Glomerular Filtration&RBF-Exam 2 Flashcards
What are the three renal processes?
Glomerular filtration
Tubular reabsorption
Tubular secretion
Where is the glomerular filtration process?
From glomerular capillaries to Bowman’s capsule
Where is tubular reabsorption?
From renal tubules to peritubular capilaries
Where is tubular secretion?
From peritubular capillaries to renal tubules
What is the equation for excretion?
Excretion = Filtration - Reabsorption + Secretion
How many membranes must be crossed for excretion?
2
Increased sodium; increased filtration; decreased reabsorption=
Increased excretion
Most substances see _______ filtration and _______ reabsorption rate
High; high
Small changes in filtration/reabsorption will produce significant changes in what?
Excretion rate
Why is there a high filtration rate?
- Allows rapid removal of waste products
- Allows multiple passes of blood vol. through kidneys/day
- Allows rapid and precise control of body fluid volume nad composition
What is the normal GFR?
180 L/day or 125 mls/min
How many liters of plasma volume is normal?
3-4 L
Plasma volume gets filtered how many times each day?
6x/day
Waste products depend on what for adequate removal?
Filtration (not reabsorbed or secreted)
What is the filtration fraction equation?
Filtration fraction = GFR/ Renal Plasma Flow
What is the normal filtration fraction?
20%; Each minute 20% of plasma flowing through the kidneys is filtered
What is normal reabsorption?
178.5 L/day (123 mls/min)
What is normal urine output?
180-178.5 = 1.5 L/day
125 (GFR) -123 (reabsoprtion) = 2 mls/min
How does the glomerular capillary membrane compare to the normal capillaries?
Glomerular capillary filters significantly more volume than normal capillaries; thicker but more porous
How many major layers are in the glomerular capillary membrane?
3 layers
What are the major layers of the glomerular capillary membrane?
- Endothelial cell layer
- Basement membrane layer
- Epithelial cell layer (podocyets)
What are podocytes
surround outer surface of basement membrane
Describe the anatomy of the endothelial layer.
Perforated by thousands of fenestrations (small holes)
How is protein passage prevented in the endothelial layer?
Negative charge on surface of endothelial cells
The basement membrane allows movement of what?
Water and small molecules
How is protein passaged prevented in the basement memebrane?
Proteoglycan mesh and negative charge
Describe the anatomy of the epithelial layer
Not continuous; slit pores present between adjacent podocytes; allows free movement of water and small solutes
What hinders protein filtration in the epithelial layer?
Negative charge surround epithelial cells
What is the overall pore size of the glomerular capillary membrane?
8 nm; 80 angstroms
What does a filterability of 1.0 mean?
Freely filtered; at the same rate as water (concentration in filtrate will equal plasma)
What does a filterability of 0.75 mean?
Filtered 75% as quickly as water; filtrate concentration < plasma concentration
How big is albumin?
6nm
What prevents passage of albumin through pores?
Negative charge
How does albumin size compare to pore size?
Albumin- 6nm
Pore size- 8nm
What type of charge lines the pores?
Negative charges; prevents passage of proteins which are also negatively charged
What are dextrans?
Polysaccharides that can be made with specific charges
In some renal diseases, what happens first before any histological changes are seen?
The negative charge of the basement membrane is lost
What is an early indicator of renal disease?
Appearance of albumin in urine; since there is a loss of negative charge in the basement membrane albumin can now pass
What is the equation for GFR?
Kf (glomerular capillary filtration coefficient) x Net filtration pressure
Kf
glomerular capillary filtration coefficient
What is the normal net filtration pressure?
10 mmHg
What forces promote filtration?
Glomerular hydrostatic pressure (60 mmHg)
Bowman’s capsule oncotic pressure (0mmHg)- factor with disease
What forces inhibit filtration?
Glomerular oncotic pressure (32 mmHg)
Bowman’s capsule hydrostatic pressure (18 mmHg)
How do you get a net filtration pressure of 10 mmHg?
Glomerular hydrostatic P(60) - Bowman’s capsule P (18)- Glomerular oncotic pressure (32)
What is glomerular capillary filtration coefficient affected by?
Overall hydraulic conductivity and surface area of glomerular capillaries
Can glomerular capillary filtration coefficient be measured directly?
No
What is the normal Kf?
125 mls/min / 10 mmHg = 12.5 mls/min/mmHg
4.2 mls/min/mmHg / 100 gm tissue
Normal Kf other capillaries
0.01 mls/min/mmHg/100gm
What is the relationship between filtration coefficient and GFR?
Direct positive relationship; usually not part of day-to-day control of GFR
What do HTN and diabetes mellitus do to glomerular membrane?
Increasing thickness of membrane (decreased hydraulic conductivity)
What are examples of how disease can affect filtration coefficient and GFR?
Decreasing number of functional glomerular capillaries (decreased surface area)
What are some of the major factors affecting GFR?
Colloid osmotic pressure & filtration fraction
Hydrostatic pressure
Increased glomerular oncotic pressure does what to GFR?
Decreases GFR
Decreased glomerular oncotic pressure does what to GFR
Increases GFR
As blood passes through glomerulus, plasma oncotic pressure will increase by how much?
20% (20% of fluid is filtered producing increased protein)
What is the plasma oncotic pressure entering the glomerulus?
28 mmHg
What is the glomerular oncotic pressure as blood leaves glomerulus?
36 mmHg
What is the average pressure in the glomerulus
32 mmhg average (28 mmHg in and 36 mmHg out)
What are two major factors affecting glomerular oncotic pressure?
Plasma protein concentration of arterial blood
Fraction of plasma being filtered (filtration fraction)
Increased plasma protein concentration will __________ glomerular oncotic pressure, which will _________ GFR
increase; decrease
What does increased filtration fraction mean?
More plasma is being filtered from each ml of blood in the glomerulus
As blood is concentrated, the oncotic pressure of blood remaining in the glomerulus ________ which will _________ GFR
increases; decrease
A decrease in RBF ( no initial change in GFR) will do what to filtration fraction and GFR?
Increase the filtration fraction
Decrease in GFR
Changing RBF with constant glomerular hydrostatic pressure will have what effect on GFR
Increased RBF
Decreased fraction
Decreased glomerular oncotic pressure
increased GFR
Increased pressure = _________ GFR
increased
Decreased pressure =__________ GFR
decreased
What are the primary means for controlling GFR?
- Arterial pressure
- Afferent arteriole resistance
- Efferent arteriole resistnace
Increased MAP = ___________ GFR
increased
How is MAP/GFR relationship buffered?
Autoregulation of flow to keep consistent glomerular pressure
How does increased afferent arteriole constriction affect pressure and GFR?
Decreased pressure, decreased GFR
How does decreased afferent arteriole constriction affect pressure and GFR?
increased pressure; increased GFR
As afferent arteriole constriction increases, what does RBF do?
It also decreases
As afferent arteriole constriction increases, what does GFR do?
Decreases; at a faster rate than RBF decreases
As efferent arteriole resistance increases constriction, what happens to pressure and GFR?
Increased pressure
Increased GFR
As efferent arteriole resistance decreases, what happens to pressure and GFR?
decreased pressure
decreased GFR
As efferent arteriole resistance constriction increases, what happens with RBF/glomerular pressure?
RBF decreases
Glomerular pressure increases
Initially in efferent arteriole resistance, what has more effect than decrease in RBF?
The change in glomerular pressure; which produces an overall increase in GFR
Increase in glomerular pressure is _________ (greater/less) than decrease in RBF
greater
As efferent arteriole resistnace continues to increase, what beings to play a role?
Filtration fraction change
What does increased filtration fraction result in?
(Decreased BF, increased GFR)
Higher glomerular colloid oncotic pressure which decreases GFR
When the effect of the increase in glomerular oncotic pressure exceeds the effect of the hydrostatic pressure, what will happen to GFR?
Decrease
Increased hydrostatic pressure = ________ GFR
Decreased
Decreased hyrostatic pressure = ________ GFR
Increased
Does hydrostatic pressure (bowman’s capsule) normally play a primary role in controlling GFR?
No
Obstruction of the urinary tract could produce what?
Big increase in pressure with big decrease in GFR
RBF provides flow for basic metabolic needs of what?
kidneys and excess flow for plasma filtration
Renal O2 consumption is how many x that of the brain?
2x
RBF is how many x that of the brain?
7x
Most of O2 consumed in kidneys supports what?
Sodium reabsorption ( direct relationship)
What is the equation for RBF?
(Renal artery pressure - Renal vein pressure)/ Total renal resistance
Arterial: 100 mmHg; Vein 4 mmHg
Percentage of renal vascular resistance: afferent arterial
26%
Percentage of renal vascular resistance: Efferent arterial
43%
Percentage of renal vascular resistance: interlobar, arcuate, interlobular arteries
16%
Resistance of afferent arterial, efferent arterial, & interlobar/arcuate/interlobular arteries are controlled by what?
Sympathetic nervous system, hormones, local control within kidneys
Increased resistance of 3 areas tends to do what to RBF?
Reduce RBF
Decreased resistance of 3 areas tends to do what to RBF?
increase RBF (assume no change in arterial or venous pressures)
What percent of RBF goes to renal cortex?
98-99%
What percent of RBF goes to renal medulla vai the vasa recta?
1-2% (key part of ability to concentrate urine)
Which vessels receive sympathetic activation?
All vessels
Strong activation of sympathetic system results in what?
Constriction; decrease RBF and GFR
Mild to moderate activation of sympathtic system results in what?
moderate decrease in BP with corresponding baroreceptor response; little effect on RBF or GFR
When is sympathethic activation most important?
When body face with life threating problem ex. severe hemhorrage; very little effect in healthy normal person
What kind of effect do epinephrine and norepinehprine have
similar to effect of SNS
Endothelin is released by what?
release by damaged vascular endothelial cells of kidneys and other tissue; plays role in hemostasis
When is the concentration of endothelin increased?
during toxemia of pregnancy; acute renal failure; chronic uremia; powerful vasoconstrictor
Angiotensin II
potent vasoconstrictor; noramlly circulating and produced locally
What vessels show weak if any response to angiotensin II?
Preglomerular vessels; bc of simultaneous release of vasodilators such as nitric oxide and prostaglandins
What does angiotensin II have a strong effect on?
Efference arterial producing increased glomerular pressure and decreased renal blood flow
What does giving nitric oxide inhibitor do?
Increases renal vascular resistance
Decresaes GFR and urinary excretion of sodium
If continued will result in an increase in MAP due to the increased sodium levles
Bradykinin & Prostaglandins
Potent vasodilators
Tend to increase RBF and GFR
Dampen effect of sympathetic nerves and angiotensin II; may help prevent excessive decreases in RBF and GFR
What are bradykinin and prostaglandins inhibited by?
Administration of nonsteroidal anti-inflammatory agents
What is the purpose of autoregultaion of RBF and GFR?
maintain noraml GFR and allow control of renal excretion of water and solutes; prevents big changes in water/solute excretion with normal changes in BP
