Form and Function: The Physiological Implications of the Anatomy of the Respiratory System

Learning Objectives

To define the key anatomic components of the controller.
To delineate the functions, in addition to gas exchange, that the controller must be designed to address.
To identify receptors, located throughout the body, that provide important information to the controller.
To define the key anatomic components of the ventilatory pump.
To describe the interplay between the muscles and the rib cage in the generation of a negative intrathoracic pressure during inspiration.
To delineate the role of accessory muscles of ventilation in assisting the diaphragm during inspiration under conditions of high metabolic demand or abnormal chest wall function.
To describe the role of the pleura in linking the motion of the chest wall and the lungs.
To outline the peripheral nerves that are important in linking the controller and the ventilatory pump.
To define the anatomic components of the gas exchanger.
To describe the functional implications, particularly with regard to dead space and resistance, of the anatomy of the airways.
To describe the functional implications, with particular regard to diffusion of gas, of the anatomic relationship between alveoli and capillaries.
To delineate how the anatomic arrangement of alveoli contributes to their stability and minimizes the probability of alveolar collapse.
To outline how the response of pulmonary arterioles to hypoxia improves gas exchange.

As a general principle, form and function are intimately related in the human body. Nature selects for features that provide the organism with a survival advantage. With this perspective, we may occasionally use teleological reasoning - that is, an analysis that views anatomic development of the respiratory system in the context of its function as we understand it today to hypothesize links between anatomy and physiology. We consider the respiratory system in light of its major roles, not only with respect to gas exchange but also with an eye toward ways that the system supports other activities and assists in the maintenance of homeostasis.

The basic goal of the respiratory system is to transport oxygen from the atmosphere to the alveoli, the distal air sacs in the lung, where it can be picked up by hemoglobin in red blood cells (RBCS) and transported to metabolically active tissue. At the tissue level, oxygen is used within mitochondria to support aerobic metabolism, one byproduct of which is carbon dioxide. Carbon dioxide is then transported out of the body. However, the system must also serve as the "first responder" in the event of metabolic acid-base disorders. In addition, it must support speech, and the muscles of ventilation may, at times, be called upon to assist in other activities performed by the body.