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Chapter 20, part 3 The Heart.

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Presentation on theme: "Chapter 20, part 3 The Heart."— Presentation transcript:

1 Chapter 20, part 3 The Heart

2 Contractile Cells Resting membrane potential of approximately –90mV
Action potential Rapid depolarization A plateau phase unique to cardiac muscle Repolarization Refractory period follows the action potential

3 Calcium Ion and Cardiac contraction
Cardiac action potentials cause an increase in Ca2+ around myofibrils Ca2+ enters the cell membranes during the plateau phase Additional Ca2+ is released from reserves in the sarcoplasmic reticulum

4 Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle

5 Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle

6 The cardiac cycle The period between the start of one heartbeat and the beginning of the next During a cardiac cycle Each heart chamber goes through systole and diastole Correct pressure relationships are dependent on careful timing of contractions PLAY Animation: Intrinsic Conduction System

7 Figure 20.16 Phases of the Cardiac Cycle

8 Figure 20.16 Phases of the Cardiac Cycle

9 Pressure and volume changes: atrial systole
rising atrial pressure pushes blood into the ventricle atrial systole the end-diastolic volume (EDV) of blood is in the ventricles

10 Pressure and volume changes: ventricular systole
Isovolumetric contraction of the ventricles: ventricles are contracting but there is no blood flow Ventricular pressure increases forcing blood through the semilunar valves

11 Pressure and volume changes: ventricular diastole
The period of isovolumetric relaxation when all heart valves are closed Atrial pressure forces the AV valves open

12 Figure 20.17 Pressure and Volume Relationships in the Cardiac Cycle

13 Heart sounds Auscultation – listening to heart sound via stethoscope
Four heart sounds S1 – “lubb” caused by the closing of the AV valves S2 – “dupp” caused by the closing of the semilunar valves S3 – a faint sound associated with blood flowing into the ventricles S4 – another faint sound associated with atrial contraction

14 Figure Heart Sounds Figure 20.18a, b

15 SECTION 20-4 Cardiodynamics

16 Stroke Volume and Cardiac Output
Cardiac output – the amount of blood pumped by each ventricle in one minute Cardiac output equals heart rate times stroke volume CO Cardiac output (ml/min) = HR Heart rate (beats/min) X SV Stroke volume (ml/beat)

17 Figure 20.19 A Simple Model of Stroke Volume
Figure 20.19a-d

18 Factors Affecting Heart Rate
Autonomic innervation Cardiac reflexes Tone SA node Hormones Epinephrine (E), norepinephrine(NE), and thyroid hormone (T3) Venous return

19 Figure 20.20 Factors Affecting Cardiac Output

20 Medulla Oblongata centers affect autonomic innervation
Cardioacceleratory center activates sympathetic neurons Cardioinhibitory center controls parasympathetic neurons Receives input from higher centers, monitoring blood pressure and dissolved gas concentrations

21 Figure 20.21 Autonomic Innervation of the Heart

22 Figure 20.21 Autonomic Innervation of the Heart

23 Basic heart rate established by pacemaker cells
SA node establishes baseline Modified by ANS Atrial reflex

24 Figure 20.22 Pacemaker Function

25 Figure 20.22 Pacemaker Function

26 Factors Affecting stoke volume
EDV Frank-Starling principle ESV Preload Contractility Afterload

27 Figure 20.23 Factors Affecting Stroke Volume

28 Figure 20.23 Factors Affecting Stroke Volume

29 Autonomic Activity Sympathetic stimulation Positive inotropic effect
Releases NE Parasympathetic stimulation Negative inotropic effect Releases ACh

30 Exercise and Cardiac Output
Heavy exercise can increase output by percent Trained athletes may increase cardiac output by 700 percent Cardiac reserve The difference between resting and maximal cardiac output PLAY Animation: Cardiac cycle

31 Summary: Regulation of Heart Rate and Stroke Volume
Sympathetic stimulation increases heart rate Parasympathetic stimulation decreases heart rate Circulating hormones, specifically E, NE, and T3, accelerate heart rate Increased venous return increases heart rate EDV is determined by available filling time and rate of venous return ESV is determined by preload, degree of contractility, and afterload

32 Figure 20.24 A Summary of the Factors Affecting Cardiac Output

33 SECTION 20-5 The Heart and the Cardiovascular System

34 The heart is part of the cardiovascular system
The goal of the cardiovascular system is to maintain adequate blood flow to all body tissues The heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal

35 You should now be familiar with:
The organization of the cardiovascular system. The location and general features of the heart, including the pericardium. The differences between nodal cells and conducting cells as well as the components and functions of the conducting system of the heart. The electrical events associated with a normal electrocardiogram.

36 You should now be familiar with:
The events of the cardiac cycle including atrial and ventricular systole and diastole, and the heart sounds related to specific events in the cycle. Cardiac output, heart rate and stroke volume and the factors that influence these variables. How adjustments in stroke volume and cardiac output are coordinated at different levels of activity.

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