Respiratory System Development Lecture Notes PDF

Development of the Respiratory System Dra. Mar Cuadrado-Tejedor [email protected] Introduction Upper respiratory tract: nose, nasal cavity and pharynx Lower respiratory tract: larynx, trachea, bronchi and lungs Upper respiratory tract development Development of upper respiratory tract and developmen...

Development of the Respiratory System Dra. Mar Cuadrado-Tejedor [email protected] Introduction Upper respiratory tract: nose, nasal cavity and pharynx Lower respiratory tract: larynx, trachea, bronchi and lungs Upper respiratory tract development Development of upper respiratory tract and development of larynx (Head & Neck, SOI II) Larynx Pharyngeal arches Lower respiratory tract development Development of lower respiratory tract: 4th week Larsen * Iniatially appears as the “respiratory diverticulum” which is a ventral outgrowth of the ventral foregut Cepahalo-caudal folding Lateral folding Lateral folding Larsen - Parietal mesoderm lines embrionic body cavity - Visceral mesoderm covers endodermal gut tube - Gut tube suspended from body wall by dorsal mesentery (double layer of mesoderm) Lower respiratory tract development Development of lower respiratory tract: 4th week endoderm mesoderm Larsen * Take home message Endoderm Mesoderm epithelium of the internal respiratory system cartilage, connective tissue and smooth muscle of the respiratory system Splitting of foregut into esophagus and trachea - The tracheoesophageal septum gradually separates the ventral respiratory diverticulum from the dorsal part of the foregut. - The pharynx is divided into: a ventral portion, “the respiratory primordium” and a dorsal portion, “the esophagus”. Endoderm Splachnic mesoderm - esophagus tracheoesophageal septum trachea Trachea-esophageal fistulas -Chedesophageal fistula Larsen (eef) a closed Blocked - Incomplete separation and/or atresia of trachea or esophagus - Likely due to a defect of mesoderm. Usually associated with other anormalities of mesoderm development (cardiovascular malformations, VATER, VACTERL) * VATER: Vertebral anomalies, Anal atresia, Tracheaesophageal fistula, Esophagus atresia, Renal atresia * VACTERL: VATER + Cardiac defects & Limbs defects Trachea-esophageal fistulas Moore-Persaud ü 1/3000 births ü Prenatal: polyhydramnios ü Postnatal: regurgitation after feeding Development of the septum transversum and the diaphragm Larsen Development of the septum transversum and the diaphragm ü It grows from front to back ü At week 4 it is at C1 level - caudally ü At week 8 it is at T7 level (front) and T12 (back) ü Innervation C3-C5 (phrenic nerves) week 4 week 7 week 6 week 8 * Extension of the septum transversum partially divides the thoracic and abdominal cavities Development of the diaphragm Larsen Diaphragm: ü Septum transversum ü Pleuroperitoneal membranes ü Muscles from dorso-lateral body wall ü Esophagus mesentery Congenital diaphagmatic hernias ü 1/2000 births ü Failure of pleuroperitoneal membranes to close the pleuroperitoneal cannals. ü Clinical impact: herniated content may interfere with lung developtment. Congenital diaphagmatic hernias Usually on the left side (80-90%): Bochdalek hernia Growth of lungs into the body cavity Lung buds together with the pleuropericardial folds grow into the pericardioperitoneal cannals dividing the thoracic cavity in pleural spaces and the pericardial space. Growth of lungs into the body cavity. Pleural cavities Carlson, 1998 ü Pleuropericardial folds separate pleural and pericardial cavities Pericardioperitoneal canals – pleural cavities Basmajian, 1971 Pericardioperitoneal canals Visceral pleura parietal pleura Trachea Splacnic mesodem somatic mesodem Pleural cavity Moore-Persaud, 1999 Innitial patterning of the lungs Thrachea is divided into two primary bronchi Left primary bronchus is divided into two secondary bronchi (corresponding to the two lobes of the left lung). Right primary bronchus is divided into three secondary bronchi (corresponding to the three lobes of the right lung). Eight terciary (segmental) brochi are formed in the left lung and ten in the right lung. 5 week Carlson, 1998 7 week * Branching regulation: members of the fibroblast growth factor (FGF): FGF2 and FGF10 Stages of maturation of the lungs Pseudoglandular period (5-16 week): Branching has continued to form terminal bronchioles. No respiratory bronchioles or alveoli are present. Canalicular period (16-26 week): each terminal bronchiole divides into 2 or 3 respiratory bronchioles which in turn divide into 3-6 alveolar ducts. Terminal sac period (26 week to birth): terminal sacs (primitive alveoli) form, and capilaries establish close contact. Alveolar period (8 months to childhood): mature alveoli have well developed epithelial endothelial (capillary) contacts. Stages of maturation of the lungs Pseudoglandular stage (6-16 week) Terminal sac (26 week-birth) Canalicular stage (16-26 week) Alveolar stage (32 week-postnatal) Recap Development of respiratory System starts at week 4th Lungs and trachea (from lung bud) Larynx Pharyngeal arches Type II neumocytes: SURFACTANT ü ü ü ü Pseudoglandular stage Canalicular stage Terminal sac stage Alveolar stage