2 RBF and GFR Flashcards
Kidneys receive _________ (fraction) of cardiac output.
1/4 - High flow not needed for metabolism - Needed to support filtration (20% of plasma is filtered)
__% of plasma is filtered.
20
______ liters of filtrate formed per day.
180
FF = _______
GFR/RPF
RBF (constant) = _______
1.1 L/min
RPF (formula) = ________
(1 - Hct)RBF Normal values: (1 - 0.45)(1.1 L/min) = 605 ml/min
Normal GFR = _______
125 ml
Normal FF = _________
GFR/ RPF 125 ml / 605 ml = 0.2 = 20%
What are the vasoconstrictors that regulate RBF and what is their effect on RBF?
- Sympathetic nerves (A1 receptors; decrease RBF and GFR) -Molecules: Angiotensin II, ADH, ATP, and endothelin (decrease RBF and GFR) - Ang II constricts both the afferent and efferent, but the efferent arteriole is more sensitive
What are the vasodilators that regulate RBF and what is their effect on RBF?
Atrial natriuretic peptide (ANP), glucocorticoids, NO, Prostaglandins (PGE2, PGI2) -Increase RBF and GFR
How is autoregulation related to blood flow and GFR?
It maintains a constant blood flow and GFR at different arterial pressures
What can override autoregulation?
large increases in sympathetic tone
During severe blood loss how are RBF and GFR affected?
they both decrease (hypotension)
Throughout what arterial blood pressure range is blood flow regulated (constant)?
80-180 mmHg
What are the 2 mechanisms for autoregulation?
Myogenic mechanism - Intrinsic to VSMC (vascular SM cells) ; contract in response to stretch
Tubuloglomerular feedback (“flow dependent”) - Increasing GFR increases NaCl delivery to LOH; sensed by the macula densa which causes the resistance of the afferent arteriole (Ra) to increase thereby decreasing BF and GFR
the signal affects RBF and GFR mainly by changing the resistnace of the __________ arteriole.
afferent
Purpose of tubuloglomerular feedback
Maintains constancy of salt load delivered o distal tubule
Protein _______ normally pass the filter in significant quantities.
does not
All small-MW solutes that are not protein-bound appear in the filtrate in _________ concentrations as in blood plasma.
the same
The fluid in Bowman’s capsule is essentially a ___________ filtrate of blood plasma.
protein-free
All the composition of plasma and glomerular filtrate will be the same except _________. It will be much higher in the _________.
protein; plasma
Put these in order of the route of the filtrate: basal lamina, fenestrae, filtration slits (between pedicels)
fenestrae, basal lamina, filtration slits
Glomerular filter: substances are separated by ________ and ________.
Size (MW 7000 - can pass, 70,000 - can’t pass)
Electrical charge (basal lamina and slits are coated with negative charges –> proteins (-) are repelled)
In the glomerular filter: the main barriers to proteins are ________ and ________.
basal lamina (-); filtration slits (-)
Write out the starling equation: GFR = ?
GFR = Kf[(Pgc - Pbc) - (πgc- πbc)]
where Kf = filtration coefficient
the rest = the net filtration pressure (NFP)
Note: πbc is ~0 b/c proteins don’t pass into bowman’s capsule
Kf is the filtration produced by each ______ of _________ pressure
mmHg net filtration pressure
Kf for glomerular capillaries versus Kf for capilllaries of skin and muscle?
the Kf for glomerular capillaries is 50-100 times greater than that for capillaries in skin and muscle
Kf can be altered by __________ cells. What affect?
Mesangial, all reduces Kf
Use Kf to calculate GFR
GFR = Kf x NFP
Example:
GFR = 15 ml/min/mmHg x 8 mmHg
= 120 ml/min
What is the main effect of the Pgc on GFR?
driving force of GFR
What is the effect of Pbc on GFR??
Pbc = back pressure in bowman’s capsule –> retards GFR
What is the effect of πgc (oncotic pressure of glomerular cap bed)?
Retards GFR (proteins are unable to cross barrier –> higher concentration in glomerular cap –> pressure towards the higher protein conc.)
What are the average pressures for Pgc, Pbc, IIgc, Iibc, and Kf?
Pgc = 45 mmHg Pbc = 10 mmHg Iibc = ~0 IIgc = 26 mmHg Kf = 14 ml/min/mmHg
How does increased Ra affect Pgc and RBF?
It deccreases Pgc (less afferent = less blood in capillary) It decreases RBF (less flow)
How does increased Re affect Pgc and RBF?
It increases Pgc (like a traffic jam that builds up at the capillary) RBF decreases (any increase in resistance will decrease RBF)
If there is equal increases in Ra AND Re, how will this affect Pgc and RBF?
Pgc will be unaffected (no net difference b/c the two resistances cancel out) The RBF will be severely decreased (lots of resistance)
Name the direct determinants of GFR that, when increased, increase GFR
Kf (glomerular surface area) and Pgc (?renal arterial pressure, ?Ra, ?Re)
Name the direct determinants of GFR that, when increased, decrease GFR
Pbc (intratubular pressure b/c obstruction)
IIgc (systemic-plasma oncotic pressure –> sets IIgc at beginning of glomerular capillaries, ?Renal plasma flow –> increased rise of Iigc along glomerular capillaries)
