Embriología del pulmón
Embryology of the Lung
Introduction to Lung Embryology
- Estela Roma introduces the topic of lung embryology, emphasizing the significance of neural plate and groove formation during the third week of development.
- The cardiovascular system emerges as a crucial component, with the heart acting as a pump to circulate nutrients necessary for lung development.
Early Development Stages
- By mid-fourth week (days 22-26), an embryo takes on a cylindrical shape, revealing structures such as the cardiac loop and primitive intestine.
- The primitive intestine connects to the yolk sac via the vitelline duct, while extraembryonic structures include both this duct and yolk sac.
Formation of Laryngeal and Tracheal Structures
- A diverticulum known as the laryngotracheal bud forms from the ventral side of the primitive intestine, which will give rise to both larynx and trachea.
- The lung develops from interactions between three germ layers: endoderm (epithelial lining), mesoderm (connective tissues), and ectoderm (nervous tissue).
Structural Development in Embryogenesis
- The laryngotracheal bud undergoes dichotomous branching accompanied by lateral mesoderm layers that contribute to pleural space formation.
- This intraembryonic coelom allows for further division and development of pulmonary structures.
Stages of Pulmonary Development
Pseudoglandular Stage
- The pseudoglandular stage occurs from weeks 5 to 16 post-fertilization, characterized by centrifugal growth patterns leading to airway formation.
Canalicular Stage
- From weeks 16 to 26, bronchioles develop into respiratory bronchioles and alveolar ducts; initial alveoli appear alongside vascular remodeling.
Saccular Stage
- Between weeks 26 until birth, alveolar structures increase in number with surfactant production beginning; connective tissue decreases during this phase.
Alveolar Stage
Development of the Pulmonary System
Stages of Pulmonary Development
- The alveolar stage marks the final phase of lung development, extending until approximately 8 years of age. This stage is characterized by an increase in the number of alveoli and improved efficiency of the alveolar-capillary barrier.
- During this stage, type I pneumocytes become flattened, facilitating gas exchange. There is a significant reduction in extra-alveolar connective tissue, while capillaries not only increase in number but also align closely along the alveolar walls.
Embryonic Development Process
- Lung development originates from the distal portion of the laryngotracheal bud, which undergoes dichotomous branching. This process involves a centrifugal growth pattern for pulmonary structures.
- For proper lung formation and division of the laryngotracheal bud, adequate space within the thoracic cavity is essential. This space is represented by the pleural coelom formed between two layers of lateral mesoderm.
- The parietal layer forms from one mesodermal layer to create part of the pleura, while another layer gives rise to visceral pleura and connective tissues (muscular, cartilaginous, lymphatic) associated with lungs.
Role of Germ Layers in Lung Formation
- The involvement of all three embryonic germ layers—endoderm, mesoderm, and ectoderm—is crucial for lung development. Epithelial-mesenchymal interactions are vital; endoderm contributes to epithelial and glandular linings while mesoderm forms connective tissues.
Key Phases in Lung Structure Development
- In pseudoglandular stages (weeks 5 or 6 to week 16), conducting airways develop. Later canalicular and saccular stages lead to gas exchange pathways forming alongside alveoli emergence.