The Kidneys - Online Tutor, Practice Problems & Exam Prep

The kidneys are protected by the renal capsule, a tough collagenous layer, and supported by renal fascia and an adipose capsule, which acts as a shock absorber. Internally, the kidney consists of the renal cortex, the outer layer, and the renal medulla, which contains renal pyramids and columns. Urine forms in these regions and drains into the renal pelvis, a funnel-shaped structure that connects to the ureter. The minor calyx collects urine from the papilla of the pyramids, while major calyces converge to drain into the renal pelvis, facilitating excretion.

External Anatomy

Alright. Let's dive into the external anatomy of our kidneys. So, the exterior of the kidney is covered in something called the renal capsule. The renal capsule is basically a thin layer of a collagenous connective tissue. Despite how thin it is, this layer is very tough and vibrant. So if you've ever looked at a kidney in a dissection or in an anatomy photo, that outer layer of the kidney that you're seeing is the renal capsule. It is considered a bit of a protective layer because of how tough and fibrous it can be.

Next up, we have one of the most characteristic features of the kidney which is the renal hilum. The renal hilum is the left that you see on the medial surface of the kidney, and that kind of gives it its characteristic little dip that gives it that kidney bean shape. This is going to be the location where the ureter and the blood vessels can enter and exit our kidney. So if you're looking at our kidney image over here, this kind of very classic characteristic side view of a kidney, this little dip in that surface is the renal hilum. I'll go ahead and label that right now.

Our kidneys are held in place and protected by two additional layers of tissue. First up, we have our renal fascia. Renal fascia, like all fascia that we've seen in the human body, is just going to be a dense collagenous connective tissue that will help to anchor the kidneys to the abdominal wall and hold them in place. We also have the adipose capsule, which is a thick layer of adipose or very fatty tissue. That nice thick adipose capsule is basically going to act as a kind of shock absorber if we have any kind of trauma happening near our kidneys. It's a very nice cushiony protective layer in case we get any kind of injuries near the kidney.

If we look down at our image here, I'm just going to kind of orient you to this one here, on the left because it is a little bit of an odd view if you're not used to it

The Kidneys Example 1

Okay. So this one asks us, which of the following answer choices correctly names the 3 protective layers surrounding each kidney from innermost to outermost? So if we are thinking of the innermost protective layer of the kidney, that is going to be our renal capsule because it's basically just covering the kidney itself. It's like the outer layer of the kidney and made of that nice, connective tissue. It's very tough and fibrous. So, our first one here has to be renal capsule. So looking at our answer choices, it looks like B starts with that one. Then we can see this is going in the correct order. We have that nice, thick fatty adipose capsule in the middle and then our renal fascia at the outermost layer, which helps, surround our kidney and anchor it to the abdominal wall and keep it nice and supported. So our answer here is going to be B: from innermost to outermost, we have our renal capsule, our adipose capsule, and then our renal fascia. There you have it.

In the event of a traumatic injury, which layer surrounding the kidney provides a cushioning effect due to its fatty composition?

• A. Renal capsule.
• B. Adipose fascia.
• C. Nephron tissue.
• D. Adipose capsule.

Internal Anatomy

Okay. Let's get into the internal anatomy of our kidney. There are 3 main regions within the kidney. So first up, we have our renal cortex. Now we often think of the brain when we hear cortex, but keep in mind that cortex is just an anatomical term that refers to the outermost layer of something. So, this is the most superficial region of the inside of our kidney. It tends to be quite light in color and has a bit of a granular appearance to it. That's our renal cortex. Next up, we have our renal medulla which is the middle region. And the renal medulla contains 2 separate structures. So first, we have our renal pyramids, which are cone-shaped masses that are made up of parallel bundles of tubes and capillaries. And those parallel running tubes and capillaries give them a striated or striped appearance. And these tend to be quite darker in color. They're like very visible little triangles within our kidney. And the tip of these pyramids is called the papilla.

Now, within our medulla, we also have structures called renal columns. The renal columns are inward extensions of cortical tissue, and that's, of course, renal cortical tissue, not brain cortex, and they we separate those pyramids. So if we look down at our image here, we have a little cross-section of a kidney, and you can see we have this nice superficial lightly colored region running here, and that is our renal cortex. And then we have this sort of middle portion right here, which is going to be our renal medulla. You can see how within the renal medulla, we have these cone-shaped masses here. Those are the renal pyramids. And the tip of those pyramids is called the papilla. And then you can see we have the structure. It's kind of separating those pyramids, and those are the renal columns. You can see how the renal columns look just like the renal cortex. It's the exact same type of tissue that we have cortical tissue just kind of dipping down into that medulla and that is what our renal column is.

One thing to note is that the renal cortex and the renal medulla are the urine forming structures of our kidney. So this is where we are actually forming the urine. And then the urine is going to drain into our urine collection structure, which is our renal pelvis. So scooching down to our renal pelvis, this is going to be a funnel-shaped tube. And I'm going to warn you, I'm going to say the word funnel-shaped tube like 15 times in the next minute. So please forgive me. There's just a lot of things that are shaped like funnels in this part of the kidney. So sometimes anatomy is weird, it is what it is.

Our renal pelvis is a funnel-shaped tube that is continuous with the ureter. So, again, this is kind of the urine collection structure in our kidney. And our renal pelvis is made of 2 types of structures. So first up, we have a minor calyx. A minor calyx is a little funnel-shaped tube that collects urine at the papilla of the renal pyramid. And then a major calyx is going to be a slightly larger funnel-shaped tube that is formed by the convergence of about 3 to 4 of those minor calyces. And then the major calyx surrounds and drains urine into the renal pelvis. So if we are looking at our kidney now, you can see this sort of central structure is the renal pelvis. And you can see right here how it is continuous with the ureter. The ureter is right here is a big open tube and the renal pelvis can drain right into that ureter. And then you can see we have a minor calyx, and I'll point to that on the image in just one second.

So we're going to have a little minor calyx right at the tip of those pyramids, right at that papilla. Basically, urine is going to be getting created within the renal medulla. It's going to come out of that papilla and drain right into one of these little teeny tiny minor calyces. And then, kind of formed by the convergence of 1, 2, 3 minor calyces, we have this major calyx here. Typically, we're going to see that there's going to be about 3 to 4 major calyces that will drain into the renal pelvis.

Okay. So this is not a perfectly accurate image of what a kidney would look like. That's kind of the idea that we're going for. And I know that, you know, the renal pelvis and the major calyx can look like they're kind of one big continuous structure. But really, the renal pelvis is really this, like, central portion that's going to be draining directly into that ureter, and the minor calyces are these kind of like funnel-like or cup-like structures that are going to be formed right at the convergence of 3 of those little tiny minor calyces, like funnel-shaped structures. So basically what's happening here is that we've got urine forming in the cortex. It's forming in the medulla. It's coming down. It's getting excreted out of the tip of the pyramid, the papilla. It'll get collected into a minor calyx, which will get dumped. It'll then get dumped into a major calyx. It will then drain into the renal pelvis, and then it will drain out into the ureter.

Alright. So that is the internal anatomy of our kidney, and I will see you guys in the next one. Bye bye.

The Kidneys Example 2

Alright. So this one reads, which of the following statements best describes the renal pelvis? Let's run through them and see what we have here. Statement A reads, "It is the outermost layer surrounding the kidney," and no, that would be the renal capsule. So A is out. Statement B reads, "It is located within the renal medulla," but the renal medulla and the renal pelvis are separate structures within our kidneys, so B is also out. C reads, "It consists of renal pyramids and is the main location of blood filtration." So, renal pyramids are found within the renal medulla, remember, and there is no filtration happening in the pelvis. It's simply acting as a collecting pool for urine. So C is out, and we are left with D. "It is a funnel-shaped structure where urine collects," and that is absolutely correct. Remember our renal pelvis? Think of our actual pelvis. It's that nice kind of funnel V shape to it. This is just the structure in the kidney where our urine is actually kind of pooling together and collecting. So our answer here is D.

The kidneys are surrounded by a tough, fibrous layer of tissue called the:

• A. The renal capsule.
• B. The renal cortex.
• C. The renal medulla.
• D. The adipose capsule.

Here’s what students ask on this topic:

What is the function of the renal capsule in the kidneys?

The renal capsule is a thin but tough layer of collagenous connective tissue that covers the exterior of the kidney. Its primary function is to provide a protective barrier for the kidney, shielding it from physical damage and infections. Despite its thinness, the renal capsule is very fibrous and resilient, making it an effective protective layer. This capsule also helps maintain the shape of the kidney and supports its internal structures.

What are the main regions of the internal anatomy of the kidney?

The internal anatomy of the kidney is divided into three main regions: the renal cortex, the renal medulla, and the renal pelvis. The renal cortex is the outermost layer, light in color with a granular appearance. The renal medulla is the middle region, containing renal pyramids and renal columns. The renal pyramids are cone-shaped structures made up of parallel bundles of tubes and capillaries, while the renal columns are extensions of cortical tissue that separate the pyramids. The renal pelvis is a funnel-shaped tube that collects urine from the renal medulla and drains it into the ureter.

How does urine flow through the kidney?

Urine formation begins in the renal cortex and renal medulla. It then flows from the renal pyramids' papilla into the minor calyces, which are small funnel-shaped structures. Multiple minor calyces converge to form major calyces. The major calyces then drain the urine into the renal pelvis, a larger funnel-shaped structure. Finally, the renal pelvis channels the urine into the ureter, which transports it to the bladder for excretion.

What is the role of the renal fascia and adipose capsule in kidney protection?

The renal fascia and adipose capsule play crucial roles in protecting the kidneys. The renal fascia is a dense layer of collagenous connective tissue that anchors the kidneys to the abdominal wall, helping to hold them in place. The adipose capsule is a thick layer of fatty tissue that surrounds the kidneys, acting as a shock absorber to cushion the kidneys from physical trauma. Together, these layers provide structural support and protection for the kidneys.

What structures are involved in urine collection within the kidney?

Urine collection within the kidney involves several structures. The process starts at the renal pyramids' papilla, where urine is collected by the minor calyces. These minor calyces are small funnel-shaped tubes that converge to form larger structures called major calyces. The major calyces then drain the urine into the renal pelvis, a central funnel-shaped tube. The renal pelvis is continuous with the ureter, which transports the urine to the bladder for storage and eventual excretion.