Tubular Transport Flashcards
Glomerular filtration rate (GFR) is the sum of ______ and driven by ______
- filtration rates of all functioning nephrons per unit of time
- driven by Starling forces
What is creatine used to measure?
GFR because it’s not reabsorbed or secreted
GFR is used to determine…
health of kidney function
- decrease in GFR = increase in kidney disease progression
Hydrostatic pressure of glomerular capillaries (Pgc) is usually at what mmHg?
58 mmHg
- outward force that moves fluid from glomerular capillaries to Bowman’s capsule
Hydrostatic pressure of glomerular capillaries (Pgc) is maintained high by…
- large diameter of afferent arterioles
- small diameter of efferent arterioles
What is the main force that affects GFR?
Hydrostatic pressure of glomerular capillaries (Pgc)
What happens if there is an increase in hydrostatic pressure of glomerular capillaries (Pgc)?
- decrease in afferent arteriole resistance
- increase in efferent arteriole resistance and renal arteriolar pressure
Hydrostatic pressure of fluids in Bowman’s capsule (Pb) is usually at what mmHg?
15 mmHg
- inward force that opposes filtration
Hydrostatic pressure of fluids in Bowman’s capsule (Pb) increases when…
nephron is obstructed
- makes sense since it opposes filtration
Colloid osmotic pressure of glomerular capillary proteins (PIgc) is usually at what mmHg?
30 mmHg
- inward force that opposes filtration
Colloid osmotic pressure of Bowman’s capsule is usually at…
zero
How do disease states affect intrinsic permeability and glomerular SA available (k)?
decrease K because there is a decreased SA
What can increase intrinsic permeability and glomerular SA available (k)?
drugs that dilate afferent arteriole
GFR is a function of…
filtration pressure and filtration coefficient of the filtration membrane over time
How can you measure GFR indirectly?
by measuring renal clearance, which is the volume of plasma cleared of a given substance by kidney over time
What are the four possible scenarios for a filtered substance during renal clearance?
- filtered only (Csolute = GFR)
- filtered and partly reabsorbed (Csolute < GFR)
- filtered and all reabsorbed (Csolute = 0)
- filtered and some secreted (Csolute > GFR)
What gives us a direct indication of GFR?
substances that are only filtered
- has to freely filter across glomerulus into Bowman’s capsule
- not be reabsorbed or secreted by nephron
- not metabolized or produced by kidney
What is the most accurate way to determine GFR?
by measuring inulin clearance
- not made or metabolized by cells
- filtered only
- administered via IV
What is the average GFR for males and women?
- average: 125 mL/min
- males: 90-140 mL/min
- females: 80-125 mL/min
What is the most widely used method for clinical estimate of GFR and what are the advantages and disadvantages?
creatinine, which occurs during skeletal muscle metabolism
- advantage: relatively constant concentration so no IV needed
- disadvantage: some is secreted by PCT
T/F: all plasma entering the kidneys is filtered
F, not all of it is filtered
- portion that is filtered contributes to filtration fraction (Ff)
Filtration fraction is normally what percent of plasma volume?
15-20%
How does renal plasma flow (RPF) affect filtration fraction?
- decrease in RPF = increase in filtration fraction (occurs via hemorrhage, vasoconstriction)
- increase in RPF = decrease in filtration fraction (occurs b/c of diruetics)
RPF is usually what mL/min?
625mL/min
How do you find renal blood flow (RBF)?
aortic pressure - renal venous pressure
T/F: GFR and RBF are held within narrow limits
T via autoregulation
- holds it constant between a MAP range of 80-180 mmHg
What are some local mechanisms responsible for autoregulation?
- tubuloglomerular feedback through juxtaglomerular apparatus (JGA)
- myogenic mechanism
- endothelium derived products
- inflammatory mediators
- mesangial cells
