The Renal system lecture 2 Flashcards
what is the ultrafiltration barrier composed of ?
- Fenestrated endothelium
- Basement membrane
- Podocytes
what does the fenestration pore of the glomerular endothelial cell prevent ?
prevents filtration of blood cells but allows all components of blood plasma to pass through
what does the Basal lamina of the glomerulus prevent ?
prevents filtration of larger proteins
what does the slit membrane between pedicels prevent ?
prevents filtration of medium-sized proteins
who described ultrafiltration ?
using micropuncture, wearn and richards described ultrafiltration
what is the definition of glomerular filtrate ?
the fluid formed by ultrafiltration
what does the term glomerular filtration rate or GFR refer to ?
The rate at which the 2 kidney’s form ultra filtrate is GFR.
what does the term single nephron GFR refer to ?
the rate at which a single nephron forms ultra filtrate
what substances are freely filtered?
substances of low molecular weight are freely filtered. water urea glucose inulin myoglobin
what molecules are retrcietd ?
large molecules
give me 3 examples of molecules that are restricted
haemoglobin, serum, albumin
what molecules are more restricted ? negatively or positively
negatively charged molecules like albumin
what governs GFR ?
a balance of hydrodynamic forces
what are the two forces that oppose each other that constitute the hydrodynamic forces ?
Hydrostatic pressure (plasma leaves capillaries because of pressure ) oncotic pressure beacause of the protein that remained in the plasma because of size and charge
why does oncotic pressure oppose hydrostatic force ?
because of capillary pressure
what does the term net filtration pressure refer to ?
small oncotic pressure from bowman’s space opposing hydrostatic pressure
what is Pc?
Capillary hydrostatic pressure Pc - the pressure that will force fluid out from the capillary
What is Pi?
Interstitial hydrostatic pressure Pi - the pressure that will force fluid out from the interstitial space
What is πc?
Capillary oncotic pressure πc - the osmotic pressure that will force the fluids to enter the capillary from the interstitial space
What is πi?
Interstitial oncotic pressure πi- the osmotic pressure that will force the fluids to enter the interstitial space from the capillary
what is fluid filtration determined by ?
Fluid filtration is determined by the difference of hydrostatic pressures across the capillary
Pc - Pi
what is fluid reabsorption determined by ?
Fluid reabsorption is determined by the difference of osmotic pressures across the capillary
Πc - Πi
in systemic capillaries is there a net flow out of capillaries ?
no
what is the value of Pc in the renal corpuscle ?
55 mmHg
what is the value of Pi in the renal corpuscle ?
15 mmHg
what is the value of Πc in the renal corpuscle ?
30 mm Hg
what is the value of Πi in the renal corpuscle ?
0.3 mmHg
what is the formula of GFR ?
GFR=[(PC –PBC)–(Πc–ΠBC)].K
whats the net glomerular filtration pressure ?
10 mmHg
what would an increase in Pc lead to ?
An increase in PC increases GFR
what would a decrease in Pc decreases GFR ?
A decrease in PC decreases GFR
what would an increase Pbc do ?
An increase in PBC decreases GFR,
such as stones in the urinary tract, or retention of urine
what would a decrease in ΠC lead to ?
A decrease in ΠC increases GFR, i.e. liver failure
what would an increase in ΠBC lead to ?
An increase in ΠBC decreases GFR, i.e. renal failure
how can GFR be measured ?
It can’t be measured, but it can be estimated.
• By measuring the rate of excretion of substances that are:
1. Freely filtered.
2. Not reabsorbed or secreted by tubules.
3. Have no influence on renal function (e.g. blood flow)
Inulin meets these criteria.
what is the definition of renal clearance ?
the volume of plasma completely cleared of a given substance in 1 min
what is the GFR for inulin clearance ?
120-130 ml/min for adult humans. in a day that is 180 litres of plasma filtered
why is inulin not convenient for clinical measurement of GFR?
it’s concentration in the plasma is not steady - not accurate
what substance fits the criteria already found in plasma ?
creatinine - however small amounts of creatinine are secreted into the proximal tubule
Homeostasis requires kidneys to maintain a relatively constant GFR ?
Too high – substances pass too quickly and are not reabsorbed
• Too low – nearly all reabsorbed and some waste products not adequately excreted
give me three reasons for renal failure ?
pre-renal (e.g poor blood supply)
renal ( loss of nephrons or nephron function )
post-renal ( e.g blockage of ureter and lower tract)
