1. Dr. Sama ul Haque

2.   Discuss the formation of the lung buds.  Describe the development of larynx.  Explain the mechanism of formation of trachea, bronchi and lungs.  Differentiate between the periods of lung maturation.  Discuss the congenital anomalies of the respiratory system. 2 Objectives

3. Respiratory System  Upper respiratory tract:  Nose  Nasal cavity & paranasal sinuses  Pharynx  Lower respiratory tract:  Larynx  Trachea  Bronchi  Lungs

4.   In 4 weeks old embryo, the respiratory diverticulum (lung bud) = The laryngeotracheal diverticulum appears as an outgrowth from the ventral wall of the foregut.  Epithelium of the internal lining of the larynx, trachea, and bronchi, as well as that of the lungs, is entirely of endodermal origin. 4 Formation of the Lung Buds

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6.   The cartilaginous, muscular, and connective tissue components of the trachea and lungs are derived from splanchnic mesoderm surrounding the foregut. 6 Formation of the Lung Buds

7.  A longitudinal tracheo-esophageal septum develops and divides the diverticulum into a:  Dorsal portion: primordium of the oropharynx and esophagus  Ventral portion: primordium of larynx, trachea, bronchi and lungs

8.  The proximal part of the respiratory diverticulum remains tubular and forms larynx & trachea.  The distal end of the diverticulum dilates to form lung bud, which divides to give rise to 2 lung buds (primary bronchial buds)

9.   The internal lining of the larynx: glands and epithelium, develops from Endoderm  The cartilages and muscles: From mesenchyme of the 4 th and 6 th Pharyngeal arches.  The opening of the laryngotracheal diverticulum into the primitive foregut becomes the laryngeal orifice.  Proliferating mesenchyme of the two arches transforms into the thyroid, cricoid, and arytenoid cartilages.  Temporary occlusion of the laryngeal lumen occurs due to the proliferation of laryngeal epithelium. 9 Development of the Larynx

10.   Recanalization produces a pair of lateral recesses, the laryngeal ventricles (recesses are bounded by folds of tissue that differentiate into the false and true vocal cords).  Since musculature of the larynx is derived from mesenchyme of the 4 th & 6 th pharyngeal arches, all laryngeal muscles are innervated by branches of the 10 th cranial nerve (vagus nerve).  The superior laryngeal nerve innervates derivatives of the fourth pharyngeal arch, and  the recurrent laryngeal nerve innervates derivatives of the sixth pharyngeal arch. 10 Development of Larynx

11.  11 Pharyngeal arches: Each arch contains a cartilaginous component, a cranial nerve, an artery, and a muscular component. Development of Larynx

12. Development of the Trachea  The endodermal lining of the laryngotracheal tube distal to the larynx differentiates into the epithelium and glands of the trachea and pulmonary epithelium  The cartilages, connective tissue, and muscles of the trachea are derived from the mesoderm.

13.  13 Development of Trachea, Bronchi & Lungs  During its separation from the foregut, the lung bud forms the trachea and two lateral outpocketings, the bronchial buds.  At the beginning of the 5 th week, each of these buds enlarges to form right and left main bronchi.  The right then forms three secondary bronchi, and the left, two.  By the end of the 6 th month, approximately 17 generations of subdivisions have formed. Before the bronchial tree reaches its final shape, however, an additional six divisions form during postnatal life.

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15.  15 Development of Trachea, Bronchi & Lungs

16.   The right main bronchus is slightly larger than the left one and is oriented more vertically  The embryonic relationship persists in the adult.  The main bronchi subdivide into secondary and tertiary (segmental) bronchi which give rise to further branches.

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18.  18 Maturation of the Lungs

19.  19 Maturation of the Lungs

20.   The pleuroperitoneal and pleuropericardial folds separate the pericardioperitoneal canals from the peritoneal and pericardial cavities, respectively, and the remaining spaces form the primitive pleural cavities.  The splanchnic mesoderm, which covers the outside of the lung, develops into the visceral pleura. 20 Development of Pleura

21.  21 Growth of the lung buds into the pericardioperitoneal canals. Note the pleuropericardial folds. Development of Pleura

22.  22 Development of Pleura

23.   The somatic mesoderm layer, covering the body wall from the inside, becomes the parietal pleura.  The space between the parietal and visceral pleura is the pleural cavity. 23 Development of pleura

24.  24 The Visceral and Parietal Pleura

25.   Abnormalities in partitioning of the esophagus and trachea by the tracheoesophageal septum result in esophageal atresia with or without tracheoesophageal fistulas (TEFs). 25 Congenital anomalies of the Respiratory System

26.  26 Congenital anomalies of the Respiratory System

27.   Respiratory distress syndrome (RDS) or (Hyaline membrane disease): When surfactant is insufficient, the air-water (blood) surface membrane tension becomes high, so alveoli will collapse during expiration.  Blind-ending trachea with absence of lungs.  Agenesis of one lung. 27 Congenital anomalies of the Respiratory System

28.   Abnormal divisions of the bronchial tree.  Ectopic lung lobes arising from the trachea or esophagus from additional respiratory buds of the foregut that develop independently of the main respiratory system.  Congenital cysts of the lung, which are formed by dilation of terminal or larger bronchi. 28 Congenital anomalies of the Respiratory System

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