Plan
► Respiration: definition, stages of respiration.
► Mechanisms of lung ventilation:
• basic terms of lung ventilation (pleural cavity, pleural pressure, respiratory muscles, elastic recoil, negative pressure);
• modern concepts of lung ventilation.
► Diffusion processes in lungs and tissues and transport of oxygen and CO2 by blood. Oxyhemoglobin dissociation curve.
► Methods of investigation of respiration.
Respiration: Definition. Stages of Respiration
Respiration in higher animals and humans is understood as a complex of processes that provide delivery of oxygen to the internal environment of the body, utilization of oxygen for oxidation of organic substances with production of CO2, and release of CO2 from the body into the external environment.
Stages of respiration:
► 1st stage. Ventilation of lungs - exchange of gases between alveolar gas and atmospheric air;
► 2nd stage. Exchange of gases between alveoli and blood;
► 3d stage. Transport of oxygen from lungs to tissues, and of CO2 from tissues to lungs;
► 4th stage. Gas exchange between blood and tissues.
► 5th stage. Tissue, or internal, respiration.
The last stage is the subject ofbiochemistry and molecular biology. The first four ones are traditionally studied by physiology and will be examined in this and in the following lecture.
Ventilation of Lungs
Thoracic Cavity and Respiratory Muscles. The thoracic cavity (the chest) is an air-tight cavity limited with the diaphragm from the bottom and with the rib cage from the sides. The diaphragm is a skeletal muscle consisting of radially arranged muscle fibers. Muscle fibers of the diaphragm are fixed with one end to the inner surface of the rib cage and with the other end to the central tendon of the diaphragm. The central tendon of the diaphragm has a hole for passage of the esophagus and of neurovascular fascicles. At relative physiological rest the diaphragm takes a dome-shaped configuration (with the convexity up) formed under influence of the abdominal pressure that exceeds the intrathoracic pressure. When muscles of the diaphragm contract, it flattens and descends, thus expanding the vertical volume of the chest. The bony framework of the chest is formed by the spine, ribs and the sternum. Ribs that form the basic structure of the framework, make two joints with the vertebrae: one with the vertebral body, and the other with its transverse process. In front, the ribs are sufficiently rigidly fixed to the sternum by cartilages. Contraction of external intercostal muscles changes the volume of the chest in the forward and sagittal directions: the ribs and the sternum go upward, and the ribs slightly diverge. The diaphragm and external oblique intercostals provide inspiration at relative physiological rest. Expiration at physiological rest is a passive process resulting from relaxation of these muscles. When activity of an organism increases, metabolic demands in tissues increase, and breathing becomes deeper and more rapid and recruits accessory muscles. Accessory muscles participating in inspiration, include major and minor pectoral muscles, scalenes, sternocleidomastoid muscles and serrate muscles. Accessory muscles participating in forced expiration, include internal oblique intercostal muscles and muscles of the anterior abdominal wall.