Cardiovascular Physiology

Cardiovascular - Cardiovascular Physiology Dr James Rogers Frenchay Hospital Bristol UK Introduction The heart Electrophysiology of the heart

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Cardiovascular Physiology Dr James Rogers, Frenchay Hospital, Bristol, UK. Introduction Systemic circulation The heart Blood flow: Hagen-Poisseuille formula Electrophysiology of the heart Control of systemic circulation Cardiac cycle Control of arterial pressure Coronary circulation Cardiovascular responses to anaesthesia Cardiac output Introduction The cardiovascular system consists of the heart and two vascular systems, the systemic and pulmonary circulations. The heart pumps blood through two vascular systems - the low pressure pulmonary circulation in which gas exchange occurs, and then the systemic circulation, which delivers blood to individual organs, matching supply to metabolic demand. Blood pressure and flow is largely controlled by the autonomic nervous system ( The Autonomic Nervous System , Update in Anaesthesia 1995; 5: 3-6), and is also influenced by surgery and anaesthetic drugs. A good working knowledge of cardiovascular physiology is necessary to practice safe anaesthesia. The heart The heart comprises four chambers, and is divided into a right and left side, each with an atrium and a ventricle. The atria act as reservoirs for venous blood, with a small pumping action to assist ventricular filling. In contrast, the ventricles are the major pumping chambers for delivering blood to the pulmonary (right ventricle) and systemic (left ventricle) circulations. The left ventricle is conical in shape and has to generate greater pressures than the right ventricle, and so has a much thicker and more muscular wall. Four valves ensure that blood flows only one way, from atria to ventricle (tricuspid and mitral valves), and then to the arterial circulations (pulmonary and aortic valves). The myocardium consists of muscle cells which can contract
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spontaneously, also pacemaker and conducting cells, which have a specialised function. Electrophysiology of the heart Myocardial contraction results from a change in voltage across the cell membrane (depolarisation), which leads to an action potential. Although contraction may happen spontaneously, it is normally in response to an electrical impulse. This impulse starts in the sinoatrial (SA) node, a collection of pacemaker cells located at the junction of the right atrium and superior vena cava. These specialised cells depolarise spontaneously, and cause a wave of contraction to pass across the atria. Following atrial contraction, the impulse is delayed at the atrioventricular (AV) node, located in the septal wall of the right atrium. From here His-Purkinje fibres allow rapid conduction of the electrical impulse via right and left branches, causing almost simultaneous depolarisation of both ventricles, approximately 0.2 seconds after the initial impulse has arisen in the sinoatrial node. Depolarisation of the myocardial cell membrane causes a large increase in the concentration of calcium within the cell, which in turn causes contraction by a temporary binding between two proteins, actin and myosin. The cardiac action potential is
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This note was uploaded on 10/03/2010 for the course BIO 2402 taught by Professor Lipsync during the Spring '10 term at Aberystwyth University.

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Cardiovascular - Cardiovascular Physiology Dr James Rogers Frenchay Hospital Bristol UK Introduction The heart Electrophysiology of the heart

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