Author: Dr Peter de Souza
Last modified: 17 December 2020


In this tutorial, I'm going to talk to you a little bit the blood supply inside the kidney because this can be a little bit confusing sometimes.


We're looking here at the abdominal aorta, the inferior vena cava and the right and left kidneys and you can see the renal veins and arteries coming off these major vessels and entering the kidney at the hilum together with the ureter. You can see the ureter here. We're going to take a look inside the kidney and see what's going on with the blood supply.

We're looking at a slice of the left kidney here. You can see the renal artery, the renal vein and you can see the ureter and renal pelvis at the hilum.   As the renal artery approaches the hilum, it splits into two branches.   You’ve got an anterior branch and a posterior branch.


These branches split further into segmental arteries. These segmental arteries then pass up along the renal columns.   You can see how the segmental artery passes around the side of the medullary pyramid. These arteries running up the sides are called the interlobar arteries.


They're called 'interlobar' because inter- means 'between' and –lobar refers to the renal lobes.   A renal lobe consists of the renal medulla combined with the cortex that sits above it. I'll just draw on a renal lobe in green. I've just drawn a couple more on that. They're called interlobar arteries because the arteries run alongside the medullary pyramids between the renal lobes.   The interlobar arteries come off the segmental arteries.


At the base of the medullary pyramid, the artery curves around and it's called the arcuate artery.   It 'arcs' around the base of the medullary pyramid.


And then coming off at 90° to the arcuate artery, you've got these little extensions that radiate into the cortex. These arteries are called the interlobar artery.


it can get a bit confusing because interlobar and interlobular are very similar, but if you just remember that interlobar are called that because they lie between the renal lobes (on the sides of the medullary pyramids), then it'll help you to remember the difference between the interlobular and interlobar.


The renal lobes are actually divided into little lobules and you've also got the corresponding interlobular veins.


Now we're just going to zoom into one of these renal lobes and take a look at what happens with the blood there.


We just zoomed in to a renal lobe. I'll just orientate you a bit. So you can see our arcuate arteries in red arcing around the boundary, the border of the medullary pyramid and you've got the corresponding arcuate vein.


And coming off the arcuate artery and vein, you've got the interlobular artery and vein, so the interlobular vessels.


Beneath these arteries and veins, you've got the medulla and outside is the cortex.   The interlobular artery gives off branches called the afferent arteriole, which forms the glomerulus, which is this network of capillaries contained within the glomerular capsule. This called is called a Bowman's capsule or glomerular capsule.   These two structures contain the glomerulus and the glomerular capsule or Bowman's capsule to form the renal corpuscle.


After the glomerulus, the pathway of the blood is different depending on what nephron we're looking at.   In the kidney, you've got two types of nephron. You've got cortical nephron and juxtamedullary nephron. They're determined depending on the location of their renal corpuscle and their loops of Henle.


The juxtamedullary nephrons have their renal corpuscle right next to the medulla. That gives them their name juxta- meaning 'next to' and –medullary referring to the medullary pyramids.   Just imagine that this renal corpuscle here lies closer to the medulla.   That’s the juxtamedullary nephron.


Their loops of Henle extend right into the substance of the medulla.   The loop of Henle is quite deep.


Let’s just say this is the cortical nephron. A cortical nephron has the renal corpuscle further away from the medulla deeper into the cortex. I've just drawn on to this diagram and paint. I've kind of massacred Grace's beautiful artwork, but this yellow thing is a proximal convoluted tubule.   The loop of Henle of a cortical nephron is much shorter. It doesn't penetrate as far into the medulla.


A cortical nephron, renal corpuscle is further away from the medulla and the loop of Henle is much shorter. A juxtamedullary nephron has its renal corpuscle right next to the medulla, so juxtamedullary and its loop of Henle penetrates much further into the renal medulla.


Why did I bother explaining all that to you? Well, going back to the blood supply, we've just come off the interlobular artery forming the afferent arteriole, which goes into the glomerulus. And then after the glomerulus comes the efferent arteriole.


In a juxtamedullary nephron, the efferent arteriole forms the vasa recta. Again, this is more Latin and it just means 'straight vessels'. These vessels follow the loop of Henle downwards, straight downwards, hence the name. It has this sort of hairpin turn and it follows it again up, straight up.


And then the vasa recta back into the interlobular vein. And then the interlobular vein drains into the arcuate vein. The arcuate vein drains into the interlobar vein. Remember that run downs the side of the medullary pyramid. And the interlobar vein drains into the renal vein.


What happens with the cortical nephron? Well, we've got this vessel; we've got the afferent arteriole coming off the interlobular artery. It goes into the glomerulus within the Bowman's capsule and then out comes the efferent arteriole.


And then these efferent arterioles form these peritubular capillaries.    Peri- meaning 'around'. Tubular referring to the renal tubule.   You’ve got this sort of network of capillaries running over the renal tubule. And then this drains back into the interlobular vein and then it follows the same course back into the arcuate vein, back into the interlobar veins and then ultimately back into the renal vein.


That’s the blood supply of the kidneys.