Description

Kidney Anatomy: Topography, Structures, and Function

This video covers a comprehensive overview of the kidneys, including their topography, functions, external and internal structures, and nephron anatomy.

1. Topography of the Kidney

• The right kidney is slightly lower than the left.
• Both kidneys start at T12.
• Left kidney: Ends at L2.
• Right kidney: Ends at L3.

2. Functions of the Kidney

• Plasma Filtration: Through nephrons.
• Excretion: Removal of metabolic waste.
• Acid-Base Homeostasis: Regulates pH balance.
• Hormone Production: Erythropoietin, Renin.
• Vitamin D Metabolism: Activation of Vitamin D.

3. External Structures

• Weight: 120-200 grams.
• Size: 10-13 cm long, 5-6 cm wide, 4 cm thick.
• Inferior Pole (Extremitas Inferior).
• Superior Pole (Extremitas Superior): Suprarenal gland located on top.
• Lateral Border (Margo Lateralis).
• Medial Border (Margo Medialis): Contains the hilum (Hilum Renalis).

4. Coverings of the Kidney

• Fibrous Capsule (Capsula Fibrosa).
• Perinephric Fat (Capsula Adiposa).
• Renal Fascia (Fascia Renalis):
  • Anterior Layer: Prerenal Layer (Lamina Prerenalis) / Fascia of Toldt.
  • Posterior Layer: Retrorenal Layer (Lamina Retrorenalis) / Fascia of Zuckerkandl.
  • Both layers fuse laterally.
• Peritoneum.

5. Internal Structures

Renal Sinus

• Sinus Renalis: Fat-filled space inside the kidney.
• Renal Pelvis (Pelvis Renalis): Central collecting region.
• Renal Calyces (Calyces Renales): Divided into:
  • Minor Renal Calyces (Calyx Renales Minor).
  • Major Renal Calyces (Calyx Renales Major).

Renal Medulla

• Renal Pyramids (Pyramides Renales).
• Renal Lobes (Lobi Renales).
• Renal Papillae (Papillae Renales): Tip of pyramids.
• Renal Medullary Rays (Radii Medullares): Contain nephrons’ loops.
• Loop of Henle and Collecting Ducts.
• Openings of Papillary Ducts (Foramina Papillaria).

Renal Cortex

• Thickness: 4-11 mm.
• Renal Columns (Columna Renalis): Extension of the cortex into the medulla.
• Contains Renal Corpuscles, Proximal & Distal Convoluted Tubules.

6. Renal Lobe & Nephron

Renal Corpuscle (Corpusculum Renis)

• Glomerulus: Network of capillaries.
• Afferent Arteriole (Vas Afferens): Brings blood in.
• Efferent Arteriole (Vas Efferens): Drains blood out.
• Glomerular Capsule (Capsula Glomeruli): Encases glomerulus.

Nephron Tubules

• Proximal Convoluted Tubule (Tubulus Proximalis): Reabsorbs nutrients.
  • Has a convoluted part and a straight part.
• Loop of Henle (Ansa Nephroni):
  • Descending Limb.
  • Ascending Limb.
• Distal Convoluted Tubule (Tubulus Distalis): Fine-tunes ion balance.
• Collecting Duct (Ductus Colligentes): Final urine concentration.
• Papillary Duct (Ductus Papillares): Empties into minor calyx.

7. Clinical Relevance

• Polycystic Kidney Disease (PKD): Genetic disorder causing multiple cysts in the kidney.
• Kidney Stones (Nephrolithiasis): Crystallized minerals causing obstruction.
• Acute Kidney Injury (AKI): Sudden loss of kidney function.
• Chronic Kidney Disease (CKD): Progressive decline in kidney function.

Sources Used:

• Memorix Anatomy (2nd Edition) – Hudák Radovan, Kachlík David, Volný Ondřej.
• Complete Anatomy by 3D4Medical.
• Biorender.
• University notes and lectures.

Transcript

Introduction
0:03
What’s up.
0:04
Meditay here.
0:05
Let’s talk about the anatomy of the urinary system.
0:07
In this segment, we will be talking about the anatomy of the Kidneys.
0:10
Alright, so the Urinary system consists of all the organs involved in handling the urine.
0:15
These are the Kidneys, the Ureter, the Urinary bladder, and the urethra.
0:20
Our goal is to cover the anatomy of all these structures you see here, step by step, and
0:25
we’ll start with the Kidneys In this video, we’re first going to talk about
0:28
the functions of the kidneys.
0:30
Then we’ll talk about the external structures and the coverings of the kidneys.
0:34
After that, we’ll open up the kidney and cover the internal structures.
0:39
When we’re done with the kidneys, we’ll talk about the general anatomy of the nephron,
0:42
which is the functional unit of the kidney.
Topography of Kidney
0:45
Alright, so here you see an anterior view of the body.
0:48
The kidneys are these bean-shaped paired organs you have on the backside within the ribs.
0:54
The first thing you need to keep in mind is that the Right kidney is placed a little lower
0:58
than the left kidney, possibly because the liver occupies a huge part of the right side
1:03
of the abdominal cavity.
1:04
But they both start approximately from the 12th thoracic vertebrae.
1:08
But the left one ends at approximately the 2nd lumbar vertebra, and the right kidney
1:13
ends at approximately the 3rd Lumbar Vertebra.
1:15
Ok, so first off, what are the functions of the kidneys?
Functions of Kidneys
1:19
There are three main functions that the kidneys have.
1:22
And they are Plasma filtration, Excretion of waste products, and acid-base homeostasis.
1:28
And the kidneys are able to do all that with the help of something we call a nephron.
1:33
We’ll talk a little more detail through the nephron at the end of this video, but
1:37
the head of the nephron, is called a Renal Corpuscle, and this is the part that primarily
1:42
filtrates the plasma.
1:44
So, what is plasma?
1:45
When you first draw blood from the body, into a tube, you’ll get whole blood.
1:50
And if you put this tube with whole blood into a centrifuge, and start the machine,
1:55
it’ll spin around so fast, that it’s going to separate the blood, as you see here.
2:00
Now we’re left with Pure erythrocytes at the bottom, buffy coat, consisting of white
2:05
blood cells mainly, and plasma.
2:07
So when whole blood goes through the renal corpuscle, the plasma is going to get filtrated.
2:12
So that’s what we mean with plasma filtration.
2:15
Next, excretion of waste products.
2:16
So the plasma consists of everything that’s not cells.
2:19
That is water, proteins, nutrients, electrolytes, and here in bold.
2:25
Metabolic Waste products.
2:26
As you see here.
2:27
So what kind of metabolic waste products do we have?
2:28
We have (ammonia, uric acid, urea, creatine, creatinine, and different types of amino acids)
2:35
are considered as metabolic waste products, and they get excreted out through the renal
2:41
corpuscle, and this si very important, it’s dangerous if we get too much of these waste
2:46
products.
2:47
Now, your body is in a perfect state when there’s a balance between acid and base,
2:53
around 7.35 to 7.45 is our natural state where all processes within us happen optimally.
3:00
But sometimes, something happens that makes our blood either acidic or alkaline, called
3:06
acidosis and alkalosis.
3:07
We don’t like that, and when the pH gets too deviated, it gets even worse.
3:13
And this process is usually regulated primarily through the lungs and the kidneys.
3:18
There are other functions the kidneys have as well, such as hormone production, producing
3:22
hormones like erythropoietin that stimulate RBC production, and Vit D metabolism by activating
3:28
vit D, since most vitamin D in our blood is in an inactive state.
3:33
So that’s the functions of the kidneys- They’re very important to our body, kidneys
3:36
are.
External Structures
3:37
Now let’s start with the kidneys anatomy by looking at the external structures.
3:42
So the kidneys are about 120-200 grams, these numbers really deviate depending on the source
3:48
you’re studying from, but they’re about 10 to 13 centimeters long and 5-6 centimeters
3:54
wide, and about 4 cm thick.
3:56
The kidney has an inferior Pole, and a Superior Pole.
4:00
And on the superior pole, you’ll find the suprarenal gland resting on it as you see
4:05
here.
4:06
They also have two margins.
4:07
There’s a lateral border or lateral margin, and there’s the medial border.
4:12
The medial border has an area called hilum of the Kidneys, and if you remember what a
4:17
hilum is.
4:18
A hilum is the entrance into an organ.
4:20
So this place is the only place structures can go in and out from the kidneys.
4:24
You’ll find blood vessels and nerves and lymph vessels going in and out, as well as
4:29
the ureter.
Coverings of the Kidneys
4:30
So that was all the external structures of the kidneys.
4:33
Let’s now look how the kidneys are covered.
4:36
Here you see a posterior view of the body.
4:39
Let’s now make a transverse cut and look at the kidneys from this perspective to see
4:43
how the kidneys are covered.
4:44
Ok, So here are two kidneys, superior view.
4:48
Here is the Vertebra and in front of them are the Inferior vena cava and the abdominal
4:53
aorta.
4:54
So the first covering that’s around the kidneys are the fibrous capsule, which are
4:59
dense fibers that protect the kidneys.
5:02
Around the fibrous capsule, there are the adipose capsule, we call it the perinephric
5:06
fat, peri means around, so the fat around the kidneys.
5:10
And as you see here, this fat is thicker posteriorly than anteriorly.
5:14
And it’s quite logical if you think about it as the kidneys are closer to the posterior
5:19
abdominal wall, this fatty capsule protects it from any concussion, as well as protecting
5:25
them from becoming cold.
5:27
Ok, sot that’s these two.
5:31
Then, externally to the fatty layer, we have a fasciae covering it, called the Renal Fascia.
5:37
And this fascia has two parts or two layers.
5:40
We have an anterior layer and a posterior layer.
5:43
Laterally, they’re both going to fuse, as you see here.
5:48
Both these posterior layers are going to go in front of the vertebra and fuse with it,
5:54
while the anterior layer will go in front of the blood vessels and fuse with the other
5:59
layer on the other side.
6:00
The anterior layer or prerenal layer is also called Fascia of Toldt.
6:06
While the Posterior later, or the Retrorenal Layer, which is also called Layer of Zuckerkandl.
6:14
And they both lie behind the peritoneum.
6:17
These two layers remain separated below the kidneys, creating a space between them.
6:23
So that’s generally how the kidneys are covered.
Internal Structures of Kidneys
6:26
Now let’s go ahead and open up the kidney, just like that, to cover the internal structures
6:31
of it.
6:32
The kidneys have a compartment within them called the Sinus Renalis, or the Renal Sinus.
6:38
And it’s filled up by fat called the renal sinus fat.
6:41
And between the fat, you’ll find the renal pelvis and the renal calyces, which lead the
6:47
urine from the kidneys down to the ureter.
6:50
And I’ll show you this in a little more detail in a minute.
6:53
But the actual kidneys consist of the renal medulla and the renal cortex.
6:58
Some parts of the cortex are also going to extend down between the medulla.
7:02
So let’s first cover the Renal Cortex.
7:04
So the renal cortex is dark brown in color and soft and granule in consistence.
7:09
It can be between 4-11mm thick.
7:13
Again these numbers deviate a lot from source to source, but we also got parts of the cortex
7:19
going down in between the medulla, which are just extensions of the cortex, called the
7:24
renal columns.
7:25
Now, what makes up the renal cortex?
7:28
If we take a small bit of the kidneys and zoom in.
7:31
Remember the kidneys main functional unit are the nephrons.
7:34
There’s gonna be a lot of nephrons within one kidney, around 1 to 1,5 million nephrons.
7:40
And if we divide the nephron like this.
7:42
You’ll see that parts of it lie in the cortex, and part of it lies in the medulla.
7:47
So the renal Cortex is composed of the renal corpuscle, the proximal convoluted tube, and
7:52
the distal convoluted tube.
7:54
The rest of the nephron is in the Medulla, so let’s talk about the medulla a little
7:58
bit.
7:59
The renal medulla consists of these renal pyramids.
8:01
There are about 7-18 of those within one kidney.
8:05
Here comes the tricky part with these pyramids.
8:07
Each of these pyramidal structures together with their adjacent cortex will form lobes
8:13
we call renal lobes.
8:15
Now the renal pyramid is called a pyramid because of its shape.
8:19
There’s going to be a base that is directed towards the cortex.
8:23
And on the other side, there’s going to be the apex of the renal pyramid.
8:27
And these apices will fuse together and form a renal papilla.
8:33
I’ll show you this in a little more detail when we go through the nephron.
8:36
But another thing that’s important to mention when talking about the renal medulla is that
8:41
there are going to be parts of the medulla that radiated towards the cortex, which we
8:47
call renal medullary rays.
8:50
Now let’s go back to this picture again.
8:52
Now we know that when we talk about the renal medulla.
8:55
We’re talking about the Pyramid.
8:56
And you’ll find the rest of the nephron here.
8:58
Which is the Loop of Henle, and the collecting duct.
9:02
Ok.
9:03
So let’s continue from the renal papilla.
9:05
The renal papilla is going to have these openings of the papillary ducts, which lead the urine
9:12
from the pyramids, towards the Minor Renal Calyces.
9:16
And these minor renal calyces are going to fuse into the major renal calyces.
9:22
There are usually 2 or 3 of these major renal calyces.
9:27
The urine will then flow into the renal pelvis, to then go down towards the Ureter.
9:33
So that’s all we need to know for the anatomy of the kidney.
Renal Lobe – Nephron
9:36
Now let’s do the anatomy of the nephron.
9:39
And to do that, we’re going to isolate one renal lobe, and look at a detailed view of
9:44
it.
9:45
So the renal cortex and its renal colums go between the renal pyramids.
9:52
And below the renal pyramid, you’ll find the minor renal calyces.
9:58
Alright.
10:00
SO the nephron consists of a Renal Corpuscle, located in the renal cortex.
10:05
And the renal corpuscle consists of a glomerulus, which are many capillary loops as you see
10:11
here.
10:12
So blood will flow in through an afferent arteriole, remember a stands for arrive.
10:18
So afferent arterioles arrive into the glomerulus, and they exit as efferent arteriole.
10:24
E for exit.
10:26
And the glomerulus is surrounded by a glomerular capsule.
10:30
Which as you see here consists of an internal part and an external part.
10:35
And between them is where the tubular system is going to continue, so the urine flows between
10:40
the two layers you see here.
10:42
So that’s the renal corpuscle.
10:44
After the renal corpuscle is the Proximal Convoluted tube, which also lies in the cortex.
10:50
The proximal convoluted tube has two parts.
10:53
There’s a convoluted part, which curves, and a straight part.
10:58
Then the nephron continues into the renal pyramid as the Loop of Henle.
11:02
There’s a descending part and an ascending part, which extends up to the renal cortex
11:09
as the Distal Convoluted Tube.
11:11
Now up until this step.
11:14
The plasma has been filtrated into primary urine.
11:17
Electrolytes and other minerals have been reabsorbed and secreted out throughout the
11:21
whole tube.
11:22
And at this point.
11:23
The urine is now finished to be called secondary urine, which is what we generally call urine.
11:29
Now the urine will continue through the collecting ducts.
11:32
These collecting ducts will all come together, fuse, and form the papillary ducts.
11:37
At this point, the papillary ducts will open up as small openings, into the minor renal
11:43
calyces.
11:44
So that was everything I had for the anatomy of the kidneys.
11:47
I really hope this video helped you understand the anatomy of it.
11:52
In the next video, we’re going to talk about the anatomy of the Ureter, Urinary bladder,
11:57
and the Urethra n both male and female.