RESPIRATION PHYSIOLOGY: VENTILATION -- Physiological Anatomy

A. Rib Cage

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1. the thoracic cavity is bounded by the muscles of ventilation (skeletal or "voluntary" muscle)
2. the mediastinum (heart, great vessels, etc) somewhat isolate the two lungs
3. the intrapleurnal space is a potential space
4. normally, the visceral and parietal pleura can slide easily over each other.

B. Gas Exchange

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1. Airways are divided into those in the Conducting Zone (role: air flow) and the Respiratory Zone (role: gas diffusion and exchange)

C. Airways

1. Role of secretions and cilia: Trap (secretions) and remove (cilia) inspired particulate matter

Because of branching, total cross section area increases as air proceeds down the airways, so linear velocity decreases:

Flow = Area x Velocity

At low velocity, the larger inspired particles tend to deposit on the airway walls, and thus are eventually removed from the airways by ciliary action. (velocity 1-2 mm/min mouthward)

Note: Smallest particles may reach the terminal bronchioles and some may remain in lungs (ingested by macrophages, can lead to fibrosis)

Pathophysiology: In cystic fibrosis, the thick, viscous brochial secretions accumulate in the airways, leading to obstruction and tendency to pulmonary infection

2. Role of smooth muscle: adjust airway diameter and thus control airflow resistance and ventilation distribution (bronchodilation, bronchoconstriction)