Development of Respiratory System i lung bud & larynx

ANATOMY

1. DEVELOPMENT OF RESPIRATORY SYSTEM Introduction RS has differents parts like nose, nasopharynx & oropharynx ,larynx, trachea, bronchi & lungs). Here we will discuss from larynx to lungs. RS develops from Respiratory diverticulum (LUNG BUD), which appears as an outgrowth from the ventral wall of the primitive foregut, at 4 th week of intrauterine life.

2. primitive foregut

3. IMPORTANT POINTS Respiratory system is ENDODERMAL in origin. RS develops from RESPIRATORY DIVERTICULUM > ( LUNG BUD ) . Lungs develop from Lung bud. RS develops at 4 th week of IUL. Factors responsible for development of RS are 1> Retinoic acid –produced by adjacent mesoderm 2> Transcription factor TBX4 – present in endoderm of GUT TUBE (GIT) LINING EPITHELIUM of LARYNX,TRACHEA ,BRONCHI & LUNG is derived from ENDODERM CARTILAGES,MUSCLES & CONNECTIVE TISSUE OF RS is derived from SPLANCHNIC MESODERM surrounding the foregut.

4. FORMATION OF LUNG BUD/RESPIRATORY DIVERTICULUM/LARYNGOTRACHEAL DIVERTICULUM a midline groove called Laryngotracheal groove The groove deepens to form a longitudinal diverticulum ( Laryngotracheal diverticulum ) / [LD] Which is in open communication with the foregut. Tracheoesophageal ridge develop from side form septum called Tracheoesophageal septum , which separates the distal part of LD from foregut ( esophagus ). But communicates with pharynx through Laryngeal inlet . The separated part of LD grows downwards to enter thorax & form TRACHEA & Rt.& Lt. BRONCHIAL BUD . The cranial most part of LD gives development of LARYNX.

5. .

6. FORMATION OF LUNG BUD / RESPIRATORY DIVERTICULUM / LARYNGOTRACHEAL DIVERTICULUM This diverticulum is 1 st seen as a midline groove called Laryngotracheal groove in the endodermal lining of primitive pharynx just caudal to hypobronchial eminence during 4 th week of IUL. The groove deepens to form a longitudinal diverticulum called Laryngotracheal diverticulum which is in open communication with the foregut. As the LD expand caudally, two longitudinal ridge/fold called Tracheoesophageal ridge develop that grow medially & fuse to form septum called Tracheoesophageal septum , which separates the distal part of LD from foregut ( esophagus ).whereas the cranial part continues to communicate with pharynx. This communication with pharynx forms Laryngeal inlet . The separated part of LD grows downwards to enter thorax & form TRACHEA & Rt.& Lt. BRONCHIAL BUD . The cranial most part of LD gives development of LARYNX. Each bronchial bud invaginates into Pericardioperitoneal canal .This canal forms the pleural cavities .

7. DEVELOPMENT OF LARYNX

8. LARYNX Cartilage & muscle of larynx ,originate from mesenchyme of 4 th &6 th pharyngeal arches Mesenchyme proliferate rapidly & form laryngeal cartilages like- thyroid,cricoid&arytenoid and these cartilages change the shape of laryngeal inlet from slit like to T-shaped . * EPIGLOTTIS develop from caudal part of Hypobronchial eminence. NERVE SUPPLY OF LARYNX-by nerve of 4 th & 6 th Ph.Arches – vagus . 1> superior laryngeal nerve supply derivatives of 4 th ph. Arch 2> Recurrent laryngeal nerve innervates derivative of 6 th ph. Arch. Internal lining of Larynx Originates from Endoderm This lining epithelium proliferates rapidly & temporarily close the lumen of the Larynx. Then vacuolization & recanalization occur As a result a pair of lateral recesses (space) formed, called Laryngeal ventricle . These recesses are bounded by folds of tissue called Vestibular fold & vocal fold , that form false and true vocal cord respectively.

9. APPLIED RELATED TO DEVELOPMENT OF LARYNX 1>Laryngeal atresia & stenosis - d/t failure of recanalization of larynx , leading to obstruction of U RT.it is also called congenital high airway obstruction syndrome. 2>Laryngeal web- an abnormal membranous ,web like tissue is present in the lumen of larynx , near the vocal fold. This also partially obstruct the airway. 3>One or more laryngeal cartilage may be absent . 4> MAY BE DOUBLE LARYNX OR SOME PART OF IT MAY BE DOUBLE 5>LARYNGOPTOSIS - the larynx lies at lower level , it may lies behind the sternum. 6>LARYNCOELE- In this condition the laryngeal saccule (ventricles) is abnormally large & forms swelling in the neck.