Development of the Respiratory System PDF

DEVELOPMENT OF THE RESPIRATORY SYSTEM MOHD ASIM KHAN ASSISTANT PROFESSOR- KKU (KSA) [email protected] LEARNING OBJECTIVES ▪ At the end...

DEVELOPMENT OF THE RESPIRATORY SYSTEM MOHD ASIM KHAN ASSISTANT PROFESSOR- KKU (KSA) [email protected] LEARNING OBJECTIVES ▪ At the end of this lecture, the students should be able to: 1. Describe the development of the respiratory system from the endodermal and mesodermal components 2. Describe the main steps in the development of the lungs 3. Describe the developmental aberrations responsible for the following malformation: 1. Tracheoesophageal fistula ADDITIONAL RESOURCE https://www.youtube.com/watch?v=ZoLuOUaddbE Development of The Trachea , Bronchi & Lungs  DEVELOPMENT OF THE RESPIRATORY SYSTEM MNEMONIC DEVICE LUNG= 4 ALPHABETS= 4 WEEK 1. The lower respiratory organs begin to form during the 4th week 2. The laryngotracheal groove, the primordium of the lower respiratory system develops caudal to the 4th pair of pharyngeal pouches Groove: A deep line or depression cut into a surface Drawings illustrating the human branchial or pharyngeal arches A: Lateral view of the cranial part of an early embryo B: Horizontal section through the cranial region of the embryo Reference: Color Atlas of Clinical Embryology, By Moore, 2nd Edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM 3. The endodermal lining of the laryngotracheal groove gives rise to the epithelium and 3 4bronchi, and5 pulmonary epithelium 2 glands of the larynx, trachea, 4. The connective tissue, cartilage, and smooth muscle in the above-mentioned structures develop from the splanchnic mesoderm surrounding the foregut Transverse sections through the laryngotracheal tube at 4 weeks Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM ▪ LARYNGOTRACHEAL DIVERTICULUM (RESPIRATORY DIVERTICULUM) 1. A pouch like structure forms by the end of the 4th week as the laryngotracheal diverticulum 2. Located ventral to the caudal part of the foregut Diverticulum: Outpouching of a hollow structure in the bod 3. First sign of respiratory system development Fig. 1 Fig. 2 Sagittal section of the cranial half of the embryo showing lateral view at 4 weeks Fig. 3 Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Sagittal section through the cephalic end of a 5- week embryo Reference: Medical Embryology by Langman, 9th Edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM ▪ LARYNGOTRACHEAL DIVERTICULUM (RESPIRATORY DIVERTICULUM) 1. Caudal to hypobranchial eminence (hypopharyngeal eminence) and is in the floor of developing pharynx 2. Midline evagination from the ventral wall of pharyngeal part of the foregut 3. Extends in caudal direction and elongates Fig. 1 Fig. 2 Horizontal section through the cranial region of the embryo showing pharyngeal arches Laryngeal groove caudal to hypobranchial eminence Reference: Medical Embryology by Langman, 9th Edition Reference: Human Embryology, By Inderbir Singh, 11th edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM 4. The distal end of the laryngotracheal diverticulum enlarges to form the lung bud (respiratory bud) 5. The laryngotracheal diverticulum separates with the primordial pharynx, but maintains communication with it through the primordial laryngeal inlet A B C Successive stages in the development of the tracheoesophageal septum during the 4th and 5th weeks of development A to C: Lateral views of the caudal part of the primordial pharynx, showing the laryngotracheal diverticulum and partitioning of the foregut into the esophagus and the laryngotracheal tube Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM 6. The laryngotracheal diverticulum elongates and is invested by splanchnic mesoderm 7. Longitudinal tracheoesophageal folds develop in the laryngotracheal diverticulum, approach each other, and fuse to form a partition, the tracheoesophageal septum Successive stages in the development of the tracheoesophageal septum during the 4th and 5th weeks of development Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF THE RESPIRATORY SYSTEM 8. The tracheoesophageal septum divides the cranial part of the foregut into: 1. Ventral part, the laryngotracheal tube (Primordium of the larynx, trachea, bronchi, and lungs) 2. Dorsal part (Primordium of the oropharynx and esophagus) 9. The opening of the laryngotracheal tube into the pharynx becomes the primordial laryngeal inlet Successive stages in the development of the tracheoesophageal septum during the 4th and 5th weeks of development Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  MNEMONIC DEVICE ORDER OF STRUCTURES IN THE DEVELOPMENT OF THE RESPIRATORY SYSTEM GOOD = GROOVE (LARYNGOTRACHEAL) DISSECTION = DIVERTICULUM (LARYNGOTRACHEAL) FOR = FOLD (TRACHEOESOPHAGEAL) STUDENT = SEPTUM (TRACHEOESOPHAGEAL) TEACHING = TUBE (LARYNGOTRACHEAL) Note: Laryngotracheal diverticulum is also known as respiratory diverticulum Tracheoesophageal fold is also known as tracheoesophageal ridge A-C. Successive stages in development of the respiratory diverticulum Reference: Medical Embryology by Langman, 13th Edition  DEVELOPMENT OF LARYNX 1. Develops from the cranial most part of the laryngotracheal tube 2. The opening of the respiratory diverticulum into the foregut becomes the laryngeal orifice or inlet of larynx Fig. 1 Fig. 2 Midsagittal view of the pharynx Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition  DEVELOPMENTAL COMPONENTS OF LARYNX ▪ Laryngeal epithelium and glands - Derived from endoderm of the cranial part of the laryngotracheal tube ▪ Cartilages of the larynx (Thyroid, Cricoid, Arytenoid, Corniculate, and Cuneiform) - Derived from mesenchyme of the 4th and 6th pharyngeal arches Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition Schematic lateral view of the head and neck of a 24-week fetus illustrating the adult derivatives of the arch cartilages Reference: Color Atlas of Clinical Embryology, By Moore, 2nd Edition  DEVELOPMENTAL COMPONENTS OF LARYNX ▪ Epiglottis - Develops from the caudal part of the hypopharyngeal eminence, produced by the proliferation of the mesenchyme in the ventral ends of the 3rd and 4th pharyngeal arches TEST YOURSELF Name the structure that develops from the rostral part of the hypopharyngeal eminence? Successive stages in the development of the larynx A: At 4 weeks; B: At 5 weeks; C: At 6 weeks; D: At 10 weeks Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENTAL COMPONENTS OF LARYNX ▪ LARYNGEAL MUSCLES - Derived from mesenchyme of the 4th and 6th pharyngeal arches - All the muscles of the larynx are innervated by branches of the vagus nerve (X cranial nerve) A: Sketch of lateral view of the head and neck region of a 4- week embryo showing the branchial or pharyngeal muscles B: Sketch of the head and neck of a 20- week fetus dissected show the muscles derived from the branchial or pharyngeal arches Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition  DEVELOPMENT OF TRACHEA ▪ FORMATION 1. The respiratory diverticulum elongates considerably before the bronchial buds appear 2. The elongated portion of the respiratory diverticulum forms the trachea Development of the respiratory system at weeks 4-6 Reference: High-Yield Embryology By Ronal W. Dudek, 2nd Edition  DEVELOPMENT OF TRACHEA ▪ SOURCES 1. The endodermal lining of the laryngotracheal tube distal to the larynx differentiates into the epithelium and the glands of the trachea and the pulmonary epithelium 2. The cartilage, connective tissue, and muscles of the trachea are derived from the splanchnic mesoderm surrounding the laryngotracheal tube A B C Transverse sections through the laryngotracheal tube, showing progressive stages in the development of the trachea A: At 4 weeks; B: At 10 weeks; C: At 11 weeks Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  CLINICAL CORRELATION- TRACHEOESOPHAGEAL FISTULA (TEF) 1. ▪ DEFINITION Abnormal communication (fistula) between the trachea and esophagus that results from improper division of foregut by the tracheoesophageal septum 2. Generally associated with esophageal atresia and polyhydramnios Narrowing oftheoppening 3. The most common type (90% of all cases) is esophageal atresia with a fistula between the esophagus and the distal one-third of the trachea TERMS 1. Atresia: Absence or abnormal narrowing of an opening or passage in the body Tracheoesophageal fistula 2. Fistula: Reference: High-Yield Embryology By Ronald W. Dudek, 2st Edition An abnormal or surgically made passage between a hollow or tubular organ and the body surface, or between two hollow or tubular organs  CLINICAL CORRELATION- TRACHEOESOPHAGEAL FISTULA (TEF) ▪ CLINICAL FEATURES 1. Excessive accumulation of saliva or mucus in the infant’s nose and mouth 2. Episodes of gagging and cyanosis after swallowing milk 3. Abdominal distention after crying 4. Reflux of gastric contents into lungs, causing pneumonitis and pneumonia ▪ DIAGNOSTIC FEATURES: 1. Inability to pass a catheter into the stomach and radiographs demonstrating air in the infant’s stomach Reference: High-Yield Embryology By Ronald W. Dudek, 2st Edition Radiograph of an infant with esophageal atresia Air in the distal gastrointestinal tract indicates the presence of a tracheoesophageal fistula Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition (arrow, blind proximal esophageal sac)  DEVELOPMENT OF BRONCHI AND LUNGS 1. The respiratory bud (lung bud) that developed at the caudal end of the laryngotracheal diverticulum during the 4th week soon divides into two outpouchings called primary bronchial buds Fig.1 Fig.2 Fig.3 Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Human Embryology, By Inderbir Singh, 11th edition  DEVELOPMENT OF BRONCHI AND LUNGS 2. Later, secondary and tertiary bronchial buds form and grow laterally into the pericardioperitoneal canals 3. Together with the surrounding splanchnic mesoderm, the bronchial buds differentiate into the bronchi and their ramifications in the lungs Fig. A Fig. B Fig. C Illustrations of the growth of the developing lungs into the splanchnic mesoderm adjacent Expansion of the lung buds into the to the medial walls of the pericardioperitoneal canals (primordial pleural cavities) pericardioperitoneal canals Development of the layers of the pleura is also shown A: At 5 weeks; B: At 6 weeks Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Medical Embryology By Langman, 13th Edition  DEVELOPMENT OF BRONCHI AND LUNGS 4. Early in the 5th week, the connection of each bronchial bud with the trachea enlarges to form the primordia of main bronchus 5. The main bronchi subdivide into secondary bronchi that form lobar, segmental and intrasegmental branches Successive stages in the development of the bronchial buds, the bronchi, and the lungs Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF BRONCHI AND LUNGS 6. The segmental bronchi – 10 in the right lung and 8 or 9 in the left lung begin to form in the 7th week 7. Each segmental bronchus, with its surrounding mass of mesenchyme, is the primordium of a bronchopulmonary segment 8. By 24 weeks, approximately 17 orders of branching have occurred, and respiratory bronchioles have developed 9. An additional 7 orders of airways develop after birth Development of the major branching patterns of the lung at week 7 Reference: Human Embryology and Developmental Biology, By Carlson, 3rd Edition  DEVELOPMENT OF BRONCHI AND LUNGS ▪ SOURCES 1. Splanchnic mesenchyme gives rise to: * Bronchial smooth muscle and connective tissue * Cartilaginous plates * Pulmonary connective tissue and capillaries 2. Visceral pleura: Derived from the splanchnic mesoderm ; Parietal pleura: Derived from somatic mesoderm 3. Endoderm gives rise to bronchial epithelium and glands Fig. A Fig. B Fig. C Illustrations of the growth of the developing lungs into the splanchnic mesoderm adjacent to the medial walls of the pericardioperitoneal canals (primordial pleural cavities) Development of the layers of the pleura is also shown A: At 5 weeks; B: At 6 weeks Reference: Medical Embryology By Langman, 13th Edition Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  MATURATION OF LUNGS 1. The lung matures in a proximal–distal direction, with the largest bronchi and proceeding outward 2. As a result, lung development is heterogeneous; proximal pulmonary tissue will be in a more advanced period of development than distal pulmonary tissue A: 5 Weeks B: 6 Weeks C: 8 Weeks Stages in development of the trachea and lungs Reference: Medical Embryology By Langman, 13th Edition  MATURATION OF LUNGS ▪ DIVIDED INTO FOUR STAGES A. PSEUDOGLANDULAR PERIOD B. CANALICULAR PERIOD C. TERMINAL SAC PERIOD D. ALVEOLAR PERIOD Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  STAGES OF LUNG DEVELOPMENT Reference: High-Yield Embryology By Ronald W. Dudek, 2nd Edition