Transcript lec1.Development of Respiratory System.ppt

DEVELOPMENT OF
LARYNX, TRACHEA AND
BRONCHI
Dr. Mujahid Khan
Lower Respiratory Organs
 The
lower respiratory organs i.e. larynx,
trachea, bronchi and lungs begin to form
during the fourth week
respiratory primordium ‫االولي ( في المرحله‬
) ‫ الجنينيه‬is indicated by a median ‫وسط‬
outgrowth from the caudal end ‫النهايه السفليه‬
of the ventral wall ‫ للجهه االماميه‬of the
primordial pharynx ‫للبلعوم االولي‬
 The
Laryngotracheal Groove ‫التجويف‬
‫الداخلي‬
 Is
a primordium of the tracheobronchial
tree
caudal ‫ بشكل سفلي‬the fourth pair of
pharyngeal pouches ‫ هي التي‬: ‫الحبيبات البلعوميه‬
‫تتطور لتعطي الراس والرقبه‬
 Develops
 The
endoderm lining the laryngotracheal
groove gives rise to bronchi and
pulmonary epithelium
Respiratory Diverticulum ‫تفرع‬
‫جانبي يخرج من التفرع االصلي‬

By the end of fourth week, the laryngotracheal
groove has evaginated ‫ تفرع جانبي‬to form a
pouch ‫ جييب‬like respiratory diverticulum or lung
bud ‫تبرعم‬

Is located ventral ‫ بشكل خلفي‬to the caudal part ‫للجزء‬
‫ السفلي‬of the foregut ‫المعي االمامي‬

This diverticulum elongates and invested with
splanchnic mesenchyme and its distal ‫ خلفي‬end
enlarges to form a globular tracheal bud ‫برعم‬
‫تنفصل عن بعضها بمرور الزمن حتى تكون المرئ والقصبه الهوائيه في النهايه‬
Tracheoesophageal folds &
Septum

Longitudinal ‫ الطولي‬tracheoesophageal folds
develop in the laryngotracheal diverticulum ‫كما‬
‫في السهم في الشريحه السابقه‬

These folds approach each other and fuse to
form a partition called tracheoesophageal
septum

This septum divides the cranial ‫علوي‬part of the
foregut into a ventral ‫ امامي‬part, the
laryngotracheal tube and a dorsal ‫ خلفي‬part,
oropharynx and esophagus
Development of Larynx

The epithelial lining of the larynx develops from
endoderm of the cranial ‫ العلوي‬end of
laryngotracheal tube

The cartilages of the larynx develop from the
cartilages in the fourth and sixth pairs of
pharyngeal arches ‫العقد نفسها الحبيبات البلعوميه في‬
3 ‫الشريحه‬

The laryngeal cartilages develop from the
mesenchyme that is derived from neural crest
cells
Development of Larynx

The laryngeal epithelium proliferates rapidly
resulting in temporary occlusion ‫ سد مؤقت‬of the
laryngeal lumen ‫تجويف‬

Recanalization ‫ اعاده فتح السدد‬of larynx normally
occurs by the tenth week

‫فائده هذا السدد وانفتاحه‬: 1-Laryngeal ventricles ‫بطين‬
form during this recanalization

2-These recesses ‫ تجويفات‬are bounded by folds of
mucous membrane that become the vocal folds
and vestibular folds
Epiglottis ‫لسان المزمار‬
It develops from the caudal ‫ سفلي‬part of the
hypopharyngeal ‫ الجزء السفلي من البلعوم‬eminence
‫بروز‬
 The rostral part ‫االبرز‬- ‫الجز االوضح‬of this eminence
forms the posterior third or pharyngeal part of
the tongue ‫اللسان‬


Growth of the larynx and epiglottis is rapid
during the first three years after birth

By this time the epiglottis has reached its adult
form
Development of Trachea
 The
endodermal lining of the
laryngotracheal tube distal ‫ خلفي‬to the
(larynx differentiates ‫) المتطوره‬into the
epithelium and glands of the trachea and
pulmonary epithelium
 The
cartilages, connective tissue, and
muscles of the trachea are derived from
the splanchnic mesenchyme surrounding
the laryngotracheal tube
Tracheoesophageal Fistula
‫هو حاله‬
‫تشوه جنيني ال يتم فيها تكوين المرئ و القصبه الهوائيه بشكل صحيح‬
‫مما ينتج عنه وجود اتصال بينهما‬
 It is an abnormal passage between the trachea
and esophagus

Occurs once in 3000 to 4500 live births

Most affected infants are males  ‫مساكيييين‬

In more than 85% of cases, the fistula is
associated with esophageal atresia ‫تضيق‬

It results from incomplete division of the cranial
part of the foregut ‫ المعي‬into respiratory and
esophageal parts
Development of Bronchi and Lungs
bud ‫ بريعمات‬divides into two
outpouchings, called primary bronchial
buds ‫انظر الصوره الصفحه القادمه‬
 Tracheal
 These
buds grow laterally into the
pericardioperitoneal canals, the primordia
‫ العضو االولي‬of pleural cavities
 Bronchial
bronchi
buds differentiate into the
Development of Bronchi and Lungs

Connection of each bronchial bud with the
trachea enlarges to form the primordium ‫العضو‬
‫ االولي‬of a main bronchus

The right main bronchus is slightly larger than
the left one and is oriented more vertically

The embryonic relationship persists ‫ دائم‬in the
adult

The main bronchi subdivide into secondary
bronchi that form lobar ‫فصوص‬, segmental and
intersegmental branches
‫اللون الزهري هو تكون الرئه والحظ عدد‬
‫الفصوص يختلف من اليمنى لليسرى‬
Development of Bronchi and Lungs

The segmental bronchi, ten in right lung and
eight or nine in the left lung begin to form by the
seventh week

The surrounding mesenchyme also divides

Each segmental bronchus with its surrounding
mass of mesenchyme is the primordium ‫العضو‬
‫ االولي‬of a bronchopulmonary segment ‫جزء الرئه‬
‫والشعيبات الموصله بها‬
Development of Bronchi and Lungs
 By
24 weeks, about 17 orders of branches
have formed and respiratory bronchioles
have developed
 An
additional seven orders of airways
develop after birth
 As
the bronchi develop, cartilaginous
plates develop from the surrounding
splanchnic mesenchyme
Development of Bronchi and Lungs

The bronchial muscle and pulmonary connective
tissue and capillaries are also derived from this
mesenchyme

As the lungs develop they acquire a layer of
visceral pleura from splanchnic mesenchyme

The thoracic body wall becomes lined by a layer
of parietal pleura derived from the somatic
mesoderm
Maturation of the Lungs
It is divided into four periods ‫يتم على اربع مراحل‬:

Pseudoglandular ‫ الغدي الكاذب‬period

Canalicular period

Terminal saccular period

Alveolar period
 ‫تفصل بالشرائح القادمه‬
1- Pseudoglandular Period
(6-16 weeks)

Developing lungs somewhat resembles ‫ تشبه‬an
exocrine gland during this period

By 16 weeks all major elements of the lung have
formed except those involved with gas exchange

Respiration is not possible

Fetuses born during this period cannot survive
2-Canalicular Period
(16-26 weeks)

Cranial ‫ العلوي‬segments of the lungs mature
faster than caudal ‫ السفلي‬ones

Lumina of bronchi and terminal bronchioles
become larger

Lung tissue becomes highly vascular

By 24 weeks each terminal bronchiole has given
rise to two or more respiratory bronchioles
Canalicular Period
(16-26 weeks)

Each of the respiratory bronchioles divide into 3
to 6 tubular passages called alveolar ducts

Respiration is possible at the end of this period
because some thin-walled terminal saccules
(primordial alveoli) have developed at the end of
respiratory bronchioles

Lung tissue is well vascularized

Fetus born at the end of this period may survive
3- Terminal Saccular period
(26 weeks - birth)
 Many
more terminal saccules develop
 Their
epithelium becomes very thin
 Capillaries
begin to bulge into developing
alveoli
 By
26 weeks, the terminal saccules are
lined by squamous epithelial cells of
endodermal origin, type I pneumocytes
‫خاليا مسؤوله عن تبادل الغازات‬
Terminal Saccular period
(26 weeks - birth)

Gas exchange occurs across type I
pneumocytes

Scattered ‫ تتناثر‬among the squamous epithelial
cells are rounded secretory epithelial cells, type
II alveolar cells or pneumocytes ‫المسؤؤوله عن االفراز‬

Type II pneumocytes secrete a mixture of
phospholipids called surfactant ‫راجع الفسيو‬

Surfactant forms as a monomolecular film over
the internal walls of the terminal saccules
Terminal Saccular period
(26 weeks - birth)

Surfactant production increases during the
terminal stages of pregnancy

Surfactant reduces surface tension and
facilitates expansion of the terminal saccules

Fetuses born prematurely at 24-26 weeks may
survive if given intensive care

Fetuses may suffer from respiratory distress due
to surfactant deficiency
Terminal Saccular period
(26 weeks - birth)

Surfactant production begins by 20 weeks

By 26 – 28 weeks the fetus usually weighs about
1000 gm

Sufficient ‫ كافي‬terminal saccules ‫ كيسسات هوائيه‬and
surfactant ‫ماده المانعه لالحتكاك‬are present to permit
‫لتجعل من الممكن‬survival of a prematurely born
infants

Pulmonary vasculature and sufficient surfactant
are critical to the survival of the premature infant
4- Alveolar Period
32 weeks – 8 years

Definition of the term alveolus depends on the
change of terminal saccular period to alveolar
period

Structures analogous to alveoli are present at 32
weeks saccules

The epithelial lining of the terminal sacs
attenuates ‫ يضعف‬to an extremely thin squamous
epithelial layer

Type I pneumocytes become so thin that the
adjacent capillaries bulge into the terminal
saccules
Alveolar Period
32 weeks – 8 years
 At
the beginning of the alveolar period,
each respiratory bronchiole terminates in a
cluster ‫ عنقود‬of thin-walled terminal
saccules, separated from one another by
loose connective tissue
 These
terminal saccules represent future
alveolar ducts
Alveolar Period
32 weeks – 8 years
The transition from dependence on the placenta
for gas exchange to autonomous gas exchange
requires the following adaptive changes in the
lungs:

Production of adequate surfactant in the alveoli

Transformation of the lungs from secretory into
gas exchanging organs

Establishment of parallel pulmonary and
systemic circulations
Alveolar Period
32 weeks – 8 years
 Characteristic
mature alveoli do not form
until after birth
 95%
 Most
of alveoli develop postnatally ‫بعد الوالده‬
increase in the size of the lungs
results from an increase in the number of
respiratory bronchioles and primordial
alveoli rather than from an increase in the
size of the alveoli
Alveolar Period
32 weeks – 8 years
 From
third to eight year or so, the number
of immature alveoli continues to increase
 Unlike
mature alveoli, immature alveoli
have the potential for forming additional
primordial alveoli
 About
50 million alveoli, one sixth of the
adult number are present in the lungs of a
full-term newborn infant
Alveolar Period
32 weeks – 8 years


By about the eighth year, the adult complement
of 300 million alveoli is present
Breathing movements occur before birth,
exerting ‫ جهد‬sufficient ‫ كافي‬force to cause
aspiration ‫ شفط‬of some amniotic fluid into the
lungs ‫الجنين يتقيرد وياحول يتنفس ببطن امه فيدخل بعض من‬
:( ‫السائل المحيط به بالرئه بس هذا طبيعي‬
 These breathing movements are not continuous
and are detected by real-time ultrasonography
Alveolar Period
32 weeks – 8 years
 By
birth the fetus has had the advantage
of breathing exercise for months
 These
movements stimulate lung
development
 At
birth the lungs are half filled with fluid
derived from the amniotic cavity, lungs and
tracheal glands
Alveolar Period
32 weeks – 8 years
The fluid in the lungs is cleared at birth by
three routes:
 Through
the mouth and nose by pressure
on the fetal thorax during delivery
 Into
 Into
the pulmonary capillaries
the lymphatics and pulmonary arteries
and veins
Alveolar Period
32 weeks – 8 years

Near term the pulmonary lymphatic vessels are
relatively larger than in the adults

Three factors are important for normal lung
development:

Adequate thoracic space for lung growth

Fetal breathing movements

Adequate amniotic fluid volume
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‫قولوا لهذا الدكتور ال عمره يكتب‬
‫محاضرات‬
‫لحسه ‪...‬‬