Respiration

Respiration Respiration Is the vital exchange of oxygen and carbon dioxide that occurs in the lungs. The air-blood barrier consists of alveolar type I cells, basal lamina, and capillary endothelial cells. The alveolar type II cells secrete surfactant. Inspiration Occurs when the ribs and sternum (or thoracic cage) are elevated by the following muscles: the diaphragm; external, internal (interchondral part), and innermost intercostal muscles; sternocleidomastoid; levator costarum; serratus anterior; scalenus; pectoralis major and minor; levator costarum; and serratus posterior superior muscles. Involves the following processes: 1. Contraction of the diaphragm Pulls the dome inferiorly into the abdomen, thereby increasing the vertical diameter of the thorax. 2. Enlargement of the pleural cavities and lungs Reduces the intrapulmonary pressure (creates a negative pressure ), thus allowing air to rush into the lungs passively because of atmospheric pressure. 3.Forced inspiration Involves contraction of the intercostal muscles and elevation of the ribs (superolateral movement), with the sternum moving anteriorly like a bucket handle . (When the handle is raised, the convexity moves laterally.) Results in increased transverse and anteroposterior diameters of the thoracic cavity. The abdominal volume is decreased with an increased abdominal pressure. Expiration Involves the following muscles: the muscles of the anterior abdominal wall, internal intercostal (costal part) muscles , and serratus posterior inferior muscles. Involves the following processes: 1. Overall process Involves relaxation of the diaphragm, the internal intercostal muscles (costal part), and other muscles; decrease in thoracic volume; and increase in the intrathoracic pressure. The abdominal pressure is decreased , and the ribs are depressed. 2. Elastic recoil of the lungs Produces a subatmospheric pressure in the pleural cavities. Thus, much of the air is expelled. (Quiet expiration is a passive process caused by the elastic recoil of the lungs, whereas quiet inspiration results from contraction of the diaphragm.) 3. Forced expiration Requires contraction of the anterior abdominal muscles and the internal intercostals (costal part). ◄.....Go back to the Gross Anatomy homepage