Download Embryology of the Respiratory System

9/15/2010
EMBRYOLOGY
OF
THE
RESPIRATORY
SYSTEM
Formation of Embryonic Disk
(first three weeks)
Gastrulation
15 days
y
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Formation of Embryonic Disk
(first three weeks)
Implantation of blastocyst
– Exocoelomic cavity
– Inner cell mass
Formation of amniotic cavity inside inner cell mass
Formation of primary yolk sac cavity inside exocoelomic cavity
– Formation of bilaminar embryonic disc between amniotic
cavity & yolk sac
Epiblast Layer (amniotic cells - epiblasts
epiblasts)) – Future Ectoderm
Hypoblast Layer (primary yolk sac cells) – Future Endoderm
Gastrulation::
– Gastrulation
Formation of primitive streak & groove on surface of Epiblast
Migration of Epiblast cells to Hypoblast & formation of Endoderm
Formation of Intraembryonic Mesoderm between Ectoderm &
Endoderm from Epiblast cells
Formation of the Ectoderm from cells remaining in Epiblast
– Formation of Trilaminar Enbryonic Disc between amniotic
cavity & yolk sac
ESTABLISHMENT of GENERAL BODY
FORM
(at the beginning of the fourth week)
Folding of the flat trilaminar embryonic
disk into a cylindrical embryo.
– Longitudinal Folding in the Median Plane:
Cranial and caudal folding
– Transverse Folding in Horizontal Plane:
Right and left lateral to medial folding.
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Trilaminar Embryonic Disk (3 weeks)
Trilaminar Embryonic Disk (3 weeks)
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Folding in Median & Horizontal Plane (4
th
week)
Folding in Median & Horizontal Plane (4
th
week)
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Oropharyngeal membrane (ruptures at 24 days)
Cloacal Membrane (ruptures at the end of 7th week)
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DEVELOPMENT OF THE FACE
(from fourth to eighth weeks)
weeks)
DEVELOPMENT OF THE PRIMITIVE
MOUTH – STOMODEUM (beginning
k)
off 4th week)
Rupture of oropharyngeal;
oropharyngeal; membrane (24th day)
DEVELOPMENT OF THE NASAL
week))
CAVITY (from the end of 4th week
Rupture
off oronasall membrane
R t
b
(6th week)
k)
Development of paranasal air
sinuses from deverticuli of nasal
walls during late fetal life & after birth
DEVELOPMENT OF THE PRIMITIVE MOUTH
(STOMODEUM)
It develops from five facial primordia:
– Frontonasal prominence
p
It constitutes cranial boundary
– Paired maxillary prominences
They form lateral boundaries
– Paired mandibular prominences
They constitute caudal boundary
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Stomodeum & Nasal Placodes
Stomodeum
DEVELOPMENT OF THE NASAL CAVITY
Nasal placodes (bilateral right & left oval thickenings of surface
ectoderm) develop on each side of inferior part of frontonasal
prominence by the end of the fourth week.
Horseshoe--shaped elevations at margins of these placodes are
Horseshoe
formed
Medial & lateral sides of each elevation (surrounding one placode
placode)) are called
as Medial & Lateral Nasal Prominences respectively
Nasal placodes now lie in depressions called Nasal Pits
Progressive deepening of nasal pits form Nasal Sacs
Medial & Lateral Nasal Prominence form a boundary of Naris
p
y by
y oronasal
Nasal sacs are separated
from oral cavity
membrane, which ruptures during the sixth week
This forms primitive choanae
choanae,, which lie posterior to primitive palate
After secondary palate develops, choanae lie at junction of nasal cavity and
nasopharynx
Nasal septum, incisive bone & central part of upper lip develop
from merged medial nasal prominences.
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Formation of Nasal Placodes
Formation of Nasal Pits & Sacs
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Boundaries of Right Nasal Pit
Merging of Medial Nasal Prominences
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Formation of Nasal Prominences
Beginning of Merging of Medial Nasal Prominences
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Merging of Medial Nasal Prominences is Completed
Derivatives of Merged Medial Nasal Prominences
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Development of Nasal Cavity
Components of Inferior Nasal Wall in Adult
View from Oral Cavity
Interpalatine suture
Secondary Palate
or Incisive bone
(primary palate)
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Congenital Anomalies of Middle Face Area:
Oblique cleft of the face (persistent nasolacrimal
grove)
– It connect mouth to medial palpebral angle of the orbit
N
l i ld
– Nasolacrimal
ductt iis presentt as open grove
It results from failure of fusion of lateral nasal and maxillary
prominences
Cleft upper lip, superior alveolar arch and palate
– It results from failure of fusion of medial nasal and maxillary
prominences
They could be unilateral or bilateral
Bilateral Oblique Cleft of the Face
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Unilateral Cleft Upper Lip, Superior Alveolar Arch & Palate
Right
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Bilateral Cleft Upper Lip, Superior Alveolar Arch & Palate
After Orthopedic Correction
Remaining Bilateral Cleft Palate in Adult
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DEVELOPMENT OF THE
BRANCHIAL APPARATUS
(arches, pouches, grooves,
membranes)
Branchial arches (from 1 to 6) develop
early in week 4 as neural crest cells
migrate through the mesenchyme to the
future
head
f t
h d and
d neck
k region,
i
fforming
i
elevations of mesoderm on each side of
the primitive pharynx.
BRANCHIAL APPARATUS
INCLUDES:
Branchial arches
Branchial grooves
Branchial pouches
Branchial membranes
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A Typical Branchial Arch Contains:
An aortic arch
Derivatives of branchial arch arteries
A cartilaginous road
Derivatives of branchial arch cartilages
A nerve
Derivatives of branchial arch nerves
A muscular component
Derivatives of branchial arch muscles
Development of Branchial Apparatus
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FURTHER DEVELOPMENT OF
THE BRANCHIAL
APPARATUS AND ITS
DERIVATIVES
DEVELOPMENT OF THE
LARYNX, TRACHEA,
BRONCHIAL TREE, LUNGS AND
PLEURA
Development of Lower Airway & Lungs
The lower airway and lungs develop as an outgrowth
from the primitive gut.
A laryngotracheal diverticulum buds out from the
primitive pharynx about the fourth week
week.
– Its blind end forms the lung bud.
The tracheoesophageal septum separates the
growing lung bud from the esophagus.
The lung bud continues to elongate and branch into
bronchial buds, secondary bronchi etc.
About 24 orders of branches are eventuallyy formed,, with the last few
being formed after birth.
The endoderm of the lung bud gives rise to the
epithelium and glands of the lower airway.
airway.
The mesenchyme, that surrounds the bud, gives rise
to connective tissue, cartilage, muscle, vessels &
pleurae.
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Scheme of Development of Lower Airway & Lungs
Scheme of Development of Lower Airway & Lungs
Lung
Bud
Bronchial
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View of Developing Lower Airway & Lung Bud
Development of Laryngeal Inlet
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Development of Trachea & Lung Buds
Separation of Trachea from Esophagus
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CONGENITAL ABNORMALITIES OF TRACHEA:
Tracheoesophageal Fistula (Common):
Communication connecting trachea & esophagus that
occurs in every 2500 births
It has four main varieties:
1. Superior portion of esophagus ends blindly
(esophageal atresia), inferior portion joins trachea near its
bifurcation (most common – 90%)
2. Esophagus has communication with trachea near its
bifurcation
3. Upper end of esophagus has communication with
trachea near its bifurcation, whereas the lower portion
ends blindly
4. Upper end of esophagus has communication with
trachea, whereas the lower portion of esophagus also has
communication with trachea near its bifurcation
Tracheal Stenosis (narrowing) and Atresia (closure)
Tracheal diverticulum
Tracheoesophageal Fistula - 1
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Tracheoesophageal Fistula - 2
Tracheoesophageal Fistula - 3
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Tracheoesophageal Fistula - 4
Development of Lungs
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Development of Lungs
Development of Lungs
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Development of Lungs
Development of Lung Buds: 4141-45 days
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Development of Lungs: 13 weeks
Posterior View
Adult Lungs – Front View
Not Smoker
Smoker
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Periods of Lung Development
Pseudoglandular period (5 – 17
weeks))
Canalicular period (16 – 25 weeks)
Terminal sac period (24 weeks to
birth)
Alveolar period (late fetal period to 8
years after birth)
Periods of Lung Development
From 55-17 weeks the branching forms the
bronchi and terminal bronchioles.
From 17
17--24 weeks the diameter of the tube
increases and respiratory bronchioles and
alveolar ducts develop.
At 25 weeks the alveolar sacs give rise to
primitive alveoli with cuboidal epithelium. By 26
weeks the alveoli have become vascularized.
vascularized
By this stage the production of surfactant has
begun and the fetus might survive if born
prematurely.
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Periods of Lung Development
Pseudoglandular (5
(5--17 w) & Canalicular (16
(16–
–25 w) Periods
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Canalicular (16
(16–
–25 w) & Terminal Sac (24w to birth) Periods
Periods of Lung Development
Barriers to survival born by 26 week are the
small surface area available for gas exchange,
lack of adequate development of the pulmonary
vasculature and insufficient surfactant
production.
The lung must develop further however before it
is mature.
This process of maturation continues for about
eight years, as the number of alveoli increase.
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Developed Respiratory System
CONGENITAL ABNORMALITIES:
INFANT RESPIRATORY DISTRESS
SYNDROME ((IRDS):
(IRDS)):
– Also called Hyaline Membrane Disease
Congenital Lung Cysts
Agenesis of Lungs or one Lung
Lung
Hypoplasia
L
H
l i
Accessory Lung
Lobe of Azygos Vein
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Features of Respiratory Distress Syndrome
Infants born premature with weights of up to 1.5 kg
show RDS
Their surfactant producing cells (type II pneumocytes
& Clara cells) are not properly developed
Deficiency of pulmonary surfactant
In absence of surfactant alveoli tend to collapse during exhalation
Lungs are under inflated, alveoli contain a fluid of high
protein content that resembles a hyaline (glassy)
membrane
Prolonged intrauterine asphyxia may also produce
irreversible changes in type II alveolar cells
(responsible for surfactant production)
Infants develop rapid, labored breathing
Infants must inhale each time with extra force to reopen alveoli on
next breath and they rapidly becomes exhausted
DEVELOPMENT OF THE
PLEURA AND PLEURAL
CAVITIES
Pleural cavities develop from the Intraembryonic
Coelom
– Right pleural cavity forms from Right PericardioPericardio-Peritoneal
Canal
– Left pleural cavity forms from Left Pericardio
Pericardio--Peritoneal
Canal
Pleurae develop from the Lateral Mesoderm of Three
Laminar Embryonic Disc
– Parietal Pleura – from Somatopleure
– Visceral Pleura – from Splanchnopleure
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3 Somite Embryo of 21 Days
Position of Intraembryonic Coelom
Intraembryonic Coelom
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Development of Pleural Cavities
Development of Pleural Cavities
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Development of Diaphragm
Diaphragm develops from 4 sources:
– 1) Septum Transversum
– 2) Pleuroperitoneal Membranes
– 3) Dorsal Mesentery of Esophagus
– 4)) Bodyy Wall
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Diaphragmatic Hernias
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FETAL CIRCULATION: Oxygenated Blood
Oxygenated Blood from Placenta Æ
Umbilical vein Æ
Branch of Hepatic Portal Vein Æ Ductus venosus Æ
Inferior Vena Cava (Mixture with Venous blood) Æ
Right atrium Æ
Foramen Ovale Æ
Left atrium Æ
Left ventricle Æ
Aorta Æ
– Mixture with Venous blood from Pulmonary trunk
Systemic circulation Æ
Umbilical artery Æ
Placenta Æ
FETAL CIRCULATION: Deoxygenated Blood
Venous blood from Superior Vena Cava Æ
Right atrium Æ
Right ventricle Æ
Pulmonary trunk Æ
Left pulmonary artery Æ
Ductus arteriosus Æ
Left end of aortic arch Æ
Descending aorta: Mixture with Arterial blood Æ
Umbilical artery Æ
Placenta Æ
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Prenatal circulation
Aeration of Lung at Birth
Lungs at birth are half filled with amniotic
fluid because breathing movements occur
before birth to cause aspiration of amniotic
fluid into the lungs
Fluid in lungs is cleared by three routes:
– Through mouth and nose by pressure on
thorax during delivery
– Into pulmonary capillaries and blood vessels
– Into lymphatic capillaries and vessels
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CHANGES THAT OCCUR AFTER BIRTH
After birth, the circulation of fetal blood through the
placenta ceases:
– Delivery of oxygenated blood to fetus via umbilical vein
ceases
– The sphincter of ductus venosus constricts so all blood
entering the liver passes through the hepatic sinusoids
– Fall of blood pressure in the IVC and right atrium occur
– Hypoxia of all tissues is increasing
– Respiratory centers of the brain stem are stimulated by
carbon dioxide
p
y muscles contract, thoracic cage
g is expanded
p
– Inspiratory
– Expansion of the lungs and First Breath takes place
– Inspired air enters respiratory passageways, pushes the
contained fluids out of the way and inflates the
bronchial and respiratory trees
– Infant’s lungs begin to function and newborn infant
utters a loud cry
CHANGES THAT OCCUR AFTER BIRTH
Fall in pulmonary vascular resistance
Ductus arteriosus constricts
Increase in pulmonary blood flow
Left atrium pressure becomes higher than in
right atrium
Valve of oval foramen is pressed against
p
septum
secondum
Foramen ovale closes
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Postnatal circulation
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