Alveolar Stage

Definition

The alveolar stage is a critical phase in the embryonic development of the respiratory system, where the lungs undergo significant structural and functional changes to prepare for postnatal respiration.

5 Must Know Facts For Your Next Test

1. The alveolar stage typically occurs between 24-40 weeks of gestation, with the majority of alveolar development occurring in the last trimester.
2. During this stage, the number of alveoli increases exponentially, from approximately 20 million at birth to over 300 million in the adult lung.
3. Type I and type II alveolar cells differentiate, with type II cells producing surfactant to facilitate gas exchange.
4. Vascularization of the alveolar walls increases to support the growing number of alveoli and prepare for postnatal respiration.
5. Lung compliance, the ability of the lungs to stretch and expand, also increases during the alveolar stage, improving respiratory function.

Review Questions

• Explain the significance of the alveolar stage in the embryonic development of the respiratory system.
  • The alveolar stage is a crucial phase in the development of the respiratory system, as it is during this time that the lungs undergo significant structural and functional changes to prepare for postnatal respiration. This includes the exponential increase in the number of alveoli, the differentiation of alveolar cells, the production of surfactant, and the increased vascularization of the alveolar walls. These changes are essential for the lungs to be able to effectively facilitate gas exchange after birth.
• Describe the relationship between the alveolar stage and the preceding stages of respiratory system development.
  • The alveolar stage follows the pseudoglandular and canalicular stages of respiratory system development. In the pseudoglandular stage, the bronchial tree and acini are formed, but alveoli have not yet developed. The canalicular stage then sees the formation of the terminal bronchioles and primitive alveoli. The alveolar stage builds upon these earlier stages, with the number of alveoli increasing exponentially and the alveolar cells differentiating to produce surfactant and support gas exchange. Each stage is essential for the proper development and function of the respiratory system.
• Analyze the importance of surfactant production during the alveolar stage and how it contributes to respiratory function.
  • The production of surfactant by type II alveolar cells is a critical event during the alveolar stage of respiratory system development. Surfactant is a complex mixture of lipids and proteins that reduces the surface tension within the alveoli, preventing their collapse during expiration. This increased lung compliance is essential for effective gas exchange, as it allows the alveoli to expand and contract more easily. Without adequate surfactant production, the lungs would be less able to inflate and the infant would experience respiratory distress. Therefore, the alveolar stage's role in facilitating surfactant production is a key factor in preparing the respiratory system for postnatal function.

Related terms

Pseudoglandular Stage: The stage preceding the alveolar stage, where the bronchial tree and acini are formed, but alveoli have not yet developed.

Canalicular Stage:

The stage between the pseudoglandular and alveolar stages, where the terminal bronchioles and primitive alveoli begin to form.

Surfactant:

A complex mixture of lipids and proteins produced by type II alveolar cells that reduces surface tension within the alveoli, preventing their collapse.