![]() ![]() Because smaller species have a greater surface area to body weight ratio, they have a greater surface for heat loss and less heat storage capacity so they need higher basal metabolism to generate more heat. This difference is largely due to the metabolic requirements necessary to maintain constant body temperature. For example, the 20-gram mouse consumes six times more oxygen per unit body mass than does a 70-kg pig. The consequence of this relationship is that smaller species consume more oxygen per kilogram of body weight than do larger species. ![]() Basal metabolism, the metabolism of the resting animal, is a function of metabolic body weight (M 0.75). Oxygen consumption and carbon dioxide production vary with the metabolic rate, which is dependent on the animal’s level of activity. The respiratory system provides oxygen (O 2) to support tissue metabolism and removes carbon dioxide (CO 2). ![]() The oropharynx is a passageway for both air and food.The Respiratory System’s Primary Function Is the Transport of Oxygen and Carbon Dioxide Between the Environment and the Tissues This connection is why colds often lead to ear infections. In addition, auditory (Eustachian) tubes that connect to each middle ear cavity open into the nasopharynx. Both the uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity. The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate. The pharyngeal tonsils are large in children, but interestingly, tend to regress with age and may even disappear. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. A pharyngeal tonsil, also called an adenoid, is an aggregate of lymphoid reticular tissue similar to a lymph node that lies at the superior portion of the nasopharynx. At the top of the nasopharynx are the pharyngeal tonsils. The nasopharynx is flanked by the conchae of the nasal cavity, and it serves only as an airway. The pharynx is divided into three regions: the nasopharynx, the oropharynx, and the laryngopharynx. ![]()
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