DEVELOPMENT OF LARYNX, TRACHEA AND BRONCHI Dr. Mujahid Khan

DEVELOPMENT OF DEVELOPMENT OF LARYNX, TRACHEA AND LARYNX, TRACHEA AND

BRONCHIBRONCHI

Dr. Mujahid KhanDr. Mujahid Khan

Lower Respiratory OrgansLower Respiratory Organs

The lower respiratory organs i.e. larynx, The lower respiratory organs i.e. larynx, trachea, bronchi and lungs begin to form trachea, bronchi and lungs begin to form during the fourth weekduring the fourth week

The respiratory primordium The respiratory primordium ( في في ) االولي االوليالجنينيه ( الجنينيه (المرحله is indicated by a median is indicated by a median المرحلهالنهايه النهايه outgrowth from the caudal end outgrowth from the caudal end وسطوسطاالماميه of the ventral wall of the ventral wall السفليهالسفليه االماميه للجهه of of للجههthe primordial pharynx the primordial pharynx االولي االولي للبلعوم للبلعوم

Laryngotracheal Groove Laryngotracheal Groove التجويف التجويف الداخليالداخلي

Is a primordium of the tracheobronchial treeIs a primordium of the tracheobronchial tree

Develops caudal Develops caudal سفلي سفلي بشكل the fourth pair the fourth pair بشكلof pharyngeal pouches of pharyngeal pouches : البلعوميه البلعوميه : الحبيبات الحبيبات

والرقبه الراس لتعطي تتطور التي والرقبه هي الراس لتعطي تتطور التي هي

The endoderm lining the laryngotracheal The endoderm lining the laryngotracheal groove gives rise to bronchi and pulmonary groove gives rise to bronchi and pulmonary epitheliumepithelium

Respiratory Diverticulum Respiratory Diverticulum تفرع تفرعاالصلي التفرع من يخرج االصلي جانبي التفرع من يخرج جانبي

By the end of fourth week, the laryngotracheal By the end of fourth week, the laryngotracheal groove has evaginated groove has evaginated جانبي جانبي تفرع to form a to form a تفرعpouchpouchجييبجييب like respiratory diverticulum or lung like respiratory diverticulum or lung bud bud تبرعمتبرعم

Is located ventral Is located ventral خلفي خلفي بشكل to the caudal to the caudal بشكلpartpart السفلي السفلي للجزء االمامي of the foregut of the foregut للجزء االمامي المعي المعي

This diverticulum elongates and invested with This diverticulum elongates and invested with splanchnic mesenchyme and its distal splanchnic mesenchyme and its distal خلفيخلفي end end enlarges to form a globular tracheal bud enlarges to form a globular tracheal bud برعمبرعم

والقصبه المرئ تكون حتى الزمن بمرور بعضها عن تنفصلالنهايه في الهوائيه

Tracheoesophageal folds & Tracheoesophageal folds & SeptumSeptum

Longitudinal Longitudinal الطوليالطولي tracheoesophageal folds tracheoesophageal folds develop in the laryngotracheal diverticulum develop in the laryngotracheal diverticulum كما كما

السابقه الشريحه في السهم السابقه في الشريحه في السهم في

These folds approach each other and fuse to These folds approach each other and fuse to form a partition called tracheoesophageal form a partition called tracheoesophageal septumseptum

This septum divides the cranial This septum divides the cranial علويعلويpart of the part of the foregut into a ventral foregut into a ventral اماميامامي part, the part, the laryngotracheal tube and a dorsal laryngotracheal tube and a dorsal خلفيخلفي part, part, oropharynx and esophagusoropharynx and esophagus

Development of LarynxDevelopment of Larynx

The epithelial lining of the larynx The epithelial lining of the larynx develops from develops from endodermendoderm of the cranial of the cranial العلويالعلوي end of end of laryngotracheal tubelaryngotracheal tube

The cartilages of the larynxThe cartilages of the larynx develop from the develop from the cartilages in the fourth and sixth pairs of cartilages in the fourth and sixth pairs of pharyngeal arches pharyngeal arches البلعوميه الحبيبات نفسها البلعوميه العقد الحبيبات نفسها العقد

الشريحه الشريحه في 33في

The laryngeal cartilagesThe laryngeal cartilages develop from the develop from the mesenchyme that is derived from neural crest mesenchyme that is derived from neural crest cellscells

Development of LarynxDevelopment of Larynx

The laryngeal epithelium proliferates rapidly The laryngeal epithelium proliferates rapidly resulting in temporary occlusion resulting in temporary occlusion مؤقت مؤقت سد of the of the سدlaryngeal lumen laryngeal lumen تجويفتجويف

Recanalization Recanalization السدد فتح السدد اعاده فتح of larynx normally of larynx normally اعادهoccurs by the tenth weekoccurs by the tenth week

:: وانفتاحه السدد هذا وانفتاحه فائده السدد هذا 11فائده -Laryngeal ventricles -Laryngeal ventricles form during this recanalizationform during this recanalization بطينبطين

2-These recesses 2-These recesses تجويفاتتجويفات are bounded by folds are bounded by folds of mucous membrane that become the vocal of mucous membrane that become the vocal folds and vestibular foldsfolds and vestibular folds

Epiglottis Epiglottis المزمار المزمار لسان لسان

It develops from the caudal It develops from the caudal سفليسفلي part of the part of the hypopharyngeal hypopharyngeal البلعوم من السفلي البلعوم الجزء من السفلي الجزءeminenceminence e بروزبروز

The rostral part The rostral part - االبرز االوضح االبرز -الجز االوضح of this of thisالجزeminence forms the posterior third or pharyngeal eminence forms the posterior third or pharyngeal part of the tongue part of the tongue اللساناللسان

Growth of the larynx and epiglottis is rapid Growth of the larynx and epiglottis is rapid during the first three years after birth during the first three years after birth

By this time the epiglottis has reached its adult By this time the epiglottis has reached its adult formform

Development of TracheaDevelopment of Trachea

The endodermal lining of the The endodermal lining of the laryngotracheal tube distal laryngotracheal tube distal خلفيخلفي to the to the (larynx differentiates (larynx differentiates المتطورهالمتطوره )into the )into the epithelium and glands of the trachea and epithelium and glands of the trachea and pulmonary epitheliumpulmonary epithelium

The cartilages, connective tissue, and The cartilages, connective tissue, and muscles of the trachea are derived from muscles of the trachea are derived from the splanchnic mesenchyme surrounding the splanchnic mesenchyme surrounding the laryngotracheal tubethe laryngotracheal tube

Tracheoesophageal Fistula Tracheoesophageal Fistula حاله حاله هو هوالهوائيه القصبه و المرئ تكوين فيها يتم ال جنيني الهوائيه تشوه القصبه و المرئ تكوين فيها يتم ال جنيني تشوه

بينهما اتصال وجود عنه ينتج مما صحيح بينهما بشكل اتصال وجود عنه ينتج مما صحيح بشكل It is an abnormal passage between the trachea It is an abnormal passage between the trachea

and esophagusand esophagus

Occurs once in 3000 to 4500 live birthsOccurs once in 3000 to 4500 live births

Most affected infants are males Most affected infants are males مساكيييينمساكيييين

In more than 85% of cases, the fistula is In more than 85% of cases, the fistula is associated with esophageal atresia associated with esophageal atresia تضيقتضيق

It results from incomplete division of the cranial It results from incomplete division of the cranial part of the foregut part of the foregut المعيالمعي into respiratory and into respiratory and esophageal parts esophageal parts

Development of Bronchi and LungsDevelopment of Bronchi and Lungs

Tracheal bud Tracheal bud بريعماتبريعمات divides into two divides into two outpouchings, called primary bronchial outpouchings, called primary bronchial buds buds القادمه الصفحه الصوره القادمه انظر الصفحه الصوره انظر

These buds grow laterally into the These buds grow laterally into the pericardioperitoneal canals, the primordia pericardioperitoneal canals, the primordia

االولي االولي العضو of pleural cavitiesof pleural cavities العضو

Bronchial buds differentiate into the Bronchial buds differentiate into the bronchi bronchi


Connection of each bronchial bud with the Connection of each bronchial bud with the trachea enlarges to form the primordium trachea enlarges to form the primordium العضو العضوof a main bronchusof a main bronchus االولياالولي

The right main bronchus is slightly larger than The right main bronchus is slightly larger than the left one and is oriented more verticallythe left one and is oriented more vertically

The embryonic relationship persists The embryonic relationship persists دائمدائم in the in the adultadult

The main bronchi subdivide into secondary The main bronchi subdivide into secondary bronchi that form lobar bronchi that form lobar فصوصفصوص, segmental and , segmental and intersegmental branchesintersegmental branches

الرئه تكون هو الزهري اللونمن يختلف الفصوص عدد والحظ

لليسرى اليمنى


The segmental bronchi, ten in right lung and The segmental bronchi, ten in right lung and eight or nine in the left lung begin to form by the eight or nine in the left lung begin to form by the seventh weekseventh week

The surrounding mesenchyme also dividesThe surrounding mesenchyme also divides

Each segmental bronchus with its surrounding Each segmental bronchus with its surrounding

mass of mesenchyme is the primordium mass of mesenchyme is the primordium العضو العضوالرئه of a bronchopulmonary segment of a bronchopulmonary segment االولياالولي الرئه جزء جزء

بها الموصله بها والشعيبات الموصله والشعيبات


By 24 weeks, about 17 orders of branches By 24 weeks, about 17 orders of branches have formed and respiratory bronchioles have formed and respiratory bronchioles have developedhave developed

An additional seven orders of airways An additional seven orders of airways develop after birthdevelop after birth

As the bronchi develop, cartilaginous As the bronchi develop, cartilaginous plates develop from the surrounding plates develop from the surrounding splanchnic mesenchymesplanchnic mesenchyme


The bronchial muscle and pulmonary connective The bronchial muscle and pulmonary connective tissue and capillaries tissue and capillaries are also derived from this are also derived from this mesenchymemesenchyme

As the lungs develop they acquire a layer of As the lungs develop they acquire a layer of visceral pleura from visceral pleura from splanchnic mesenchymesplanchnic mesenchyme

The thoracic body wall becomes lined by a layer The thoracic body wall becomes lined by a layer of parietal pleura derived from the of parietal pleura derived from the somatic somatic mesodermmesoderm

Maturation of the LungsMaturation of the Lungs

It is divided into four periods It is divided into four periods مراحل اربع على مراحل يتم اربع على ::يتم

Pseudoglandular Pseudoglandular الكاذب الكاذب الغدي periodperiod الغدي

Canalicular periodCanalicular period

Terminal saccular periodTerminal saccular period

Alveolar periodAlveolar period القادمه بالشرائح القادمه تفصل بالشرائح تفصل

1- Pseudoglandular Period 1- Pseudoglandular Period (6-16 weeks)(6-16 weeks)

Developing lungs somewhat resembles Developing lungs somewhat resembles تشبهتشبه an an exocrine gland during this period exocrine gland during this period

By 16 weeks all major elements of the lung have By 16 weeks all major elements of the lung have formed except those involved with gas exchangeformed except those involved with gas exchange

Respiration is not possibleRespiration is not possible

Fetuses born during this period cannot surviveFetuses born during this period cannot survive

2-Canalicular Period 2-Canalicular Period (16-26 weeks)(16-26 weeks)

Cranial Cranial العلويالعلوي segments of the lungs mature segments of the lungs mature faster than caudal faster than caudal السفليالسفلي onesones

Lumina of bronchi and terminal bronchioles Lumina of bronchi and terminal bronchioles become largerbecome larger

Lung tissue becomes highly vascularLung tissue becomes highly vascular

By 24 weeks each terminal bronchiole has given By 24 weeks each terminal bronchiole has given rise to two or more respiratory bronchiolesrise to two or more respiratory bronchioles

Canalicular Period Canalicular Period (16-26 weeks)(16-26 weeks)

Each of the respiratory bronchioles divide into 3 Each of the respiratory bronchioles divide into 3 to 6 tubular passages called alveolar ductsto 6 tubular passages called alveolar ducts

Respiration is possible at the end of this period Respiration is possible at the end of this period because some thin-walled terminal saccules because some thin-walled terminal saccules (primordial alveoli) have developed at the end of (primordial alveoli) have developed at the end of respiratory bronchiolesrespiratory bronchioles

Lung tissue is well vascularizedLung tissue is well vascularized

Fetus born at the end of this period may surviveFetus born at the end of this period may survive

3- Terminal Saccular period3- Terminal Saccular period(26 weeks - birth)(26 weeks - birth)

Many more terminal saccules developMany more terminal saccules develop

Their epithelium becomes very thinTheir epithelium becomes very thin

Capillaries begin to bulge into developing Capillaries begin to bulge into developing alveolialveoli

By 26 weeks, the terminal saccules are lined By 26 weeks, the terminal saccules are lined by squamous epithelial cells of endodermal by squamous epithelial cells of endodermal origin, type I pneumocytes origin, type I pneumocytes عن مسؤوله عن خاليا مسؤوله خاليا

الغازات الغازات تبادل تبادل

Terminal Saccular periodTerminal Saccular period(26 weeks - birth)(26 weeks - birth)

Gas exchange occurs across type I Gas exchange occurs across type I pneumocytes pneumocytes

Scattered Scattered تتناثرتتناثر among the squamous epithelial among the squamous epithelial cells are rounded secretory epithelial cells, type cells are rounded secretory epithelial cells, type II alveolar cells or pneumocytes II alveolar cells or pneumocytes عن عن المسؤؤوله المسؤؤولهاالفرازاالفراز

Type II pneumocytes secrete a mixture of Type II pneumocytes secrete a mixture of phospholipids called surfactant phospholipids called surfactant الفسيو الفسيو راجع راجع

Surfactant forms as a monomolecular film over Surfactant forms as a monomolecular film over the internal walls of the terminal sacculesthe internal walls of the terminal saccules


Surfactant production increases during the Surfactant production increases during the terminal stages of pregnancyterminal stages of pregnancy

Surfactant reduces surface tension and Surfactant reduces surface tension and facilitates expansion of the terminal sacculesfacilitates expansion of the terminal saccules

Fetuses born prematurely at 24-26 weeks may Fetuses born prematurely at 24-26 weeks may survive if given intensive caresurvive if given intensive care

Fetuses may suffer from respiratory distress due Fetuses may suffer from respiratory distress due to surfactant deficiencyto surfactant deficiency


Surfactant production begins by 20 weeksSurfactant production begins by 20 weeks

By 26 – 28 weeks the fetus usually weighs about By 26 – 28 weeks the fetus usually weighs about 1000 gm1000 gm

Sufficient Sufficient كافيكافي terminal saccules terminal saccules هوائيه هوائيه كيسسات كيسساتand surfactant and surfactant لالحتكاك المانعه لالحتكاك ماده المانعه are present are presentمادهto permit to permit الممكن من الممكن لتجعل من survival of a survival of aلتجعلprematurely born infantsprematurely born infants

Pulmonary vasculature and sufficient surfactant Pulmonary vasculature and sufficient surfactant are critical to the survival of the premature infantare critical to the survival of the premature infant

4- Alveolar Period4- Alveolar Period32 weeks – 8 years32 weeks – 8 years

Definition of the term alveolus depends on the Definition of the term alveolus depends on the change of terminal saccular period to alveolar change of terminal saccular period to alveolar periodperiod

Structures analogous to alveoli are present at 32 Structures analogous to alveoli are present at 32 weeks sacculesweeks saccules

The epithelial lining of the terminal sacs The epithelial lining of the terminal sacs attenuates attenuates يضعفيضعف to an extremely thin squamous to an extremely thin squamous epithelial layerepithelial layer

Type I pneumocytes become so thin that the Type I pneumocytes become so thin that the adjacent capillaries bulge into the terminal adjacent capillaries bulge into the terminal sacculessaccules

Alveolar PeriodAlveolar Period32 weeks – 8 years32 weeks – 8 years

At the beginning of the alveolar period, At the beginning of the alveolar period, each respiratory bronchiole terminates in a each respiratory bronchiole terminates in a cluster cluster عنقودعنقود of thin-walled terminal of thin-walled terminal saccules, separated from one another by saccules, separated from one another by loose connective tissueloose connective tissue

These terminal saccules represent future These terminal saccules represent future alveolar ductsalveolar ducts


The transition from dependence on the placenta The transition from dependence on the placenta for gas exchange to autonomous gas exchange for gas exchange to autonomous gas exchange requires the following adaptive changes in the requires the following adaptive changes in the lungs:lungs:

Production of adequate surfactant in the alveoli Production of adequate surfactant in the alveoli

Transformation of the lungs from secretory into Transformation of the lungs from secretory into gas exchanging organsgas exchanging organs

Establishment of parallel pulmonary and Establishment of parallel pulmonary and systemic circulationssystemic circulations


Characteristic mature alveoli do not form Characteristic mature alveoli do not form until after birthuntil after birth

95% of alveoli develop postnatally 95% of alveoli develop postnatally بعد بعدالوالدهالوالده

Most increase in the size of the lungs Most increase in the size of the lungs results from an increase in the number of results from an increase in the number of respiratory bronchioles and primordial respiratory bronchioles and primordial alveoli rather than from an increase in the alveoli rather than from an increase in the size of the alveolisize of the alveoli


From third to eight year or so, the number From third to eight year or so, the number of immature alveoli continues to increaseof immature alveoli continues to increase

Unlike mature alveoli, immature alveoli Unlike mature alveoli, immature alveoli have the potential for forming additional have the potential for forming additional primordial alveoliprimordial alveoli

About 50 million alveoli, one sixth of the About 50 million alveoli, one sixth of the adult number are present in the lungs of a adult number are present in the lungs of a full-term newborn infantfull-term newborn infant


By about the eighth year, the adult complement By about the eighth year, the adult complement of 300 million alveoli is presentof 300 million alveoli is present

Breathing movements occur before birth, Breathing movements occur before birth, exerting exerting جهدجهد sufficient sufficient كافيكافي force to cause force to cause aspiration aspiration شفطشفط of some amniotic fluid into the of some amniotic fluid into the lungs lungs فيدخل امه ببطن يتنفس وياحول يتقيرد فيدخل الجنين امه ببطن يتنفس وياحول يتقيرد الجنين

طبيعي بعضمن بعضمن بسهذا بالرئه به المحيط طبيعي السائل بسهذا بالرئه به المحيط السائل (:(: These breathing movements are not continuous These breathing movements are not continuous

and are detected by real-time ultrasonographyand are detected by real-time ultrasonography


By birth the fetus has had the advantage By birth the fetus has had the advantage of breathing exercise for monthsof breathing exercise for months

These movements stimulate lung These movements stimulate lung developmentdevelopment

At birth the lungs are half filled with fluid At birth the lungs are half filled with fluid derived from the amniotic cavity, lungs and derived from the amniotic cavity, lungs and tracheal glandstracheal glands


The fluid in the lungs is cleared at birth by The fluid in the lungs is cleared at birth by three routes:three routes:

Through the mouth and nose by pressure Through the mouth and nose by pressure on the fetal thorax during deliveryon the fetal thorax during delivery

Into the pulmonary capillariesInto the pulmonary capillaries

Into the lymphatics and pulmonary arteries Into the lymphatics and pulmonary arteries and veinsand veins


Near term the pulmonary lymphatic vessels are Near term the pulmonary lymphatic vessels are relatively larger than in the adultsrelatively larger than in the adults

Three factors are important for normal lung Three factors are important for normal lung development:development:

Adequate thoracic space for lung growthAdequate thoracic space for lung growth

Fetal breathing movementsFetal breathing movements

Adequate amniotic fluid volumeAdequate amniotic fluid volume

Thank youThank youعمره ال الدكتور لهذا عمره قولوا ال الدكتور لهذا قولوا

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DEVELOPMENT OF LARYNX, TRACHEA AND BRONCHI Dr. Mujahid Khan