Development_of_the_Respiratory_System_Ford_2023.pptx

Development of the Respiratory System RESP-I, 2023 Bonny Ford, PhD Objectives • Describe the early development of the lower respiratory system and diaphragm. • Describe development of the larynx, trachea, bronchial tree, and alveoli from the lung bud. • Describe the critical steps of respiratory d...

Development of the Respiratory System RESP-I, 2023 Bonny Ford, PhD Objectives • Describe the early development of the lower respiratory system and diaphragm. • Describe development of the larynx, trachea, bronchial tree, and alveoli from the lung bud. • Describe the critical steps of respiratory development which determine the viability of a pre-term fetus. • Discuss the mechanism and general presentation of a tracheoesophageal fistula with esophageal atresia, congenital diaphragmatic hernias, and eventration of the diaphragm. Early Development: Gut Tube Formation • The gut tube develops because of body folding: o inner layer of endoderm and o outer layer of splanchnic lateral plate mesoderm. FIGURE 15.3. Transverse sections through embryos through various stages of development. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Early Development: Lung Bud Formation from the Gut Tube • The lung bud (respiratory diverticulum) forms as a ventral extension of the gut tube. Thus, it will have the same composition as the gut tube: o inner layer of endoderm and o outer layer of splanchnic lateral plate mesoderm. FIGURE 15.1. Transverse sections through embryos through various stages of development. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Early Development: Lung Bud Formation from the Gut Tube FIGURE 14.1. Embryo of approximately 25 days’ gestation. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Splanchnic lateral plate mesoderm Endoderm Connective tissues including cartilages & muscle Epithelium and glands Lung Bud Branching and Formation FIGURE 11.1. Development of the respiratory diverticulum. Schoenwolf, GC et al. Larsen’s Human Embryology, 6th Edition. Elsevier, Inc., 2021. Larynx Formation • The epithelium and glands of the larynx form from the endoderm of the proximal lung bud. • Note: The muscles and cartilages of the larynx arise from structures called pharyngeal arches. You do not need to worry about the pharyngeal arches right now. • After undergoing a process called recanalization, the laryngeal orifice will remain in communication with the pharynx. This represents the only communication between the pharynx and the lower respiratory passages. FIGURE 17.9. Derivative structures formed by the cartilaginous components of the various pharyngeal arches. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Larynx Formation • Larynx is the only part of the lower respiratory passages that maintains patency with the gut. • The rest of the respiratory diverticulum will be separated. FIGURE 14.4. Laryngeal orifice and surrounding swellings at successive stages of development. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. 8 Trachea Formation • Trachea forms from the proximal unbranched part of the lung bud. • The epithelium and glands of the trachea will arise from the endoderm of the lung bud. • Muscles, cartilages, connective tissues will arise from the splanchnic lateral plate mesoderm. FIGURE 10.5. Transverse sections through the laryngotracheal tube illustrating progressive stages in the development of the trachea. Moore, Persaud, and Torchia. The Developing Human, 11th Edition. Elsevier, Inc., 2020. Trachea Formation • The tracheoesophageal septum will separate the tracheal portion of the airways from the esophageal portion of the gut. • Abnormal partitioning here will lead to a tracheoesophageal fistula with esophageal atresia. FIGURE 14.2. Successive stages in the development of the respiratory diverticulum. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. FIGURE 10.2. Successive stages in the development of the tracheoesophageal septum during the fourth and fifth weeks. Moore, Persaud, and Torchia. The Developing Human, 11th Edition. Elsevier, Inc., 2020. Bronchi (and Distal) Formation • Remember: Epithelium and glands will arise from the endoderm of the lung bud; and muscles and connective tissues (including cartilages) will arise from the splanchnic lateral plate mesoderm. • Pleura forms from the somatic and splanchnic layers of the lateral plate mesoderm-lined body cavity. FIGURE 14.5. Stages in development of the trachea and lungs. A. 5 weeks B. 6 weeks C. 8 weeks Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Development of Pleural Membranes FIGURE 14.6 and 14.7. Expansion of the bronchial buds into the pericardioperitoneal canals. Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Note: The pleura are the membranes that surround the lungs. There will be a visceral and parietal layer just like with the serous pericardium surrounding the heart. Lung Maturation: Stages of Lung Formation As a physician, you need to know whether the lungs of a preterm baby are going to be viable or not. So, knowing the major developments in each of these stages is vital. 32 weeks) FIGURE 10.10. Diagrammatic sketches of histologic sections illustrating the stages of lung development. Moore, Persaud, and Torchia. The Developing Human, 11th Edition. Elsevier, Inc., 2020. Formation of the Diaphragm and Partitioning of the Thoracic and Abdominal Cavities The diaphragm will form from 4 sources of tissue (the first two are 2. most important): 1. Septum transversum 2. Pleuroperitoneal folds 3. Muscular ingrowth from body wall 4. Esophageal mesentery 4. 3. 1. FIGURE 7.7. Development of the diaphragm. Sadler TW. Langman’s Medical Embryology, 13th Edition. Wolters Kluwer Health, Inc., 2015. Formation of the Diaphragm and Partitioning of the Thoracic and Abdominal Cavities • The septum transversum forms from somitic mesoderm (C3, C4, C5 somites) in the neck. – It then migrates caudally to ultimately form the bulk of the diaphragm that will separate the thoracic and abdominal cavities. • When the diaphragm first forms, it has two large holes in it posteriorly. These openings are called pericardioperitoneal canals. FIGURE 7.5. Drawing showing the ventral view of an embryo at 24 days of gestation (A). Sadler TW. Langman’s Medical Embryology, 14th Edition. Wolters Kluwer Health, Inc., 2022. Formation of the Diaphragm and Partitioning of the Thoracic and Abdominal Cavities The diaphragm will form from 4 sources of tissue (the first two are 2. most important): 1. Septum transversum 2. Pleuroperitoneal folds 3. Muscular ingrowth from body wall 4. Esophageal mesentery 4. 3. 1. FIGURE 7.7. Development of the diaphragm. Sadler TW. Langman’s Medical Embryology, 13th Edition. Wolters Kluwer Health, Inc., 2015. References 1. Sadler TW. Langman’s Medical Embryology, 15th edition. Wolters Kluwer. 2024. https://meded-lwwhealthlibrary-com.ezproxy.ad.bcomnm.org/content.aspx?sectionid=253320708&bookid=3221 Accessed November 1, 2023 2. Moore KL, Persaud TVN, and Torchia MG. The Developing Human, 11th edition. Elsevier Inc. 2020. https://www-clinicalkey-com.ezproxy.ad.bcomnm.org/#!/browse/book/3-s2.0-C20170011084 Accessed November 1, 2023 3. Schoenwolf GD, Bleyl SB, Brauer PR, and Francis-West PH. Larsen’s Human Embryology, 6th edition. Elsevier Inc. 2021. https://www-clinicalkey-com.ezproxy.ad.bcomnm.org/#!/browse/book/3-s2.0-C20180032296 Accessed November 1, 2023 This lecture PPT is a modification of slides presented by Cindy Funk, PhD in the RESP-I course during Fall 2022.