RBF & GFR - Rao Flashcards
Hydrostatic and oncotic pressure in the glomerulus?
Hydrostatic high; oncotic lower but goes up
In which arteries does hydrostatic pressure drop occur?
Afferent arteriole, efferent arteriole
In which arteries does oncotic pressure go up?
Glomerulus
What is an example of a substance that is freely filtered and neither reabsorbed or secreted?
Inulin
What is an example of a substance that is freely filtered, partly reabsorbed, and not secreted?
urea
What is an example of a substance that is freely filtered, not reabsorbed, but secreted from tubules?
Creatinine
What is an example of a substance that is freely filtered but completely reabsorbed?
Glucose
What is the difference in ion concentration between plasma and filtrate?
Filtrate has 5% more anions and 5% less cations
What is a normal GFR?
120-130ml/min
What is filtration fraction?
GFR/RPF, or basically the fraction of kidney blood supply that is filtered through glomeruli per minute
What would ureteral obstruction do to GFR and FF?
Reduce
What would renal artery stenosis do to RPF and FF?
Reduce RPF, increase FF
What is Kf?
Filtration coefficient
Kf=Hydraulic conductivity*SA of glomerulus capillary
Measures capillary permeability to solutes
Much much higher in glomerulus than anywhere else
What happens to Kf during DM?
Reduced bc of thickening of basement membrane and capillary damage
Which two forces favor filtration?
Glomerulus hydrostatic and Bowman’s space oncotic pressure
Which two forces oppose filtration?
Glomerulus oncotic pressure and Bowman’s space hydrostatic pressure
What is a normal Kf?
.08
How does capillary oncotic pressure change during slow plasma flow/change in protein concentration in glomerulus?
Low capillary flow causes increased filtration fraction, leading to increased glomerular oncotic pressure, then lower net filtration pressure and lower GFR
The kidney autoregulates GFR by controlling this variable tightly
RPF
How is RPF controlled?
Changes in relative vascular resistance
What are the two major ways to autoregulate?
Myogenic - direct arteriolar smooth muscle stimulation
Tubuloglomerular feedback via juxtaglomerular complex monitoring
What does the macula densa do when it senses high NaCl?
Increase afferent resistance to lower GFR
What does the macula densa do when it senses low NaCl?
Decrease afferent resistance to raise GFR
Explain the renin-angiotensin system
A reduction in arterial pressure or EC fluid volume lowers the glomerular hydrostatic pressure and GFR. MD senses the reduced Cl- since filtration has slowed, and the juxtaglomerular cells of MD secrete renin. Renin activates angiotensin I from a2-globulin, which in turn activates angiotensin II. ATII causes aldosterone release from the adrenal cortex, resulting in increased sodium and water retention.
