General Structure of the Kidney

00:01 It's important before we look at the urinary system, and particularly the kidney, to at least understand its growth or general structure. On this slide, there is a list of important structures. On the left-hand side, there is a diagram in the center of the kidney. And on the right-hand side, there is a diagram of the region of the cortex and the medulla illustrating the nephrons. And I want to just go through the central diagram and explain a few points about the general anatomical structure of the kidney.

00:42 You can see a renal artery comes into the kidney at the hilum of the kidney.

00:47 The hilum is the region where blood vessels, nerves, and in this case, the ureter, pass in or out of an organ. Where the renal artery travels in to the kidney, it breaks up into various components and then supplies the different lobes of the kidney which I'll describe shortly. Then this artery divides into an interlobar artery and travels up between the lobes, and then bends around and travels parallel to this region as an arcuate artery. And this region that these vessels have travelled through is the medulla of the kidney. These arcuate arteries then give rise to interlobular arteries that travel up through the cortex. And those interlobular arteries are going to supply the glomerulus, a component of nephron we'll mention in a moment. And the vein is drawing back through the renal vein. So the kidney is divided into the medulla and the cortex. In the cortex on the right-hand side diagram, you can see the structure of a cortical nephron, and I will describe its structure in a moment. But really, if you look at the cortical nephron, the glomerulus, and the major components are up high in the cortex. And then you see these straight tubules passing down into the medulla region. I want you to push that last little bit or last loop from the medulla up into the cortex, because really, the very thin loop you see there, the very thin loop of Henle it's called, doesn't really extend down into the medulla from these cortical nephrons. There is also a juxtaglomerular, or should I say juxtamedullary nephron, where the nephron and the glomerulus sit on the border between the cortex and the medulla. And in this case, those straight tubules do descend in the medulla. So, when you see parts of medulla, you can see tubules running in the same parallel direction, and they tend to be of different length. And because of that, when you look at the growth structure of the kidney, you can see pyramids. These pyramids, labelled on the diagram, represent all these tubules, these straight tubules and the collecting ducts running in parallel. And those pyramids are the boundaries of the lobe of the kidney. On either side are the interlobar arteries that I referred to earlier. And then when neuron passes all through the tubules and down through the collecting duct, that collecting duct opens at the base of this, or should I say the apex of this pyramid because the base is actually up against the border of the cortex. The pyramid, by name, is a triangular-shaped region of all these straight tubules and the collecting ducts, as I mentioned before.

04:18 So you imagine the triangle with the base up against the cortex and the apex is at the tip, the papilla of the pyramid that actually opens into the minor calyx.

04:33 So urine will drip into that minor calyx and then flow into the major calyxes and then out through the ureter, that you can see on the diagram. So that's a general arrangement of the kidney, mainly its anatomical details, but also some of the microscopic details you'll see in a moment, particularly of the nephron. Let's now look at the kidney in more detail. Here is a section of the kidney on the left-hand side, low power. This is actually a section through the lobe of a kidney. And on the right-hand side is a higher magnification of the cortex of the kidney. I want you to look at this section, or both these sections, very carefully.

05:21 Look at the cortex and then locate the medulla. This medullary region represents a section through the pyramid that I've described earlier. That pyramid will open at the papilla, the apex of the pyramid, into the minor calyx which is shown there, and then the urine will flow out through the ureter, as I explained before.

05:45 And you can see components of the heart and there're also a bit of fatty tissue, but you also see a very small artery, a branch of the renal artery. Now, on either side of that pyramid or that medullary region, you have components of the cortex more or less overflowing the lobe. They're called the renal columns. Turn your attention now to the right hand section of the cortex, and you could see little dots or specs.

06:15 They represent the renal corpuscle. That's the filtering component of the nephron, and I will describe that in more detail in a moment. You can also see some straight tubules that are called medullary rays. There are number of these in this section, several. Have a look at the section and just see if you see regions where they appears to be parallel tubules arranged next to each other.

06:45 They represent the straight tubules in the cortex and collecting tubules as well, and some of the collecting ducts. And they actually define the central component of the kidney lobule. And if you look in the middle towards the middle part of that section, and also a little bit towards the top, you can see the renal corpuscles are arranged in a sort of a line. And that's because the peripheral border of the kidney lobule is in fact the interlobular artery. They run up on the periphery of the lobule and they give rise to blood to supply the glomerulus inside those renal corpuscles, and then the glomeruli then filter that blood from a filtrate which goes through all the tubule systems, and then follows the collecting ducts in those medullary rays. So again, the medullary rays are the centre of the lobule, and the interlobular arteries are on the periphery. It's hard to see here, I know, because there aren't connective tissue components that separate the lobules apart, as you see in other organs.