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Cardiac Physiology I

Cardiac Physiology I. PHIS 206 Roland Pittman September 22, 2014 Reading: Chap 9, pp 229-243. Circulatory System. Three basic components Heart Serves as pump that establishes the pressure gradient needed for blood to flow to tissues Blood vessels

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Cardiac Physiology I

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  1. Cardiac Physiology I PHIS 206 Roland Pittman September 22, 2014 Reading: Chap 9, pp 229-243

  2. Circulatory System • Three basic components • Heart • Serves as pump that establishes the pressure gradient needed for blood to flow to tissues • Blood vessels • Passageways through which blood is distributed from heart to all parts of body and back to heart • Blood • Transport medium within which materials being transported are dissolved or suspended

  3. Circulatory System • Pulmonary circulation • Closed loop of vessels carrying blood between heart and lungs • Systemic circulation • Circuit of vessels carrying blood between heart and other body systems

  4. Systemic circulation Capillary networks of upper body Systemic arteries (to upper body) Pulmonary circulation Pulmonary circulation Systemic veins Aorta Pulmonary artery Pulmonary artery Pulmonary vein Pulmonary vein Capillary network of right lung Capillary network of left lung Systemic veins Systemic arteries (to lower body) Capillary networks of lower body KEY = O2-rich blood = O2-poor blood Systemic circulation Fig. 9-1, p. 230

  5. Circulatory System • Anatomy of the heart • Hollow, muscular organ about the size of a clenched fist • Positioned between two bony structures – sternum and vertebrae • Position makes it physically possible to manually drive blood from heart when it is not pumping effectively (CPR)

  6. Circulatory System • Heart is a dual pump • Right and left sides of heart function as two separate pumps • Divided into right and left halves and has four chambers • Atria (upper chambers) • Receive blood returning to heart and transfer it to lower chambers • Ventricles (lower chambers) • Pump blood from heart

  7. Circulatory System • Heart • Arteries • Carry blood away from ventricles to tissues • Veins • Vessels that return blood from tissues to the atria • Septum • Continuous muscular partition that prevents mixture of blood from the two sides of heart

  8. To systemic circulation (upper body) Superior vena cava (returns blood from head, upper limbs) Aorta Right and left pulmonary arteries (to lungs) Right pulmonary veins (return blood from right lung) Left pulmonary veins (return blood from left lung) Pulmonary semilunar valve (shown open) Left atrium Aortic semilunar valve (shown open) Right atrium Right atrioventricular valve (shown open) Left atrioventricular valve (shown open) Right ventricle Left ventricle Inferior vena cava (returns blood from trunk, legs) Septum KEY O2-rich blood O2-poor blood To systemic circulation (lower body) (a) Blood flow through the heart Fig. 9-2a, p. 231

  9. Right atrium Right ventricle Pulmonary artery Venae cavae Other systemic organs Systemic circulation Pulmonary circulation Digestive tract Brain Lungs Kidneys Muscles Aorta Pulmonary veins Left ventricle Left atrium (b) Dual pump action of the heart Fig. 9-2b, p. 231

  10. Right ventricular wall Left ventricular wall (c) Thickness of right and left ventricles Fig. 9-2c, p. 231

  11. Circuit of Blood Flow • The venae cavae are veins returning blood to the right atrium. Oxygen has been extracted from this blood. Carbon dioxide has been added to it. This blood is pumped from the right ventricle through the pulmonary artery to the lungs. • The lungs add oxygen to this blood received from the right side of the heart. Carbon dioxide is removed from this blood. This blood flows through pulmonary veins to the left atrium of the heart. This oxygen rich blood is pumped from the left ventricle through the aorta, a large artery.

  12. Heart Valves • Atrioventricular (AV) valves • Right and left AV valves are positioned between atrium and ventricle on right and left sides • Prevent backflow of blood from ventricles into atria during ventricular emptying • Right AV valve • Also called tricuspid valve • Left AV valve • Also called bicuspid valve or mitral valve • Chordae tendinae • Fibrous cords which prevent valves from being everted • Papillary muscles

  13. Heart Valves • Semilunar valves • Aortic and pulmonary valves • Lie at juncture where major arteries leave ventricles • Prevented from everting by anatomic structure and positioning of cusps • No valves between atria and veins • Reasons • Atrial pressures usually are not much higher than venous pressures • Sites where venae cavae enter atria are partially compressed during atrial contraction

  14. When pressure is greater behind the valve, it opens. Valve opened When pressure is greater in front of the valve, it closes. Note that when pressure is greater in front of the valve, it does not open in the opposite direction; that is, it is a one-way valve. Valve closed; does not open in opposite direction Fig. 9-3, p. 232

  15. Aorta Pulmonary artery Superior vena cava Pulmonary valve Pulmonary veins Left atrium Pulmonary veins Left AV valve Right atrium Aortic valve Right AV valve Chordae tendineae Papillary muscle Left ventricle Right ventricle Septum Inferior vena cava (a) Location of the heart valves in a longitudinal section of the heart Fig. 9-4a, p. 233

  16. Right AV valve Left AV valve Aortic or pulmonary valve (b) Heart valves in closed position, viewed from above Stepped Art Fig. 9-4b, p. 233

  17. Right atrium Right AV valve Chordae tendineae Direction of backflow of blood Septum Right ventricle Papillary muscle (c) Prevention of eversion of AV valves Fig. 9-4c, p. 233

  18. Heart Wall • Consists of three distinct layers • Endothelium • Thin inner tissue • Epithelial tissue, lines entire circulatory system • Myocardium • Middle layer, composed of cardiac muscle • Constitutes bulk of heart wall • Epicardium • Thin external layer which covers the heart

  19. Cardiac Muscle Fibers • Interconnected by intercalated discs and form functional syncytia • Within intercalated discs – two kinds of membrane junctions • Desmosomes • Gap junctions

  20. Intercalated discs (a) Cardiac muscle fibers branch and are interconnected by intercalated discs. Fig. 9-5a, p. 234

  21. Plasma membranes of adjacent cardiac muscle fibers Desmosome Action potential Gap junction Intercalated disc (b) Intercalated discs contain two types of membrane junctions: mechanically important desmosomes and electrically important gap junctions. Fig. 9-5b, p. 234

  22. Electrical Activity of Heart • Heart beats via autorhythmicity • Two specialized types of cardiac muscle cells • Contractile cells • 99% of cardiac muscle cells • Do mechanical work of pumping • Normally do not initiate own action potentials • Autorhythmic cells • Do not contract • Specialized for initiating and conducting action potentials responsible for contraction of working cells

  23. Noncontractile Cells Capable of Autorhymicity • Sinoatrial node (SA node) • Specialized region in right atrial wall near opening of superior vena cava (pacemaker of the heart) • Atrioventricular node (AV node) • Small bundle of specialized cardiac cells located at base of right atrium near septum • Bundle of His (atrioventricular bundle) • Cells originate at AV node and enters interventricular septum • Divides to form right and left bundle branches which travel down septum, curve around tip of ventricular chambers, travel back toward atria along outer walls • Purkinje fibers • Small, terminal fibers that extend from bundle of His and spread throughout ventricular myocardium

  24. Interatrial pathway Atrioventricular (AV) node Sinoatrial (SA) node Left atrium Right atrium Internodal pathway Left branch of bundle of His Right ventricle Left ventricle Right branch of bundle of His Purkinje fibers (a) Specialized conduction system of the heart Fig. 9-7a, p. 235

  25. Interatrial pathway AV node SA node Right atrium Left atrium Bundle of His Interatrial pathway Electrically nonconductive fibrous tissue Left ventricle Purkinje fibers Right ventricle (b) Spread of cardiac excitation Fig. 9-7b, p. 235

  26. Electrical Activity of Heart • Cardiac impulse originates at SA node • Action potential spreads throughout right and left atria • Impulse passes from atria into ventricles through AV node (only point of electrical contact between chambers) • Action potential briefly delayed at AV node (ensures atrial contraction precedes ventricular contraction to allow complete ventricular filling) • Impulse travels rapidly down interventricular septum by means of bundle of His • Impulse rapidly disperses throughout myocardium by means of Purkinje fibers • Rest of ventricular cells activated by cell-to-cell spread of impulse through gap junctions

  27. + 30 Ca2+ in slow Plateau phase of action potential PCa2+, L; PK+ (ordinary voltage-gated) 0 Membrane potential (mV) K+ out fast Na+ in fast Threshold potential – 70 – 250 90 Time (msec) Fig. 9-9, p. 239

  28. Electrical Activity of Heart • Atria contract as single unit followed after brief delay by a synchronized ventricular contraction • Action potentials of cardiac contractile cells exhibit prolonged positive phase accompanied by prolonged period of contraction • Ensures adequate ejection time • Plateau primarily due to activation of slow L-type Ca2+ channels

  29. Electrical Activity of Heart • Ca2+ entry through L-type channels in T tubules triggers larger release of Ca2+ from sarcoplasmic reticulum • Ca2+ induced Ca2+ release leads to cross-bridge cycling and contraction

  30. Action potential in cardiac contractile cell mV Time Travels down T tubules Entry of small amount of Ca2+ from ECF through L-type Ca2+ channels Release of large amount of Ca2+ from sarcoplasmic reticulum through Ca2+ -release channels Ca2+- induced Ca2+ release Cytosolic Ca2+ Troponin–tropomyosin complex in thin filaments pulled aside Cross-bridge cycling between thick and thin filaments Thin filaments slide inward between thick filaments Contraction Fig. 9-10, p. 239

  31. Electrical Activity of Heart • Because long refractory period occurs in conjunction with prolonged plateau phase, summation and tetanus of cardiac muscle is impossible • Ensures alternate periods of contraction and relaxation which are essential for pumping blood

  32. Action potential Contractile response 30 0 Relative cardiac muscle fiber tension Membrane potential (mV) Refractory period 70 90 0 100 200 300 Time (msec) Fig. 9-11, p. 240

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