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75 Cards in this Set

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What is the fundamental unit of the kidney?
The nephron with its vasculature
What is the initial step in urine formation?
Bulk filtration in the glomerulus
How much plasma is filtered from the glomerulus each minute?
125 ml/min
What happens to the filtrate filtered by the glomerulus?
It undergoes reabsorption in the tubule.
How much fluid filtered at the glomerulus is reabsorbed?
99%
What is secretion?
Transfer of substances from ECF into the tubular lumen.
What is Excretion the sum of?
Filtration + Secretion - Reabsorption
How many nephrons do we have?
1 million
What makes up the outer kidney?
Cortex / nephrons
What makes up the inner kidney?
Medulla
What is the kidney divided up into?
8-18 pyramids
What does a pyramid consist of?
-Cortex
-Outer medulla (papilla)
-Inner medulla
What % of body weight is the kidney?
0.5%
How much cardiac output does the kidney recieve?
20-25%
What is the order of Renal vasculature? (10 steps)
1. Renal artery
2. Segmental arteries
3. Interlobar arteries
4. Arcuate arteries
5. Interlobular arteries
6. Afferent arteriole
7. Glomerular capillaries
8. Efferent arteriole
9. Peritubular capillaries
10. Venous system
2 types of nephrons:
1. Cortical
2. Juxtamedullary
3 main differences between Cortical and Juxtamedullary nephrons:
1. Glomeruli in juxtamedullary nephrons are 2-3x bigger
2. There are 10X more cortical nephrons than juxtamedullary
3. Juxtamedullary have longer loops of henle that extend all the way into the inner medulla where cortical nephrons only extend to outer medulla.
3. Efferent arterioles have different functions
What do the efferent arterioles of cortical nephrons become?
Peritubular capillaries
What do the efferent arterioles of juxtamedullary nephrons become?
Vasa recta
What is the function of peritubular capillaries and vasa recta?
Reabsorption of fluid into ECF
In addition to having longer loops of henle, how are the limbs of henles loops different in juxtamedullary nephrons?
They have thin ascending and descending limbs.
So the 2 capillary beds in the renal circulation are:
-Glomerular
-Peritubular
-These are in series
What is the primary factor that results in the high rate of filtration in the glomerulus?
High glomerular capillary hydrostatic pressure of ~60 mm Hg!
What facilitates the reabsorption in the peritubular capillaries?
Low capillary hydrostatic pressure - ~8 mm Hg
High oncotic pressure ~32 mm hg
What is the pressure drop in the
-Renal artery
-Interlobar/arcuate/interlobular
-Afferent arteriole
Renal a: 100 - 100 mm Hg
Conduate aa: 100 - 85 mm Hg
Afferent aa: 85-60 mm Hg
What is the pressure in glomerular capillaries?
60
What is the normal systemic capillary hydrostatic pressure?
~28 - so we see that it's much higher in glomerular caps!
What is the pressure drop in the Efferent arteriole? What does this tell us?
60 - 18; shows that the Efferent arteriole is HIGH resistance.
What do the kidney processes determine overall?
The composition of urine
What is glomerular filtrate?
An ultrafiltrate of plasma
What is the composition of glomerular filtrate like?
Same concentration as that in plasma, except for proteins and cellular elements.
What is the normal GFR?
3 L / half hour - the entire plasma volume!

6 L/hr - 2x the entire plasma volume!
What are the forces directed outward at the glomerulus?
Capillary Hydrostatic - 60 mm Hg
that's it.
What are the forces direct inward at the glomerulus?
-Capillary oncotic - 32 mm Hg
-Bowman's capsule hydrostatic - 18 mm Hg
So what is the net inward force at the glomerulus?
32 + 18 = 50
What is the net filtration pressure at the glomerulus?
60 - 50 = 10 directed outward
(times filtration coefficient)
Why is there no bowman's capsule oncotic pressure at the glomerulus?
Because no protein is filtered.
Equation for GFR:
(Ultrafilt Coeff)(Sum of all forces opposing and favoring filtration)
What is the ultrafiltration coefficient?
The product of the hydraulic permeability and the surface area of glomerular capillary membranes.
How does the ultrafiltration coefficient compare between normal systemic caps and glomerular caps?
It is 100X higher for glomerular capillaries.
3 layers of the glomerular filtration barrier:
1. Capillary wall with 700 angstrom fenestrations
2. Basement membrane
3. Podocytes
What special features of podocytes enable them to contribute to the glomerular filtration barrier?
-Foot processes
-40x140 angstrom slit pores
2 characteristics of molecules that the glomerular filtration barrier is selective for:
1. Size
2. Charge
What sized molecules are more filterable at the glomerulus?
Small
What charge of molecules are more filterable at the glomerulus?
Positively charged
2 proteins that make up the slit membranes between podocytes:
Nephrin
P-cadherin
What happens when Nephrin is mutated?
Pores are much larger and protein gets filtered - nephrotic syndrome.
What 4 substances are freely filtered based on molecular weight?
-Water
-Sodium
-Glucose
-Inulin
What is less filterable?
Myoglobin
What is not filtered because it's so big?
Albumin
How will RBF, GFR, and Filtration fraction change if you increase preglomerular resistance, but don't change post?
RBF - decreases
GFR - decreases
FF - won't change
How will RBF, GFR, and FF change if you increase postglomerular resistance, but don't change pre?
RBF - decreases
GFR - increases
FF - increases
How will RBF, GFR, and FF change if you decrease preglomerular resistance, but don't change post?
RBF - increases
GFR - increases
FF - won't change
How will RBF, GFR, and FF change if you decrease postglomerular resistance, but don't change pre?
RBF - increases
GFR - decresaes
FF - decreases
What is the Filtration Fraction?
GFR / RPF
3 factors that can decrease the Kf:
-Renal disease
-Diabetes mellitus
-Hypertension
What can increase bowman's space hydrostatic pressure?
Urinary tract obstruction
What can increase glomerular oncotic pressure?
-Decreased renal bloodflow
-Increased plasma proteins
What can decrease glomerular hydrostatic pressure?
Decreased afferent arterial pressure
Does decreasing afferent arterial pressure contribute much often to decreasing glom. hydrostatic pressure? Why?
no; because of autoregulation.
3 ways to decrease glomerular hydrostatic pressure:
-Decrease arterial pressure
-Decrease efferent arterial resistance
-Increase afferent arterial resistance
How can you decrease efferent arterial resistance?
By decreasing Ang II
How can you increase afferent arterial resistance?
By decreasing sympathetic activity or giving vasoconstrictor hormones.
What happens to glomerular capillary colloid pressure as you go from afferent end to efferent end?
It increases as water is taken out of the plasma.
What is renal arterial blood flow?
-% of CO
-ml/min
20-25% of Cardiac output
1200 ml/min
What is Renal arterial plasma flow?
700 ml/min
How is renal plasma flow calculated?
RPF = RBF(1-Hct)
Normal GFR:
125 ml/min
Filtration Fraction Range
15-25%
How is FF calculated?
GFR/RPF x 100
How do you calculate filtered load?
GFR x Pconc
How much of filtered solute/water is reabsorbed?
-%
-ml/min
99%
124 ml/min
What is secretion?
Transport of solutes from blood into tubular lumen
What is excretion? Normal amt?
Urine flow - 1ml/min
What is normal venous bloodflow from the kidney?
1199 ml/min