Respiration

Abstract

The respiratory system is responsible for gas transfer between the tissues and the out side air. Carbon dioxide that is produced by metabolism in the tissues must be moved by the blood to the lungs, where it is lost to the outside air, and oxygen that is supplied to the tissues must be extracted from the outside air by the lungs.

The nose, mouth, pharynx, larynx, trachea, broncheal trees, lung air sacs and res piratory muscles are the structures that make up the respiratory system (Fig. 14.1). The nasal cavities are specialized for warming and moistening inspired air and for fil tering the air to remove large particles. The larynx, or “ voice box,” contains the vocal folds that vibrate as air passes between them to produce sounds. Below the larynx the respiratory system divides into airways and alveoli. The airways consist of a series of branching tubes that become smaller in diameter and shorter in length as they extend deeper into the lung tissue. They terminate after about 23 levels of branches in blind sacs, the alveoli. The terminal bronchioles represent the deepest point of the bronchial tree to which inspired air can penetrate by flowing along a pressure gradient. Beyond the terminal bronchioles, simple diffusion along concentration gradients is primarily responsible for the movement of gases.