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Transcript
The cardiovascular system The heart Gunnar Tobin Department of Pharmacology The Sahlgrenska Academy at the University of Gothenburg, Sweden Heart Physiological differences between cardiac muscle, skeletal muscle and smooth muscle cells. Cardiac function and capacity. The electrophysiology of the cardiac muscle cell and its connection to the ECG recording. The function of the conductive system. The afferent and efferent innervation of the heart and effects at stimulat ion. The cardiac cycle: Different phases, diastole, systole. Pressure and volume in the cardiac atria and ventricles. Normal sounds of the pumping heart and their relation to the ECG. Two principle mechanisms in the regulation of contraction force. Pre- and afterload. The metabolism of the heart. Basic knowledge of the ECG The student should be able to understand: - How the heart functions as a pump. - Pathophysiological mechanisms at ischemic heart diseases and cardiac failure. HEART (PUMP) REGULATION CARDIOVASCULAR SYSTEM VESSELS (DISTRIBUTION SYSTEM) AUTOREGULATION NEURAL HORMONAL RENAL-BODY FLUID CONTROL SYSTEM ARTERIES HEART DIASTOLE VEINS CAPACITY VESSELS 80 mmHg 120 mmHg SYSTOLE CAPILLARIES Work output External Kinetic Functions of the Heart Generating blood pressure Routing blood – Heart separates pulmonary and systemic circulations Ensuring one-way blood flow – Heart valves ensure one-way flow Regulating blood supply – Changes in contraction rate and force match blood delivery to changing metabolic needs Heart Wall Three layers of tissue – Epicardium: This serous membrane of smooth outer surface of heart – Myocardium: Middle layer composed of cardiac muscle cell and responsibility for heart contracting – Endocardium: Smooth inner surface of heart chambers Cardiac muscle •fibers arranged in a latticework •is striated •each cell has one nucleus •has typical myofibrils that contain actin and myosin filaments •functions as a Syncytium; intercalated discs and gap junctions •autorhythmic cells and action potentials of longer duration and longer refractory period CARDIAC MUSCLE - Functional Syncytium - Automaticity STRIATED MUSCLE SKELETAL MUSCLE - Motor Units - Stimulated by Motor Nerves Unlike skeletal muscles, cardiac muscles have to contract in more than one direction. Cardiac muscle cells are striated, meaning they will only contract along their long axis. In order to get contraction in two axis, the fibres wrap around. The function of valves Cardiac cycle LATE DIASTOLE DIASTOLE ISOMETRIC VENTRICULAR RELAXATION ATRIAL SYSTOLE VENTRICULAR ISOMETRIC VENTRICULAR EJECTION CONTRACTION Fick’s principle Right heart: 160 ml/l Left heart: 200 ml/l Thus, one liter of blood has to pass for 40 ml O2 to be absorbed 200 ml of O2 is absorbed every min (spirometry) FICK’S PRINCIPLE CO= VO2/([O2]a - [O2]v) = 5L/min Cardiac output=Oxygen absorbed per min/arteriovenous O2 difference (ml/l) CO= HR x SV CO SV = HR = 5 L/min = 0.0714 L or 71.4 ml 70 beats/min Regulation of the Heart Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation – Frank-Starling’s law of the heart Extrinsic regulation: Involves neural and hormonal control – Parasympathetic stimulation • Supplied by vagus nerve, decreases heart rate, acetylcholine secreted – Sympathetic stimulation • Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released Autoregulation (Frank-Starling “Law of the Heart”) CARDIAC OUTPUT = STROKE VOLUME x HEART RATE Contractility Sympathetic Nervous System Parasympathetic Nervous System Autonomic innervation Reflexes in heart regulation Medulla Blood pressure Afferents: Bainbridge reflex T-tubule SARCOLEMMA 20% 80% Mitochondria 10% Ca++ SR THICK MYOFILAMENT THIN MYOFILAMENT Effects of the autonomic nervous systems CARDIAC MUSCLE TENSION TOTAL TENSION ACTIVE TENSION PASSIVE TENSION MUSCLE LENGTH HEART SYSTOLIC PRESSURE CURVE Isotonic (Ejection) Phase PRESSURE After-load Isovolumetric Phase Stroke Volume Pre-load End Systolic Volume DIASTOLIC PRESSURE CURVE End Diastolic Volume HEART SYSTOLIC PRESSURE CURVE Isotonic (Ejection) Phase PRESSURE After-load Isovolumetric Phase Stroke Volume Pre-load End Systolic Volume DIASTOLIC PRESSURE CURVE End Diastolic Volume HEART SYSTOLIC PRESSURE CURVE Isotonic (Ejection) Phase PRESSURE After-load Isovolumetric Phase Stroke Volume Pre-load End Systolic Volume DIASTOLIC PRESSURE CURVE End Diastolic Volume HEART SYSTOLIC PRESSURE CURVE Isotonic (Ejection) Phase PRESSURE After-load Isovolumetric Phase Stroke Volume Pre-load End Systolic Volume DIASTOLIC PRESSURE CURVE End Diastolic Volume CARDIAC FUNCTION CURVE STROKE VOLUME Cardiac Output = Stroke Volume x Heart Rate If: Constant Then: CO reflects SV DIASTOLIC FILLING Right Atrial Pressure (RAP) reflects Diastolic Filling CARDIAC FUNCTION CURVE 15- 10- Pressure CARDIAC OUTPUT (L/min) THE FRANK- STARLING “LAW OF THE HEART” 5- Volume -4 0 +4 RAP mmHg +8 CARDIAC FUNCTION CURVE CARDIAC OUTPUT (L/min) THE FRANK- STARLING “LAW OF THE HEART” 15- 10- 5- -4 0 +4 RAP mmHg +8