RP3: Glomerular Filtration, Renal Blood Flow and Their Control Flashcards
What is the filtration fraction?
Filtration Fraction = GFR/RPF
RPF - renal plasma flow
Blood in Glomerular Capillaries separated from Bowman’s Space by a…
Filtration Barrier
What are the three layers of the filtration barrier?
- Capillary endothelium (Fenestrated)
- Basal Lamina (Basement Membrane)
- Podocytes (Visceral Layer of Bowman’s Capsule)
- Foot processes that cover outside of basal lamina
- Creates Filtration Slits
What determines the ability of a solute to penetrate the golmerular membrane?
- size (smaller filter better)
- charge (cations filter better)
What is GFR usually high?
high hydrostatic pressure
high Kf
What is the equation for GFR?
GFR = Kf x NFP (Net Filtration Pressure)
What is the usual values for starlings forces in the glomerular membrane?
glomerular hydrostatic pressure (Pg) = 60 mmHg
bowman’s capsule pressure (Pb) = 18 mmHg
glomerular oncontic pressure (Ng) = 32
What is the usual net filtration pressure (NFP)?
10 mmHg
125 mL/min
180 L/day
What is Kf?
the glomerular capillary filtration coefficient (Kf)
Kf = hydraulic conductivity x surface area
What is the primary control point for GFR?
glomerular hydrostatic pressure (Pg)
What are factors that influence glomerular hydrostatic pressure (Pg)?
- arterial pressure (effect is buffered by autoregulation)
- afferent arteriolar resistance
- efferent arteriolar resistance
What are diseases that can affect GFR via bowman’s capsule pressure (Pb)?
- Tubular Obstruction
(kidney stones, tubular necrosis) - Urinary tract obstruction
(prostate hypertrophy/cancer)
GFR _________ along length of capillary.
decreases
Glomerular Capillary Colloid Osmotic Pressure (πG) ________ along length of glomerular capillary
Increases
Hydrostatic Pressure in Glomerular capillaries (Pg) can be altered by
altering the resistance of the…
afferent and efferent arterioles
Constricting the afferent arteriole ______ GFR via Pg
decreases
Constricting the efferent arteriole ______ GFR via Pg
increases
Dilating the efferent arteriole ______ GFR via Pg
decreases
Dilating the afferent arteriole ______ GFR via Pg
increases
What diseases causes a decrease in Kf?
Renal disease
diabetes mellitus
hypertension
all have decreased GFR
What diseases cause increased Pb?
urinary tract obstruction
decreased GFR
What diseases cause increased πG?
increased plasma proteins
dehydration
decreased GFR
What is the function of myogenic autoregulation?
Keeps RBF and GFR relatively constant in spite of changes in MAP
What is the reflex associated with myogenic autoregulation?
vessel constriction in response to increased MAP
What is the function of tubuloglomerular feedback (TGF)?
Helps ensure a nearly constant delivery of Na+ and Cl- to the distal nephron – Keeps GFR constant
What regulatory method is the juxtaglomerular apparatus associated with?
Tubuloglomerular Feedback (TGF)
What are the two cells of the juxtaglomerular apparatus?
Juxtaglomerular cells
Macula densa cells
What do the juxtaglomerular cells do?
- Primarily in walls of afferent
arterioles - Secrete Renin
What cells secrete renin?
juxtaglomerular cells
What do the macula densa cells do?
➢ In close contact with JG cells
➢ Sense [Na+] and [Cl-] in filtrate
What are the stimuli for renin release?
- decreased blood pressure
- decreased renal blood flow
- decreased NaCl delivery to macula densa
What can increase proximal NaCl reabsorption?
- macula densa
- increased amino acids
- increased glucose
What paracrines/autocrines are vasoconstrictors at the local control level?
endothelin
dopamine (kinda)
What paracrines/autocrines are vasodilators at the local control level?
prostaglandins
NO
bradykinin
dopamine (kinda)
What are vasoconstrictors at the systemic level?
sympathetic nervous system
epinephrine
Renin-angiotensin system
ANP for efferent
What are vasodilators at the systemic level?
ANP for afferent
What is Epi/NE effect on renal blood flow and GFR?
decrease both
What is endothelins effect on renal blood flow and GFR?
decrease both
What is angiotensin IIs effect on renal blood flow and GFR?
decrease renal blood flow
increase GFR
What is ANP, PGE, bradykinin, and NO’s effect on renal blood flow and GFR?
increase both for all of them
What are some other factors that increase GFR and RBF?
- high protein diet
- high blood glucose levels
Both of these increase GFR and result in reduced NaCl delivery to macula densa.
What is the filtered load equation?
Fx = (GFR) ([X]plasma)
What is the excretion rate equation?
Ex = (Uv)([X]urine)
What is the clearance rate equation?
Clx = Ex/[X]plasma
➢ Clinulin and Clcreatinine used as index of GFR
➢ ClPAH used as index of RBF (Renal Blood Flow)
