1. The Cardiovascular System Dr. Mona Soliman, MBBS, MSc, PhD Dr. Mona Soliman, MBBS, MSc, PhD Department of Physiology College of Medicine KSU

2. Structure of the Heart

3. The Atria Thin walled Thin walled Receives blood from: Receives blood from: the systemic circulation (right atrium) the systemic circulation (right atrium) the pulmonary circulation (left atrium) the pulmonary circulation (left atrium) Open into the ventricles via the: Open into the ventricles via the: Atrioventricular valves Atrioventricular valves (AV valves) Structure of the Heart

4. The Ventricles Thick muscular walled (why?) Thick muscular walled (why?) Pump blood into: Pump blood into: Pulmonary trunk (right ventricle) Pulmonary trunk (right ventricle) Aorta (left ventricle) Aorta (left ventricle) A fibrous tissue ring separate the atria from the ventricles (importance: electrical activity, AV valve) A fibrous tissue ring separate the atria from the ventricles (importance: electrical activity, AV valve) Structure of the Heart

5. The Valves of the Heart The Atrioventricular Valves 1. The Tricuspid Valve… between the right atrium and the right ventricle, 3 cusps 2. The Mitral Valve (bicuspid valve) … between the left atrium and the left ventricle, 2 cusps

6. Prevent back flow of blood from the ventricles to the atria Prevent back flow of blood from the ventricles to the atria Held by chordae tendineae to papillary muscle Held by chordae tendineae to papillary muscle Contraction of papillary muscle… Contraction of papillary muscle… The Valves of the Heart The Atrioventricular Valves

9. The Valves of the Heart The Semilunar Valves Located at the origin of the pulmonary artery and aorta Located at the origin of the pulmonary artery and aorta Open during ventricular contraction…why? Open during ventricular contraction…why? Close during ventricular relaxation…why? Close during ventricular relaxation…why? 1. The Aortic Valve 2. The Pulmonary Valve

11. Cardiac muscle cell

12. Cardiac Muscle cell

13. Striated Striated Contain actin and myocin filaments arranged in sarcomeres…contract by sliding mechanism Contain actin and myocin filaments arranged in sarcomeres…contract by sliding mechanism Branch and interconnect Branch and interconnect Cardiac Muscle cell

14. Gap junctions Gap junctions Trans-membrane channel proteins, connecting the cytoplasm of the cells Trans-membrane channel proteins, connecting the cytoplasm of the cells Allow spreading of the action potential from one fiber to another Allow spreading of the action potential from one fiber to another Allow cardiac muscle to function as a syncytium “all or none law”: stimulation of a single muscle fiber results in contraction of all the muscle fibers Allow cardiac muscle to function as a syncytium “all or none law”: stimulation of a single muscle fiber results in contraction of all the muscle fibers Intercalated discs Intercalated discs Cardiac Muscle cell

16. Electrical Activity of the Heart

17. Automaticity: capable of originating action potential Automaticity: capable of originating action potential

18. Resting membrane potential in myocardial cells -90 mV Resting membrane potential in myocardial cells -90 mV Stimulation of myocardial cell Myocardial action potential

20. Phases of cardiac AP Ionic changes Rapid depolarization (+20 mV) Na + in Partial repolarization (5-10mV) K + out Action potential plateau (0 mV) Ca 2+ in (slow) Repolarization (back to RMP) K + out Myocardial action potential

21. Conduction of Impulses The sinoatrial node (SA node): Located in the right atrium Pacemaker of the heart Is capable of originating action potentials Highest frequency The atrioventricular (AV) node Located at the junction of the atria and the ventricles Delay in the conduction of impulses…why?

22. Conduction of Impulses The atrioventricular (AV) bundle (Bundle of His) The atrioventricular (AV) bundle (Bundle of His) The right and left bundle branches The right and left bundle branches Purkinje fibers Purkinje fibers Spread within the muscle of the ventricular walls Spread within the muscle of the ventricular walls Highest speed of conduction Highest speed of conduction

23. Contractility Contractility is the ability of cardiac muscle to convert chemical energy into mechanical work Contractility is the ability of cardiac muscle to convert chemical energy into mechanical work

24. Depolarization of myocardial cell Opening of Ca 2+ channels Ca 2+ increase in the cytoplasm Ca 2+ binds to troponin Contraction Contractility

25. Repolarization of myocardial cell Ca 2+ OUT Ca 2+ decrease in the cytoplasm Relaxation Contractility

26. Absolute refractory period Absolute refractory period Cardiac muscle cannot be excited while it is contracting … benefit? Cardiac muscle cannot be excited while it is contracting … benefit? Long ARP Long ARP Time: depolarization & 2/3 of repolarization Time: depolarization & 2/3 of repolarization Relative refractory period Relative refractory period Time: last 1/3 repolarization Time: last 1/3 repolarization Strong stimulus can give rise to contraction Strong stimulus can give rise to contraction