Description

Functions and Anatomy of the Lungs

This video covers the functions, parts, segments, and pleura of the lungs, as well as the surrounding mediastinum.

1. Functions of the Lungs:

• Essential organ of respiration.
• Facilitates gas exchange (O₂ uptake and CO₂ removal).

Muscles of Inspiration:

• Sternocleidomastoideus.
• External Intercostal Muscles.
• Diaphragm.

Muscles of Expiration:

• Internal Intercostal Muscles.
• Abdominal Muscles.

Functional Unit of the Lungs:

• Alveolar Sacs (Sacculi Alveolares): Site of gas exchange.

2. Parts and Surfaces of the Lungs:

• Apex of Lung (Apex Pulmonis) – superior-most part.
• Base of Lung (Basis Pulmonis) – rests on the diaphragm.
• Costal Surface (Facies Costalis) – faces the ribs.
• Diaphragmatic Surface (Facies Diaphragmatica) – contacts the diaphragm.
• Mediastinal Surface (Facies Mediastinalis) – faces the mediastinum.
• Hilum of Lung (Hilum Pulmonis) – entry point for bronchi, vessels, and nerves.
• Pulmonary Ligament (Ligamentum Pulmonale) – stabilizes lung position.
• Root of Lung (Radix Pulmonis) – contains pulmonary vessels and bronchi.

Hilum Orientation Mnemonic:

• Right Lung: BRIGHT IS RIGHT – Highest structure is the Bronchus, followed by Pulmonary Arteries, then Pulmonary Veins.
• Left Lung: Highest structure is the Pulmonary Artery, followed by the Bronchus, then Pulmonary Veins.

Margins of the Lungs:

• Inferior Margin (Margo Inferior): Separates costal and diaphragmatic surfaces.
• Anterior Margin (Margo Anterior): Forms a distinct border.
• Cardiac Notch (Incisura Cardiaca Pulmonis Sinistri): Indentation in the left lung.
• Lingula of Left Lung (Lingula Pulmonis): Tongue-like projection of the left superior lobe.

3. Pulmonary Lobes:

• Oblique Fissure (Fissura Obliqua) – divides superior and inferior lobes.
• Horizontal Fissure (Fissura Horizontalis) – divides right lung into three lobes.

Lobes of the Lungs:

• Right Lung: 3 lobes – Superior, Middle, Inferior.
• Left Lung: 2 lobes – Superior, Inferior.

4. Pulmonary Segments:

Right Lung (10 Segments):

• Superior Lobe: Apical, Posterior, Anterior.
• Middle Lobe: Lateral, Medial.
• Inferior Lobe: Superior, Basal Medial, Basal Anterior, Basal Lateral, Basal Posterior.

Left Lung (8-9 Segments):

• Superior Lobe: Apicoposterior, Anterior, Superior Lingular, Inferior Lingular.
• Inferior Lobe: Superior, Basal Anterior, Basal Lateral, Basal Posterior, (±Basal Medial).

5. Pleura of the Lungs:

• Visceral Pleura (Pleura Visceralis): Covers the lungs directly.
• Parietal Pleura (Pleura Parietalis):
  • Costal Part.
  • Diaphragmatic Part.
  • Mediastinal Part.
  • Pleural Part.

Pleural Cavity (Cavitas Pleuralis):

• Space between visceral and parietal pleura.

Pleural Recesses:

• Costodiaphragmatic Recess (Recessus Costodiaphragmaticus).
• Costomediastinal Recess (Recessus Costomediastinalis).
• Vertebromediastinal Recess (Recessus Vertebromediastinalis).
• Phrenicomediastinal Recess (Recessus Phrenicomediastinalis).

6. Mediastinum:

• Superior Mediastinum (Mediastinum Superius): Above the heart.
• Inferior Mediastinum (Mediastinum Inferius): Divided into:
  • Anterior Mediastinum.
  • Middle Mediastinum.
  • Posterior Mediastinum.

7. Sources:

• Memorix Anatomy, 2nd Edition by Hudák Radovan, Kachlík David, and Volný Ondřej.
• Complete Anatomy by 3D4Medical.
• Biorender.
• University notes and lectures.
• Snell’s Clinical Anatomy, 10th Edition.

Transcript

Introduction
0:03
Hey, what’s up, Meditay here. Let’s talk about the anatomy of the respiratory system.
0:07
In this segment, we will be talking about the anatomy of the Lungs and the pleura. Alright, so
0:12
the respiratory system consists of all the organs involved in breathing. These are the Nasal Cavity,
0:17
Pharynx, Larynx, Trachea, Bronchi, and the Lungs.
0:21
Now let’s look detailed into the anatomy of the Lungs.
0:25
So In this video, we’re first gonna go through the functions of the lungs.
0:29
Then we’re gonna go through the parts, and surfaces, and margins of the lungs.
0:34
After that, we’ll look at how the right and left lungs are divided into lobes and segments.
0:39
When we’re done with the Lungs, we’ll go through the Pleura, which is the coverings of the lungs.
0:44
We’ll look at its parts and its recesses and then finish up by looking at the mediastinum.
0:50
Basically, what’s between the right and the left lung.
0:53
Now, the lungs are the primary organ in the respiratory system, because it’s the essential
Lung Function
0:58
organ of respiration. But it doesn’t work alone. You have muscles called muscles of inspiration,
1:04
which aids in expanding the thoracic cavity to further decrease the pressure so that
1:09
air can come in. And examples of those are the Diaphragm and the external intercostal muscles,
1:15
as well as some accessory muscles of inspiration like the sternocleidomasteoid. Similarly,
1:20
there are muscles that aid with expiration, even though this process happens passively due to the
1:26
recoil system. The Internal Intercostal muscles and the abdominal muscles are some examples
1:31
of muscles that aid with expiration. So let’s first have a basic understanding
1:35
of the functional unit of the lungs. Now when you look at the lung microscopically,
1:41
you’ll be able to see the alveolar sacs, and these alveolar sacs are what we reffere to as the
1:47
functional unit of the lungs because they give it its function. So if we zoom in into one alveolus,
1:53
you’ll see that they’re highly vascularized so that oxygen can get into the bloodstream,
1:58
while waste products like carbondioxide can get excreted out through diffusion.
Parts and Surfaces of the Lungs
2:04
So that was just a quick introduction of how the lungs primarily function.
2:09
Let’s now start with its anatomy by looking at the Parts and surfaces of the lungs!
2:13
The uppermost cone shaped part is what we call the Apex of the Lung,
2:18
and at the bottom, we call this the base of the lung. The lung has some surfaces aswell and There
2:30
are 4 surfaces in total. The first surface we’re going to have is the Costal surface,
2:35
which is directed towards the ribs as you see here. So this whole surface, which are covered by
2:40
the ribs is what we call the costal surface. Below the lungs you’ll find a perfectly drawn Diaphragm,
2:46
which means that the bottom surface is called the diaphragmatic surface.
2:51
Between the lungs, you’ll find a space filled with structures, called the Mediastinum. So
2:56
this will be the mediastinal surface. Now the mediastinal surface is very important, because
Hilum of the Lung
3:01
this is the surface where you’ll find the Hilum of the Lung. Think of the Hilum as an entrance,
3:06
or a hallway which leads into the lung. And this entrance is bordered by the Pulmonary Ligament.
3:13
And all structures that come into and out from the lungs, are called the Root of the lung.
3:20
Here’s an image that I really liked from the book Snell’s Clinical Anatomy, 10th edition. The reason
3:24
why I liked it is because it perfectly shows how the Hilum of the Lung look like. You see it’s
3:30
kind of a depression, or a hallway that leads into the lung bordered by the Pulmonary Ligament, and
3:37
structures go in and out as the root of the lung. And there’s actually a special arrangement that
3:42
make the right lung differ from the left lung. In the Right Lung, the highest structure which
3:48
enters the lung is the bronchus. Below it are the Pulmonary Arteries, then the Pulmonary Veins. On
3:55
the root of the left lung, the highest structure here is going to be the pulmonary Artery, then the
4:01
bronchus below it and then the pulmonary Veins. There’s a mneumonic you can use if you need to
4:07
know this arrangement that goes Bright is Right. Where the B stands for bronchus,
4:12
just to remember that the right lung is where the bronchus is the highest structure. So that
Parts and Surfaces of the Lungs (revisited)
4:18
was the Mediastinal surface. The last surface is located between each lobe of the lungs
4:24
called interlobar surface, which is a veery small surface that indicate the separation between the
4:30
lobes. So that was all for the surfaces. Now let’s look at the margins of the lungs.
Margins of the Lungs
4:35
Each lung has two margins. The inferior margin is thin and sharp, and it separates the costal
4:43
and mediastinal surface form the Diaphragmatic surface. The other margin we have is a vertical
4:49
one, called the anterior margin. And as you see, the anterior margin on both lungs
4:54
are different. On the right lung, it’s almost Vertical, but the anterior margin on the left
4:59
lung is not, and it kind of makes sense if you think about it. Because remember the heart is in
5:03
the middle, but the apex of the heart is directed toward the left, which forms this cardiac notch
5:09
of the left lung. And this cardiac notch is limited by a thin slip of pulmonary tissue
5:15
called the Lingula of the left lung Now, anatomically and functially,
Pulmonary Lobes
5:25
the lungs are divided into lobes. So here’s the lateral view of both lungs. The lobes are
5:31
Limited by this groove called the Oblique Fissue. It goes obliquely down, and it exists on both
5:37
lungs. But the Right lung has an extra fissure that goes horizontally, called the horizontal
5:42
fissure. The fissures are important because they divide the lungs into a Superior Lobe, an inferior
5:49
lobe, and a middle lobe. Only the right Lung has a middle lobe. Each Lobe is further subdivided
5:55
into Segments. And think about it, why is it important to subdivide the lungs into segments?
6:00
Imagine there are.. tumors… granulomas… or any indications that may require you to surgically
6:06
remove a part of the lung. Based on the knowledge you have about the lobes of the lungs, you can
6:12
remove segments without harming the other segments in the same lobe. Because each lobe has its own
6:19
supply of bronchi and blood vessels, and then each segment has their own bronchiolar branches
6:25
with further divide into alveolar branches. So that’s really the whole idea of lobes and segmens.
Segments of Right Lung
6:31
Now. Let’s go through the segments on the right lung first, and then do the left lung. So the
6:37
Right lung again has a superior, middle and inferior lobe, and the whole lung is divided
6:44
into 10 segments in total. 3 segments for the superior lobe. 2 segments in the middle lobe
6:50
and 5 segments in the inferior lobe. And to look at those segments in a little more detail.
6:55
We need to look at the right lung both laterally and medially. And again,
6:59
there’s the superior lobe, middle lobe and inferior lobe. With the Hilum of the lung here.
7:04
The superior Lobe can be divided into the Apical Segemnt, Posterior Segment and the
7:09
Anterior Segment. The Middle lobe can be divided into the Lateral and Medial Segment.
7:15
The Inferior Lobe can be divided into the Superior Segment, Basal Medial, Basal Anterior,
7:21
Basal Lateral and basal posterior segment. So that is the segments for the right lobe.
Segments of Left Lung
7:27
The left lung remember consist of the Superior lobe and the inferior lobe. And they divide
7:32
into a total of 8 segments, not 10 like the right lung. There are some variantions here,
7:38
in some people some segments might be fused and form 8 segments, in some people there might be
7:44
9 segments. I’ll show you the difference as we go through them. So the superior lobe consist
7:50
of the Apicoposterior Segemnt, Anterior segment, Superior Linguar and Infeiror Linguar segment.
7:58
The inferior lobe is divided into the Superior segment,
8:02
Basal Anterior, Basal Lateral and Basal posteropr segment. Giving you a total of 8 segments. In some
8:09
people the basal anterior is divided into basal anterior and basal medial segment,
8:15
adding a total of 9 segments. So that was it for the anatomy of the lungs. Let’s now do the Pleura!
Pleura of the Lungs
8:23
The Pleura is the coverings of the lungs, and we have two different types of pleura
8:28
around the lungs. The innermost Pleura is called visceral pleura, which is in direct contact with
8:34
the Lungs. Externally to that, you’ll find the Parietal pleura, which is in contact
8:40
with all surrounding structures. And since it’s in contact with different structures,
8:44
we also divide it into parts, just like we did with the lungs in the beginning of this video.
8:50
We have the costal part, which is in contact with the ribs. We have the diaphragmatic part,
8:55
towards the diaphragm. There’s the mediastinal part towards the mediastinum.
8:59
Then there’s the Pleural Cupula, which is where the parietal pleura covers the apex of the lung.
9:06
Now, as you study the covering of the lungs, you’ll see that the parietal Pleura and the
9:10
visceral Pleura meet at a certain point. And here’s a schematic picture I made to visualize it.
9:17
Here is the Trachea and the Bronchi. And around the lungs you’ll see the visceral pleura in green
9:23
and the parietal pleura in oragnge, with the perfectly drawn diaphragm down here. So again,
9:29
there’a point where the visceral pleura and the parietal pleura meet. And that point is here.
9:35
At the Hilum of the Lung. And when they meet, they form a covering around all structures that
9:41
make up the root of the lungs, and as they do that, they form a double layer of pleura,
9:47
which form the so called Pulmonary Ligament we talked about earlier. Makes a little more sense
9:51
now, right? SO again the pulmonary ligament is formed by a double layer of pleura. So
9:57
that is the Visceral and the Parietal Pleura. Now between these two, there’s a cavity, called
10:03
the pleural cavity, which is filled with serous fluid. The serous fluid function as a lubricant
10:10
that reduces friction as the lungs are constantly expanding and deflating. One last thing we need to
10:17
cover in order to understand the complete anatomy fo the Pleura, are the so called Pleural Recesses
10:22
Where a recess means a narrow space. So the first space is the Costodiaphragmatic Recess,
10:29
which is the biggest recess we have in our pleural cavity. Just keep in mind all structures I
10:34
pinpoint goes for both lungs. And then we have the Costomediastinal recess, which lies behind the
10:40
sternum. And then we have the Vertebromediastinal Recess in front of the vertebral column between
10:46
the costal surface and the mediastinal surface. And then the last surface is the
10:50
Phrenicomediastinal recess. And this recess lies only on the left side between the diaphragmatic
10:56
surface and the mediastinal surface. So that’s all for the pleura. Now the last thing I wanna
Mediastinum
11:02
talk bout in this video is the Mediastinum. The mediastinum is the earea between the lungs
11:08
filled with structures. Let’s now make a vertical cut right about here and look at the mediastnum
11:13
from this perspective. We’ll see this. And just for orientation here we have the sternum
11:18
and the diaphragm, with he central tendinous part in red and the muscular part in orange.
11:25
The mediastinum is generally divided into two regions. We have the superior
11:30
mediastinum, and the inferior mediastinum. But the inferior mediastinum is dicided into
11:35
three regions, the anterior, middle, and posterior mediastinum. And each of them contain specific
11:43
structures, wether we’re talking about specific organs or arteries or nerves. So fore xample,
11:48
the superior mediastinum will consist of the Esophagus, Trachea, Thymus,
11:53
and many blood vessels and nerves. The anterior mediastinum will consist of many blood vessels and
11:59
possibly also a part of pericardium. The middle mediastinum concist of the heart and pericardium,
12:04
and the posterior mediastinum will also consist of many blood vessels and nerves, as well as
12:08
the esophagus. And with that my friends, we’re done with the anatomy of the respiratory system.