Circulation III. [antikvár]

CHAPTER 49Integrated aspects of cardiovascular regulationB. FOLKOW C. HEYMANS E. NEILDepartment of Physiology, University of Göteborg, SivedenDepartment of Pharmacology and Therapeutics, University of Ghent,Department of Physiology, Middlesex Hospital Medical School, University of London, EnglandCHAPTER CONTENTSHistorical Development Basic ConsiderationsFunctional Differentiation of the Cardiovascular System Principal Characteristics of Cardiovascular Effector Cells Extrinsic Regulatory Mechanisms Prmciples of Reflex and Central Nervous Regulation of the Cardiovascular System Reflex Control Mechanisms Mechanoreceptors Chemoreceptors Higher Center Influences on the Cardiovascular System Cardiovascular Reaction Patterns in Response to Normal DemandsCardiovascular Adjustments in Muscular Work Quantitative considerations Principles of integration Emotional Influences on the Circulation Cardiovascular Adjustments During Digestion Quantitative considerations Principles of integration Cardiovascular Changes in Exposure to Heat and Cold Hot environment Cold environment Cardiovascular Adjustments to Hypoxia Altitude hypoxia The diving reflex Reflex Control of Blood Volume Effects of Body Posture on the CirculationTHE PRIMARY FUNCTION OF THE CIRCULATION is tO furnish an adequate blood flow through the tissuecapillaries allowing thereby a satisfactory exchange of metabolic materials with the tissue cells. The huge surface area of the capillaries, everywhere in close contact with the tissue cells, facilitates this diffusion exchange. In essence, all other parts of the cardiovascular system subserve the regulation of capillary flow, which is made possible by the establishment of a pressure gradient between the end points of the different circuits.The problem of maintaining the tissue blood supply lies essentially in keeping up the output of the cardiac pump. This in turn presupposes an adequate return of blood from the periphery. Blood flows back to the heart from the capillaries via veins which offer little resistance to its passage. Due to the huge venous capacity, however, alterations of venous caliber can profoundly modify the absolute volume of blood actually returned to the heart. The right heart pumps blood through the pulmonary circuit for gaseous exchange with the external environment across the pulmonary capillaries; oxygenated blood is delivered to the left heart for subsequent ejection. The rhythmic contraction of the left heart which expels blood into the aorta allows the development of a mean pressure of some 100 mm Hg in this and other arteries. The central venous pressure measured in the vicinity of the right atrium is only i or 2 ml HjO above atmospheric. Despite extensive variations in circulatory conditions, such as may be seen in heavy exercise,1787