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Embryology of the Respiratory System

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Embryology of the Respiratory System 9/15/2010 EMBRYOLOGY OF THE RESPIRATORY SYSTEM Formation of Embryonic Disk (first three weeks) Gastrulation 15 days 1 9/15/2010 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 - epiblastsepiblasts)) – Future Ectoderm Hypoblast Layer (primary yolk sac cells) – Future Endoderm – Gastrulation: Formation of primitive strstreakeak & 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. 2 9/15/2010 Trilaminar Embryonic Disk (3 weeks) Trilaminar Embryonic Disk (3 weeks) 3 9/15/2010 Folding in Median & Horizontal Plane (4th week) Folding in Median & Horizontal Plane (4th week) 4 9/15/2010 Oropharyngeal membrane (ruptures at 24 days) Cloacal Membrane (ruptures at the end of 7th week) 5 9/15/2010 DEVELOPMENT OF THE FACE (from fourth to eighth weeks) DEVELOPMENT OF THE PRIMITIVE MOUTH – STOMODEUM (beginning off4 4th week) Rupture of oropharyngeal;oropharyngeal; membrane (24th day) DEVELOPMENT OF THE NASAL CAVITY (from the end of 4th week) RtRupture o f oronasalll memb(6brane (6th week) 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 It constitutes cranial boundary ––PairedPaired maxillary prominences They form lateral boundaries –Paired mandibular prominences They constitute caudal boundary 6 9/15/2010 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 formed Medial & lateral sides of eacheach elevation (surrounding one placodeplacode)) 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 Nasal sacs are seppyyarated from oral cavity by oronasal membrane, which ruptures during the sixth week This forms primitive choanaechoanae,, 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. 7 9/15/2010 Formation of Nasal Placodes Formation of Nasal Pits & Sacs 8 9/15/2010 Boundaries of Right Nasal Pit Merging of Medial Nasal Prominences 9 9/15/2010 Formation of Nasal Prominences Beginning of Merging of Medial Nasal Prominences 10 9/15/2010 Merging of Medial Nasal Prominences is Completed Derivatives of Merged Medial Nasal Prominences 11 9/15/2010 Development of Nasal Cavity Components of Inferior Nasal Wall in Adult View from Oral Cavity Interpalatine suture Secondary Palate or Incisive bone (primary palate) 12 9/15/2010 Congenital Anomalies of Middle Face Area: Oblique cleft of the face (persistent nasolacrimal grove) – It connect mouth to medial palpebral angle of the orbit – Nasol lildtiacrimal duct is presen t 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 13 9/15/2010 Unilateral Cleft Upper Lip, Superior Alveolar Arch & Palate Right 14 9/15/2010 Bilateral Cleft Upper Lip, Superior Alveolar Arch & Palate After Orthopedic Correction Remaining Bilateral Cleft Palate in Adult 15 9/15/2010 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 ftfuture h ea d an d nec k reg ion, form ing elevations of mesoderm on each side of the primitive pharynx. BRANCHIAL APPARATUS INCLUDES: Branchial arches Branchial grooves Branchial pouches Branchial membranes 16 9/15/2010 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 17 9/15/2010 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. – 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. The mesenchyme, that surrounds the bud, gives rise to connective tissue, cartilage, muscle, vessels & pleurae. 18 9/15/2010 Scheme of Development of Lower Airway & Lungs Scheme of Development of Lower Airway & Lungs Lung Bronchial Bud 19 9/15/2010 View of Developing Lower Airway & Lung Bud Development of Laryngeal Inlet 20 9/15/2010 Development of Trachea & Lung Buds Separation of Trachea from Esophagus 21 9/15/2010 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 --11 22 9/15/2010 Tracheoesophageal Fistula --22 Tracheoesophageal Fistula --33 23 9/15/2010 Tracheoesophageal Fistula --44 Development of Lungs 24 9/15/2010 Development of Lungs Development of Lungs 25 9/15/2010 Development of Lungs Development of Lung Buds: 4141--4545 days 26 9/15/2010 Development of Lungs: 13 weeks Posterior View Adult Lungs – Front View Not Smoker Smoker 27 9/15/2010 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 5-5-1717 weeks the branching forms the bronchi and terminal bronchioles. From 1717--2424 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. By this stage the production of surfactant has begun and the fetus might survive if born prematurely. 28 9/15/2010 Periods of Lung Development Pseudoglandular (5(5--1717 w) & Canalicular (16(16––2525 w) Periods 29 9/15/2010 Canalicular (16(16––2525 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. 30 9/15/2010 Developed Respiratory System CONGENITAL ABNORMALITIES: INFANT RESPIRATORY DISTRESS SYNDROME ()(IRDS): – Also called Hyaline Membrane Disease Congenital Lung Cysts Agenesis of Lungs or one Lung LHLung Hypop lilasia Accessory Lung Lobe of Azygos Vein 31 9/15/2010 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
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