Anatomy of the Kidney (Nursing)

00:01 Now, we're going to talk about the urinary system which has a very important role in filtering blood as well as helping maintain blood pressure.

00:12 The workhorse of the urinary system are the kidneys where the actual filtration of blood takes place.

00:18 And then, after it's been filtered, that filtrate will be passed down the ureters, down to the urinary bladder where it's eventually expelled from the body.

00:29 Now, sometimes, when you see an anatomy book, you see the abdomen open and you just see kidneys sitting there and that's not exactly how the kidneys sit.

00:37 In fact, they're actually behind that lining of the abdominal cavity that we call the peritoneum.

00:45 Along with other structures.

00:47 So, we see other retroperitoneal things such as the abdominal aorta and the inferior vena cava.

00:54 So, the kidney along with these other structures are retroperitoneal unlike a lot of the digestive structures that occupy the majority of the peritoneal cavity itself.

01:04 The other thing that you don't really notice in a lot of pictures is that the kidneys don't just sit there as kidneys.

01:11 They're surrounded by a lot of prerenal fat.

01:15 So, it actually takes a lot of effort to actually reach the kidneys if you're going through the abdominal cavity because, again, you'd have to go passed the peritoneum and generally, you would have a lot of surrounding fat.

01:30 Let's talk a little bit about the structure of a kidney, so, the kidney is encased in a thin but fairly tough renal capsule and it has, like a lot of organs, one spot where that capsule's not present for things to enter and exit called the renal hilum.

01:48 Hilum's a term that exists in a lot of organs such as the spleen, the lungs, lymph nodes.

01:56 Anything that's generally solid but has one entry and exit point.

02:02 The outer portion of the kidney that's called the cortex and there's an inner portion called the medulla.

02:12 And again, those terms are pretty common for a lot of structures.

02:15 Cortex means bark like the bark of a tree.

02:18 So, cortex, whenever you see that, means it's the sort of outer portion of an organ.

02:24 And the medulla's arranged into these triangular-shaped things called pyramids that are separated from each other by little columns of cortex that come down in between them.

02:35 The tips of those pyramids point into the beginning of what's called the collecting system and that first portion of the collecting system are called the calyces.

02:47 Before we talk about where that collecting system goes, let's talk about how things enter and exit at this renal hilum.

02:57 So, eventually, food's going to exit out the ureters which are going to be the posterior-most structure of the hilum.

03:06 Then, just anterior to that will be the renal artery which is going to branch and supply the kidney.

03:12 And then, more anterior to that is going to be where the renal vein enter that renal hilum.

03:19 Okay. So, back to this collecting system.

03:23 So, if we zoom in a little bit, we again have the renal pyramid which has a little tip at the end call the renal papilla and it's through these little renal papilla that the very beginnings of urine are going to drop out through and they're going to drop into small little spaces called minor calyces which will merge to form major calyces.

03:49 And then, all of the calyces together are going to mergeinto a single relatively large space called the renal pelvis.

04:00 The renal pelvis is going to drain into the ureter at the renal hilum.

04:07 And so, this is an area where it's going to go from very wide and broad to a fairly narrow tube.

04:12 So, we're going to see that that has a lot of clinical significance.

04:15 For example, if a stone were to be floating around in the pelvis, it might become lodged in the relatively narrow ureter.

04:25 So, in order to really understand the kidney, we have to talk a little bit about the microanatomy and we have to understand at least the concept of what a nephron is and how blood is actually being filtered.

04:38 So, out in the cortex, there are these little tuffs of capillaries called glomeruli and that's where the blood is going to actually be filtered.

04:50 But it's not enough to just filter blood.

04:52 That filtered blood or filtrate or early beginnings of urine need to be further modified, so, it'll go through a long tube, initially, a twisty tube called the proximal convoluted tubule and then, a loop of Henle that actually dips down into the medulla.

05:12 And then, another twisty part called the distal convoluted tubule before entering into a larger duct called the collecting duct which is really the last chance to modify filtrate, usually, by either pulling out water or letting more water in because these collecting ducts are eventually going to empty at the renal papillae into the minor calyx after which, it can't be modified any further. It can just be passed all the way out the body as urine.

05:44 So, here, we have a close-up view of a very small branch of the renal artery supplying something called the afferent or afferent arteriole that branches into a tuft of capillaries and those are the glomerular capillaries where filtration will take place.

06:02 And then, it will exit as the efferent or efferent arteriole.

06:07 And surrounding this tuft of capillaries is something called the glomerular capsule which is a very special type of epithelium that's going to interact very, very closely with these capillaries to make sure that filtration is only going to filter out the things we want filtered out and not the things we want to stay in the blood, for example, cells and proteins.

06:31 That filtration will then work its way down through all of these tubules and collecting duct and be further modified by either tubular reabsorption or secreting things back out into the tubules.