ABSTRACT
Respiratory organs provide the first interface between molecular oxygen in the ambient environment and the aerobic machinery of the body. Their design and construction (i.e., the assembly and size of their constitutive parts) influence the effectiveness of their transfer of oxygen and, consequently, of the generation of energy through oxidative phosphorylation. Therefore, the oxidative capacity of an animal is greatly affected by the efficiency of its respiratory organs/structures. Body size, habitat occupied, respiratory medium utilized, phylogenetic status reached, and lifestyles pursued determine the
MD: MASSARO, JOB: 03313, PAGE:
MD: MASSARO, JOB: 03313, PAGE:
structure and function of the respiratory organs. Because the physics of the respiratory gases is determined by the immutable laws that govern their behavior, the basic principles of gas exchange should fundamentally be the same in all animals irrespective of their various phylogenetic levels of development. At the gas exchange level, lungs have certain common structural attributes. These include vast surface area, large capillary blood volume, and thin partitioning between air and blood. These features confer a high diffusing capacity for the respiratory gases. An extensive respiratory surface area is produced through internal subdivision and branching of the airways; a large pulmonary capillary blood volume by intense vascularization of the surfaces of the terminal gas exchange units; and a thin tissue barrier by remodeling of tissue and cellular components over the blood-gas barrier (2,3).
