7 Renal Blood Supply Flashcards
What are the Vesa Recta?
efferent arterioles from the glomeruli which run into portal vessels, then plunging deep into the medulla before resurfacing, a bit like the loop of henle
What are the functions of the Vesa Recta?
take water and solvents from interstitial space after absorption by the tubules
supply substances into the interstitial space where they can be secreted by the tubules
What is the significance of the vesa recta being permeable?
oncotic pressure changes with local interstitial osmolality
How does vesa recta osmolality change?
In the descending limb, the vessels are exposed to an increasing concentrated interstitium, the vessels hence lose water
In the ascending limb, water is reabsorbed
What happens to flow rates through the vesa recta?
At first it is roughly equal to the renal plasma flow rate, minus the lot which is filtered (GFR)
by the other side, the flow rate will be equal to the renal plasma flow rate, minus the rate of urine production
the net effect is therefore reabsorption of water
What are the 2 autoregulation mechanisms of renal blood flow?
myogenic response (regulates the total blood flow) tubuloglomerular reflex (regulates single nephron GFR, but may affect many nephrons)
why is autoregulation ‘autoregulation’…?
becuase is still occurs when the kidney is ex vivo, so it can’t depend on CNS output
What is the significance of the autoregulatory range?
at the level of normal blood pressure, increasing the pressure does not significantly increase the renal plasma flow rate, as the vessels contract to reduce resistance
this works because changing the resistance has a far bigger effect on flow than pressure changes does
What is the basis of the myogenic response?
when the afferent arterioles are stretched, they contract, increasing resistance and reducing blood flow
How can we tell that a small amount of vasoconstriction is required to negative pressure increases?
in poiseuille’s equation, R is to the 4, where P is not. so there.
What is the cellular mechanism behind the myogenic response?
stretch activated cation channels depolarise the smooth muscle cells increases Ca2+ influx VGC Ca2+ open contraction Bayliss effect
Why do we have the myogenic response?
to maintain GFR regardless of mean arterial pressure, allowing independent regulation of different stuff!
could also reduce impact of high systolic pressures, as the reflex is far more sensitive to the peak than to the mean pressure
How does the tubuloglomerular feedback mechanism work?
High GFR in a single tubule causes high Na+ in the distal tubules
this is sensed by macula densa, which then releases ATP.
the ATP is then hydrolysed into adenosine, which constricts afferent arterioles
this lowers glomerular hydrostatic pressure
Name 2 factors opposing autoregulation of blood
renal innervation
circulating hormones
What is the character of renal innervation?
most efferent nerves are sympathetic (vasoconstriction)
there are afferent sensory neurones although we don’t really understand them
