KEY POINTS

Respiratory Function

1. The respiratory system's primary function is the transport of oxygen and carbon dioxide between the environment and the tissues.

Ventilation

1. Ventilation is the movement of gas into and out of the lung.

2. Ventilation requires muscular energy.

3. The respiratory muscles generate work to stretch the lung and overcome the frictional resistance to airflow.

4. Lung elasticity results from tissue and surface tension forces.

5. The lung is mechanically connected to the thoracic cage by the pleural liquid.

6. Airflow is opposed by frictional resistance in the airways.

7. Smooth muscle contraction affects the diameters of the trachea, bronchi, and bronchioles.

8. Dynamic compression can narrow the airways and limit airflow.

9. The distribution of air depends on the local mechanical properties of the lung.

10. In some species, air travels between adjacent regions of lung through collateral pathways.