KEY POINTS

Defense Mechanisms of the Respiratory System

1. The extensive, delicate gas exchange surface of an animal's lung is protected by a variety of specific and nonspecific defense mechanisms.

2. Particle deposition onto the mucociliary system depends on particle size and occurs by impaction, sedimentation, and diffusion.

3. The respiratory tract is lined by a mucociliary blanket consisting of a ciliated epithelium overlaid with a layer of mucus.

4. Alveolar macrophages scavenge particles deposited on the alveolar surface.

5. Cytokines and Chemokines coordinate the defense mechanisms of the lung.

Pulmonary Fluid Exchange

1. The lung continuously produces lymph as a result of the net fluid movement from the pulmonary microvasculature into the pulmonary interstitium.

2. The small volume of pleural fluid originates by filtration from capillaries in the visceral and parietal pleura.

Metabolic Functions of the Lung

1. The lung removes many hormones and toxins from the blood and inactivates many others.