Pleural fluid reduces friction on the lung surface.

The anatomical setup of lungs in thorax is such that any change in the volume of the thoracic cavity will be  reflected in the lung (pulmonary) cavity. Such an arrangement is essential for breathing, as we cannot directly alter the pulmonary volume.

The tracheae, primary, secondary and tertiary bronchi and initial bronchioles are supported by complete cartilaginous rings.

During swallowing, the glottis can be covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx.