Development of the Respiratory System | Stages of Lung Development | Embryology
Summary
TLDRThis educational video script delves into the intricate development of the respiratory system, starting from the final structures and tracing back to the embryonic stage. It outlines the formation of the respiratory tree, lungs, and pleural cavities, highlighting the roles of the three germ layers. The script explains the stages of lung maturation, from the pseudoglandular to the alveolar stage, and the crucial transition at birth when the lungs shift from fluid-filled to air-filled, enabling gas exchange. A must-watch for those curious about the complex journey of respiratory system development.
Takeaways
- 🌟 The respiratory system develops from the lower airways, starting from the trachea, which divides into bronchi, bronchioles, and finally into alveoli where gas exchange occurs.
- 🔍 The respiratory tree includes the trachea, bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, and alveolar sacs, with the latter two being part of the respiratory zone.
- 🏠 The lungs are situated within the pleural cavities, which are lined by two layers of pleura: the visceral pleura attached to the lung and the parietal pleura attached to the chest wall.
- 🧬 The development of the respiratory system involves the interaction of the three germ layers: ectoderm, mesoderm, and endoderm, with different structures of the airways deriving from these layers.
- 🌱 The respiratory system begins to form at week four of development with the outgrowth of the respiratory diverticulum from the primitive gut tube, leading to the formation of the lung bud.
- 🔄 The trachea and esophagus initially share a connection, which is later separated by the formation of the tracheoesophageal septum, preventing a potential tracheal-esophageal fistula.
- 🌀 The bronchial buds from the lung bud grow into the pericardial peritoneal canals, which eventually form the pleural cavities, with the communication between these cavities closing off through the formation of membranes.
- 🌿 The bronchi further branch into secondary and tertiary bronchi, which supply individual lung lobes and bronchopulmonary segments, respectively.
- 📈 Lung development is divided into four histological stages: the pseudoglandular stage, the canalicular stage, the saccular stage, and the alveolar stage, each characterized by specific developmental milestones.
- 👶 At birth, the transition from fetal life to independent breathing involves the lungs filling with air, a decrease in pulmonary vascular resistance, and the closure of cardiac shunts, enabling gas exchange.
- 📚 Understanding the stages of lung maturation is crucial for recognizing potential developmental issues and the functionality of the respiratory system post-birth.
Q & A
What are the main structures of the respiratory system discussed in the video?
-The main structures discussed are the airways (respiratory tree), the lungs, and the pleural cavities.
What is the respiratory tree?
-The respiratory tree refers to the branching network of airways starting from the trachea down to the bronchioles and alveolar sacs.
How does the trachea divide and what does it lead to?
-The trachea divides into the right and left main primary bronchi, which enter the right and left lungs, respectively.
What is the function of the conducting zone in the respiratory system?
-The conducting zone's function is to transport air towards the lower airways without gas exchange.
What is the respiratory zone and where does gas exchange occur?
-The respiratory zone includes respiratory bronchioles, alveolar ducts, and alveolar sacs, where gas exchange takes place.
What are the two layers of the pleura and their respective attachments?
-The two layers are the visceral pleura, which is attached to the lung, and the parietal pleura, which is attached to the chest wall.
What germ layer does the pleura originate from?
-The pleura originates from the mesoderm, one of the three primary germ layers.
What is the respiratory diverticulum and its role in lung development?
-The respiratory diverticulum is an outgrowth from the primitive gut tube that forms the lung bud, which eventually develops into the respiratory tree.
What is the tracheoesophageal septum and its importance?
-The tracheoesophageal septum is a structure that separates the trachea and esophagus, preventing a tracheal-esophageal fistula.
What are the stages of lung maturation mentioned in the video?
-The stages of lung maturation are the pseudoglandular stage, canalicular stage, saccular stage, and alveolar stage.
How does the process of gas exchange begin at birth?
-At birth, the baby takes the first breath, filling the lungs with air, resorbing the fluid, reducing pulmonary vascular resistance, and closing cardiac shunts, allowing blood to flow through the lungs for gas exchange.
Outlines
😀 Development of the Respiratory System Structures
The first paragraph introduces the respiratory system's development, focusing on the final structures such as the respiratory tree, lungs, and pleural cavities. It outlines the airways from the trachea to the alveolar sacs, distinguishing between the respiratory zone for gas exchange and the conducting zone. The paragraph also explains the embryological origins of the airways' walls, including the epithelial lining from the endoderm and other components from the mesoderm. The development process begins at week four with the respiratory diverticulum, which will form the trachea, larynx, and lung bud, and continues with the formation of bronchi and bronchioles. It also touches on the tracheoesophageal septum's role in separating the trachea from the esophagus, a critical development to prevent tracheoesophageal fistula.
😀 Lung Branching and Maturation Stages
The second paragraph delves into the branching of the respiratory system, detailing the formation of secondary and tertiary bronchi, which supply individual lung lobes separated by fissures. It describes the lung's segmentation into bronchopulmonary segments, with 10 on each side, and the overlapping histological stages of lung development: the pseudoglandular, canalicular, saccular, and alveolar stages. The pseudoglandular stage (5 to 17 weeks) is characterized by the lung's gland-like appearance, while the canalicular stage (16 to 26 weeks) sees the formation of new canals and an increase in capillaries. The saccular stage (26 weeks to birth) involves the formation of primitive alveoli with type 1 and type 2 cells, the latter producing surfactant to reduce surface tension. The alveolar stage (from birth to eight years) is when alveoli mature and proliferate, increasing in number for efficient gas exchange. The paragraph concludes with the physiological changes at birth that enable the lungs to take over gas exchange from the placenta.
😀 Conclusion and Call to Action
The final paragraph serves as a conclusion to the video, encouraging viewers to like and subscribe for more educational content. It provides a brief recap of the respiratory system's development and invites the audience to engage with the channel for future videos.
Mindmap
Keywords
💡Respiratory System
💡Airways
💡Pleural Cavities
💡Germ Layers
💡Respiratory Diverticulum
💡Tracheoesophageal Septum
💡Bronchial Buds
💡Pseudoglandular Stage
💡Surfactant
💡Alveolar Stage
💡Gas Exchange
Highlights
Introduction to the development of the respiratory system with a focus on the final structures.
Description of the respiratory tree, including the trachea, bronchi, bronchioles, and alveolar sacs.
Differentiation between the respiratory zone for gas exchange and the conducting zone for air passage.
Explanation of the pleural cavities and the two layers of pleura: visceral and parietal.
Embryological origins of the respiratory system from the three germ layers: ectoderm, mesoderm, and endoderm.
Development process starting from the primitive gut tube and the formation of the respiratory diverticulum.
Formation of the trachea, larynx, and lung bud from the diverticulum.
Formation of the tracheoesophageal septum and its importance in separating the trachea and esophagus.
Development of the pleural cavities from the pericardial peritoneal canals.
Differentiation of the bronchial buds into bronchi and bronchiolar buds into bronchioles.
Description of the secondary and tertiary bronchi, and their role in supplying individual lung lobes.
Explanation of the histological stages of lung development: pseudoglandular, canalicular, saccular, and alveolar stages.
Importance of type 1 and type 2 cells in the alveoli for gas exchange and surfactant production.
The maturation and proliferation of alveoli from birth to eight years of age.
The transition at birth from fluid-filled lungs to air-filled lungs and the initiation of gas exchange.
The physiological changes at birth that enable the lungs to take over gas exchange from the placenta.
Encouragement to like and subscribe for more educational content on the respiratory system.
Transcripts
hello and welcome to bite size med this
video is on the development of the
respiratory system
so first let's look at the final picture
the structures that are going to develop
and then we'll go backwards and see how
that happens
so what are the structures i'm talking
about the airways that's the respiratory
tree
the lungs and the pleural cavities
so we're going to be looking at the
development from the lower airways
starting from the trachea downwards
the trachea divides into the right and
left main primary bronchi
these are going to enter the right and
left lungs they then divide into
secondary bronchi and tertiary bronchi
the tertiary bronchi divide into
bronchioles which lead into terminal
bronchioles
and then into respiratory bronchioles
each of the respiratory bronchioles
leads into a few alveolar ducts which
then lead into alveolar sacs
so this portion is the respiratory zone
where gas exchange takes place
while the rest is the conducting zone
which just conducts
air towards the lower airways
now that was the tree the lungs are
inside the pleural cavities
that's lined by pleura there are two
layers
one layer is sort of stuck to the lung
inside and that's the visceral pleura
and the one that stores the chest wall
that's the parietal pleura
now the pleura is mesodermal in origin
remember those three germ layers
the ectoderm the mesoderm and the
endoderm
now let's remove the ectoderm these two
they form different
portions the airways have different
structures in their walls
now what's actually in the wall would
differ depending upon what level of
airway we're looking at
overall some of the things that can be
there would be an epithelial lining
there can be smooth muscle cartilage and
of course connective tissue
the epithelial lining is from the
endoderm while all the other stuff is
from the mesoderm
so those are the embryological
derivatives
so now that we know it's going to form
let's look at how they form
we start at week four this is the
primitive gut tube
from the upper portion that's the
cranial portion there's an
outgrowth this is a diverticulum the
respiratory diverticulum
the lower or the caudal portion of this
diverticulum
is going to form the lung bud
the diverticulum is surrounded by
splanchnic mesenchyme
to form all those mesodermal derivatives
we talked about earlier
so the upper portion of this
diverticulum would contribute to the
trachea and the larynx
but the lung bud that's gonna form the
respiratory tree
that's how it is so the bronchial birds
will form bronchi
and the bronchiolar buds form
bronchioles
so from the lung but there's the right
and left primary bronchial buds
but before we go any further you can see
right now the trachea
and the gut tube which is going to form
the esophagus they are currently
connected
now that has to close how for that we
need to flip it over and look at it from
above
so this is the developing trachea in
front and the esophagus behind
there are folds that are going to form
longitudinally
these are the tracheoesophageal folds
they fuse in the midline to form the
tracheoesophageal septum
so now both of them are separate with a
ventral trachea and a dorsal esophagus
now what would happen if something went
wrong here a fistula
the communication remains that's the
tracheal
esophageal fistula so once the septum
forms
the trachea is now separate these
bronchial buds
with their mesenchyme they push into
canals
called the pericardial peritoneal canals
now these canals are going to form the
pleural cavities
so if you look at the name you can see
that they connect the pericardial
and the peritoneal cavities now as the
buds grow into these canals
the communications between these
cavities that has to close
and that happens by folds which then
form membranes
so to separate from the pericardial
cavity there's a pleural pericardial
membrane
and from the peritoneal cavities there's
a plural peritoneal membrane
so that's how they separate but remember
the pleural cavity is lined
so the portion that's sort of attached
to the lung that's the visceral pleura
that will also develop from the splunk
neck mesoderm
the parietal pleura is towards the body
wall so that's from the somatic mesoderm
now the bronchial buds they form the
right and left primary main bronchi
these are going to branch again and form
secondary bronchi
secondary bronchi are low bar bronchi
which means they supply individual lung
lobes
the lungs are divided by fissures
antelopes
there are three on the right and two on
the left so that means there are three
secondary bronchi on the right
and two on the left these secondary
bronchi then branch into tertiary
bronchi
now these are segmental bronchi so they
each supply
a bronchopulmonary segment these
segments are both anatomical and
functional
there are 10 on each side though
sometimes they can fuse on the left so
there might be lesser
and now we're at seven weeks so this
whole thing was during the embryonic
stage of development
now further branching is divided into
stages and these are histological stages
and they overlap
so the division of weeks for each stage
is different in different books
so i just picked the one that repeated
the most and was the easiest
to understand this first we're going to
bring back the respiratory tree
so from the tertiary bronchi we have the
bronchioles and then the terminal
bronchioles
the respiratory bronchioles alveolar
ducts and then alveolar sacs
now we're going to split them into two
each the first
two the next two and the alveolar sacs
the stages overlap so it can't actually
be divided like this
but this is just something i did to make
it easier to remember
the tertiary bronchi they form
bronchiolar butts which give rise to the
bronchioles
and they lead into terminal bronchioles
now remember that these are histological
stages so these are the terminal
bronchioles with their lining
and around that is the mesenchyme which
gives rise to connective tissue
and also importantly is where
capillaries form
so at this point the lung sort of looks
like a gland
so it's called a pseudoglandular stage
and that's from
5 to 17 weeks though i think the easier
to remember one is between
6 and 16 weeks
now the next two steps that's the
respiratory bronchioles
leading into the alveolar ducts this is
the canalicular stitch
so from the terminal bronchioles we have
the respiratory bronchioles
and each respiratory bronchiole leads
into a few alveolar ducts
so new smaller canals are forming and
the canals which were formed in the
previous steps like the bronchi and the
bronchioles
they're going to get wider so it's all
about those canals that's why it's the
quinolicular stitch
and the capillaries that were formed in
the previous stage they are going to
increase
now so this is from around 16
to 26 weeks the alveolar ducts they lead
into sacks called the alveolar sacs
this is the terminal sac stage or the
saccular stage
from 26 weeks to birth these alveoli are
primitive
now the lining flattens so the cells are
flatter these are the type
1 cells why is that important because
they're needed for gas exchange
the capillaries start to come really
close to the alveolus
so it makes sense that the type 1 cells
are thin to make it easier for gas
exchange
there are also type 2 cells now these
form surfactant
that's important because once air enters
the alveoli
there's an air fluid interface that can
create surface tension
which can cause small alveoli to
collapse
surfactant is a phospholipid it lines up
inside each alveolus and reduces the
surface tension
it gets synthesized during this stage
but just synthesis isn't enough
we need a sufficient amount so the
levels increase with gestation
so you think we'll be done here but no
these are primitive allele
and they have to mature and proliferate
we need lots of alveoli
there are millions at birth but we need
millions and millions more
so that's the alveolar stage from birth
to eight years
where they mature and proliferate so
that's the four stages of
lung maturation the pseudoglandular
stage when it looks like a gland
the canalicular stage when it looks more
like a lung
the saccular stage when the alveolar
sacs form
and the alveolar stage when the alveoli
proliferate
and no we're still not done yet for gas
exchange we need circulation as well
so what happens at birth during fetal
life
the lungs are filled with fluid and the
alveoli are collapsed
the pulmonary vascular resistance is
high the heart has shunts
like the ductus arteriosus and the
foramen ovale
to bypass the lungs because the
oxygenation is being done by the
placenta
at birth the baby takes a breath the
lungs fill with air and the fluid gets
resorbed
the pulmonary vascular resistance drops
the cardiac shunts close
and blood flows through the lungs so now
their function of gas exchange begins
and that is how the respiratory system
develops if this video helped you give
it a thumbs up and subscribe to my
channel
thanks for watching and i'll see you on
the next one
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