Description

Trachea and Bronchial Tree: Anatomy and Structure

This video covers the anatomy, layers, and function of the trachea, bronchi, and alveolar tree, along with a comparison of their structural differences.

1. Trachea (Windpipe):

• Divides into bronchi at the level of T4-T5.
• Length: 9-15 cm.
• Diameter: 2-2.5 cm.
• Skeletopy: Extends from C6-C7 to T4-T5.

Parts of the Trachea:

• Tracheal Cartilages (Cartilagines Tracheales): C-shaped cartilages maintaining airway patency.
• Annular Ligaments (Ligamenta Anularia): Connect tracheal rings.
• Membranous Part (Paries Membranaceus): Posterior part containing smooth muscle.
• Tracheal Bifurcation (Bifurcatio Tracheales): Division into right and left main bronchi.
• Carina of Trachea (Carina Tracheae): Internal ridge at the bifurcation, directs airflow.

Layers of the Trachea:

• Tunica Mucosa: Contains tracheal lymphoid nodules and tracheal glands (Noduli Lymphoidei Tracheales and Glandulae Tracheales).
• Tela Submucosa: Supports the mucosal layer.
• Tunica Adventitia: Outermost connective tissue layer.

2. Bronchi:

Main Bronchi (Bronchi Principales):

• Right Main Bronchus (Bronchus Principalis Dexter): Shorter, wider, and more vertical.
• Left Main Bronchus (Bronchus Principalis Sinister): Longer, narrower, and more oblique.
• Enter the lungs through the hilum of the lungs (hilum pulmonis).

Lobar Bronchi (Bronchi Lobares):

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

Segmental Bronchi (Bronchi Segmentales):

• Further divisions supplying bronchopulmonary segments.

Foreign Body Aspiration:

• Foreign objects are more likely to fall into the right main bronchus due to its vertical orientation.

3. Bronchial Tree (Arbor Bronchialis):

• Left & Right Principal Bronchi: Enter through the pulmonary hilum.
• Lobar Bronchi (Bronchi Lobares): Secondary bronchi.
• Segmental Bronchi (Bronchi Segmentales): Tertiary bronchi.
• Terminal Bronchi (Bronchi Terminales): Smallest non-respiratory bronchi.
• Epithelium Changes: Respiratory epithelium transitions to cuboidal epithelium in smaller bronchioles.

4. Alveolar Tree (Arbor Alveolaris):

• Terminal Bronchioles (Bronchi Terminales): Last part of conducting airways.
• Respiratory Bronchioles:
  • Primary, Secondary, and Tertiary Respiratory Bronchioles.
• Alveolar Ducts (Ductus Alveolares): Transport air to alveolar sacs.
• Alveolar Sacs (Sacculi Alveolares): Clusters of alveoli for gas exchange.

5. Comparison of Walls: Trachea, Bronchus, and Bronchiole

Tracheal Wall:

• Tunica Mucosa: Lined with pseudostratified ciliated epithelium.
• Tela Submucosa: Contains mucus-secreting glands.
• Tracheal Cartilage: C-shaped rings.
• Smooth Muscles (Membranous Part): Adjusts airway diameter.
• Tunica Adventitia: External connective tissue layer.

Bronchial Wall:

• Tunica Mucosa: Lined with pseudostratified ciliated epithelium.
• Tela Submucosa: Contains mucus-secreting glands.
• Fibromusculocartilaginous Layer (Tunica Fibromusculocartilaginea): Cartilage plates replace C-shaped rings.
• Tunica Adventitia: External connective tissue layer.

Bronchiolar Wall:

• Tunica Mucosa: Lined with simple columnar or cuboidal epithelium.
• Tela Submucosa: Lacks cartilage.
• Tunica Muscularis: Well-developed smooth muscle layer.
• Tunica Adventitia: External connective tissue layer.

6. Sources:

• Memorix Anatomy, 2nd Edition by Hudák Radovan, Kachlík David, and Volný Ondřej.
• Biorender.
• University notes and lectures.

Transcript

Introduction
0:03
Hey, What’s up. Meditay here. Let’s talk about the anatomy of the respiratory system.
0:08
In this segment, we will be talking about the anatomy of the Trachea and the Bronchi.
0:12
Alright, so the respiratory system consists of all the organs involved in breathing.
0:17
These are the Nose and the nasal cavity, Pharynx, Larynx, Trachea, Bronchi and the
0:22
Lungs. In our last two videos, we covered the anatomy of the nasal cavity and the Larynx.
0:28
Now let’s do the anatomy of the Trachea and Bronchi.
0:32
So In this video, we’re going to cover the anatomy of the Trachea, which includes the
0:36
parts that make up the trachea, and the layers of the tracheal wall. Then we’re gonna cover
0:41
the bronchial tree and the Alveolar tree and then we’re going to compare the Layers of the Tracheal,
0:47
Bronchial, and Bronchiolar wall to really understand the anatomical differences
0:52
of structures as you get closer to the lungs. Alright, so here we see the anterior view of
Topography of the Trachea
0:57
the chest. The Larynx is up here, and inferior to it, you’ll see the trachea. Now, let’s remove
1:03
the bones to see them better. As the trachea descends, it divides into two mini tracheas that
1:09
enter each lung. If we now remove the lungs, you’ll be able to see those mini tracheas,
1:15
we call them bronchi. So now, let’s remove the bronchi to focus on the anatomy of the trachea.
1:21
Now another name for the Trachae is a windpipe as it’s a tube responsible for directing the air
1:27
into and from the lungs. And the trachea can be
1:31
between 9 to 15cm long. and roughly about 2 to 2 and 0.5 cm in diameter. And the trachea goes
1:38
from the six-seven cervical vertebrae down to the fourth, fifth thoracic vertebrae.
Parts of the Trachea
1:44
Let’s now focus on the specific parts that make up the Trachea. The first thing you notice are those
1:49
horseshoe shaped cartilages shown here in green, and their horseshoe-shaped because they don’t
1:55
really cover the backside as you see right here. And you have many horseshoe-shaped cartilages
2:00
stacked up on top of each other for a smooth airflow. These cartilages are
2:05
called Tracheal Cartilages, and they very much resemble a horseshoe as you see here.
2:11
And between each of these tracheal Cartilagines, you’re gonna have ligaments connecting them as you
2:16
see right here in green. And those ligaments are called Annular Ligaments, containing
2:21
strong fibers that connect each adjacent cartilage together. And then on the backside,
2:26
as you see right here in green, you’re gonna have a fibromuscular membrane connecting the tracheal
2:32
cartilages together at their dorsal edges, we call it the membranous part of the Trachea. So again it
2:38
consist of Tracheal muscles and connective tissue. So that’s basically the structures of the trachea.
2:44
Now let’s look at the layers of tracheal wall, by making a transverse cut.
Tracheal Wall
2:49
Remember we’re still going to have the membranous part back here and the tracheal cartilages.
2:54
Now I want to focus a little bit on the tracheal walls with the inner
2:58
walls highlighted right here in blue. So the innermost structure you’ll find is this one,
3:03
the tunica mucosa. And the tunica mucosa contains Tracheal Lymphoid Nodules which help fight against
3:09
microorganisms in the air, and it also contains tracheal glands that lubricates the surface of the
3:15
respiratory tract that make it more adhesive to any irritants or organisms in the air,
3:21
and once these irritants are cought, you’d usually start coughing to aid in removing these.
3:27
So that’s the tunica mucosa. The next layer we have is the tela submucosa,
3:33
which contains loose connective tissue and blood vessels. Then you know we have the cartilages and
3:39
the membranous part of the trachea, but externally to that, we have the outermost layer called tunica
3:45
adventitia consists of dense connective tissue for protection. So it do have the general layout
3:49
of any tube in our body. Now the trachea starts off at the Larynx and then goes all the way down
3:54
until it splits, and the area where it splits is called the tracheal bifurcation, as you see here.
4:00
And at the region where they split, you’ll find a small elevation on the inside. So if
4:06
we make a transverse cut a look at it from this perspective, you will see this right. There’s an
4:12
elevation here at the bifurcation we call Carina of Trachea, which is essentially just a ridge
4:18
of the last cartilage protruding into the lumen of the trachea, right before it becomes the Bronchi.
4:24
And just don’t forget that the esophagus is still located right behind the trachea here.
Bronchi
4:30
Now, let’s do the anatomy of the bronchi. So, as a trachea splits into two bronchi.
4:36
We get the right primary bronchus, or the right main bronchus, and the left primary bronchus.
4:42
And they split at the region of the fourth, fifth thoracic vertebrae as you see here,
4:47
where the trachea ends. Alright. The right primary bronchus and the left primary bronchus
4:54
differ in that, the right one is about 2.5 cm long before it enters the lungs. So It’s shorter,
5:02
wider, more vertical than the left one. The left one is about 5 cm long before it enters the lungs.
5:09
It’s longer and more narrow. And this is before they both enter the lungs really important you
5:14
get that principle. And here is something I need you to never forget, that the left main
5:20
bronchus curves more than the right main bronchus as you see here aswell. And why is this important?
Foreign Body Aspiration
5:27
Well, in clinical perspective, there’s a condiction called foreign body aspiration,
5:32
where a person inhales a foreign object into their airways, this ostly happen in children. But
5:38
imagine, when a person inhales any type of object, small enough to enter the respiratory tract.
5:44
If it gets far enough, which side do you think the object will fall into?
5:49
Most commonly into the right one, since it doesn’t deviate much from the tracheal axis
5:54
as you see here. If the object haven’t gone far down the respiratory tract,
5:58
you could try the Heimlich manneuver. If it’s far down into the lower respiratory tract,
6:03
you gotta get in there with a bronchoscopy and either suck or pluck it out.
6:07
Now I reckon you’ll never forget this. So The right and left primary bonchi will enter the lung
Bronchi (revisited)
6:14
through the Hilum of the lung, which is the entrance into the lung,
6:19
and from here it’s going to divide into smaller bronchi according to the lobes of each lung.
6:24
There are three lobes on the right lung, so the right one will divide into 3 Lobar Bronchi, or
6:30
bronchi lobares dexter. The left lung has only two lobes, and this give us two left lobar bronchi.
6:37
So after that, after they’ve divided into each lobe, they’ll further divide into segmental
6:43
bronchi. The right one will divide into 10 segments and the left one into 8 segments,
6:49
according to how the lungs are built. Alright. So again the primary bronchus becomes lobar bronchi,
6:55
which then becomes segmental bronchi Let’s now do that one more time,
7:00
but this time a little more detailed cuz it’s important to know this.
7:04
Primary bronchus goes through the hilum of the lungs. As you see the right lung has 3 lobes,
7:10
the left one has 2 lobes. So the right one will brach off as the Superior Lobar Bronchus,
7:16
Middle Lobar Bronchus and the Inferior Lobar Bronchus. The left one will branch off as the
7:22
superior and inferior lobar bronchus. Now let’s do the full bronchial tree on the right side.
7:30
Here is the right lung. It has a Superior Lobe, Middle Lobe and Infeiror Lobe. And if we look from
7:36
this direction, youll be able to see the hilum of the lung, the place where the bronchi enters
7:42
the lung, and branch off to each of these lobes as the superior, middle and inferior lobar bronchi.
7:49
Each of the Lobes are anatomically divided into Segments. The right lobe is divdided into 10
7:55
segments and the left is divided into 8 segments in total. And this is where the lobar bronchi will
8:01
divide into segmental bronchi, according to the segments of the lobe. And this is also surgically
8:07
important because if there are any tumors or any other indications to surgically resect a
8:13
part of the lung, we can do that according to the segments. In this way we won’t damage other
8:19
parts of the lungs by damaging these bronchi. So I made a quick scheme which you can use if
Bronchial Tree
8:24
you want to, but the bronchial tree consist of the right and left main bronchi, which divide into 2
8:31
or 3 lobar bronchi. 3 on the right lung and 2 on the left lung. They will divide into segmental
8:37
bronchi. 10 for the right lung and 8 for the left lung. And they will keep splitting 6-12 times
8:45
until they become reeealy small, approximately 0.5-1 mm in diamenter, now called bornchioles,
8:52
or Terminal Bronchioles. Which will be the end of the bronchial tree. Now what is specific with the
8:58
bronchial tree? The inner lining of the bronchial tree consist of respiratory epithelium, which are
9:04
specifalized epithelium with cilia, those hail like structures on the surface are cilia. The only
9:10
function the bronchial tree has is air conduction and protection, by catching whatever irritants
9:17
may be in the airway, and pull them upwards so you can cough them up. But as you get deeper into the
9:23
lungs, these lining epithelia starts flattening out, so at the end of the bronchial tree,
9:29
approximately at the terminal bronchioles, these respiratory epithelium will change into cuboidal
9:35
like epithelium, and this is where we say that the bronchial tree continue as the alveolar tree.
Alveolar Tree
9:41
So again we have terminal bronchioles, which will continue as primary bronchioles
9:47
And already here, you can see these bumps on surace of the alveolar tree, called alveoli. The
9:53
alveoli are our primary area for gas exchange, so that we can receive oxygen. You’ll notice that the
9:59
deeper into he lungs we get, the more alveoli we’re going to have. So secondary bronchioles
10:05
are gonna have even more alveoli, and tertiary bronchioles are gonna have even more alveoli.
10:12
These names really depend on which sources you’re studying from. They’re also called Respiratory
10:17
bronchioles in some sources. After the tertiary bronchiole, we’re going to have the alveolar
10:22
ducts, which is going to lead into our alveolar sacs, which are sacs with a lot fo alveoli for
10:28
gas exchange. They’re highøy vascularized as you see here. Now again, the bronchial tree will have
Different Types of Epithelium
10:35
respiratory epithelium, the deeper ito the lungs you get, the flatter the epithelium will become,
10:42
and in the alveolar tree, we’re mostly going to have these simple squamous epithelium, which are
10:48
thin epithelium that help with the gas exchange. Now lastly, let’s compare the layers of the
Layers of the Tracheal, Bronchial, and Bronchiolar Wall
10:54
tracheal, bronchial and bronchiolar wall. And we’ll start by going through the trachea again.
11:00
So the inner layer is tunica mucosa, remember, lined by respiratory epithelium. And then you’re
11:07
gonna have the Tela submucosa with a lot of loose connective tissue. Then the horseshoe-shaped
11:13
Tracheal Cartilage with the smooth muscles on the backside called the membranous part of trachea.
11:19
And then they’re all protected by the layer of tunica adventitia.
11:22
So as we look at the bronchus, we also have tunica mucosa on the inside,
11:27
lined by respiratory epithelium, since it’s a part of the conductive airways.
11:32
Underneath, we have the loose CT, called Tela submucosa. Then externally to that,
11:38
the muscle layer, the cartilage, and the fibrous layer are gonna blend into eachother, into a layer
11:45
called FibroMusculoCartilaginous Layer, simply add fibers, muscle and cartilage together. Notice here
11:53
that the horseshoe-shaped cartilage is gradually starting to disappear as it become fibers. So
12:00
externally to that again, tunica adventitia, the dense connective tissue for protection.
12:06
As we look at the bronchiole. The inner layer is still gonna be tunica mucosa, lined by either
12:13
cuboidal or simple squamous epithelium. and then Tela submucosa. And then, the cartilage and the
12:21
fibers are completely replaced by smooth muscles called tunica muscularis. And then you’re gonna
12:27
have a layer of Tunica adventitia on the outside. So that was all I had for the anatomy of the
12:32
Trachea and the Bronchi of the respiratory system. Our next video is going to be about the Lungs.