Respiratory System Development Quiz

Respiratory System Development

• Respiratory system development begins during the fourth week of pregnancy.
• Development is primarily controlled by molecular regulation, specifically an increase in acid secreted by surrounding mesoderm.
• Respiratory diverticulum develops from the ventral wall of the cranial part of the foregut.
• The lining of the respiratory tract is endodermal, except for the nose, which is ectodermal.

Specific Developmental Stages

• Other respiratory system components (smooth muscle, cartilage, connective tissue, and vessels) originate from splanchnic lateral plate mesoderm.
• Neural crest cells are involved in forming the laryngeal cartilages, ganglia, and nerves that supply the respiratory system.
• The cranial part of the foregut develops into two parts:
  • Dorsal part: forms pharynx and esophagus.
  • Ventral part: forms larynx and trachea.
• Initial connection remains between the pharynx and larynx. This later separates further.
• Trachea and esophagus are demarcated by tracheoesophageal folds to form a septum.
• Respiratory diverticulum develops and branches into larynx, trachea, and further into two lung buds.
• The lining epithelium of the respiratory tract proliferates, causing obliteration, followed by recanalization.
• Larynx recanalization shapes true and false vocal folds and the laryngeal ventricle.

Laryngeal Anomalies

• Laryngeal atresia: results from failed recanalization.
• Laryngeal web: incomplete canalization between vocal folds.
• Laryngomalacia: soft, immature cartilage of the larynx collapses inward during inhalation, causing chronic stridor.

Tracheal Anomalies

• Tracheal atresia: incomplete recanalization.
• Tracheal stenosis: narrowing of the trachea due to incomplete recanalization.
• Tracheomalacia: soft tracheal cartilages collapse, especially during increased airflow.
• Tracheo-esophageal fistula (TEF): abnormal partitioning of the cranial foregut by the tracheoesophageal septum. Can lead to polyhydramnios in newborns.
• Neonates with TEF may have choking.
• Some TEF cases are part of VACTERL association - a group of anomalies.

Bronchial Tree Development

• Stems of lung buds form right and left primary bronchi.
• Right bronchi divide into three lobar bronchi; left divides into two.
• Lobar bronchi further branch into 10 segmental bronchi on the right and 8-10 on the left, based on lung lobes.
• 17 generations of subdivisions occur before birth.
• 6 more generations are formed after birth until 10 years of age.
• Fibroblast growth factor (FGF) guides branching development.

Lung Maturation Stages

• Pseudo-glandular stage (5-16 weeks): terminal bronchioles form.
• Canalicular stage (16-26 weeks): respiratory bronchioles and alveolar ducts form.
• Terminal sac stage (26 weeks-birth): primitive alveoli form.
• Alveolar stage (childhood): alveoli increase in number, pneumocyte type I becomes flattened and matures for blood/air barrier function, alveoli develop mature contacts with capillaries, pneumocyte type II develops and secretes surfactant.

Respiratory Distress Syndrome

• Respiratory distress syndrome (RDS), also known as hyaline membrane disease, affects approximately 1% of newborns and can cause up to 20% of neonatal deaths.
• RDS is caused by insufficient surfactant production, especially in premature infants.
• Collapse of alveoli without adequate ventilation, high protein fluid within alveoli.

Other Lung Anomalies

• Lung agenesis or hypoplasia.
• Ectopic lung lobe.
• Supernumerary lobules.
• Congenital cysts of lung.

Pleura Development

• Lung buds develop into primitive pleurae.
• Pericardio-peritoneal canals divide during intraembryonic development to separate pleural cavities from peritoneal and pericardial cavities.
• Splanchnic lateral plate mesoderm forms visceral pleura.
• Somatic lateral plate mesoderm forms parietal pleura.
• A space, the pleural cavity, located between the visceral and parietal pleurae, contains lubricating fluid that reduces friction during breathing.

Test your knowledge on the development of the respiratory system, which starts in the fourth week of pregnancy. This quiz covers key stages and components, including the roles of mesoderm and endoderm in respiratory system formation.