12_heart.ppt
- 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 17 Heart Purkinje fibers
- 2. Functions of the Heart 1. Generating blood pressure • Required for blood flow through the blood vessels 2. Routing blood • Two pumps, moving blood through the pulmonary and systemic circulations 3. Regulating blood supply • Adjusts blood flow by changing the rate and force of heart contractions as needed
- 3. Systemic and Pulmonary Circulation • Pulmonary circulation – The flow of blood from the heart through the lungs back to the heart – Picks up oxygen and releases carbon dioxide in the lungs • System circulation – The flow of blood from the heart through the body back to the heart – Delivers oxygen and picks up carbon dioxide in the body’s tissues Fig. 17.1
- 4. Location, Shape, and Size of the Heart • Location – Anterior to the vertebral column, posterior to the sternum – Left of the midline – Deep to the second to fifth intercostal spaces – Superior surface of diaphragm • Shaped like a blunt cone, with an apex and a base • Approximately the size of your fist
- 5. Fig. 17.2
- 6. Anatomy of the Heart • The heart consists of two atria and two ventricles • 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 lines the surface of the heart • They are separated by the fluid-filled (pericardial fluid) pericardial cavity
- 7. Anatomy of the Heart • The pericardium – Fibrous pericardium • Protects and anchors the heart • Prevents overfilling of the heart with blood – Serous pericardium • Allows for the heart to work in a relatively friction- free environment
- 8. Heart in the Pericardium Fig. 17.3
- 9. Anatomy of the Heart • The heart wall has three layers – Epicardium • Visceral layer of the serous pericardium (visceral pericardium) • Provides protection against the friction of rubbing organs – Myocardium • Cardiac muscle layer forming the bulk of the heart • Responsible for contraction – Endocardium • Endothelial layer over crisscrossing, interlacing layer of connective tissue • Inner endocardium reduces the friction resulting from the passage of blood through the heart • Ventricles have ridges called trabeculae carneae • The inner surfaces of the atria are mainly smooth – Auricles have raised areas called musculi pectinati
- 11. Anatomy of the Heart • Atria – Receiving chambers of the heart – Each atrium has a protruding auricle – Pectinate muscles mark atrial walls – Veins entering the right atrium carry blood to the heart from the systemic circulation • Inferior vena cava • Superior vena cava • Coronary sinus – Veins entering the left atrium carry blood to the heart from the pulmonary circulation • Four pulmonary veins
- 12. Anatomy of the Heart • Ventricles – Discharging chambers of the heart – Papillary muscles and trabeculae carneae muscles mark ventricular walls – Arteries carrying blood away from the heart • Pulmonary trunk exits the right ventricle carrying blood to the pulmonary circulation • Aorta exits the left ventricle carrying blood to the systemic circulation
- 13. Anatomy of the Heart • External Anatomy – Each atrium has a flap called an auricle – The coronary sulcus separates the atria from the ventricles – The interventricular grooves separate the right and left ventricles • Heart Chambers – The interatrial septum separates the atria from each other – The fossa ovalis is the former location of the foramen ovalis through which blood bypassed the lungs in the fetus – The interventricular septum separates the ventricles
- 15. Surface View of the Heart Fig. 17.5c
- 16. Anatomy of the Heart • 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 – Tricuspid valve: separates the right atrium and ventricle – Bicuspid valve: separates the left atrium and ventricle
- 17. Anatomy of the Heart • Heart valves (cont.) – Semilunar valves prevent backflow of blood into the ventricles – Aortic semilunar valve: lies between the left ventricle and the aorta – Pulmonary semilunar valve: lies between the right ventricle and pulmonary trunk
- 18. Internal Anatomy of the Heart Fig. 17.6
- 20. Function of the Heart Valves Fig. 17.8
- 21. Route of Blood Flow Through the Heart • Blood from the body flows through the right atrium into the right ventricle and then to the lungs • Blood returns from the lungs to the left atrium, enters the left ventricle, and is pumped back to the body
- 23. Blood Supply to the Heart • Coronary arteries branch off the aorta to supply the heart • Blood returns from the heart tissues to the right atrium through coronary sinus and cardiac veins Fig. 17.10
- 24. Page 497
- 25. Histology of the Heart • Fibrous Skeleton of the Heart – Consists of a plate of fibrous connective tissue – Forms fibrous rings around the AV and SL valves for support – Provides a point of attachment for heart muscle – Electrically insulates the atria from the ventricles
- 26. Histology of the Heart • Cardiac Muscle Cells – Are branched and have a centrally located nucleus – Actin and myosin are organized to form sarcomeres (striated) – T tubules and sarcoplasmic reticulum are not as organized as in skeletal muscle – Normal contraction depends on extracellular Ca2+ – Rely on aerobic respiration for ATP production • They have many mitochondria and are well supplied with blood vessels – Joined by intercalated disks • Allow action potentials to move from one cell to the next, thus cardiac muscle cells function as a unit
- 27. Histology of the Heart Fig. 17.11
- 29. Electrical Activity of the Heart • Action Potentials 1. After depolarization and partial repolarization, a plateau phase is reached, during which the membrane potential only slowly repolarizes 2. The opening and closing of voltage-gated ion channels produce the action potential • The movement of Na+ through Na+ channels causes depolarization • During depolarization, K+ channels close and Ca2+ channels begin to open • Early repolarization results from closure of the Na+ channels and the opening of some K+ channels • The plateau exists because Ca2+ channels remain open • The rapid phase of repolarization results from the closure of the Ca2+ channels and the opening of many K+ channels
- 30. Electrical Activity of the Heart • Refractory Periods – Absolute refractory period • Cardiac muscle cells are insensitive to further stimulation – Relative refractory period • Stronger than normal stimulation can produce an action potential – Cardiac muscle has a prolonged depolarization and thus a prolonged absolute refractory period, which allows time for the cardiac muscle to relax before the next action potential causes a contraction
- 31. Fig. 17.12
- 33. Electrical Activity of the Heart • Autorhythmicity of Cardiac Muscle – Some cardiac muscle cells are autorhythmic because of the spontaneous development of a prepotential • Prepotential: slowly developing local action potential – The sinoatrial (SA) node is the pacemaker of the heart • Collection of cardiac muscle cells capable of spontaneously generating action potentials – The prepotential results from the movement of Na+ and Ca2+ into the SA node cells – The duration of the prepotential determines heart rate
- 34. Electrical Activity of the Heart • Conducting System of the Heart – The sinoatrial (SA) node and the atrioventricular (AV) node are in the right atrium – The AV node is connected to the bundle branches in the interventricular septum by the AV bundle – The bundle branches give rise to Purkinje fibers, which supply the ventricles
- 35. Electrical Activity of the Heart • Conducting System of the Heart – The SA node initiates action potentials, which spread across the atria and cause them to contract • SA node generates impulses about 75 times/minute – Action potentials are slowed in the AV node, allowing the atria to contract and blood to move into the ventricles • AV node delays the impulse approximately 0.11 seconds – Then the action potentials passes from atria to ventricles via the atrioventricular bundle
- 37. Electrical Activity of the Heart • Conducting System of the Heart – 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
- 38. Fig. 17.13
- 40. Electrical Activity of the Heart • Electrocardiogram (ECG) – Records only the electrical activities of the heart – P wave corresponds to depolarization of the atria (SA node) – QRS complex corresponds to ventricular depolarization – T wave corresponds to ventricular repolarization – Atrial repolarization record is masked by the larger QRS complex • Based on the magnitude of the ECG waves and the time between waves, ECGs can be used to diagnose heart abnormalities
- 41. Fig. 17.14
- 42. Cardiac Cycle • Repetitive contraction and relaxation of the heart chambers • Overview of Systole and Diastole • Atrial systole is contraction of the atria • Systole is contraction of the ventricles • Atrial diastole is relaxation of the atria • Diastole is relaxation of the ventricles
- 43. Cardiac Cycle • Overview of Systole and Diastole (cont.) – During systole • AV valves close • Pressure increases in the ventricles • Semilunar valves are forced to open • Blood flows into the aorta and pulmonary trunk – At the beginning of diastole • Pressure in the ventricles decreases • Semilunar valves close to prevent backflow of blood from the aorta and pulmonary trunk into the ventricles – When the pressure in the ventricles is lower than in the atria, the AV valves open and blood flows from the atria into the ventricles – During atrial systole, the atria contract and complete the filling of the ventricles
- 45. Cardiac Cycle • Events Occurring During Ventricular Systole – Ventricular depolarization • Produces the QRS complex • Initiates contraction of the ventricles, which increases ventricular pressure – The AV valves close – Semilunar valves open – Blood is ejected from the heart – The volume of blood in a ventricle just before it contracts is the end- diastolic volume – The volume of blood after contraction is the end- systolic volume
- 46. Cardiac Cycle • Events Occurring During Ventricular Diastole – Ventricular repolarization • Produces the T wave • Ventricles relax – Blood flowing back toward the relaxed ventricles closes the semilunar valves – The AV valves open and blood flows into the ventricles • Approximately 70% of ventricular filling occurs when blood flows from the higher pressure in the veins and atria to the lower pressure in the relaxed ventricles • Atrial depolarization produces the P wave • The atria contract and complete ventricular filling
- 47. Cardiac Cycle • Aortic Pressure Curve – Contraction of the ventricles forces blood into the aorta • The maximum pressure in the aorta is the systolic pressure – Elastic recoil of the aorta maintains pressure in the aorta and produces the dicrotic notch – Blood pressure in the aorta falls as blood flows out of the aorta • The minimum pressure in the aorta is the diastolic pressure
- 48. Cardiac Cycle • 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
- 49. Fig. 17.17
- 51. Tab. 17.2
- 52. Tab. 17.1
- 54. Mean Arterial Blood Pressure • Mean arterial pressure is the average blood pressure in the aorta – Adequate blood pressure is necessary to ensure delivery of blood to the tissues – Proportional to cardiac output (amount of blood pumped by the heart per minute) times peripheral resistance (total resistance to blood flow through blood vessels) – CO X PR
- 55. Mean Arterial Blood Pressure • 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 • 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 – CO (ml/min) = HR (72 beats/min) x SV (70 ml/beat) – CO = 5040 ml/min (~5 L/min) • Cardiac reserve is the difference between resting and maximal CO
- 56. Mean Arterial Blood Pressure • Venous return is the amount of blood returning to the heart – Increased venous return increases stroke volume by increasing end-diastolic volume • Increased force of contraction increases stroke volume by decreasing end-systolic volume
- 57. Regulation of the Heart • Intrinsic Regulation – Modifies stroke volume through the functional characteristics of cardiac muscle cells – Starling’s law of the heart describes the relationship between preload and the stroke volume of the heart • An increased preload causes the cardiac muscle fibers to contract with a greater force and produce a greater stroke volume – Afterload is the pressure against which the ventricles must pump blood.
- 58. Regulation of the Heart • Extrinsic Regulation – Modifies heart rate and stroke volume through nervous and hormonal mechanisms • The cardioregulatory center in the medulla oblongata regulates the parasympathetic and sympathetic nervous control of the heart • Epinephrine and norepinephrine are released into the blood from the adrenal medulla as a result of sympathetic stimulation. They increase the rate and force of heart contraction
- 59. Regulation of the Heart • Parasympathetic stimulation is supplied by the vagus nerve – Decreases heart rate. – Postganglionic neurons secrete acetylcholine, which increases membrane permeability to K. Hyperpolarization of the plasma membrane increases the duration of the prepotential • Sympathetic stimulation is supplied by the cardiac nerves – Increases heart rate and the force of contraction (stroke volume) – Postganglionic neurons secrete norepinephrine, which increases membrane permeability to Ca2+. Depolarization of the plasma membrane decreases the duration of the prepotential
- 60. The Heart and Homeostasis • Effect of Blood Pressure – Baroreceptors monitor blood pressure and the cardioregulatory center modifies heart rate and stroke volume – In response to a decrease in blood pressure, the baroreceptor reflexes increase heart rate and stroke volume – When blood pressure increases, the baroreceptor reflexes decrease heart rate and stroke volume
- 63. The Heart and Homeostasis • Effect of pH, Carbon Dioxide, and Oxygen – Carotid body and aortic chemoreceptor receptors monitor blood oxygen levels – Medullary chemoreceptors monitor blood pH and carbon dioxide levels – Chemoreceptors are not important for the normal regulation of the heart, but are important in the regulation of respiration and blood vessel constriction
- 64. Baroreceptor and Chemoreceptor Reflexes Fig. 17.18
- 65. Fig. 17.19
- 66. The Heart and Homeostasis • Effect of Ions and Body Temperature – Increased extracellular K+ decrease heart rate and stroke volume – Decreased extracellular K+ decrease heart rate – Increased extracellular Ca2+ increase stroke volume and decrease heap rate – Decreased extracellular Ca2+ levels produce the opposite effect – Heart rate increases when body temperature increases, and it decreases when body temperature decreases
- 67. Effects of Aging on the Heart • Aging results in gradual changes in the function of the heart, which are minor under resting conditions but are more significant during exercise • Some age-related changes to the heart are the following – Decreased cardiac output and heart rate – Increased cardiac arrhythmias – Hypertrophy of the left ventricle – Development of stenoses or incompetent valves – Development of coronary artery disease and heart failure • Exercise improves the functional capacity of the heart at all ages.