Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, I’m going to be talking about the structure of the kidney.
Now, “kidneys” because you do have two kidneys in your body, one on each side. You have a left kidney and a right kidney. And right now, we’re looking at them on this image where we’re looking at the abdomen ventrally. So we’re looking on the anterior view of the abdomen. And you can clearly see here the kidneys.
Now, for location, we can also see here the inferior vena cava, and you also see this important structure, this important blood vessel, which is the aorta, or more specifically, the abdominal aorta.
The kidneys are bilateral, retroperitoneal organs of the urogenital system that can be found in two places: the upper left and right abdominal quadrants. So these are locations that we usually use, especially in clinical settings.
Now, the function of these bean-shaped organs is to, then... they have several functions, including eliminating excess bodily fluid, salts, and by-products of protein metabolism.
And in this tutorial, as I mentioned before, we will be discussing the general structure of the kidneys, starting off with this one here that you see, highlighted in green. This is known as the adipose capsule of the kidney.
The adipose capsule of this organ is seen mostly from the posterior aspect of the kidneys. It acts as a cushion for the kidneys and surrounds the perirenal fat as well as the renal fascia or capsule.
The next structure that is now seen, highlighted in green, is known as the renal capsule.
The renal capsule or fibrous capsule of the kidney is a tough layer of fibrous tissue, as you can see, that covers the kidneys, clearly seen here on this image.
Now, this tough capsule acts as a protective layer preventing the kidneys from damage due to trauma.
From the renal capsule, we’re going to move on to our next structure that is found a little bit below this capsule. This is known as the renal cortex.
Now, the renal cortex is the outer layer of the kidney and is, as you can see now on this image, if I were to cut a bit of the kidney, you can expose, now, the renal cortex, seen here highlighted in green.
Now, this layer is approximately six millimeters thick and is situated between the renal capsule and the medulla, as you can see here—so the renal capsule and this area here known as the medulla.
Now, the renal cortex contains different structures that we’re going to be discussing on different tutorials, known as the glomeruli, blood vessels that you can clearly see here on this image, and convoluted uriniferous tubules. And you can also see here the renal columns that extend down between these structures, known as the pyramids of the medulla.
We’re going to move on to the next structure, seen here highlighted in green. This is known as the superior extremity of the kidney, also known as the superior pole. And this, as the name indicates, is the upper part of the kidney where the adrenal glands are situated.
And as we move on to the next image, you can clearly see here the adrenal gland being added on the superior extremity of the kidney. But right now, we’re highlighting a new structure that we’re going to be talking about. This is known as the lateral border of the kidney.
And as the name indicates, the lateral border is a conve… or has a convex shape and is found on the lateral part of the kidney. So this is basically the lateral side of the kidney, towards the edges of your body.
We’re moving on to another extremity here, now found a bit more inferiorly. This is the inferior extremity of the kidneys, also known as the inferior pole.
This is the lowest part of the kidneys, as can be seen here on the image, highlighted in green.
If we had a lateral border, we should have another one here, the medial border. And the medial border of the kidneys is concave this time and is where the hilum of the kidneys is located. And the hilum of the kidneys is the next structure that we’re going to highlight right here. So this is the hilum.
Now, the renal hilum is found on the concave medial margin of the kidney, as I mentioned before. It is here that the renal arteries (or the renal artery if you’re looking at one kidney) will enter and also enters via five different segments.
Now, this is also a point at which the renal vein and the renal pelvis exit the kidneys.
And you can all these structures that I just listed here. So this is the renal artery, the renal vein, and the renal pelvis coming out of the hilum.
Now, we’re going to continue with this list here and highlight this structure now on the screen. This is the right renal artery.
You do have a left one as well, but now we’re looking at the right kidney, so it does make sense to write down “right renal artery.” But the information that I'm going to mention now can be applied to both renal arteries.
Now, important thing to mention is that they arise from the abdominal aorta at the level of the first lumbar vertebra, L1 and L2, due to the different positioning of the kidneys.
Now, these arteries supply oxygenated blood to the kidneys, and they enter the kidney at the hilum, as we’ve seen on the previous slide.
The next one is also now seen, highlighted in green, another blood vessel that can be found on both kidneys. But now we’re looking at the right renal vein. The right renal vein, in the same way as the left renal vein, they exit the kidney at the hilum.
The renal veins, they have a function which they drain into the... or drain blood into the inferior vena cava.
The next structure is seen here, now highlighted in green, and I already have here the box showing the names, the renal pelvis. The renal pelvis is found on the hilum of the kidney and is the beginning of the ureter.
Since I mention the ureter, you can also see it now, highlighted in green, specifically the right ureter because you do have a left ureter. And both ureters are excretory ducts, and they are innervated by nerves that arise from T12 to L2 segments of the spinal cord.
I also wanted to show here, again, this image where I can clearly show you your ureters. You notice here the right ureter and the left ureter. And keep in mind that I'm talking about the subjective, the subjective’s perspective. That’s why we see here a bit of a twist on the directions.
And you can clearly see that the ureters are connecting the kidneys with another organ that we’re going to spend some time on a different tutorial, the urinary bladder. And notice here the connection between these organs.
And also important to mention that the ureter is split into two parts, one abdominal part and another one that goes into the pelvis, which we call, then, the pelvic part.
Now that I just gave you some overview on the ureters, I will spend some more time on these structures but on a separate tutorial, but I just wanted to give you an idea before we move on to the next structure.
The next structure that we’re going to talk about is now seen, highlighted in green. This is known as the adrenal gland. And the adrenal gland is also known as the suprarenal gland.
And you have two: one on top of each kidney. So these are endocrine glands that are located on the superior extremity of the kidneys.
And the adrenal glands have what is known to be as an adrenal cortex, which can be divided into three layers called the zona glomerulosa. And notice here that I'm listing here the… between parentheses, the hormones that can be produced within these layers. So on the zona glomerulosa, you will see androgens, while on the zona fasciculata, you see cortisol, and on the zona reticularis, you’ll find aldosterone.
Now, the other structure important to mention here on the adrenal gland is the medulla—the adrenal medulla where the hormones, norepinephrine and epinephrine, are secreted.
And the last structure that we saw also on the kidney, the adrenal gland also has a hilum where the central vein of the adrenal gland exits.
And from the adrenal gland, we’re going to move on to another structure, very tiny one that you can see right about here. This is known as the suprarenal vein.
Now, the suprarenal veins drain the adrenal glands. And the left suprarenal vein drains the blood from the left adrenal gland into the left renal vein, whereas the right suprarenal vein drains into the inferior vena cava. So this is important information that is always associated to the suprarenal vein and that you need to remember especially on exams. So don’t forget this.
Now, the next structure is also a very tiny group of structures that you can see here, highlighted in green. These are known as the superior suprarenal arteries. They are located on the superior surface of the adrenal glands, and these arteries are branches of the inferior phrenic artery. These arteries supply the adrenal gland.
The superior suprarenal arteries are a part of a group of three arteries, three types of arteries. The next one that we’re going to talk about is known as the middle suprarenal artery.
And the middle suprarenal arteries, as we can see here, are found on the medial side of the adrenal glands and are situated between the superior and inferior suprarenal arteries.
Now, the middle suprarenal artery is a branch of the abdominal aorta. And this artery also supplies the suprarenal gland with oxygenated blood.
And as a final structure on this tutorial, we’re going to talk about the inferior suprarenal artery that I mentioned before, briefly on the previous slide. And the inferior suprarenal arteries supply the suprarenal glands and are derived from the renal artery, which is a branch of the abdominal aorta.