Essential Idea:
The lungs are actively ventilated to ensure
that gas exchange can occur passively
Understandings:
- Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries
- Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles
- Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange
- Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension
- Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them
- Different muscles are required for inspiration and expiration because muscles only do work when they contract
Applications:
- Causes and consequences of lung cancer
- Causes and consequences of emphysema
- External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action
Skill:
- Monitoring of ventilation in humans at rest and after mild and vigorous exercise