Figure 213. The respiratory system.
(b) Warming and moistening inhaled air. The air that is carried to the
lungs is warmed in the nose by the capillaries that lie close to the surface of the mucous
membranes. These membranes also serve to moisten the air and thus help to protect
the alveoli (tiny air sacs) in the lungs.
Paranasal air sinuses
. These cavities are contained in several of the
bones of the face and head. They are lined with mucous membrane, and they open into
the nasal cavity. They are named according to the bone in which they are found. The
sinuses have several functions. They help to warm inspired air before it reaches the
lungs, they act as resonance chambers for the voice, they supply mucus for moisture,
and they lighten the skull.