Ch 12 Heart and Circulatory System

1. Ch 12 Heart and Circulatory System The Body’s Transport System

2. 4 Chambered Heart – size of clenched fist • 2 Atria • 2 Ventricles • Arteries (efferent vessels) • Veins (afferent vessels) • Layers of the Heart • Epicardium – outmost layer; covers surface of heart • Myocardium – muscle layer; contains cardiac muscle, blood vessels and nerves • Endocardium – lines heart’s chambers and valves; composed of simple squamous tissue

3. Two Circuits for Blood • Pulmonary Circuit: right side of heart; receives blood and transports de-oxygenated blood to lungs. • Systemic Circuit: left side of heart; supplies body with oxygenated blood.

4. Pericardium is the shiny covering around the heart. • Function: • To reduce friction between surrounding surfaces as heart beats • Protect the heart • Anchor the surrounding structures

5. Characteristics of Heart MuscleIntercalated discs Involuntary Striated One nuclei per cell

6. Intercalated disks; allows heart to beat as one unit

7. Location of Heart

8. Structure of the Heart

9. Main Veins into heart • Coronary Sinus • Superior Vena Cava • Inferior Vena Cava • Pulmonary Vein • Main Arteries • Coronary Artery • Pulmonary Artery • Aorta 5 1 2 6

10. Blood flow through the Heart • De-oxygenated blood from the body enters the R atrium and is pumped to the R ventricle. From the R ventricle deO2 blood is sent to the lungs where gas exchange occurs. • Oxygenated blood enters the L atria and is sent to the L ventricle where it is sent to the body via the aorta.

11. Flow of blood through heart B C A • Superior Vena Cava • Inferior Vena Cava • R. atrium • R. ventricle • Pulmonary trunk (artery) • Pulmonary vein • L. atrium • L. ventricle • Aorta A. Brachiocephalic B. L. Common Carotid C. L. Subclavian 9 1 6 5 7 3 8 4 2

12. Difference in myocardium thickness between R. ventricle and L. ventricle. • Why?

13. Valves of the Heart Atrioventricular Valves - one way valves; prevent back flow of blood -chordae tendineae - papillary muscles Tricuspid – 3 flaps Found between R atrium and R. ventricle Bicuspid (mitral) – 2 flaps Found between L atrium and L. ventricle

14. Anatomy of AV valvesOne-way valves Atrioventricular valves • Chordae tendineae • Papillary muscles

15. Located in Pulmonary Artery and Aortic Artery 3 flaps Prevents blood from flowing back into ventricles Semilunar Valves Posterior Anterior

16. Valve position when ventricles relaxed

17. Valve position when ventricles contract

18. Heart Sounds • Two sounds (lubb-dupp) associated with closing of heart valves • First sound occurs as AV valves close and signifies beginning of systole • Second sound occurs when SL valves close at the beginning of ventricular diastole • Heart murmurs: abnormal heart sounds most often indicative of valve problems

19. Aortic valvesounds heard in 2nd intercostal space at right sternal margin Pulmonary valve sounds heard in 2nd intercostal space at left sternal margin Mitral valvesounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle Tricuspid valvesounds typically heard in right sternal margin of 5th intercostal space Figure 18.19

21. Cardiac Muscle Contraction Rapid Depolarization: Threshold is reached along the membrane. • Causes Na+ channels in the sarcolemma to open • Na+ enters cell reversing membrane potential from –90 mV to +30 mV (Na+ gates close) Plateau: Calcium channels open and Ca+2 enters sarcoplasm • Ca+2 also is released from SR • Ca+2 surge prolongs the depolarization phase and delays repolarization (excess + ions in cell) Repolarization: Ca+2 begin to close; K+ channels open and K+ leaves the cell.

22. In Cardiac muscle, depolarization lasts longer. Thus cardiac muscle can’t increase tension with another impulse; tetanus doesn’t occur. Why is this important?

23. Heart Physiology: Electrical Events • Intrinsic cardiac conduction system • A network of noncontractile (autorhythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart • Nodes – cells that are responsible for starting the impulse • Conducting cells – distribute the impulse to the myocardium • 1 % of the heart’s cardiac cells have this capability

24. Internal Conduction System • 1. Sinoatrial node • 2. AV node • 3. AV bundle or Bundle of HIS • 4. R and L bundle branches • 5. Purkinge fibers Nodes – cluster of nervous tissue that begins an impulse. 5

25. Sequenceof Excitation • Sinoatrial (SA) node (pacemaker) • Generates impulses about 70-80 times/minute (sinus rhythm) • Depolarizes faster than any other part of the myocardium

26. Sequenceof Excitation • Atrioventricular (AV) node • Delays impulses approximately 0.1 second • Allows for Atria to contract • Depolarizes 40-60 times per minute in absence of SA node input

27. Conducting Cells • Atrioventricular (AV) bundle (bundle of His) • Right and left bundle branches • Two pathways in the interventricular septum that carry the impulses toward the apex of the heart Sequence of Excitation

28. Sequenceof Excitation • Purkinje fibers • Complete the pathway into the apex and ventricular walls

29. Superior vena cava Right atrium Thesinoatrial (SA) node(pacemaker) generates impulses. 1 Internodal pathway Left atrium 2 The impulses pause (0.1 s) at the atrioventricular (AV) node. Theatrioventricular (AV) bundle connects the atria to the ventricles. Purkinje fibers 3 Thebundle branches conduct the impulses through the interventricular septum. 4 Inter- ventricular septum ThePurkinje fibers depolarize the contractile cells of both ventricles. 5 (a) Anatomy of the intrinsic conduction system showing the sequence of electrical excitation Figure 18.14a

30. Electrocardiography • Electrocardiogram (ECG or EKG): a composite of all the action potentials generated by nodal and contractile cells at a given time. • Three waves • P wave: depolarization of SA node • QRS complex: ventricular depolarization (AV node) • T wave: ventricular repolarization

31. Normal EKG has 3 distinct waves. 1st wave (P) - SA node fires - Natural Pacemaker - fires around 70-80 times/minute The atria depolarize Impulse is being generated across R and L atria via diffusion. .1s after P wave, atria contract.

32. AV node – back up pacemaker - Beats 40-60 times/minute - Impulse is delayed at bundle of HIS until Atria contract. • 2nd wave (QRS) • AV Node fires; depolarization of ventricles. • Q-R interval represents beginning of atrial repolarization and AV node firing; ventricles depolarize • R-S interval represents beginning of ventricle contractions • S-T End of Ventricular depolarization

33. 3rd Wave (T) • T wave repolarization of ventricles • Ventricles return to normal relaxed state. • In a healthy heart, size, duration and timing of waves is consistent. Changes reveal a damage or diseased heart.

34. QRS complex Sinoatrial node Ventricular depolarization Ventricular repolarization Atrial depolarization Atrioventricular node S-T Segment P-Q Interval Q-T Interval Figure 18.16

35. Depolarization Repolarization SA node R R T P T P Q S 1 Atrial depolarization, initiatedby the SA node, causes theP wave. Q S 4 Ventricular depolarizationis complete. R AV node R T P T P Q S Q 2 With atrial depolarizationcomplete, the impulse isdelayed at the AV node. S 5 Ventricular repolarizationbegins at apex, causing theT wave. R R T P T P Q S Q S 3 Ventricular depolarizationbegins at apex, causing theQRS complex. Atrialrepolarization occurs. 6 Ventricular repolarizationis complete. Figure 18.17

37. Homeostatic Imbalances Defects in the intrinsic conduction system may result in: • Arrhythmias: irregular heart rhythms • Uncoordinated atrial and ventricular contractions • Fibrillation: rapid, irregular contractions; useless for pumping blood

38. Problems with Sinus Rhythms • Tachycardia: Heart rate in excess of 100 bpm when at rest • If persistent, may lead to fibrillation • Bradycardia: Heart rate less than 60 bpm when at rest • May result in grossly inadequate blood circulation • May be desirable result of endurance training

39. Homeostatic Imbalances • Defective SA node may result • Ectopic focus: abnormal pacemaker takes over • No P waves; If AV node takes over, there will be a slower rhythm (40–60 bpm) • Defective AV node may result in • Partial or total heart block • Longer delay at AV node than normal • No all impulses from SA node reach the ventricles • Ventricular fibrillation: • cardiac muscle cells are overly sensitive to stimulation; no normal rhythm is established

40. Problems with Sinus Rhythms • 2nd degree heart block; Missed QRS complex • SA node is sending impulses, but the AV node is not sending the impulses along the bundle branches • 1st degree is represented by a longer delay between P & QRS

41. (a) Normal sinus rhythm. (b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min. (d) Ventricular fibrillation. These chaotic, grossly irregular ECG deflections are seen in acute heart attack and electrical shock. (c) Second-degree heart block. Some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1. Figure 18.18

42. 1. 2. 3.

43. 4. 5. 6.

44. Pacemaker • Used to correct nodes that are no longer are in rhythm. • Becomes the new heart’s pacemaker.

45. Myocardial Infarction • A Heart Attack is caused by oxygen not getting to the heart muscle usually by blockages in the coronary arteries site of blockage

46. Stopping a Heart Attack • Breaking apart the blockage is done with: • Medication • Angioplasty • Stents • Coronary bypass surgery (CABG) stent placement

47. Congestive Heart Failure (CHF) • Progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs • Caused by • Coronary atherosclerosis • Persistent high blood pressure • Multiple myocardial infarcts

48. Mechanical Events: The Cardiac Cycle • Cardiac cycle: all events associated with blood flow through the heart during one complete heartbeat • Systole—contraction • Diastole—relaxation

49. Phases of the Cardiac Cycle • Ventricular filling—takes place in mid-to-late diastole • AV valves are open • 80% of blood passively flows into ventricles • Atrial systole occurs, delivering the remaining 20% • End diastolic volume (EDV): volume of blood in each ventricle at the end of ventricular diastole

50. Phases of the Cardiac Cycle • Ventricular systole • Atria relax and ventricles begin to contract • Rising ventricular pressure results in closing of AV valves • In ejection phase, ventricular pressure exceeds pressure in the large arteries, forcing the Semilunar valves open • End systolic volume (ESV): volume of blood remaining in each ventricle