The abdominopelvic cavity is inclosed by essentially muscular barriers.
The thoracic diaphragm is attached to the inferior margin of the rib cage and to
the bodies of the lumbar vertebrae behind. It domes upward into the thoracic cavity. As
the diaphragm contracts, it moves downward and produces a piston-like pressure on
As the thoracic diaphragm contracts and lowers, the vertical diameter of the
thoracic cavity increases. This increases the volume of the thoracic cavity. Thus, the
pressure of the air in the lungs decreases. Thus, air moves into the lungs.
The walls of the abdominopelvic cavity are stretched by the added pressure. As
this happens, the walls store potential energy. (para 7-16)
When the thoracic diaphragm relaxes, the potential energy stored in the
stretched muscular walls becomes kinetic energy, and the walls rebound. During forced
breathing, the walls contract for the amount of air to be pushed out.
When the abdominal walls rebound or contract, pressure is transferred to the
underside of the thoracic diaphragm. The relaxed thoracic diaphragm is thus pushed up
into the thoracic cavity. This decreases the vertical diameter and volume of the thoracic
cavity. This results in increased pressure within the lungs, and air is forced out through
The general functions of the supralaryngeal structures are to condition the
inflowing air and to test it. Conditioning includes cleansing, warming, and moistening.
The nares are guarded by stiff nasal hairs, which serve to remove larger particles
The excellent supply of blood to the mucoperiosteal lining of the nasal chambers
furnishes moisture and heat.
The cilia continuously drive fluids on the surface to the rear.
Finer particles carried by the inflowing air are trapped by the mucus. The
conditioning of the inflowing air depends upon direct contact with the mucoperiosteum.
The conchae serve to increase the surface area of the mucoperiosteum in the nasal
The olfactory epithelium contains special hair cells that can detect individual
molecules found in the air. Thus, the sense of smell tests the quality of inflowing air.
The paranasal sinuses are cavities found in the middle layer of various skull