Development of Respiratory System PDF

 Development of Respiratory system Pharyngeal arches  6 mesodermal thickening on each side of pharynx  They are arranged cranio-caudally  1st arch: is the most prominent arch reaching the midline & forme...

 Development of Respiratory system Pharyngeal arches  6 mesodermal thickening on each side of pharynx  They are arranged cranio-caudally  1st arch: is the most prominent arch reaching the midline & formed of maxillary and mandibular processes Stomodeum  The oral pit (stomodaeum) appears between the bulging forebrain and the heart.  The floor of the stomodaeum is formed by the buccopharyngeal which ruptures in the 5th week Anatomist “development of respiratory system”  Face / nose development Timing: 4th - 8th week Origin: Fronto-nasal process: a median prominence from head fold 2 maxillary processes: Dorsal part of 1st pharyngeal arch 2 mandibular processes: Ventral part of 1st pharyngeal arch Development Changes at fronto-nasal process: o Nasal placodes: ectodermal thickening on each side of fronto-nasal process appear in 4th week o Each placode becomes invaginated to form a nasal pit with medial & lateral nasal folds appear in 5th weekk.. o Lateral nasal fold form ala of nose o The 2 medial nasal folds with neural crest cells fuse to form "Pre-maxilla / inter-maxillary segment" which gives raise to: 1. Nasal septum 2. Philtrum of upper lip 3. Central part of upper jaw carrying upper 4 incisors 4. Primary palate 5. Tip of nose Anatomist “development of respiratory system” Changes at maxillary processes: Grow medially to fuse with medial nasal folds to form upper lip Grow laterally to fuse with mandibular process to form cheeks Grow superiorly to become separated from lateral nasal folds by nasolacrimal groove that from nasolacrimal duct. Changes at mandibular processes: fuse with: Maxillary process forming the cheek. Each other medially forming lower lip & chin. Face musculature: From mesoderm of 2nd pharyngeal arch supplied by facial nerve So the upper lip is formed of maxillary process except philtrum "formed of inter-maxillary segment So the lower lip is formed of mandibular processes So the nose development:  The ala of nose develops from lateral nasal fold  The nasal cavity: Nasal pits deepen forming the primitive nasal sacs. Each primitive nasal sac deepen and is separated from the oral cavity by oro-nasal membrane which soon ruptures making nasal & oral cavities in contact. With the formation of 2nd palate, the 2 cavities separate again  Nasal conchae are developed as elevations of the lateral nasal walls.  Nasal septum develops from inter-maxillary segment  The epithelium in roof of nasal cavity becomes specialized to form olfactory epithelium.  Paranasal sinuses Maxillary sinus develops during fetal life while others develop after birth. They reach their maximum size during puberty. Anatomist “development of respiratory system” Anomalies Oblique facial cleft: failure of fusion maxillary & lateral nasal fold. The nasolacrimal duct is exposed on the surface Cleft / hare lip o Median cleft lip: due to failure of fusion between  medial nasal folds “central upper cleft lip”  mandibular processes “central lower cleft lip” o Unilateral or bilateral cleft lip: Failure of fusion between medial nasal fold & maxillary process “unilaterally or bilaterally” Macrostomia: large mouth opening due to failure of fusion maxillary & mandibular processes Microstomia: small mouth opening due to exessive fusion maxillary & mandibular processes Anatomist “development respiratory system”  Palate development Development: Primary palate:  It is anterior triangular area carrying the 4 incisors.  It is formed by inter-maxillary segment Secondary palate:  2 shelf-like projections arise from inner side of maxillary processes to fuse in midline with the descending nasal septum from above N.B: Soft palate is formed by the non ossified part posterior to nasal septum Anomalies Cleft palate 1. Clefts of the anterior palate (clefts anterior to the incisive fossa): Failure palatine shelves to fuse with premaxilla. 2. Clefts of the posterior palate (clefts posterior to the incisive fossa): Failure of palatine shelves to fuse with each other and with the nasal septum. 3. Complete cleft palate: Failure of palatine shelves to fuse with each other, with nasal septum and with premaxilla. Anatomist “development of respiratory system”  Development of larynx & trachea & bronchi & lung & pleurae o Tracheo-esophageal septum develop in the upper part of foregut separating it into: esophagus "dorsally" & laryngo-tracheal tube "ventrally o Laryngo-tracheal tube grows caudally giving rise to larynx, trachea & 2 lung buds o Epithelial lining of respiratory system is endoderm in origin except the nose is ectoderm o The epithelia lining proliferates causing obliteration of the tract, followed by recanalization. o Other layers “muscles& connective tissue & cartilages” come from mesoderm  Cartilage of larynx & its skeletal muscles are formed of 4th & 6th pharyngeal arch  Cartilages of trachea & its smooth muscles arise from splanchnic mesoderm o Both lung buds enlarge forming right / left main primary bronchi: Right main bronchus forms 3 secondary bronchi, then 10 tertiary bronchi Left main bronchus forms 2 secondary bronchi, then 8-10 tertiary bronchi o 17 subdivisions continue before birth 6 more subdivisions are added till 8th year after birth Anatomist “development of respiratory system” Development of pleurae: Lung buds expand into pericardio-peritoneal canals causing: o Spalnchinic lateral plate mesoderm form visceral pleura. o Somatic lateral plate mesoderm form parietal pleura. o Space between parietal & visceral pleura is pleural cavity. Stages of lung development: o Pseudo-glandular stage:  Timing: 1-4 month  Only terminal bronchioles are formed” “lung resembles exocrine gland” o Canalicular stage:  Timing: 4-6 month  Terminal bronchioles divide into respiratory bronchioles which divide into alveolar ducts o Sacular stage:  Timing: 6-9 month  Primitive alveoli are formed & capillaries establish close contact  Alveoli have 2 types of cells: Type I pneumocytes which represent the main lining of alveoli. Type II pneumocytes which begin to secrete surfactant at 20th week Sufficient amount of surfactant is produced at 28th weeks. So the baby born at the end of this stage can survive if given a special care. o Alveolar stage:  Timing: up to 8 years  Mature alveoli with good contact with capillary endothelial cells Anatomist “development of respiratory system”  Anomalies of larynx  Laryngeal atresia : failed recanalization  Laryngeal web:due to incomplete canalization  Laryngo-malacia: soft immature cartilage of larynx causing stridor “commonest cause of stridor in infancy” Anomalies of trachea  Tracheal atresia  Tracheo-malacia: soft immature cartilage of trachea causing of stridor.  Tracheo-esophageal fistula:  Abnormal partitioning of cranial part of foregut by trache-oesophageal septum.  Neonates may be born preterm due to poly-hydramnios caused by esophageal atresia  Neonates with chocking after breast feeding due to presence of trachea-esophageal fistula Anomalies of lung  Lung agenesis or hypoplasia  Congenital cysts of lung  Accessory lung lobe: Arising from trachea or esophagus  Respiratory distress syndrome: (Hyaline membrane disease)  Insufficient surfactant specially in premature infants (Affects 1% of neonates)  Collapse of alveoli containing fluid with high protein forming hyaline membrane Anatomist “development of respiratory system”  Development of diaphragm It is mesodermal in origin: 1.Central tendon & sternal origin Arise from septum transversum 2.Costal origin Arises from mesoderm of lateral body walls 3. Median arcuate ligament Arise from mesoderm around aorta 4. Medial & lateral arcuate ligaments Arise from pleuro-peritoneal membranes 5. Crura of the diaphragm Arise from mesentery of oesophagus. 6. Muscular element of diaphragm: Arises from 3rd, 4th & 5th cervical myotomes dragging the phrenic nerve with them. Anatomist “Diaphragm” Congenital anomalies 1. Parasternal (Retrosternal/ Morgagni) hernia: erior part of the mesoderm of the lateral body wall. wy herniates through a small defect between sternal & costal origins 2. Congenital diaphragmatic hernia (postero-lateral defect/ Bochdalek): da pleuroperitoneal membranes. en o It is more common on the left side. o The pleural and peritoneal cavities are continuous with each other allowing abdominal viscera to herniate in thoracic H cavity compressing heart and lungs. 3. Congenital hiatus hernia: R. esophageal orifice or congenital shortening of the esophagus. a and upper part of the stomach are herniated in the thorax. D Anatomist “Diaphragm”