Kidneys (Functions, Structures, Coverings, Nephron)

What's up? Meditay here.

Let's talk about the anatomy of the urinary system.

In this segment, we'll be talking about the anatomy of the kidneys.

So the urinary system consists of all the organs involved in handling the urine.

These are the kidneys, the ureter, the urinary bladder, and the urethra.

Our goal is to cover the anatomy of all the structures you see here, step by step, and we will start with the kidneys.

So in this video, we're first going to talk about the functions of the kidneys, then we'll talk about the external structures and the coverings of the kidneys.

After that, we will open the kidneys and cover the internal structures.

When we're done with the kidneys, we'll talk about the general anatomy of the nephron, which is the functional unit of the kidney.

All right.

So here you see the anterior view of the body.

The kidneys are those bean-shaped paired organs you have in the backside within the ribs.

The first thing you need to keep in mind is that the right kidney is placed a little lower than the left kidney.

Possibly because the liver occupies a huge part of the right side of the abdominal cavity.

But they both start at approximately the 12th thoracic vertebra, but the left one ends approximately at the second lumbar vertebra, and the right one ends approximately at the third lumbar vertebra.

So first off, what are the functions of the kidneys?

There are three main functions that the kidneys have, and they are plasma filtration, excretion of waste products, and acid-base homeostasis.

And the kidneys are able to do all that with the help of something called the nephron.

And we will talk a little more detailed through the nephron at the end of this video.

But the head of the nephron is called the renal corpuscle.

And this is the part that primarily filtrate the plasma.

So what are plasma?

When you first draw blood from the body into a tube, you will get whole blood.

And if you put the tube with the whole blood into a centrifuge and start the machine, it's going to spin around so fast that it's going to separate the blood, as you see here.

Now we're left with pure erythrocytes at the bottom, buffy coat consisting of white blood cells mainly, and plasma.

So when whole blood goes through the renal corpuscle, the plasma is going to get filtrated.

And that's what we mean with plasma filtration.

So plasma consists of everything that is not cells, so water, proteins, nutrition, electrolytes.

And here in bold, metabolic waste products, as you see here.

Examples of metabolic waste products we have within us are ammonia, uric acid, urea, and creatinine, and different types of amino acids as well.

Those are all considered as metabolic waste products.

And they get excreted out through the renal corpuscle.

And this is very important, it's dangerous if we get too much of these waste products.

Now.

Your body is in a perfect state when there's a balance between acid and base, around 7.35 to 7.45.

Is our natural state where all processes within us happen optimally.

But sometimes, something happened that make our blood either acidic or alkaline.

Called acidosis or alkalosis.

We don't like that.

And when the pH gets too deviated, it gets even worse.

And this process is usually regulated primarily through the lungs and the kidneys.

Now there are other functions the kidneys have as well, such as hormone production, producing hormones like erythropoietin that stimulates red blood cells production.

And vitamin D metabolism by activating vitamin D because vitamin D in our blood is usually inactive.

So that's the function of the kidneys.

They are very important to our body.

Kidneys are.

Now, let's start with the kidney's anatomy by looking at the external structures.

The kidneys are about 120 to 200 grams.

These numbers really deviate depending on the source you're studying from, but they're about 10 to 13 centimeters long and 5 to 6 centimeters wide and about 4 centimeters thick.

The kidneys have an inferior pole and a superior pole.

And on the superior pole, you will find the suprarenal glands resting on it, as you see here.

They also have two margins, there's the lateral border or the lateral margin, and there's the medial border.

And the medial border has an area called the hilum of the kidney.

And if you remember what a hilum is, a hilum is an entrance into an organ.

So this place is the only place structures can go in and out from the kidneys, you will find blood vessels and nerves and lymph vessels going in and out from the kidneys, as well as a ureter.

So that was all for the structures of the kidneys.

Now, let's look at how the kidneys are covered.

Here you see a posterior view of the body.

Let's now make a transverse cut and look at the kidneys from this perspective to see how the kidneys are covered.

Okay.

So here are two kidneys, superior view.

Here is a vertebra, and in front of them is the inferior vena cava and the abdominal aorta.

So the first covering that's around the kidneys are the fibrous capsule.

Which are dense fibers that protects the kidneys.

Around the fibrous capsule, there are the adipose capsule.

We call the perinephric fat.

Peri means around, so the fat around the kidneys.

And as you see here, the fat is thicker posteriorly than anteriorly.

And it's quite logical if you think about it, because the kidneys are closer to the posterior abdominal wall and this fatty capsule protects it from any concussion, as well as protecting them from becoming cold because they're closest to the skin on the posterior surface.

Okay, so that's these two.

Then externally to the fatty layer, we have a fascia covering it, called the renal fascia.

And this fascia have two parts or two layers.

We have an anterior layer and a posterior layer.

Laterally, they're both going to fuse, as you see here.

And then both these posterior layers are going to go in front of the vertebra and fuse with it.

While the anterior layer will go in front of the blood vessels and fuse with the other layer on the other side.

Now the anterior layer or the prerenal layer is called the fascia of Told.

While the posterior layer or the retrorenal layer is also called a layer of Zuckerkandl or however you pronounce it.

And they both lie behind the peritoneum and keep in mind that these two layers remain separated even below the kidneys, creating a space between them.

So that's generally how the kidneys are covered.

Now, let's go ahead and open the kidneys up, just like that, to cover the internal structures of it.

The kidneys have a compartment within them called the sinus renalis or the renal sinus.

And it's filled up by fat called the renal sinus fat.

And between the fat, you will find the renal pelvis and the renal calyces.

Which leads the urine from the kidneys down to the ureter.

And I'll show you this in a little more detail in a minute.

But the actual kidneys consist of the renal medulla and the renal cortex.

Some parts of the cortex is also going to extend down between the medulla.

So let's first cover the renal cortex.

So the renal cortex is dark brown in color and soft and granular in consistence.

And it can be everything between 4 to 11 millimeters thick.

Again, these numbers deviate a lot from source to source.

But we also got parts of the cortex going down between the medulla.

That are just extensions of the cortex.

Called the renal columns.

Now, what makes up the renal cortex?

If we take a small bit of the kidneys and zoom in.

Remember, the kidney's main functional unit are the nephron.

There's going to be a lot of nephrons within one kidney.

Around 1 to 1 and a half million nephrons.

And if we divide the nephron like this, you will see that parts of it lies in the cortex and parts of it lies in the medulla.

So the renal cortex is composed of the renal corpuscle, the proximal convoluted tube, and the distal convoluted tube.

The rest of the nephron is in the medulla.

So let's talk about the medulla a little bit.

The renal medulla consists of these renal pyramids.

There are about 7 to 18 of those within one kidney.

And here comes a tricky thing with these pyramids.

Each of these pyramidal structures, together with the adjacent cortex, will form lobes.

We call renal lobes.

Now the renal pyramid is called a pyramid because of its shape.

There's going to be a base, which is directed towards the cortex.

And on the other side, there's going to be the apex of the renal pyramid.

And these apices, the apex of the renal pyramids, will fuse together to form the renal papilla.

And I'll show you this in a little more detail when we go through the nephron.

But another thing that's important to mention when we talk about the renal medulla is that.

There are going to be parts of the medulla that radiate towards the cortex.

We call these renal medullary rays.

Now, let's go back to this picture again.

Now we know that when we talk about the renal medulla, we're talking about pyramids.

And you will find the rest of the nephron here.

We have the loop of Henle and the collecting duct.

Okay, so let's continue from the renal papilla.

The renal papilla are going to have these openings of the papillary ducts.

Which leads the urine from the pyramids towards the minor renal calyces.

And these minor renal calyces are going to fuse into major renal calyces.

And there are usually two to three of these major renal calyces within one kidney.

The urine will then flow into the renal pelvis and then go down towards the ureter.

So that's all we need to know regarding the anatomy of the kidney.

Now let's do the anatomy of the nephron.

And to do that, we're going to isolate one lobe and look at the detailed view of it.

So the renal cortex and its renal columns are going to be between the renal pyramids.

Right?

And below the renal pyramids, you will find the minor renal calyces.

Which fuse together and form the major renal calyces.

All right.

So the nephron consist of a renal corpuscle located in the renal cortex.

And the renal corpuscle consist of a glomerulus.

Which are many capillary loops, as you see here.

So the blood will flow in through the afferent arteriole.

Remember, A stands for arrive.

So the afferent arteriole arrives into the glomerulus, and they exit as efferent arterioles.

So E stands for exit.

And the glomerulus is surrounded by a glomerular capsule.

Which, as you see here, consists of the internal part and an external part.

And between them is where the tubular system is going to continue.

So the urine flows between those two layers you see here.

So that's the renal corpuscle.

After the renal corpuscle is the proximal convoluted tube.

Which also lies in the cortex.

The proximal convoluted tube has two parts.

There's a convoluted part, which curves.

And a straight part.

And the nephron continues into the renal pyramids as the loop of Henle.

There's the descending part and a descending part, which extends up to the renal cortex again as a distal convoluted tube.

Now.

Up until this step, the plasma has been filtrated into the primary urine, electrolytes and other minerals have been reabsorbed and secreted out throughout the whole tube.

And at this point, the urine is now finished to be called a secondary urine.

Which is what we generally call urine.

Now the urine will continue through the collecting ducts.

And these collecting ducts will all come together and fuse and form the papillary ducts.

At this point, the papillary ducts will open up as a small openings into the minor renal calyces.

So that was everything I had for the anatomy of the kidneys.

I really hope this video helped you to understand the anatomy of it.

If you find this video helpful, please put a like, share, comment, whatever you find convenient to you.

The next video is going to be about the ureter, urinary bladder, and the urethra in both male and female.