L08-Renal blood supply Flashcards
What is the vasa recta?
The efferent arterioles from the glomeruli run into
portal vessels, which then plunge from the cortex,
deep into the medulla, forming a hairpin loop
What is the purpose of the vasa recta vessels?
They take water and solvents after reabsoption from the tubules.
They supply substances that are needed to be secreted
They help to maintain the hyperosmolality in the medulla by passively allowing solutes to enter in the descending limb and leave in the ascending limb.
What are the two key mechanisms for the autoregulation of renal flow?
Myogenic response
Tubuloglomerular reflex
What is the myogenic reflex response?
When afferent arterioles are stretched then they contract. This means that increasing perfusion actually reduces flow due to vasoconstriction. Only small changes in diameter are actually required to change the pressure in the vessel back to normal
What is the cellular mechanism behind the myogenic response?
Stretch activated cation channel depolarise the smooth muscle cells causing constriction.
What are the main two reasons for the myogenic response?
To maintain GFR at varying blood pressures.
To prevent the kidneys from being damaged by large increases in pressure.
What is tubuloglomerular feedback and how does it work?
Allows individual nephrons to control their GFR. High Na+ levels in the distal tubule are sensed by macula densa cells which release ATP. This ATP is broken down to adenosine that is a vasoconstrictor and causes a fall in GFR so the nephron is not overloaded. Can be overridden by systemic responses.
What are the two main factors opposing renal autoregulation?
renal innervation
circulating hormones
How is the kidney innervated?
It has a dense plexus of nerves,
Most efferent nerves are sympathetic and cause vasoconstriction. A key stimulus is hypotension.
There are also many afferent fibres.
How is renal plasma flow measured?
• To measure renal flow, we can use a similar
approach, measuring a compound that is
completely removed from the plasma (tubular
secretion, or filtration+tubular secretion) and then is
lost in the urine. A compound which does this is paminohippurate
(PAH)
• In this case we say:
Rate at which the compound enters kidney = Rate at
which the compound leave the kidney
What is the net water flow in the descending limb of the vasa recta?
The water flows out as the descending limb is in a hyperosmolar environment
In the myogenic response of the renal efferent arteriole how does the diameter change with an increase in pressure?
It decreases
What are the two types of receptors for noradrenaline in the renal afferent arteriole?
alpha1 adrenoceptors on the smooth muscle and beta2 adrenoceptors on the granule cells
