Transcript 05-respiratory system

RESPIRATORY PRIMORDIUM
It is formed in the (4th )
week as median
outgrowth
at the caudal end of the
Pharynx (Foregut).
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LARYNGOTRACHEAL GROOVE
The respiratory •
primordium is defined at
(26-27) days as a
Laryngotracheal
groove caudal to the
4th pair of Pharyngeal
Pouches.
LARYNGOTRACHEAL
DIVERTICULUM
By the end of the (4th
week) the
laryngotracheal
groove has
Evaginated to form
the pouch like
LaryngoTracheal
Diverticulum.
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LARYNGOTRACHEAL
DIVERTICULUM
The Endoderm of the •
Foregut will form:
The Epithelial lining and •
glands of the larynx,
trachea, bronchi and lungs.
The surrounding •
Splanchnic mesoderm
will form:
The connective tissue, •
cartilage and smooth
muscles of these
structures.
LUNG BUD
It is the expanded •
distal end of the
laryngotracheal
diverticulum.
Initially, it is in open •
communication with
the foregut.
TRACHEOESOPHAGEAL
SEPTUM
Two longitudinal •
Tracheoesophageal
folds (ridges)
develop in the
diverticulum.
They approach each •
other and fuse to
form the
tracheoesophageal
septum.
TRACHEOESOPHAGEAL
SEPTUM
The foregut will be divided •
into:
Dorsal portion •
(Esophagus).
Ventral portion (trachea •
and lung bud).
The respiratory primordium •
keeps its communication
with the pharynx through
the Laryngeal Inlet.
LARYNX
CARTILAGES : •
Derived from •
proliferation of
mesenchyme in the
4th and 6th
pharyngeal arches.
This mesenchyme is •
derived from Neural
Crest cells.
CARTILAGES
The mesenchyme of
the two arches
transforms into
Arytenoid, Thyroid
and Cricoid
cartilages.
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CARTILAGES
This proliferation •
changes the appearance
of the laryngeal orifice
(primordial Glottis)
from a narrow slit into a
T -shaped laryngeal
inlet.
EPIGLOTTIS
It is developed from •
the caudal part of the
Hypobranchial
Eminence.
It reaches its adult •
form during the first
three years after
birth.
EPITHELIAL LINING
It is derived from the
Endoderm of the
cranial part of the
laryngotracheal tube.
Its rapid proliferation
causes temporary
occlusion of the
laryngeal inlet.
Recanalization •
occurs during the 10th
week.
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EPITHELIAL LINING
The ventricles of the
larynx form during
this recanalization.
They are bounded by
two folds of mucous
membrane :
Vocal Folds (Cords)
and Vestibular
Folds.
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MUSCLES
They are derived from
myoblasts in the 4th
and 6th pharyngeal
arches.
They have nerve •
supply from the
laryngeal branches of
the Vagus nerves that
supply these arches.
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TRACHEA
The Endoderm of the •
laryngotracheal tube
distal to the larynx gives
rise to :
Epithelial lining and •
Glands.
Splanchnic Mesoderm
gives rise to:
Connective tissue, •
Cartilages and Muscles.
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BRONCHI
Bronchial Buds •
develop as two
outpouchings of the
lung bud.
They grow laterally
into the pericardio
peritoneal canals
(primordia of the
pleural cavities).
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PRIMARY (MAIN) BRONCHI
It is the enlarged •
connection between the
trachea and the bronchial
buds.
Right Primary •
Bronchus:
Larger and more vertical •
than the left(this
embryonic picture is
maintained till adult life).
SECONDARY (STEM) BRONCHI
They develop from •
subdivision of the Primary
(main ) Bronchi.
They supply the lobes of •
the lung.
On the Right : •
They are : Superior, and •
Inferior (subdivide into
Middle and lower).
On the Left : •
They are: Superior and •
Inferior.
TERTIARY (SEGMENTAL)
BRONCHI
In the Right Lung : (10) in
number.
In the Left Lung : •
(8) or (9) in number. •
BronchoPulmonary •
segment :
It is the segmental •
bronchus with its
surrounding mass of
mesenchyme.
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TERTIARY (SEGMENTAL)
BRONCHI
At (24) weeks : •
(1)17 order of •
branches are formed.
After birth (7) •
orders of branches
are formed.
(2) Respiratory •
Bronchioles have
developed .
PLEURA
VISCERAL : •
Is derived from the •
Splanchnic
mesoderm.
PARIETAL : •
Is derived from the •
Somatic mesoderm.
It lines the thoracic
body wall.
DEVELOPMENT OF THE LUNGS
It depends on : •
(1) Adequate thoracic •
space.
(2) Fetal breathing •
movements before
birth. It stimulates lung
development by
creating pressure
gradient between the
lungs and the amniotic
fluid.
MATURATION OF THE LUNGS
(3) Adequate volume •
of amniotic fluid.
Maturation of the •
lung passes through
four periods.
(1)PSEUDO GLANDULAR
PERIOD
(5-17) WEEKS: •
1. Glandular •
appearance of the lung
(as an exocrine gland).
2. All major elements •
of the lung are formed.
3. No Respiratory •
Bronchioles or Alveoli.
PSEUDO GLANDULAR PERIOD
4. Respiration is Not
possible.
5. Fetuses born •
during this period are
Unable to survive.
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(2) CANALICULAR PERIOD
(16-25) WEEKS: •
1. The lumina of •
Bronchi and Terminal
Bronchioles are larger.
2. Respiratory •
Bronchioles : Each
terminal bronchiole
divides into two or more
respiratory bronchioles.
CANALICULAR PERIOD
3. Alveolar ducts : The •
respiratory bronchioles
divide into (3-6) tubular
passages.
4. Many Blood vessels •
are developing in the
mesenchyme surrounding
the bronchi and terminal
bronchioles.
CANALICULAR PERIOD
5. (Some) Terminal
sacs : appear at the
ends of the
respiratory
bronchioles.
6. Lung tissue is well
vascularised.
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CANALICULAR PERIOD
7. Respiration is •
Possible toward the
end of this period.
8. Fetuses born May •
survive if given
intensive care.
They often die •
because of immaturity
of the respiratory and
other systems.
(3) TERMINAL SAC PERIOD
(24 WEEKS- •
BIRTH)
1. Many terminal •
sacs develop.
2. Their epithelium •
becomes very thin.
3. Capillaries begin •
to bulge into these
developing alveoli.
TERMINAL SAC PERIOD
4. This establishes •
intimate contact between
the Epithelial and
Endothelial cells.
5. The Cuboidal •
Endodermal
epithelium becomes
thin Squamous
(Type 1 Alveolar
epithelial cells) .
TERMINAL SAC PERIOD
Type 1 Alveolar cells •
(Pneumocytes)
permit adequate gas
exchange Blood –Air
Barrier (for the
survival of premature
fetuses).
(6) PULMONARY SURFACTANT
Production: •
From Type (11) Alveolar
cells, these are rounded
secretory epithelial cells
scattered among the
squamous cells.
STRUCTURE : •
A complex mixture of •
phospholipids.
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PULMONARY SURFACTANT
TIME of production: •
It begins by (20) weeks. •
It increases during the •
last (2) weeks before
birth.
FUNCTIONS : •
It forms a monomolecular •
coat over the internal
walls of the terminal
sacs.
PULMONARY SURFACTANT
(a) It lowers the surface •
tension at the air- alveolar
interface by counteracting the
tension forces.
(b) It facilitates the expansion
of the terminal sacs.
Deficiency : causes •
Respiratory Distress because
of collapse of the primitive
alveoli.
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(4) ALVEOLAR PERIOD
Late Fetal period- •
Childhood
1. Each respiratory •
bronchiole terminates in a
cluster of thin walled
terminal sacs (future
alveolar ducts).
2. The epithelial lining of the
terminal sacs becomes
Extremely Thin squamous.
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ALVEOLAR PERIOD
3. Loose connective tissue •
with large pulmonary
lymphatic vessels
separates the terminal sacs.
4. The AlveolCapillary •
Membrane (Respiratory
Membrane) is sufficiently
thin to allow gas exchange.
AUTONOMOUS GAS EXCHANGE
It requires : •
(1) Adequate amount of
Surfactant.
(2) The lung is changed
from secretory to gas
exchanging organ.
(3) Existence of parallel
pulmonary and systemic
circulations.
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ALVEOLI
1. A full term newborn •
has (50) million alveoli
(1/6) of the adult number.
2. On chest radiographs, •
the lungs of newborn
infants are denser than
adult lungs.
3. 95% of alveoli develop •
after birth( first 8 years
after birth) .
ALVEOLI
4. Immature alveoli •
have the potential for
forming additional
alveoli.
5. The primordial alveoli •
become mature by
increasing in size.
MATURATION OF THE LUNGS
1. Cranial segments •
mature faster than
caudal ones.
2. Growth of the lungs
after birth is primarily
due to an increase in
the Number of
respiratory bronchioles
and alveoli and not to
an increase in the Size
of the alveoli.
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TRACHEOESOPHAGEAL
FISTULA
Etiology •
Incomplete division of •
the cranial part of the
foregut into respiratory
and esophageal parts.
Defective •
tracheoesophageal
septum causes
abnormal communication
between the trachea and
esophagus.
TRACHEOESOPHAGEAL
FISTULA
It is the most •
common anomaly of
the lower respiratory
tract especially in
Male infants.
It is usually •
associated with other
congenital anomalies.
TRACHEOESOPHAGEAL
FISTULA
Most common •
variety:
Blind ending of the •
superior part of the
esophagus
(esophageal atresia)
and joining of the
inferior part to the
trachea near its
bifurcation.
TRACHEOESOPHAGEAL
FISTULA
Manifestations : •
Cough and choke during •
swallowing because of
accumulation of excessive
saliva in the mouth and
upper respiratory tract.
Gastric contents may •
reflux from the stomach
through the fistula into the
trachea and lungs.