Lung Development Quiz

Formation of Lung Buds

• Lung buds appear during the 4th week of embryonic development as part of the respiratory diverticulum on the ventral wall of the foregut.
• The esophagotracheal septum divides the respiratory diverticulum into ventral (respiratory primordium) and dorsal (esophagus) portions.

Lung Development Overview

• Lung buds continue to form and develop into the trachea and two bronchi (right and left) by the end of the 5th week.
• The right bronchus branches into 3 secondary bronchi, corresponding to 3 lobes.
• The left bronchus forms 2 secondary bronchi for 2 lobes, ultimately leading to the creation of tertiary bronchi (10 on the right, 8 on the left), defining bronchopulmonary segments.

Stages of Lung Maturation

• Maturation of lungs progresses through four distinct periods:

Pseudoglandular Period

• Occurs between 6 and 16 weeks of gestation.
• Formation of terminal bronchioles but no respiratory bronchioles.

Canalicular Period

• Spans from 16 to 26 weeks.
• Type I and Type II alveolar epithelial cells begin to develop; Type II cells produce surfactant.
• Terminal bronchioles divide into smaller canals, leading to the formation of respiratory bronchioles and alveolar ducts.

Terminal Sac (Primitive Alveoli) Period

• Lasts from 26 weeks until birth.
• Involves the formation of terminal sacs (primitive alveoli) and establishment of close contact between alveolar capillaries for effective gas exchange.

Alveolar Period

• This stage is significant for preparing the lungs for functioning at birth, enhancing the capacity for gas exchange.

Key Cell Types

• Type I pneumocytes: Involved in the alveolar structure.
• Type II pneumocytes: Responsible for surfactant production, crucial for reducing surface tension in the alveoli.

Summary of Lung Development Timeline

• 4th week: Appearance of lung buds.
• 5th week: Development of trachea and bronchi.
• 6-16 weeks: Pseudoglandular period, formation of terminal bronchioles.
• 16-26 weeks: Canalicular period, development of surfactant-producing cells.
• 26 weeks to birth: Formation of primitive alveoli and vascular connections.