Cardiovascular System: The Heart

1. Cardiovascular System: The Heart Dr. Michael P. Gillespie

2. Cardiovascular System • Blood • Heart • Blood vessels

3. Heart • Propels the blood through the blood vessels to reach all of cells of the body. • It circulates the blood through an estimated 100,000 km (60,000 miles) of blood vessels.

4. Heart • It beats 100,000 times every day (35 million beats / year). • It pumps about 5 liters (5.3 qt) each minute and 14,000 liters (3,600 gal) each day. • Cardiology – the study of the normal heart and diseases associated with it.

5. Size And Shape • About the size of a closed fist. • Cone-shaped. • 12cm (5 in.) Long, 9cm (3.5 in.) Wide, and 6cm (2.5 in.) Thick. • 250g (8 oz) in adult females and 300g (10 oz) in adult males.

6. Location • Lies in the mediastinum (a mass of tissue between the sternum and the vertebral column). • 2/3 of the mass is left of midline. • A cone lying on its side.

7. Anatomical Landmarks • The apex (pointed end) is directed anteriorly, inferiorly, and to the left. • The base (broad portion) is directed posteriorly, superiorly, and to the right. • Anterior surface – deep to sternum & ribs.

8. Anatomical Landmarks • Inferior surface – rests upon diaphragm. • Right border – faces the right lung. • Left border (pulmonary border) – faces the left lung.

10. Cardiopulmonary Resuscitation (CPR) • External pressure (compression) can be used to force blood out of the heart and into the circulation. • CPR is utilized when the heart suddenly stops beating. • Cardiac compressions with artificial ventilation of the lungs keeps oxygenated blood circulating until the heart can be restarted. • Self CPR (coughing).

11. Pericardium • Pericardium – membrane that surrounds and protects the heart. • Fibrous pericardium – tough, inelastic, dense irregular CT. Prevents overstretching of the heart. • Serous pericardium – thinner, more delicate layer. • Parietal layer. • Visceral layer (epicardium) – adheres to the heart. • Pericardial fluid lies in between these two layers in the pericardial cavity.

12. Layers Of The Heart Wall • Epicardium (visceral layer of the serous pericardium). • Myocardium – cardiac muscle tissue. • Endocardium – smooth lining of the chambers of the heart and valves (continuous with blood vessels).

14. Chambers Of The Heart • Atria – superior chambers. • Auricle – pouchlike structure. • Ventricles – inferior chambers. • Sulci – grooves on the surface of the heart that contain blood vessels.

15. Chambers Of The Heart • Right atrium – receives blood from three veins: superior vena cava, inferior vena cava, and coronary sinus. • Tricuspid valve. • Pectinate muscles. • Interatrial septum. • Fossa ovalis – depression (remnant of foramen ovale).

16. Chambers Of The Heart • Right ventricle – receives blood from right atrium. • Trabeculae carneae – bundles of cardiac muscle tissue. • Chordae tendineae – connects to the cusps of the tricuspid valve which are connected to papillary muscles. • Interventricular septum. • Pulmonary valve into pulmonary arteries.

17. Chambers Of The Heart • Left atrium – receives blood from the lungs through the pulmonary veins. • Bicuspid (mitral) valve. • Left ventricle – receives blood from left atrium. • Trabeculae carneae – bundles of cardiac muscle tissue. • Chordae tendineae – connects to the cusps of the bicuspid valve which are connected to papillary muscles. • Aortic valve into the ascending aorta (largest artery).

20. Myocardial Thickness • The function of the individual chambers determines their thickness. • The atria pump blood a short distance and consequently have thinner walls than the ventricles. • The left ventricle pumps blood a greater distance than the right at higher pressures and has a thicker wall.

21. Fibrous Skeleton Of The Heart • Dense CT rings that surround the valves and prevent overstretching. • Provides insertion points for bundles of cardiac muscle fibers.

23. Atrioventricular (AV) Valves • Tricuspid and bicuspid valves. • When the valve is open, the pointed cusps point into the ventricle.

24. Atrioventricular (AV) Valves • When atrial pressure is higher than ventricular pressure the valves open (the papillary muscles are relaxed and the chordae tendinae is slack. • When the ventricles contract the pressure forces the AV valves closed. The papillary muscles close concurrently. • Damaged valves allow regurgitation (flow back).

26. Semilunar (SL) Valves • The aortic and pulmonary valves. • The SL valves open when the pressure in the ventricles exceeds the pressure in the arteries.

28. Heart Valve Disorders • Stenosis (narrowing) – failure of the heart valve to open fully. • Insufficiency (incompetence) – failure of a valve to close fully. • Mitral stenosis – due to scar formation of a congenital defect.

29. Heart Valve Disorders • Mitral insufficiency – backflow of blood from the left ventricle to the left atrium. • Mitral valve prolapse (MVP) – one or both cusps protrude into the left atrium during ventricular contraction. • Aortic stenosis – the aortic valve is narrowed.

30. Heart Valve Disorders • Aortic insufficiency – backflow of blood from the aorta into the left ventricle. • Rheumatic fever – an acute systemic inflammatory disease. Antibodies produced to destroy the bacteria attack and inflame the CT of joints, heart valves and other organs.

31. Systemic And Pulmonary Circulations • Two closed systems. • The output of one becomes the input of another with each beat of the heart.

34. Coronary Circulation • The myocardium has its own blood vessels, the coronary circulation. • The coronary arteries branch from the ascending aorta and encircle the heart. • When the heart is contracting the coronary arteries are squeezed shut. • When the heart is relaxed, the high pressure from the aorta pushes blood into the coronary arteries and from the arteries to the coronary veins.

35. Coronary Arteries • Two coronary arteries, right and left coronary arteries, branch from the ascending aorta and supply oxygenated blood to the myocardium.

36. Coronary Arteries • Left coronary artery branches into: • Anterior interventricular or left anterior descending LAD (supplies ventricle walls). • Circumflex branches (supplies left ventricle and left atrium).

37. Coronary Arteries • Right coronary artery branches into: • Atrial branches (supplies right atrium). • Posterior interventricular branch (supplies the two ventricles). • Right marginal branch (supplies the right ventricle).

38. Coronary Veins • The great cardiac vein (anterior) and the middle cardiac vein (posterior) drain into the coronary sinus. • Coronary Sinus – a large bascular sinus on the posterior surface of the heart.

40. Reperfusion Damage • Reperfusion is reestablishing the blood flow to the heart muscle after a blockage of a coronary artery. • Reperfusion damages the tissue further due to the formation of oxygen free radicals from the reintroduced oxygen.

41. Histology Of Cardiac Muscle Tissue • Cardiac muscle fibers are shorter in length and less circular than skeletal muscle fibers. • Cardiac muscle fibers exhibit branching.

42. Histology Of Cardiac Muscle Tissue • Usually one centrally located nucleus is present, although it may occasionally have two nuclei. • Intercalated disc connect neighboring fibers. • The discs contain desmosomes, which hold the fibers together. • Mitochondria are larger and more numerous in cardiac muscle fiber. • Gap junctions allow for propagation of action potentials.

44. Regeneration Of Heart Cells • Infarcted (dead) cardiac muscle tissue is replaced with non-contractile fibrous scar tissue. • A lack of stem cells limits the ability of the heart to repair damage. • Some stem cells from the blood migrate into the heart tissues and differentiate into functional muscle cells and endothelial cells.

45. Autorhythmic Fibers: The Conduction System • Autorhythmic fibers are self-excitable and maintain the heart’s continuous beating. • Act as a pacemaker, setting the rhythm of electrical excitation that causes contraction of a heart. • Form a conduction system, that provides a path for the cycle of cardiac excitation through the heart.

46. Sequence Of Cardiac Conduction • Sinoatrial (SA) node – undergo spontaneous depolarization (pacemaker potential) – propagates through the atria through gap junctions. • Atrioventricular (AV) node (bundle of his) – site where action potentials are conducted from the atria to the ventricles.

47. Sequence Of Cardiac Conduction • Right and left bundle branches – propagate action potentials through the ventricles and the interventricular septum to the apex of the heart. • Purkinje fibers – conduct the action potentials from the apex, through the remainder of the ventricles stimulating contraction.

48. Pacemaker • The SA node regulates the pace of the heart. • At rest, it contracts approximately 100 time per minute. • Nerve impulses from the ANS and blood born hormones (epinephrine) modify the timing and strength of each heartbeat.

49. Pacemaker • Acetylcholine from the ANS slows the heart rate to about 75 bpm. • If the SA node becomes damaged, the AV node can pick up the job; However, at a slower rate (40 – 60 bpm). • If both nodes are damaged, an artificial pacemaker sends out electrical currents to stimulate the heart to contract.