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The Heart

The Heart. Heart Anatomy. Approximately the size of your fist Location Superior surface of diaphragm Left of the midline Anterior to the vertebral column, posterior to the sternum. Heart Anatomy. Coverings of the Heart: Anatomy.

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The Heart

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  1. The Heart

  2. Heart Anatomy • Approximately the size of your fist • Location • Superior surface of diaphragm • Left of the midline • Anterior to the vertebral column, posterior to the sternum

  3. Heart Anatomy

  4. Coverings of the Heart: Anatomy • Pericardium – a double-walled sac around the heart composed of: • A superficial fibrous pericardium • A deep two-layer serous pericardium • The parietal layer lines the internal surface of the fibrous pericardium • The visceral layer or epicardium lines the surface of the heart • They are separated by the fluid-filled pericardial cavity

  5. Coverings of the Heart: Physiology • The pericardium: • Protects and anchors the heart • Prevents overfilling of the heart with blood • Allows for the heart to work in a relatively friction-free environment

  6. Pericardial Layers of the Heart

  7. Heart Wall • Epicardium – visceral layer of the serous pericardium • Myocardium – cardiac muscle layer forming the bulk of the heart • Fibrous skeleton of the heart – crisscrossing, interlacing layer of connective tissue • Endocardium – endothelial layer of the inner myocardial surface

  8. Cardiac Muscle Bundles

  9. External Heart: Major Vessels of the Heart (Anterior View) • Vessels returning blood to the heart include: • Superior and inferior vena cava • Right and left pulmonary veins • Vessels conveying blood away from the heart: • Pulmonary trunk, which splits into right and left pulmonary arteries • Ascending aorta (three branches) – brachiocephalic, left common carotid, and subclavian arteries

  10. Left common carotid artery Brachiocephalic trunk Left subclavian artery Superior vena cava Aortic arch Right pulmonary artery Ligamentum arteriosum Left pulmonary artery Ascending aorta Left pulmonary veins Pulmonary trunk Left atrium Right pulmonary veins Auricle Right atrium Circumflex artery Right coronary artery (in coronary sulcus) Left coronary artery (in coronary sulcus) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Marginal artery Anterior interventricular artery (in anterior interventricular sulcus) Small cardiac vein Inferior vena cava (b) Apex

  11. External Heart: Arteries that Supply the Heart • Coronary circulation is the functional blood supply to the heart muscle itself • Collateral routes ensure blood delivery to heart even if major vessels are occluded

  12. External Heart: Arteries that Supply the Heart • Right coronary artery (in atrioventricular groove) • Supplies • Right atrium • Portions of both ventricles • SA and AV nodes • Branches • Marginal artery • Posterior interventricular artery

  13. External Heart: Arteries that Supply the Heart • Left coronary artery • Supply • Left atrium • Portions of both ventricles • Branches • Circumflex • Anterior interventricular

  14. Arterial Coronary Circulation

  15. External Heart: Veins that Drain the Heart • Veins that empty in the coronary sinus • Great cardiac vein • Posterior cardiac vein • Middle cardiac vein • Small cardiac vein • Vein that empty into the right atrium • Anterior cardiac vein

  16. Venous Coronary Circulation

  17. External Heart: Major Vessels of the Heart (Posterior View) • Vessels returning blood to the heart include: • Right and left pulmonary veins • Superior and inferior vena cava • Vessels conveying blood away from the heart include: • Aorta • Right and left pulmonary arteries

  18. Aorta Superior vena cava Left pulmonary artery Right pulmonary artery Left pulmonary veins Right pulmonary veins Auricle of left atrium Right atrium Left atrium Inferior vena cava Great cardiac vein Right coronary artery (in coronary sulcus) Posterior vein of left ventricle Coronary sinus Posterior interventricular artery (in posterior interventricular sulcus) Left ventricle Middle cardiac vein Apex Right ventricle (d)

  19. Aorta Superior vena cava Left pulmonary artery Right pulmonary artery Left atrium Pulmonary trunk Left pulmonary veins Right atrium Right pulmonary veins Mitral (bicuspid) valve Fossa ovalis Aortic valve Pectinate muscles Pulmonary valve Left ventricle Tricuspid valve Papillary muscle Right ventricle Chordae tendineae Interventricular septum Myocardium Trabeculae carneae Visceral pericardium Inferior vena cava Endocardium (e)

  20. Atria of the Heart • Atria are the receiving chambers of the heart • Each atrium has a protruding auricle • Pectinate muscles mark atrial walls • In the left atrium only in the wall of the auricle • Blood enters right atria from superior and inferior venae cavae and coronary sinus • Blood enters left atria from pulmonary veins

  21. Ventricles of the Heart • Ventricles are the discharging chambers of the heart • Papillary muscles and trabeculae carneae muscles mark ventricular walls • Right ventricle pumps blood into the pulmonary trunk • Left ventricle pumps blood into the aorta

  22. Right and Left Ventricles

  23. Pathway of Blood Through the Heart and Lungs • Right atrium  tricuspid valve  right ventricle • Right ventricle  pulmonary semilunar valve  pulmonary arteries  lungs • Lungs  pulmonary veins  left atrium • Left atrium  bicuspid valve  left ventricle • Left ventricle  aortic semilunar valve  aorta • Aorta  systemic circulation

  24. Heart Valves • Heart valves ensure unidirectional blood flow through the heart • Atrioventricular (AV) valves lie between the atria and the ventricles • AV valves prevent backflow into the atria when ventricles contract • Chordae tendineae anchor AV valves to papillary muscles

  25. Heart Valves • Aortic semilunar valve lies between the left ventricle and the aorta • Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk • Semilunar valves prevent backflow of blood into the ventricles

  26. Heart Valves

  27. Heart Valves

  28. Atrioventricular Valve Function

  29. Semilunar Valve Function

  30. Microscopic Anatomy of Heart Muscle • Cardiac muscle is striated, short, fat, branched, and interconnected • The connective tissue endomysium acts as both tendon and insertion • Intercalated discs anchor cardiac cells together and allow free passage of ions • Heart muscle behaves as a functional syncytium

  31. Microscopic Anatomy of Heart Muscle • Heart is resistant to fatigue • Many mitochondria • Z discs, I band, A band, • Fewer and wider T tubules • Simpler sarcoplasmic reticulum • No triads

  32. Microscopic Anatomy of Cardiac Muscle

  33. Cardiac Muscle Contraction • Heart muscle: • Is stimulated by nerves and is self-excitable (automaticity) • Contracts as a unit or does not contract at all • Has a long absolute refractory period that prevents tetany • Cardiac muscle contraction is similar to skeletal muscle contraction

  34. Heart Physiology: Intrinsic Conduction System • Autorhythmic cells: • Initiate action potentials • Have unstable resting potentials called pacemaker potentials • Use calcium influx (rather than sodium) for rising phase of the action potential

  35. The intrinsic conducting system • Hyperpolarization leads to: • Loss of K • Opening of Na channels • Membrane becomes less and less negative • Threshold is reached • Ca channels opens • Influx of Ca causes the rising phase of the action potential

  36. Pacemaker and Action Potentials

  37. Mechanisms of contraction 1) Rapid depolarization • Threshold • Opening of the voltage-regulated Na channels • Fast channels • Massive influx of Na

  38. Mechanisms of contraction 2) Plateau • Transmembrane potential approaches +30mV • Na channels close and remain inactivated • Na is actively pumped out of the cell • Voltage-regulated Ca channels opens (slow channels) • Ca enters the cytoplasma • It stimulates more Ca release from the SR

  39. Mechanisms of contraction • This influx of Ca balances out the efflux of Na • Transmembrane potential is kept near 0mV • plateau

  40. Mechanisms of contraction 3) Repolarization • Slow Ca channels start to close • Ca is reabsorbed by the SR or pumped out of the cell • Slow K channels begin to open • Efflux of K causes the repolarization

  41. Mechanisms of contraction

  42. Heart Physiology: Sequence of Excitation • Sinoatrial (SA) node generates impulses about 75 times/minute • Atrioventricular (AV) node delays the impulse • It generates impulses about 40-60 times/min • Smaller diameter of the fibers • Fewer gap junctions • Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His) • Bundle of His is the only electrical connection between atria and ventricle

  43. Heart Physiology: Sequence of Excitation • AV bundle splits into two pathways in the interventricular septum (bundle branches) • Bundle branches carry the impulse toward the apex of the heart • Purkinje fibers carry the impulse to the heart apex and ventricular walls • Depolarize spontaneously at the rate of 20-40 beats/min • They supply the papillary muscles • Contract before the rest of the ventricles

  44. Cardiac Intrinsic Conduction

  45. Heart Excitation Related to ECG SA node generates impulse; atrial excitation begins Impulse delayed at AV node Impulse passes to heart apex; ventricular excitation begins Ventricular excitation complete SA node AV node Bundle branches Purkinje fibers

  46. Extrinsic Innervation of the Heart • Heart is stimulated by the sympathetic cardioacceleratory center • Heart is inhibited by the parasympathetic cardioinhibitory center

  47. Electrocardiography • Electrical activity is recorded by electrocardiogram (ECG) • P wave corresponds to depolarization of SA node • QRS complex corresponds to ventricular depolarization • T wave corresponds to ventricular repolarization • Atrial repolarization record is masked by the larger QRS complex

  48. Electrocardiography

  49. Electrocardiography • PR interval • Atrial depolarization and contraction • QT interval • Ventricular depolarization, contraction and repolarization • PR segment • Atrial contraction • ST segment • Ventricular contraction

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