Chapter 18 – The Heart

1. Chapter 18 – The Heart

2. Heart function • Serves as the pump for the cardiovascular system • “double pump” • Right side of the heart – pulmonary circulation • Left side of the heart – systemic circulation

3. Heart Anatomy • Located within the mediastinum • 2/3 of heart left of sternum • Base is most superior portion • Angled toward right shoulder • Apex is most inferior portion • Angled toward left hip • Rests on diaphragm

4. Heart coverings • Fibrous pericardium • Tough superficial layer • Serous pericardium • Deep to fibrous layer • Parietal layer • Visceral layer • In between parietal and visceral layers is pericardial cavity filled with serous fluid

5. Heart covering abnormalities • Pericarditis • Inflammation of pericardium • Swelling can cause friction; impedes heart activity • Cardiac tamponade • Accumulation of fluid in pericardial cavity; compresses heart • Excess fluid can be drained via a syringe

6. Layers of heart walls • Superficial • Epicardium (visceral layer of serous pericardium) • Middle • Myocardium • Mainly cardiac muscle • Muscle connected by spiral/circular intercrossing connective tissue • Supports muscle; anchors in place • Thicker in high stress • Deep • Endocardium • Simple squamous epithelium • Lines heart chambers • Continuous with endothelium of blood vessels

7. Heart chambers • 4 chambers • 2 superior atria • 2 inferior ventricles • Left and right sides of heart are divided by septum • Interatrial and interventricular • 2 main sulci on surface • Coronary sulcus • Divides atria from ventricles • Interventricular sulcus • Separates two ventricles • Anterior and posterior

8. Atria (singular = atrium) • Receiving chambers of the heart • Relatively thin walled • Superficially covered by flaplike auricles • Anterior surface of RA has ridged walls – pectinate muscles • Interatrial septum has fossa ovalis • Remnant of fetal circulation • RA receives blood from 3 main vessels • Inferior and superior vena cava, and coronary sinus • LA receives blood from lungs via 4 pulmonary veins

9. Ventricles • Actual pumps of the heart • RV = most of heart’s anterior surface • Walls are thicker than atrial walls/LV thicker than RV • Internal walls have irregular muscle ridges – trabeculaecarneae • Domelike papillary muscles involved with AV valves • RV pumps blood through pulmonary trunk • LV pumps blood through aorta

10. Heart valves • Atrioventricular • RAV – tricuspid • LAV – bicuspid/mitral valve • Chordae tendinae “heartstrings” • Attaches valve cusps to papillary muscles • Allows cusps to close tightly, and not flap back into atria • Prohibits backflow of blood

11. Heart valves • Semilunar • Aortic – junction between LV and aorta • Pulmonary – junction between RV and pulmonary trunk • Both have three cusps • Open when pressure inside ventricles is higher than pressure in blood vessels; close when pressure is less in ventricles than in blood vessels • Blood flows backwards and closes valves

12. Blood vessels • Direction of blood flow • Arteries – carry blood away from heart • Veins – retun blood back to the heart • Respiratory gas content • Red – contains oxygen-rich/carbon dioxide-poor blood • Blue – contains oxygen-poor/carbon dioxide-rich blood

13. Pathway of blood through heart • Pulmonary circuit • To and from lungs • RA → RV → pulmonary trunk → pulmonary arteries → lung → pulmonary veins → LA • Systemic circuit • To and from all other body tissues • LA → LV → aorta → systemic arteries → tissues → systemic veins → RA

14. Coronary circulation • Myocardium is too thick for diffusion to occur • Coronary arteries • Supply heart with oxygen and nutrients • Branch from base of aorta (ascending aorta) • Cardiac veins • Carries carbon dioxde and wastes • Join with cardiac sinus, or enter RA directly

15. Coronary circulation abnormalities • Myocardial infarction “heart attack” • Coronary blockage leads to cell death • Cardiac muscle is amitotic • Replaced by non-functioning scar tissue

16. Remnants of fetal circulation • Blood does not need to go to lungs to get oxygenated • Fossa ovalis • Depression that was fetal foramen ovalis • allowed for blood in RA to directly enter LA • Ligamentumarteriosum • Fetal ductusarteriosum • Connected pulmonary trunk to aorta

17. Cardiac muscle fibers • Cardiac muscle cells • Striated, branched, and involuntary • Intercalated discs • Anchoring desmosomes • Keep cells associated with each other • Gap junctions • Allows ions to pass directly from cell to cell • Large, numerous mitochondria • Fatigue resistant

18. Heart physiology • Intrinsic cardiac conduction • Noncontractile cardiac cells that have the ability to initiate contraction • Located in RA in sinoatrial (SA) node “pacemaker” • Depolarization spreads via gap junctions allowing atria to contract • Impulse spread to atrioventricular (AV) node • Located immediately above tricuspid valve • Impulse is delayed to allow for complete contraction of atria before ventricular contraction

19. Heart physiology • Intrinsic cardiac conduction cont • No gap junctions between atria and ventricles • Electrical impulse from AV node to bundle of His/atrioventricular bundle • Located in atrioventricular septum • Purkinje fibers transmit impulse throughout ventricles • Extrinsic cardiac conduction • Autonomic nervous system can modify heartbeat

20. Heart physiology abnormalities • Arrhythmia • Uncoordinated atrial and ventricular contractions • Fibrillation • SA node not in control – out of phase contractions • Defibrillators • Electrical shock to heart – hopefully eliminates chaotic rhythms so SA node can re-establish normal rhythm • Tachycardia – heartbeat over 100 per minute; can cause fibrillation • Bradycardia • Heartbeat below 60 per minute

21. ECG/EKG (electrocardiogram) • Graphic recording of electrical current generated/transmitted through heart • 3 waves • P wave (small) • Depolarization from SA node to atria • QRS (large/sharp) • Ventricular depolarization (during same time, atria are re-polarizing) • T wave • Ventricular repolarization

22. Heart sounds • “lub dup” caused by closing of valves • “lub” closing of AV valves; ventricular contraction • “dup” closing of SL valves; ventricular relaxation • Shorter, sharper sound • Abnormalities • Heart murmurs • Blood more turbulent due to obstruction • Leaky valves • VSD (ventricular septal defect) • Causes blood to leak from RV into LV • Causes hissing sounds

23. Cardiac cycle • Systole – contraction of chambers • Diastole – relaxation of chambers • Cardiac cycle = one complete heartbeat • Ventricular filling • Mid-late diastole • AV valves open; SL valves closes • Atrial systole forces all blood into ventricles • Ventricular systole • AV valves close; SL valves open • Blood forced into pulmonary trunk (from right) and aorta (from left)

24. Cardiac cycle cont • Ventricular diastole – early • Backflow from pulmonary trunk and aorta causes SL valves to close • Atria fill; increase in pressure forces AV valves to open • Average cardiac cycle = 0.8 seconds • Approx 74 heartbeats per minute • Cardiac output • Amount of blood pumped out of each ventricle per minute • ~5L per minute