The Cardiovascular System: The Heart Part A

Presentation on theme: "The Cardiovascular System: The Heart Part A"— Presentation transcript:

1 The Cardiovascular System: The Heart Part A
18

2 Approximately the size of your fist Location
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 Figure 18.1

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
Figure 18.2

7 Epicardium – visceral layer of the serous pericardium
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 External Heart: Major Vessels of the Heart (Anterior View)
Vessels returning blood to the heart include: Superior and inferior venae cavae Right and left pulmonary veins Vessels conveying blood away from the heart include: Pulmonary trunk, which splits into right and left pulmonary arteries Ascending aorta (three branches) – brachiocephalic, left common carotid, and subclavian arteries

9 External Heart: Vessels that Supply/Drain the Heart (Anterior View)
Arteries – right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular arteries Veins – small cardiac, anterior cardiac, and great cardiac veins

10 External Heart: Anterior View
Figure 18.4b

11 External Heart: Major Vessels of the Heart (Posterior View)
Vessels returning blood to the heart include: Right and left pulmonary veins Superior and inferior venae cavae Vessels conveying blood away from the heart include: Aorta Right and left pulmonary arteries

12 External Heart: Vessels that Supply/Drain the Heart (Posterior View)
Arteries – right coronary artery (in atrioventricular groove) and the posterior interventricular artery (in interventricular groove) Veins – great cardiac vein, posterior vein to left ventricle, coronary sinus, and middle cardiac vein

13 External Heart: Posterior View
Figure 18.4d

14 Gross Anatomy of Heart: Frontal Section
Figure 18.4e

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

16 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

17 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

18 Pathway of Blood Through the Heart and Lungs
Figure 18.5

19 Coronary Circulation 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

20 Coronary Circulation: Arterial Supply
Figure 18.7a

21 Coronary Circulation: Venous Supply
Figure 18.7b

22 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

23 Aortic semilunar valve lies between the left ventricle and the aorta
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

24 Heart Valves Figure 18.8a, b

25 Heart Valves Figure 18.8c, d

26 Atrioventricular Valve Function
Figure 18.9

27 Semilunar Valve Function
Figure 18.10

28 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 InterActive Physiology®: Cardiovascular System: Anatomy Review: The Heart PLAY

29 Microscopic Anatomy of Heart Muscle
Figure 18.11

30 The Cardiovascular System: The Heart Part B
18

31 Cardiac Muscle Contraction
Heart muscle: Is stimulated by nerves and is self-excitable (automaticity) Contracts as a unit Has a long (250 ms) absolute refractory period Cardiac muscle contraction is similar to skeletal muscle contraction

32 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

33 Pacemaker and Action Potentials of the Heart
Figure 18.13

34 Heart Physiology: Sequence of Excitation
Sinoatrial (SA) node generates impulses about 75 times/minute Atrioventricular (AV) node delays the impulse approximately 0.1 second Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)

35 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

36 Heart Physiology: Sequence of Excitation
Figure 18.14a

37 Heart Excitation Related to ECG
Figure 18.17

38 Extrinsic Innervation of the Heart
Heart is stimulated by the sympathetic cardioacceleratory center Heart is inhibited by the parasympathetic cardioinhibitory center Figure 18.15

39 Electrical activity is recorded by electrocardiogram (ECG)
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 InterActive Physiology®: Cardiovascular System: Intrinsic Conduction System PLAY

40 Electrocardiography Figure 18.16

41 Heart sounds (lub-dup) are 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

42 Cardiac Cycle Cardiac cycle refers to all events associated with blood flow through the heart Systole – contraction of heart muscle Diastole – relaxation of heart muscle

43 Phases of the Cardiac Cycle
Ventricular filling – mid-to-late diastole Heart blood pressure is low as blood enters atria and flows into ventricles AV valves are open, then atrial systole occurs

44 Phases of the Cardiac Cycle
Ventricular systole Atria relax Rising ventricular pressure results in closing of AV valves Isovolumetric contraction phase Ventricular ejection phase opens semilunar valves

45 Phases of the Cardiac Cycle
Isovolumetric relaxation – early diastole Ventricles relax Backflow of blood in aorta and pulmonary trunk closes semilunar valves Dicrotic notch – brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves InterActive Physiology®: Cardiovascular System: Cardiac Cycle PLAY

46 Phases of the Cardiac Cycle
Figure 18.20

47 Cardiac Output (CO) and Reserve
CO is the amount of blood pumped by each ventricle in one minute CO is the product of heart rate (HR) and stroke volume (SV) HR is the number of heart beats per minute SV is the amount of blood pumped out by a ventricle with each beat Cardiac reserve is the difference between resting and maximal CO

48 Cardiac Output: Example
CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat) CO = 5250 ml/min (5.25 L/min)

49 Regulation of Stroke Volume
SV = end diastolic volume (EDV) minus end systolic volume (ESV) EDV = amount of blood collected in a ventricle during diastole ESV = amount of blood remaining in a ventricle after contraction

50 Factors Affecting Stroke Volume
Preload – amount ventricles are stretched by contained blood Contractility – cardiac cell contractile force due to factors other than EDV Afterload – back pressure exerted by blood in the large arteries leaving the heart

51 Frank-Starling Law of the Heart
Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume Slow heartbeat and exercise increase venous return to the heart, increasing SV Blood loss and extremely rapid heartbeat decrease SV

52 Preload and Afterload Figure 18.21

53 Extrinsic Factors Influencing Stroke Volume
Contractility is the increase in contractile strength, independent of stretch and EDV Increase in contractility comes from: Increased sympathetic stimuli Certain hormones Ca2+ and some drugs

54 Extrinsic Factors Influencing Stroke Volume
Agents/factors that decrease contractility include: Acidosis Increased extracellular K+ Calcium channel blockers

55 Contractility and Norepinephrine
Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system Figure 18.22

56 Regulation of Heart Rate
Positive chronotropic factors increase heart rate Negative chronotropic factors decrease heart rate

57 Regulation of Heart Rate: Autonomic Nervous System
Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone

58 Atrial (Bainbridge) Reflex
Atrial (Bainbridge) reflex – a sympathetic reflex initiated by increased blood in the atria Causes stimulation of the SA node Stimulates baroreceptors in the atria, causing increased SNS stimulation

59 Chemical Regulation of the Heart
The hormones epinephrine and thyroxine increase heart rate Intra- and extracellular ion concentrations must be maintained for normal heart function InterActive Physiology®: Cardiovascular System: Cardiac Output PLAY

60 Factors Involved in Regulation of Cardiac Output
Figure 18.23

61 Congestive Heart Failure (CHF)
Congestive heart failure (CHF) is caused by: Coronary atherosclerosis Persistent high blood pressure Multiple myocardial infarcts Dilated cardiomyopathy (DCM)

62 Developmental Aspects of the Heart
Embryonic heart chambers Sinus venous Atrium Ventricle Bulbus cordis

63 Developmental Aspects of the Heart
Figure 18.24

64 Developmental Aspects of the Heart
Fetal heart structures that bypass pulmonary circulation Foramen ovale connects the two atria Ductus arteriosus connects pulmonary trunk and the aorta

65 Examples of Congenital Heart Defects
Figure 18.25

66 Age-Related Changes Affecting the Heart
Sclerosis and thickening of valve flaps Decline in cardiac reserve Fibrosis of cardiac muscle Atherosclerosis

67