Chapter 12

1. Chapter12 The Heart

2. Introduction • All cardiovascular function depend on the heart. • It beats 100,000/day • Pumps 8000 liters of blood/day

3. The Heart and Circulatory System • The circulatory system can be subdivided into the pulmonary circuit and the systemic circuit. • Arteries carry blood away from the heart and • Veins return blood to the heart. • Capillaries are tiny vessels between arteries and veins.

5. The heart has four chambers • The right atrium • The right ventricle • The left atrium • The left ventricle

6. The Anatomy and Organization of the Heart • The heart is surrounded by the pericardial cavity • The visceral pericardium (epicardium) covers the heart’s outer surface. • The parietal pericardium lines the inner surface of the pericardial sac which surrounds the heart.

8. The coronary sulcus, a deep groove, marks the boundary between the atria and ventricles. Surface anatomy of the heart

9. The Heart Wall • The bulk of the heart consists of the muscular myocardium • The endocardium lines the inner surfaces of the heart • The fibrous skeleton supports the heart’s contractile cells and valves.

11. Cardiac muscle cells are interconnected by intercalated discs, which convey the force of contraction from cell to cell and conduct action potentials.

12. Internal Anatomy and Organization • The atria are separated by the interatrial septum and the ventricles are divided by the interventricular septum

13. The right atria receives blood from the systemic circuit via two large veins, the superior vena cava and inferior venacava

14. Blood flows from the right atrium into the right ventricle through the right atrioventricular (AV) valve (tricuspid valve. • The opening is bounded by three cusps of fibrous tissue braced by the tendinous chordae tendineae with are connected to papillary muscles.

15. Blood leaving the right ventricle enters the pulmonary trunk after passing through the pulmonary semilunar valve. • The pulmonary trunk divides to form the left and right pulmonary arteries. • The left and right pulmonary veins return blood to the left atrium

16. Blood leaving the left atrium flows into the left ventricle through the left atrioventicular valve(bicuspid valve) Blood leaving the left ventricle passes through the aorticsemilunar valve and into the systemic circuit via the aorta.

19. Anatomical difference between the ventricles reflect the functional demands on them • The walls of the right ventricle is relatively thin, while the left ventricle has a massive muscular wall. • Valves normally permit blood flow in only one direction preventing regurgitation(backflow) of blood.

20. The Blood supply to the Heart • Coronary circulation meets the high oxygen and nutrient demands of cardiac muscle cells • The coronary arteries originate at the base of the aorta

21. THE HEARTBEAT In a single heartbeat, the entire heart (atria and ventricles) contract in a coordinated manner so that blood flows in the correct direction at the proper time. Two general classes of cardiac cells are involved in the normal heartbeat: contractile cells and cells of the conductingsystem

22. Contractile Cells Uses a similar method of contraction as skeletal muscle cells, but Ca2+ ions enter the muscle fiber for a longer period creating delaying repolaization and lengthening the muscle contraction.

24. The Conduction System • The conducting system includes nodal cells and conducting cells both of which do not contract.. • The conduction system initiates and distributes electrical impulses in the heart. • Nodal cells establish the rate of cardiac contraction

25. Pacemaker cells are nodal cells that reach threshold first. • Conducting cells distribute the contractile stimulus to the general myocardium

26. Unlike skeletal muscle, cardiac muscle contracts without neural or hormonal stimulation. • Pacemaker cells in the sinoatrial (SA) node normally establish the rate of contraction. • From the SA node, the stimulus travels to the atrioventricular (AV) node .

27. From the AV node the stimulus travels to the AV bundle, which divides into bundle branches. • From there Purkinje fibers convey the impulses to the ventricular myocardium

31. The Electrocardiogram • A recording of the electrical activities in the heart is an electrocardiogram (ECG or EKG) • Important landmarks of an ECG include: the P wave (atrial depolarization) • QRS complex (ventricular depolarization • T wave (ventricular repolarization)

33. The Cardiac Cycle • The cardiac cycle consists of systole (contraction) followed by diastole (relaxation) • Both ventricle contract at the same time, and they eject equal volumes of blood. • The closing of the heart valves and the rushing of blood through the heart cause characteristic heart sounds.

34. Heart Sounds • The first heart sound (“lubb”) is produced as the AV valves close and the semilunar valves open. • The second heart sound (“dupp”) occurs when the semilunar valves close. • What is going on in the heart during each of these sounds?

36. HEART DYNAMICS • Heart dynamics refers to the movements and forces generated during contractions. • The amount of blood ejected by a ventricle during a single heat is the stroke volume (SV) • The amount of blood pumped each minute is the cardiac output (CO)

37. Factors Controlling Cardiac Output • The major factors that affect cardiac output are: • blood volume reflexes , • autonomic innervation, • and hormones.

38. Blood volume reflexes are stimulated by changes in venous return, the amount of blood entering the heart. • The atrial reflex accelerates the heart rate when the walls of the right atrium are stretched. • Ventricular contractions become more powerful and increase stroke volume when the ventricular walls are stretched.

39. The basic heart rate is established by the pacemaker cells but it can be modified by the autonomic nervous system. • Acetylcholine released by parasympathetic motor neurons lowers heart rate and stroke volume.

40. Norepinephrine released by sympathetic neurons increases the heart rate and stroke volume • Epinephrine and norpinephrine, hormones released by the adrenal medullae during sympathetic activation, increase both heart rate and stroke volume. • Thyroid hormones and glucagon also act to increase cardiac output.

42. The cardioacceleratory center in the medulla oblongata activates sympathetic neurons; • The cardioinhibitory center governs the activities of the parasympathetic neurons. • These cardiac centers receive inputs from higher centers and from receptors monitoring blood pressure and the levels of dissolved gases.