Renal 3: Filtration and Blood Flow Flashcards
What can get through the glomerular filtration barrier?
Neutral molecules smaller than 20A are freely filtered
Molecules between 20-42 A are filtered to a varying degree
Cationic molecules
Anionic molecules are hindered due to negatively charged glycoproteins on surface of glomerular filtration barrier
The glomerular capillaries have high/low resistance and a net positive/negative charge.
low, negative
Glomerular capillaries have a large/small filtration coefficient. How do we calculate it?
large. Kf = PERMEABILITYgc x AREAgc
How are filtration and molecular radius related?
higher radius means lower filterability
lower radius means higher filterability
How are filtration and ionic charges related?
Anionic: shifts curve down and left. filterability lower at same radius.
Cationic: shifts curve up and right. filterability higher at the same radius.
Why aren’t immunoglobulins filtered?
Their molecular radii are greater than 42 angstroms.
Why isn’t albumin filtered?
It is a polyanionic protein with a molecular radius of 35 angstroms.
How do we calculate net filtration pressure?
Net Ultrafiltration Pressure: Pgc - Pbs - πgc + πbs
Pgc is glomerular capillary hydrostaic pressure
Pbs is Bowman’s space hydrostatic pressure
πgc is glomerular oncotic pressure
πbs is Bowman’s space oncotic pressure
As blood moves through the glomerular capillaries what happens to the following? Pgc πgc Pbs net ultrafiltration pressure
Pgc: small decrease (low resistance capillaries)
πgc: large increase (conc of proteins that do not filter)
Pbs: no change
Net ultrafiltration pressure: decrease
How do we calculate glomerular flow?
hydraulic conductance times net pressure gradient.
GFR = Kf * (Pgc - Pbs - πgc + πbs)
How does a change in afferent arteriolar resistance affect (glomerular capillary hydrostatic pressure)
Decreased resistance increases Pgc
Increased resistance decreases Pgc
How does a change in the efferent arteriolar resistance affect Pgc (glomerular capillary hydrostatic pressure)
Decreased resistance decreases Pgc
Increased resistance increases Pgc
How does a chagne in the renal arteriolar pressure affect Pgc(glomerular capillary hydrostatic pressure)?
Increase in BP transietly increases Pgc -> inc GFR
Decrease in BP transiently decreases Pgf -> dec GFR
What happens to the following in early stage glomerulonephritis?
πgc
GFR
Pbs
decrease
increase
nothing
What happens to the following in late stage glomerulonephritis?
Pbs
GFR
increase
decrease
How do kidney stones affect Pbs and GFR?
increases Pbs
decreases GFR
What does nephritic syndome do?
increases hydraulic conductance (Kf) and causes proteinuria
What is the equation for total renal blood flow (RBF)
RBF = (P renal artery - P renal vein)/R renal vasculature
Rank the following from most to least vascularization:
inner medulla
renal cortex
outer medulla
renal cortex»_space; outer medulla»_space; inner medulla
What is the ratio of cortical nephrons to juxtamedullary nephrons
7 to 1
What types of capillaries does the renal cortex contain?
glomerular and peritublar capillaries
What types of capillaries does the renal medulla contain?
vasa recta capillaries only
What is the sequence of vessels from the renal artery to the renal vein?
Renal Artery»_space; Afferent Arterioles»_space; Glomerular Capillaries»_space; Efferent Arteriole»_space; Peritubular Capillary»_space; Intrarenal Vein»_space; Renal Vein
How does hydrostatic pressure change between the renal artery and vein?
It decreases with largest pressure decrease in afferent and efferent arterioles and smallest pressure decrease in the glomerular and peritubular capillaries
Where does oncotic pressure increase?
glomerular Capillaries (concentration of plasma proteins during filtration)
Where does oncotic pressure decrease?
Peritubular Capillaries (dilution of plasma proteins during reabsorption)
Why do changes in the afferent arteriole and efferent arteriole affect Pgc and GFR?
Constriction of either causes an increase in resistance ->. decrease flow (RBF)
Dilation of either increases flow (RBF)
Afferent constriction means less of arterial pressure is transmitted to glomerulus -> dec Pgc -> dec GFR
Efferent constriction elevates Pgc -> inc GFR
Vice versa
Do the following intrinsic factors vasoconstrict or vasodilate? endothelin nitric oxide adenosine prostaglandins dopamine
vasoconstrict vasodilate vasoconstrict vasodilate vasodilate
What are the intrinsic autoregulation components
smooth muscle myogenic
tubuloglomerular feedback
intrinsic factors
What is the autoregulatory range for arterial pressure and what happens to GFR?
100-180 mm Hg
GFR and RBF increases at arterial pressure >180 mmHg
GFR and RBF decreases at arterial pressure <100mmHg
What happens with renal shutdown?
Occurs when arterial pressure <70 mm Hg
GFR = 0ml/min but kidney is still perfused, just no urine formed
What happens with renal death?
Occurs when arterial pressure = 0 mm Hg
RBF =0ml/min; Kidney no longer perfused with blood
Describe tubuloglomerular feedback
- increased GFR
- increased NaCl concentration in tubule fluid in Henle’s loop
- signal generated by macula densa of JGA
- increased arterial resistance
- GFR decreases
How does a hemorrhage eventually lead to decreased renal excretion? List entire pathway.
hemorrhage -> dec arterial blood pressure -> inc renin secretion -> inc ANG II -> inc sodium and water reabsorption -> dec less renal excretion.
ANG II also constricts renal arterioles -> dec RBF and GFR -> dec renal excretion
dec arterial BP also inc sympathetic innervation to renal nerves -> inc renin secretion further and inc constriction of renal arteries
How does severe hypoxia affect RBF and GFR
decreases RBF and GFR (seen with high altitudes)
