(5) Renal blood flow and glomerular filtration rate (Pierce) Flashcards
Excretion rate = urine concentration * urine flow rate
60 * 0.001 = 0.06
Step 1: Identify all the variables
Step 2: Calculate clearance
Step 3: Determine GFR
B. 110 mL/min
What is a normal GFR?
Aprox 125 mL/min
A. 44.6 mL/min
A. Increase
The greater the FF, the higher the oncotic pressure in the peritubular capillaries. That is because FF represents the loss of protein free fluid into bowman’s space, thereby increasing the concentration of protein in the plasma.
What are these images denoting?
Left = PGc is the hydrostatic pressure within the glomerular capillary
Right = PBc is the hydrostatic pressure within bowman’s capsule
What are these forces?
Left= oncotic pressure within the glomerular capillary
Right = oncotic pressure within Bowman’s capsule
How do you calculate net filtration pressure by the glomerular capillaries?
Using these numbers
60-18-32 = + 10 mmHg
Being FILTERED because of the + number
What is the major equation for GFR?
Kf= ultrafiltration coefficient
Puf= Capillary ultrafiltration pressure
What will change our ultrafiltration coefficient (Kf)?
Influences to the SURFACE AREA
What are the major sites of regulation for hydrostatic pressures in renal vasculature?
Describe what is occuring in this image
Constriction/Dilation in the afferent arteriole and efferent arteriole has an effect on GFR
Constrict afferent = lower GFR
Dilate afferent = higher GFR
Constrict efferent = higher GFR
Dilate efferent = lower GFR
Approximate average GFR?
125 mL/min
What the things that regulate GFR?
Sympathetics
Vasoactive Signals
Hormones
What are the intrinsic mechanisms for regulating renal hemodynamics?
Autoregulation
Tubuloglomerular feedback
What are the extrinsic mechanisms for regulating renal hemodynamics?
Sympathetic nerves
Hormones
Composition of blood
Where are more alpha 1 receptors located?
Afferent/efferent arteriole?
FAR more on the afferent arteriole
Purpose of autoregulation?
What are the two types of reactions?
Maintains RBF and GFR within narrow limits across wide ranges of blood pressures
Local reflex: (myogenic)
Physiological feedback: (tubuloglomerular feedback)
What is the autoregulatory range?
80-170 mmHg
Describe what is occuring during local myogenic feedback reflex:
Afferent arteriolar constriction
Efferent arteriolar dilation
*When BP goes up, this reflex prevents an increase in RBF/GFR
What transduces messages regarding the glomerulus?
What secretes renin?
What “senses”?
Mesangial cells
Juxtaglomerular cells
Macula densa
What makes up the juxtaglomerular apparatus?
- Macula densa cells
- Juxtaglomerular (granular) cells
- Extraglomerular mesangial cells
Describe what tubuloglomerular feedback is
Feedback mechanism between the juxtaglomerular apparatus and the tubes to modify arteriolar resistance as needed
Signals occur b/w macula densa cells and JG cells
***Maintains constant Na+ delivery to the distal tubule and constant GFR
Describe macula densa signaling
When there is an increase in NaCl delivery to the macula densa…
Increase in ATP/adenosine….
Which vasoconstricts afferent arteriole via calcium signaling
Which lowers GFR
In the case of increased renal perfusion pressure,
Signals generated by macula densa results in…
VASOCONSTRICTION
of afferent arteriole to decrease GFR
*Mediated by Adenosine
In the case of decreased renal perfusion pressure,
what happens?
Macula densa signals to JG cells to secrete renin
Renin –> Angiotensni II (vasoconstrictor) to restore BP
Results in efferent arteriolar vasoconstriction
Macula densa causes afferent arteriolar dilation mediated by NO
Macula densa measures
NaCl levels
It’s the gatekeeper
Reduced perfusion pressure stimulates ______ secretion by the afferent arteriole
Increased perfusion pressure inhibits _______ secretion by the afferent arteriole
RENIN
Sympathetic activity increases ______ secretion via Beta-adrenergic receptor stimulation
Renin
When NaCl delivery to the macula densa is decreased, _______ secretion is enhanced
Renin
An increase in NaCl delivery to the macula densa inhibits ______ secretion
Renin
What are factors that increase sensitivity of tubuloglomerular feedback
Volume contraction
Adenosine
PGE
Thromboxane
Ang II
What are factors that decrease sensitivity of tubuloglomerular feedback
Volume expansion
ANP
NO
cAMP
PGI
*High protein diet
C. Decrease in afferent arteriolar tone
D.
B
B. 4 fold decrease in GFR
Plasma [creatinine] is inversely proportional to GFR
E. Increase in afferent arteriole tone
FF = GFR/RPF
GFR = Kf*(PG-PB-πG)
=10*(70-20-35) = 150 ml/min
FF=150/428=0.35
e) 0.35
