma clearance?
A measure of how effectively the kidneys can ‘clean’ the blood of a substance
How do you calculate clearance of substance X?
Rate of excretion/plasma concentration
What is filtration/secretion/reabsorption of H+?
Filtered, secreted but not reabsorbed
Clearance
Reabsorbed
Clearance = GFR
Neither reabsorbed or secreted
Clearance > GFR
Substance secreted
Name an exogenous organic anion used to measure renal plasma flow
Para-amino hippuric acid (PAH)
Why use PAH?
- freely filtered
- secreted into tubule
- completely cleared from plasma
Average renal plasma flow
650ml/min
Properties a clearance marker should have
Non-toxic
Inert (i.e. not metabolised)
Easy to measure
Should be filtered freely but not secreted or reabsorbed
GFR marker
Should be filtered and completely secreted
RPF
What is the filtration fraction and how do you calculate it?
The fraction of plasma flowing through the glomeruli that is filtered into the tubules
(GFR/renal plasma flow)
-remember roughly 20% is filtered
How do you calculate renal blood flow?
RPF x 1/1-Hct
Hct = haemocrit
