The Heart

1. The Heart Anatomy & Physiology Chapter 12

2. The Heart: Some Basics • Functions: • Pump blood through the circulation • Needed to transport oxygen, nutrients, wastes • Location • In a cone-shaped area in the central thorax between the lungs • The mediastinum

3. Pericardial Membranes • Three Layers of Pericardium • Fibrous • Outermost, loose strong fibrous sac • Serous, extends over diaphragm & great vessels • Parietal • Lines the fibrous pericardium • Visceral • Lines the surface of the heart (epicardium) • Serous fluid in between the parietal & visceral layer

4. Cardiac Anatomy:Chambers, Vessels, & Valves • Myocardium • Cardiac muscle in the walls of the heart • Endocardium • Simple squamous epithelium • Lines the 4 chambers, covers the valve surfaces, extends into the vessels • Smooth (prevents thrombus formation)

5. Chambers of the Heart • Two atria (atrium) (right & left) • Thin-walled upper chambers • Two ventricles (right & left) • Thick-walled lower chambers • Interatrial septum • Separates the 2 atria • Interventricular septum • Separates the 2 ventricles

6. Right Atrium • Receives venous blood from the body • Superior & inferior vena cava empty into the right atrium (RA) • Blood leaves the RA through the tricuspid valve • Has 3 flaps (cusps) • Prevents backflow from the RV during contraction

7. Right Ventricle • Receives blood through tricuspid valve from the RA • The chordae tendinae & papillary muscles attach to the cusps of the tricuspid valve • Prevents valve inversion • Right ventricle contracts, pumping blood through the pulmonary (semilunar) valve • Into the pulmonary artery

8. Pulmonary Circulation • From RV into pulmonary artery (PA) • Pulmonary artery branches to arterioles • Arterioles become capillaries • Capillaries wrap around alveoli to allow oxygen & carbon dioxide exchange • Capillaries become venules, become veins • Join to form the main pulmonary vein (PV)

9. Left Atrium • Receives oxygenated blood from pulmonary veins • Blood leaves LA through mitral (bicuspid) valve (also prevents backflow) • Atria produce • Atrial natriuretic peptide (ANP) when BP or volume is high (antagonist to aldosterone) • ANP decreases renal Na+ & H2O reabsorption

10. Left Ventricle • Receives blood through mitral valve • Also attached to chordae tendinae & papillary muscles • Thicker walls than RV, stronger pump • Blood leaves the LV through the aortic valve • Blood enters the aorta (largest artery in the body)

11. Coronary Vessels • Coronary Arteries • Blood supply to the myocardium • R & L coronary arteries (RCA & LCA) • First branches of the ascending aorta • Ischemia: condition of insufficient blood supply or perfusion • Infarct: cell death related to ischemia

12. Cardiac Cycle • Sequence of events during a single heartbeat • Simultaneous atrial contraction • Fraction of a second pause • Simultaneous ventricular contraction • Systole (contraction) • Atrial systole, ventricular systole • Diastole (relaxation)

13. Cardiac Cycle • Atrial diastole overlaps ventricular systole • Ventricular systole is longer than atrial systole • Most of the atrial blood flows passively into the ventricles, then a small contraction • Atrial kick • The veins are constantly emptying blood into the atria • AV valves (tricuspid & mitral) open when pressure is high in the RA and LA

14. Heart Sounds • Two heart sounds normally • First heart sound (S1) • Loudest, longest in duration • Caused by AV valves closing • Second heart sound (S2) • Caused by aortic and pulmonic (semilunar) valve closure

15. Heart Murmurs • Abnormal or extra heart sound caused by valvular disease • Turbulent blood flow creates a sound • Regurgitation • Incompetent or leaky valve, allows backflow of blood into atria during ventricular systole • Stenosis • Narrow valve opening, blood cannot flow easily and creates turbulence

16. Cardiac Conduction Pathway • Specific route traveled by spontaneous cardiac electrical impulses • Nerve cells are not required • This allows the orderly sequence of the cardiac cycle

17. Conducting Pathway: Anatomy • Sinoatrial node (SAN) • In RA wall • The normal pacemaker of the heart • Normal rate 60-100/min • fastest depolarization of any cardiac cells • Sends electrical impulse through atrial myocardium to the AVN • This causes atrial systole

18. Conducting Pathway: Anatomy • Atrioventricular Node (AVN) • In the inferior part of the interatrial septum • Slows the impulse (heart rate) a bit • Normal rate is 50-60/minute • Then conduction goes on to the ventricle

19. Conducting Pathway: Anatomy • Ventricular conducting pathway: slower rate of conduction: 30-40/minute • Bundle of His (AV Bundle) • Superior part of interventricular septum • Bundle Branches (right & left) • Purkinje fibers • To the rest of the ventricular myocardium • This causes ventricular systole

20. Diseases of the Conducting System • Arrhythmias (Dysrhythmias): abnormal conduction through the conducting system • May be caused by ischemia • May be irregular, too fast (tachycardia), or too slow (bradycardia) • Palpitations: • A symptom, a sense of irregular or pounding heart rate, range from harmless to critical

21. Dysrhythmia Categories • Ectopic focus • A beat generated by any other part of the myocardium than the SAN, makes the rhythm irregular • Flutter: fast rapid rate, atrial flutter • Fibrillation • Chaotic conduction outside of the usual conduction pathway • Atrial fibrillation: common chronic dysrhythmia • Ventricular conduction: common cardiac arrest rhythm • Often occurs with MI, treatment is electrical defibrillation

22. Electrocardiogram • Called ECG or EKG • Linear recording of the electrical conduction of the heart • Done via electrodes placed at standard places on the chest • Used to determine two findings: • The type of cardiac rhythm • The degree of cardiac ischemia

23. Electrocardiogram • Complexes on the EKG • P wave: atrial depolarization • QRS complex • Ventricular depolarization and • Atrial repolarization • T wave • Ventricular repolarization

24. Heart Rate • Coordinates with pulse normally • 60-80 beats/minute • Usually slightly slower than SAN rate • SAN rate slowed by parasympathetic nerves • Bradycardia • Rate less than 60/minute • Tachycardia • Rate over 100/minute

25. Heart Rates • Children • 100-140/minute • Conditioned athletes • 50/minute • Marathon runners • 35-40/minute

26. Cardiac Output • The amount of blood pumped out of the heart by the ventricle in 1 minute • Cardiac output = • Stroke volume (SV) times heart rate (HR) • SV = amount of blood pumped by ventricle in each beat (contraction), 60-80 ml/beat • Normal CO is approximately 5-6 liters/minute

27. Starling’s Law of the Heart • The more cardiac muscle fibers are stretched, the more forcefully they contract • This accounts for the increased CO during exercise • Increased venous return (of blood) to the heart • More blood stretches the cardiac fibers • They contract more forcefully, increasing SV

28. Cardiac Output • Exercise CO = twice resting CO • This difference is the cardiac reserve • Usually 15 liters or more • Ejection fraction • Percentage of ventricular blood pumped out during systole • 60-70% is normal

29. Regulation of Heart Rate • Medulla • Two cardiac centers • Accelerator center & inhibitory center • Pressoreceptors • Detect changes in BP • In carotid arteries & aortic arch • Chemoreceptors • Detect changes in oxygen content of blood • In carotid bodies & aortic body

30. Regulation of Heart Rate • Afferent Nerves • Glossopharyngeal nerve (CN 9) • Vagus nerve (CN 10) • Efferent Nerves • Sympathetic nerves • Parasympathetic nerves

31. Coronary Artery Disease • CAD • Etiology: decreased coronary artery blood flow, decreased myocardial perfusion • Most commonly due to • Atherosclerosis • Cholesterol & lipid-rich plaques in the coronary artery lumen • May cause angina

32. Myocardial Infarction • MI • Etiology is thrombus forming on ruptured plaque • More acute situation than angina • Worse ischemia than angina • Death of some myocardial cells • Complications • Dysrhythmias, ventricular fibrillation, fatalities • Cardiac failure, cardiogenic shock