The Cardiovascular System

1. November 2012 The Cardiovascular System Dr. Mona Soliman, MBBS, MSc, PhD Department of Physiology College of Medicine KSU

2. Structure of the Heart

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

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

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

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

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

11. Cardiac muscle cell

12. Cardiac Muscle cell

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

14. Cardiac Muscle cell • Gap junctions • Trans-membrane channel proteins, connecting the cytoplasm of the cells • 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 • Intercalated discs

15. Cardiac Muscle cell

16. Electrical Activity of the Heart

17. Electrical Activity of the Heart • Automaticity: capable of originating action potential

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

19. Myocardial action potential

20. 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 right and left bundle branches • Purkinje fibers • Spread within the muscle of the ventricular walls • Highest speed of conduction

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

24. Contractility Depolarization of myocardial cell Opening of Ca2+ channels Ca2+ increase in the cytoplasm Ca2+ binds to troponin Contraction

25. Contractility Repolarization of myocardial cell Ca2+ OUT Ca2+ decrease in the cytoplasm Relaxation

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

27. The Cardiac Cycle

28. The Cardiac Cycle • The repeating pattern of contraction (systole) and relaxation (diastole) of the heart • Duration of cardiac cycle = 0.8 seconds • Diastole longer than systole • Ventricular contraction follows atrial contraction (0.1 to 0.2 second later)…why?

29. The Cardiac Cycle • The end diastolic volume: the total volume of blood in the ventricles at the end of diastole (120 ml) • Stroke volume is the volume of blood pumped by each ventricle per beat (70 ml) • Residual volume: amount of blood left in each ventricle at the end of systole (50 ml)

30. The Cardiac CycleIsovolumetric ventricular contraction • Ventricles contract • Ventricular pressure: increasing • Ventricular volume: no change • AV valves: closed.. prevent backflow of blood • Semilunar valves: closed (P in ventricles < P in vessels) • Heart sounds: 1st heart sound • ECG: QRS complex

32. The Cardiac CycleEjection phase • Ventricular pressure: increasing > the pressure in the aortic and pulmonary vessels • Left ventricular pressure up to 120 mmHg • Right ventricular pressure up to 25 mmHg • Ventricular volume: decreasing • Semilunar valves: open • AV valves: closed.. prevent backflow of blood

34. The Cardiac CycleIsovolumetric relaxation • Ventricles relax • Ventricular pressure: decreasing • Ventricular volume: no change • AV valves: closed • Semilunar valves: closed • Heart sounds: 2nd heart sound • ECG: T wave

36. The Cardiac CycleRapid filling of the ventricles • Ventricular pressure: below atrial pressure ( slightly above zero) • Ventricular volume: increasing • AV valves: open when pressure in the atria> the pressure in the ventricles • Semilunar valves: closed • Passive ventricular filling via AV valves (80%)

38. The Cardiac CycleAtrial systole • Active filling of the ventricles (20%) • Ventricular volume: slight rise • Ventricular pressure: slight rise • Semilunar valves: closed • AV valves: open • ECG: P wave

40. The Cardiac Cycle • Isovolumetric contraction • Ejection phase • Isovolumetric relaxation • Rapid filling of the ventricles • Atrial systole

41. Heart Sounds • The first heart sound: • Cause: closure of the AV valves • The second heart sound: • Cause: closure of the semilunar valves

42. Cardiac Output

43. Cardiac Output • Cardiac output is the volume of blood pumped by each ventricle per minute • CO = Stroke volume x Heart rate (L/min) (ml/beat) (beat/min) = 70 X 70 = 4900 ml/min = 5 L/min • Normal cardiac output (CO) = 5 L/min

44. Cardiac Output

45. Cardiac OutputRegulation of Heart Rate • Sympathetic stimulation •  HR (positive chronotropic effect) •  CO • Parasympathetic stimulation •  HR •  CO • Cardiac centers in the medulla oblangata

46. Cardiac OutputRegulation of Stroke Volume End Diastolic Volume (EDV) • Frank- Starling Law of the Heart  venous return   EDV   length of cardiac muscle (stretch)  force of contraction  stroke volume   cardiac output

47. Cardiac OutputRegulation of Stroke Volume • Positive ionotropic effect  strength of contraction • Sympathetic stimulation • Adrenaline • Negative ionotropic effect   strength of contraction • Parasympathetic stimulation • Acetylcholine • Vagal stimulation

49. Blood Pressure

50. Blood pressure • The blood pressure is the pressure the blood exerts against the inner walls of the blood vessels • Arterial blood pressure (BP) = cardiac output (CO) x peripheral resistance Heart Stroke Rate volume Vasoconstriction • Normal BP = 120/80 mmHg