alamat buku psh
-
Upload
muhammad-luqman-hakim -
Category
Documents
-
view
233 -
download
0
Transcript of alamat buku psh
-
8/2/2019 alamat buku psh
1/13
Learning aims
www.embryology.ch/indexen.htmlAt the end of this module you should be able to:
know the various prenatal stages of lung development.
be able to list and localize the various cells that are typical for
lung tissue.
know the components of the blood-air barrier.
be able to describe the development of the various somatic
cavities.
know where the pericardio-peritoneal duct lies.
know the difference between the vasa publica and privata in thelungs.
be able to explain the occurrence of fistulas between the
esophagus and trachea based on your knowledge of the
development of the two structures.
know the various mechanisms in charge of the switch of the
circulation systems at birth.
What you should already know
Embryogenesis
Cardiovascular system
Introduction
The respiratory system starts to develop with an inconspicuous laryngo-
tracheal groove (stage 10, ca. 28 days, 10 ) that forms in the ventral
midline at the lower end of the pharynx. The caudal part of this groove
develops into the lung anlage in that it divides into right and left lung
buds (stage 12, ca. 30 days, 12 ). The upper part of this groove
remains undivided and becomes the trachea.
The two lung buds extend and form the main bronchus (stage 14, ca. 33
days, 14 ). These subdivide further and form 2 (on the left side) and 3
(on the right) lobular buds and thus the lobular bronchi. The whole lung
development takes place in five main phases that partially overlap (4);
followed by a maturation stage:
http://openscroll%28%2710%27%29/http://openscroll%28%2710%27%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#04http://openscroll%28%2714%27%29/http://openscroll%28%2714%27%29/http://openscroll%28%2712%27%29/http://openscroll%28%2712%27%29/http://openscroll%28%2710%27%29/http://openscroll%28%2710%27%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#04 -
8/2/2019 alamat buku psh
2/13
Embryonic phase (3rd - 8th week)
Pseudoglandular phase (5th - 17th week) Canalicular phase (16th - 26th week)
Saccular phase (24th week up to birth)
Alveolar phase (36th week up to the 18th month post partum)
Stage of the microvascular maturation (from birth to 2 - 3 years)
Fig. 1 - Overview of the intrauterine phases of lung development
Adult lungs have an inner surface area of140 m2. This extent can only be
achieved through an enormous increase in the inner complexity of the
pulmonary parenchyma. This is described in the following chapters.
Delving deeper
Why does a laryngo-tracheal groove form in the ventral part of the foregut?
What are the mechanisms underlying the dichotomous division of the bronchi?
Why does further branching normally occur distally in the bronchial tree and not in the
trachea?
Embryonic phase QuizQuiz 02
The embryonic phase of lung development begins with the formation of a
groove in the ventral lower pharynx, the sulcus laryngotrachealis (stage
10, ca. 28 days, 10 ). After a couple of days - from the lower part - a
bud forms, the true lung primordium (stage 12, ca. 30 days, 12 ). In
Quiz
Quiz 11
http://void%280%29/http://openscroll%28%2710%27%29/http://openscroll%28%2712%27%29/http://openscroll%28%2710%27%29/http://void%280%29/http://openscroll%28%2710%27%29/http://openscroll%28%2710%27%29/http://openscroll%28%2710%27%29/http://openscroll%28%2710%27%29/http://void%280%29/http://openscroll%28%2712%27%29/http://void%280%29/ -
8/2/2019 alamat buku psh
3/13
the further subdivision into the two main bronchi (stage 14, ca. 33 days,
14 ) the smaller bud on the left is directed more laterally than the
somewhat larger one on the right that - parallel to the esophagus - isdirected more caudally. Thus the asymmetry of the main bronchi, as they
present in adults, is already established. The subsequent divisions of the
endodermal branches also take place unequally in that on the right threefurther buds form and, on the left, only two, corresponding to the later
pulmonary lobes. In the next division step, which occurs at the end of the
embryonic period, the segments of the individual pulmonary lobes arise.
Quiz
Quiz 03
More info
It appears that the branching and growth of the lung anlage is under the
direction of the mesenchyma on which it lies. Like in the kidney, it
appears also here that an epithelio-mesenchymal interaction isimportant for the normal development of the lungs. This is shown by
recombination experiments in which the tracheal epithelium begins to
fork when it is grown on a layer of bronchial mesenchyma. (6) .
At the end of the embryonic period the first segments appear in the five
(three right and two left) lobes of the lungs. With their distended ends the
lungs resemble an exocrine gland.
At this time the pulmonary vessels have formed themselves.
Development of the lungs up tothe end of the embryonic period
1
2
3
4
5
6
7
Right main bronchus
Upper right pulmonary
lobe
Middle pulmonary lobe
Lower right pulmonary
lobe
Left main bronchus
Upper left pulmonary
lobe
Lower left pulmonarylobe
http://void%280%29/http://openscroll%28%2714%27%29/http://void%280%29/http://www.embryology.ch/anglais/turinary/urinhaute01.htmlhttp://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#06http://void%280%29/http://openscroll%28%2714%27%29/http://openscroll%28%2714%27%29/http://void%280%29/http://www.embryology.ch/anglais/turinary/urinhaute01.htmlhttp://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#06http://void%280%29/ -
8/2/2019 alamat buku psh
4/13
The pulmonary circulation system (smaller circulation system) is formed
out of the 6th pharyngeal arch artery. These develop somewhat
differently than the other 4 aortic arches in that first a vessel plexus forms
around the lung anlage, originating from the aortic sac. The true 6th
aortic arch is only then formed after vessels - also from the dorsal aorta -
grow into this plexus and thus a connection between the truncus
pulmonalis and dorsal aorta has arisen.
Fig. 3 - Development of thepulmonary vessels in stage 13
Fig. 4 - Development of thepulmonary vessels in stage 15
Legend
1
2
3
4
First aortic arch
(atrophying)
Second aortic arch
Third aortic arch
(internal carotidartery forms from the
ventral part)
Fourth aortic arch
(on the right: part
of the subclavian
artery, left: arcus
aortae)
5
6
7
8
Dorsal aorta
Lung buds
Aortic sac
Pulmonary plexus
Fig. 3
From the
aortic sac a
vessel
plexus
arises
around the
lung anlagen
that with
the lungbuds extends
caudally.
Fig. 4
Also from
the dorsal
aorta a
vessel
plexus forms
that soon
communicates
with the
ventral one
and thus
creates a
connection
between the
ventral
aortic sac
and the
dorsal
-
8/2/2019 alamat buku psh
5/13
aorta. On
the left the
arterialduct arises
from it.
Pseudoglandular phase QuizQuiz 04
At this stage the lungs resemble the development of a tubulo-acinous
gland. According to the classical view, the entire air-conducting
bronchial tree up to the terminal bronchioli are set down in this phase
(16 generations). Recent morphometric studies (3) have shown that with
the end of the pseudoglandular phase 20 generations are partially present
in the lungs, which means that at this point in time the respiratory ductshave already been formed.
The primordial system of passages, the air-conducting bronchial tree, is
initially coated by cubic epithelium. These are the precursor cells of the
ciliated epithelium and of the secretory cells. In humans, the first
ciliated epithelial cells can be found in the 13th week of pregnancy (7).
In the respiratory part the first
typically lung-specific cells,
connected to the terminal
bronchioli, appear:
the type II pneumocytes(alveolar cells) (3).
The developing broncho-
pulmonary epithelium begins to
produce amniotic fluid, which
is also found in the lungs up to
the time of birth.
Fig. 5 - Lung tissue in the
pseudoglandular phase
Legend
1
23
Lung mesenchyma
Type II pneumocytesCapillaries
Fig. 5
In the
pseudoglandularphase the lungs
resemble a
gland. At the
end of this
phase the
precursors of
the pneumocytes
can be
discerned in
the respiratory
sections ascubic
epithelium.
More info
Relatively early in the development of the lungs, endocrine-active cells
(Kultschitsky cells) appear that produce bombesin and serotonin. In
contrast to the precursors of the pneumocytes, which originate from the
endoderm, they stem from the neural crest (neuroectoderm). Via
http://void%280%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#03http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#07http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#03http://www.embryology.ch/images/vnervous/v03vesicule/v3g_lamalaire.gifhttp://void%280%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#03http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#07http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#03 -
8/2/2019 alamat buku psh
6/13
paracrine mechanisms bombesin probably plays a decisive role for
lung development in that mainly the type II pneumocytes proliferate. (1)
The differentiation of the lungs takes place in a centrifugal direction. In
the central, air-conducting portions of the lungs the epithelium begins
to differentiate into cilia-carrying cells and goblet cells. After the 10th
week cartilage and smooth muscle cells as well as bronchial glands can
be found in the wall of the bronchi. The peripheral sections partially
retain - until far beyond the pseudoglandular phase - cubic epithelium that
is still little differentiated. This is important for a further proliferation of
the bronchial tree into the surrounding mesenchymal tissue.
More infoIf one begins, roughly estimated, with a number of 15'000 terminal
bronchioli (8) per lung in adults and thereby ca. 15,000 acini and with a
theoretical assumption of a dichotomous division of the pulmonary
branches, one has the result that this stage is attained after little fewer
than 2 14 generations. In the late pseudoglandular stage one finds,
however, far more than 15'000 end pieces. Thus the lung end pieces at
this stage already represent the respiratory portions of the lungs.
Canalicular phase
In the classical description of lung development, in this phase thecanaliculi branch out of the terminal bronchioli. The canaliculi
compose the properrespiratory part of the lungs, the pulmonary
parenchyma. All of the air spaces that derive from a terminal
bronchiolus form an acinus. Each one comprises respiratory
bronchioli and the alveolar ducts and later the alveolar sacculi. The
chief characteristic of this canalicular phase is the alteration of the
epithelium and the surrounding mesenchyma. Along the acinus, which
develops from the terminal bronchiolus, an invasion of capillaries into
the mesenchyma occurs. The capillaries surround the acini and thus form
the foundation for the later exchange of gases. The lumen of the tubules
becomes wider and a part of the epithelial cells get to be flatter. From thecubic type II pneumocytes develop the flattened type I pneumocytes.
More infoHistological
image of the
canalicular
phase of
lung
development
A sufficient differentiation of the
type II pneumocytes into the type I
Fig. 6 - Lung tissue in the
canalicular phase
Legend
http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#01http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#08http://void%280%29/http://void%280%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#01http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#08http://void%280%29/http://void%280%29/ -
8/2/2019 alamat buku psh
7/13
pneumocytes and the proliferation
of the capillaries into the
mesenchyma marks an importantstep towards the fetus being able
to survive outside the uterus after
roughly the 24th week of
pregnancy.
1
2
3
Type I pneumocytes
Type II pneumocytes
Capillaries
Fig. 6
The type I
pneumocytesdifferentiate
out of the
type II
pneumocytes.
The
capillaries
approach the
walls of the
acini.
More info
The first breathing movement can be registered already at the end of the
embryonic period. They are controlled by a breathing center in the brain
stem. Nevertheless, these breathing movements are paradoxical in that
when the diaphragm contracts, the thorax moves inwardly and vice
versa. (2)
At the end of this canalicular phase which is the beginning of the
saccular phase (ca. 25 weeks) - a large part of the amniotic fluid is
produced by the lung epithelium. From this time on, the maturity of the
lungs can be measured clinically based on the activity of the type II
pneumocytes, which begin to produce the surfactant. The ratio of
lecithin to sphingomyelin in the amniotic fluid, which increases with
fetal age is determined. I
In this stage developmental damage already affects the gas-exchange
components and result in structural alterations of the later pulmonary
parenchyma.
More info
The surfactant (abbreviation forsurface active agent) consists of
glycerophospholipids, specific proteins, neutral fats and cholesterol.
It covers the alveolar surface and reduces the surface tension so that,
following birth, the alveoli do not collapse during the expiration.
Saccular phase QuizQuiz 05
http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#02http://void%280%29/http://www.embryology.ch/images/vnervous/v03vesicule/v3g_lamalaire.gifhttp://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#02http://void%280%29/ -
8/2/2019 alamat buku psh
8/13
From the last trimester whole clusters ofsacs form on the terminal
bronchioli, which represent the last subdivision of the passages that
supply air. In the saccular phase the last generation of air spaces in therespiratory part of the bronchial tree is born. At the end of each
respiratory tract passage smooth-walled sacculi form, coated with type I
and type II pneumocytes. The septa (primary septa) between the sacculi
are still thick and contain two networks of capillaries that come from the
neighboring sacculi. The interstitial space is rich with cells and the
proportion of collagen and elastic fibers is still small. This matrix,
though, plays an important role for the growth and differentiation of the
epithelium that lies above it (9).
At the end of this phase the interstitial fibroblasts begin with the
production of extracellular material in the interductal and intersaccular
space.
Fig. 7 - Histological scheme of
the saccular phase
Fig. 8 - Blood-air barrier in the
lung
Legend
1
2
3
Type I pneumocyte
Type II pneumocyte
Capillaries
1
2
3
4
5
6
Type I pneumocyte
Saccular space
Type II pneumocyte
Basal membrane of the
air passage
Basal membrane of the
capillaries
Endothelium of the
capillaries
Fig. 7
The
capillaries
multiply
around the
acini. They
push close
to the
surface and
form a
common basal
membrane
with that of
the
epithelium.
Fig. 8
The blood-
air barrier
in the lungs
is reduced
to three,
thin layers:
type I
pneumocyte,
fusioned
basal
membrane,
and
http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#09http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#09 -
8/2/2019 alamat buku psh
9/13
endothelium
of the
capillary.
At birth, i.e., at the end of the saccular phase, all generations of the conducting and
respiratory branches have been generated. The sacculi are thin, smooth-walled sacks and
correspond to the later alveolar sacculi.
Alveolar phase
Depending on the author, the alveolar phase begins at varying times.
Probably in the last few weeks of the pregnancy, new sacculi and, from
them, the first alveoli form. Thus, at birth, ca. 1/3 of the roughly 300
million alveoli should be fully developed. The alveoli, though, are onlypresent in their beginning forms. Between them lies the parenchyma,
composed of a double layer of capillaries, that forms the primary septa
between the alveolar sacculi.
Fig. 9 - Alveolar phase before birth Legend
12
3
4
5
6
Alveolar duct
Primary septum
Alveolar sac
Type I pneumocyte
Type II pneumocyte
Capillaries
Fig. 9
In the
alveolar
phase the
alveoli form
from theterminal
endings of
the alveolar
sacculi and
with time
increase
their
diameter.
Already before birth these alveolar sacculi get to be increasingly complex
structurally. Thereby, a large number of small protrusions form along the
primary septa. Soon, these become larger and subdivide the sacculi into
-
8/2/2019 alamat buku psh
10/13
smaller subunits, the alveoli, which are delimited by secondary septa.
Ultrastructural investigations show that overall where such alveoli
appear, they are surrounded by elastic fibers that form the interstitialsepta between two capillary nets.
In the first 6 months, their number increases massively. This
"alveolarization" and therewith the formation ofsecondary septa should
- to a limited extent still - continue up to the first year and a half of life.
Fig. 10 - Alveolar phase following birth Legend
1
2
3
4
5
6
Alveolar duct
Secondary septum
Alveoli
Type I pneumocyte
Type II pneumocyte
Capillaries
Fig. 10
In the
alveolar
phase after
birth more
and more
alveoli form
from the
terminal
endings of
the alveolar
sacculi and
with time
increase in
diameter.
They are
delimited by
secondary
septa.
Classification in the adult lung QuizQuiz 06
In the adult lung one distinguishes between conducting and respiratory
zones.
In the conducting zone, all branches of the bronchial tree, the walls of
which contain cartilage tissue and seromucous glands, are bronchi. As
soon as cartilage and glands are no longer present, bronchioli are
involved.
Quiz
Quiz 13
Quiz
Quiz 07
Fig. 11 - Overview of the wall construction in the lungs Legend
http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/ -
8/2/2019 alamat buku psh
11/13
1
2
3
4
5
6
7
8
910
11
12
Ciliated epithelium
Goblet cell
Gland
Cartilage
Smooth muscle cell
Clara cell
Capillary
Basal membrane
SurfactantType I pneumocyte
Alveolar septum
Type II pneumocyte
Fig. 11
Diagrams for
comparing theconstructions
of the walls
in the
respiratory
tract.
According to their function the respiratory tract passages are divided into
conducting and respiratory zones:
Conducting zone = 16 generations
Segmental bronchi are continued by several generations of Intersegmental bronchi (up to ca. 1 mm diameter). After these
follow the
Bronchioli (< 1mm diameter) that after several divisions go over
into
Terminal bronchioli (ca. 0.4 mm diameter). They subdivide
numerous times and represent the end stretch of the purely
conductive respiratory tract. The measurements come from
histological findings.
More info
Histological
image of
respiratory
epithelium.
Respiratory zone = 7 generations More info
http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/ -
8/2/2019 alamat buku psh
12/13
Out of the terminal bronchioli several generation of
Respiratory bronchioli (= 3 generations) proceed. From themfollow several generations of
Alveolar ducts (= 3 generations) that in
Alveolar sacculi (last generation = 23rd generation) end
Histological
image of an
alveolarduct.
Fig. 12 - Overview of prenatal lung development
More info
For the branching out of ever new lung buds an interaction between the
respiratory endodermal epithelium and the surrounding pulmonary
mesenchyma is primarily responsible. Mainly the epidermal growth
factor (EGF) and the extracellular form of the transforming growth
factors (TGF-) appear to be important for lung development.In addition, one finds specific extracellular matrix components like
collagen of types I and III, as well as proteoglycan and the fibronectin
and syndecan glycoproteins. These molecules are found around the
http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/ -
8/2/2019 alamat buku psh
13/13
passages and in the forks of the bronchial tree. They are responsible for
the stabilization of the already formed structures - these are not present
in the regions of the newly formed branches.Epimorphine, a further protein, appears to promote the formation of
epithelial passages. If epimorphine is blocked by antibodies, the
epithelium that lies above it can not form itself into tubes and remains
unorganized. (5)
http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#05http://www.embryology.ch/anglais/rrespiratory/bibliorespi01.html#05