Renal blood supply Flashcards
What are the Vasa Recta?
Capillaries derived from the efferent arterioles of the juxtamedullary nephrons. The arterioles run from the glomeruli to portal vessels by plunging into the medulla to form a hair pin loop. The vasa recta span this loop.
What is the function of the vasa recta?
To provide nutrients and remove waste from the medulla without removing the solutes needed for hypertonicity. Takes the waste back to the venous system after reabsorption or supplies substances into the interstitium for secretion.
How far does the portal loop descend into the medulla?
The more reabsorption to occur, the further into the medulla the loop descends
What is the osmolality of the plasma?
Isotonic with the intersititium at the top of the loop as the vasa recta DILUTE on the descending limb but CONCENTRATE on the ascending limb.
How is movement between the vasa recta and interstitium achieved?
The plasma, water and solutes moves passively with net movement INTO capillaires due to their low hydrostatic pressure and high oncotic, after having provided the filtrate, and the high hydrostatic pressure of the interstitium.
How does the osmolality of the plasma vary as it forms the loop?
As it descends osmolality increases as the concentration of Na and urea increases in the medulla. Water reabsorbed on ascending limb as moving from low osmolality in medulla to high in cortex.
How does the flow rate vary in the vessels?
Flow rate decreases on descending as water leaves the vessels, but increases on ascending as water arrives. Most of the water filtered is reabsorbed but the rate increases if more water present.
How is the blood flow regulated?
Myogenic response to regulate total renal flow
Tubuloglomerular reflex to regulate a single nephron GFR.
No neural or hormonal influence over the BP autoregulatory range.
What happens to flow at low blood pressures if the BP starts to rise?
Flow will increase
What will happen to flow if BP is within the autoregulatory range?
RBF and GFR stay constant
What happens to flow if BP start to rise to high levels?
When reaching high BP,resistance is increased due to vasoconstriction to maintain the flow at a constant level.
What is the myogenic response?
When the afferent arterioles are stretched by an increased perfusion pressure, they vasoconstrict to narrow the vessels and increase resistance to reduce the flow rate.
Small change in radius = large change in BP
Uses stretch-activaction cation channels to depolarise the smooth muscle for Ca influx to cause a contraction = Bayliss effect.
What is the purpose of the myogenic response?
To maintain GFR at a constant rate regardless of BP and to reduce kidney damage during high systolic pressures.
What is tubuloglomerular feedback?
High Na in the DISTAL tubule is detected by MACULA DENSA as more Na gets transported by NKCC2. Macula densa cells release ATP to be broken down into ADENOSINE to cause vasoCONSTRICTION of the afferents to reduce glomerular hydrostatic and GFR.
-ve feedback.
How can the autoregulatory range be opposed and why is this necessary?
Opposed by hormones and innervation.
Used to match the needs of the body against the wants of the kidney to maintain a constant GFR. Blood flow may need to be diverted from the kidneys to increase blood flow to another area e.g. shock
