Phases of Respiration in Animals

The procedures of respiration in these animals have the following phases.

i) External respiration is usually described as breathing. It involves organs which bring oxygen from the environment to the respiratory surface of the body. The system as well serves the aim of removing carbon dioxide from the body to the environment. The respiratory surface may frequently be within the body of the animal. The respiratory surface may be integument, gills, tracheae or lungs.

ii) The second phase of respiration has the transportation of oxygen from respiratory surface to the body tissues and carbon dioxide from the tissues to the respiratory surface. In higher animals the transportation of respiratory gases is frequently performed through blood.

iii) Throughout this phase oxygen is consumed by the cells and carbon dioxide is produced by them as a result of oxidative processes that liberate energy for physiological activities of the body. It is the sum of enzymatic reactions, oxidative and non- oxidative processes, through which energy is made available to maintain the vital activities. This phase is internal respiration or tissue respiration.