2nd Lecture - Cardiovascular System for 200L Optometry and Pharmacy 2023-2024 PDF

GOOD MORNING CLASS 6/20/2024 Jesus is Lord 1  TODAY MARKS THE LAST DAY TH OF THE 8 WEEK ST OF THE 1 SEMESTER OF THE 2023/2024 ACADEMIC SESSION (June 17 th – June 21st 2024) 6/20/2024 Jesus is Lord 2 ...

GOOD MORNING CLASS 6/20/2024 Jesus is Lord 1  TODAY MARKS THE LAST DAY TH OF THE 8 WEEK ST OF THE 1 SEMESTER OF THE 2023/2024 ACADEMIC SESSION (June 17 th – June 21st 2024) 6/20/2024 Jesus is Lord 2  SECOND LECTURE FRIDAY 21 ST JUNE, 2024 (8:00am – 10:00am) 6/20/2024 Jesus is Lord 3 CARDIOVASCULAR SYSTEM (PHS213 & OPT218) Dr. Eghe Osawaru AIHIE Department of Physiology, School of Basic Medical Sciences, College of Medical Sciences, University of Benin. Benin City, Nigeria. COURSE OUTLINE: CARDIOVASCULAR SYSTEM Definition and functions of the cardiovascular system Cardiac muscle Cardiac myoelectrophysiology Cardiac cycle Circulation of blood: cardiac output and regulation Blood pressure Haemodynamics and microcirculation Pulmonary, Coronary, Splanchnic and muscle circulation. Shock and cardiovascular changes in exercise. 6/20/2024 Jesus is Lord 5  Cardiac Muscle 6/20/2024 Jesus is Lord 6  Cardiac Muscle The heart is composed of three major types of cardiac muscle: 1. Atrial muscle 2. Ventricular muscle 3. Specialized excitatory and conductive muscle fibers. 6/20/2024 Jesus is Lord 7  Cardiac Muscle contd. The atrial and ventricular types of cardiac muscle contract in the same way as the skeletal muscle. The duration of contraction of the cardiac muscle is much longer. 6/20/2024 Jesus is Lord 8  Cardiac Muscle contd. The specialized excitatory and conductive fibers of the heart exhibit either: automatic rhythmical electrical discharge in the form of action potentials or conduction of the action potentials through the heart. 6/20/2024 Jesus is Lord 9  Cardiac Muscle contd. This provides an excitatory system that controls the rhythmical beating of the heart. The cardiac muscle is a syncytium of many heart muscle cells. The cardiac cells are so interconnected that when one cell becomes excited, the action potential rapidly spreads to all of them. 6/20/2024 Jesus is Lord 10  Cardiac Muscle contd. The heart actually is composed of two functional syncytiums: 1. The atrial syncytium, which constitutes the walls of the two atria. 2. The ventricular syncytium, which constitutes the walls of the two ventricles. 6/20/2024 Jesus is Lord 11 Figure 1: Syncytial, interconnecting nature of cardiac muscle fibers. Jesus is Lord 12 6/20/2024  Cardiac Muscle contd. The division of the muscle of the heart into two functional syncytiums plays a vey significant role: It allows the atria to contract a short time ahead of the contraction of the ventricles. This is important for effectiveness of the heart as a pump. 6/20/2024 Jesus is Lord 13  The specialized excitatory and conductive fibers of the heart It is made up of the following: 1. The sinus node (also called sinoatrial or S-A node) 2. The atrial internodal pathways 3. The atrioventricular (A-V) node 4. The A-V bundle (also known as the bundle of His) 5. The left and right bundle branches of Purkinje fibers. 6/20/2024 Jesus is Lord 14 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 15 6/20/2024  The Sinus Node It is also called sinoatrial or SA node. Normally, the action potential of the heart is initiated in the SA node, which serves as the pacemaker. The SA node is the pacemaker for the entire heart. After the action potential is initiated in the SA node, there is a very specific sequence and timing for the conduction of action potentials to the rest of the heart. 6/20/2024 Jesus is Lord 16 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 17 6/20/2024  The Internodal Pathways The action potential spreads from the SA node to the right and left atria through the atrial internodal pathways. Simultaneously, the action potential is conducted to the AV node. 6/20/2024 Jesus is Lord 18 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 19 6/20/2024  The Atrioventricular (A-V) node Impulses from the atria are delayed before passing into the ventricles. Conduction velocity through the AV node is considerably slower than in the other cardiac tissues. This ensures that the ventricles have sufficient time to fill with blood before they are activated and contract. 6/20/2024 Jesus is Lord 20 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 21 6/20/2024  The Atrioventricular (A-V) bundle Also known as the bundle of His which conducts impulses from the atria into the ventricles. 6/20/2024 Jesus is Lord 22 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 23 6/20/2024 The left and right bundle branches of Purkinje fibers Conduct the cardiac impulses to all parts of the ventricles. Conduction through the bundle of His and Purkinje fibers is extremely fast, and it rapidly distributes the action potential to the ventricles. Rapid conduction of the action potential throughout the ventricles is essential and allows for efficient contraction and ejection of blood. 6/20/2024 Jesus is Lord 24 Figure 2: Sinus node and the Purkinje system of the heart, showing also the atrioventricular (A-V) node, atrial internodal pathways, and ventricular bundle branches. Jesus is Lord 25 6/20/2024 Figure 3: Schematic diagram showing the sequence of activation of the myocardium. The cardiac action potential is initiated in the sinoatrial node and spreads throughout the myocardium, as shown by the arrows Jesus is Lord 26 6/20/2024  CARDIAC ELECTROPHYSIOLOGY 6/20/2024 Jesus is Lord 27  Cardiac Electrophysiology Cardiac electrophysiology includes all of the processes involved in the electrical activation of the heart: i. the cardiac action potentials; ii. the conduction of action potentials along specialized conducting tissues; iii. excitability and the refractory periods; iv. the modulating effects of the autonomic nervous system on heart rate, conduction velocity, and excitability; and v. the electrocardiogram (ECG). 6/20/2024 Jesus is Lord 28  Cardiac Action Potentials 6/20/2024 Jesus is Lord 29  Cardiac Action Potentials The concepts applied to cardiac action potentials are the same concepts that are applied to action potentials in nerve, skeletal muscle, and smooth muscle. 1. The membrane potential of cardiac cells is determined by the relative conductances to ions and the concentration gradients for the permeant ions. 6/20/2024 Jesus is Lord 30  Cardiac Action Potentials contd. 2. If the cell membrane is permeable to an ion, that ion will flow down its electrochemical gradient and attempt to drive the membrane potential toward its equilibrium potential (calculated by the Nernst equation). 3. The resting membrane potential of cardiac cells is determined primarily by potassium ions (K+). The conductance to K+ at rest is high, and the resting membrane potential is close to the K+ equilibrium potential. 6/20/2024 Jesus is Lord 31  Cardiac Action Potentials contd. 4. The role of Na+ -K+ ATPase is primarily to maintain Na+ and K+ concentration gradients across the cell membrane, although it makes a small direct electrogenic contribution to the membrane potential. 6/20/2024 Jesus is Lord 32  Cardiac Action Potentials contd. 5. Changes in membrane potential are caused by the flow of ions into or out of the cell. For ion flow to occur, the cell membrane must be permeable to that ion. Depolarization occurs when there is net movement of positive charge into the cell, which is called an inward current. Repolarization occurs when there is net movement of positive charge out of the cell, which is called an outward current. Jesus is Lord 33 6/20/2024  Cardiac Action Potentials contd. 6. Two basic mechanisms can produce a change in membrane potential. i. A change in the electrochemical gradient for a permeant ion, which changes the equilibrium potential for that ion. ii. A change in conductance to an ion across the membrane. Jesus is Lord 34 6/20/2024  Cardiac Action Potentials contd. 7. Threshold potential is the potential difference at which there is a net inward current (i.e., inward current becomes greater than outward current). At threshold potential, the depolarization becomes self-sustained and gives rise to the upstroke of the action potential. Jesus is Lord 35 6/20/2024  Cardiac Action Potentials contd. The heart consists of two kinds of muscle cells: 1. Contractile cells Constitute the majority of atrial and ventricular tissues They are the working cells of the heart. Action potentials in contractile cells lead to contraction and generation of force or pressure. 6/20/2024 Jesus is Lord 36  Cardiac Action Potentials contd. 2. Conducting cells Constitute the tissues of a. the SA node b. the atrial internodal pathways c. the AV node d. the bundle of His e. the Purkinje system. 6/20/2024 Jesus is Lord 37  Cardiac Action Potentials contd. Conducting cells are specialized muscle cells that do not contribute significantly to generation of force. The specialized conducting tissues have the capacity to generate action potentials spontaneously. Except for the SA node, however, this capacity normally is suppressed. They also function to rapidly spread (conduct) action potentials over the entire myocardium. 6/20/2024 Jesus is Lord 38  Action Potentials of Conducting Cells There are extremely important differences between action potentials of contractile cells and those of the conducting cells. 1. The SA node exhibits automaticity; that is, it can spontaneously generate action potentials without neural input. 2. It has an unstable resting membrane potential, in direct contrast to contractile cells. 3. It has no sustained plateau. 6/20/2024 Jesus is Lord 39 Figure 4: Cardiac action potentials in the ventricle, atrium, and sinoatrial node. A–C. The numbers correspond to the phases of the action potentials. Jesus is Lord 40 6/20/2024  Figure 5: Ventricular Action Potential: Currents responsible. The length of the arrows shows the relative size of each ionic current. E, Equilibrium potential; ECF, extracellular fluid; ICF, intracellular Jesus is Lord fluid. 41 6/20/2024  Action Potentials of Conducting Cells contd. The SA nodal cell does not have a steady resting potential but, instead, undergoes a slow depolarization. This slow depolarization is known as a pacemaker potential; it brings the membrane potential to threshold, at which point an action potential occurs. Three ion channel mechanisms contribute to the pacemaker potential. 6/20/2024 Jesus is Lord 42 Phases of Action Potentials of Conducting Cells 1. Phase 0 (depolarization) i. is not quite as rapid or as sharp as in the other types of cardiac tissues ii. caused by an increase in calcium conductance and an inward Ca2+ current iii. carried primarily by L-type Ca2+ channels. There are also T-type Ca2+ channels in SA node, which carry part of the inward Ca2+ current. 6/20/2024 Jesus is Lord 43 Figure 6: Conducting cell action potential Jesus is Lord 44 6/20/2024 Phases of Action Potentials of Conducting Cells contd. 2. Phases 1 and 2 are absent. 3. Phase 3 (repolarization) i. As in the other cardiac cells, repolarization in the SA node is due to an increase in potassium conductance ii. there is an outward K+ current, which repolarizes the membrane potential 6/20/2024 Jesus is Lord 45 Figure 6: Conducting cell action potential Jesus is Lord 46 6/20/2024 Phases of Action Potentials of Conducting Cells contd. 4. Phase 4 (spontaneous depolarization or pacemaker potential) i. Phase 4 is the longest portion of the SA node action potential. ii. accounts for the automaticity of SA nodal cells iii. There is no true resting membrane potential iv. Rather, there is a slow depolarization 6/20/2024 Jesus is Lord 47 Phases of Action Potentials of Conducting Cells contd. v. Slow depolarization is produced by the opening of Na+ channels and an inward Na+ current termed “funny,” or F-type channels. vi. They differ from the fast Na+ current responsible for the depolarization in contractile cells. vii. rate of phase 4 depolarization sets the heart rate. 6/20/2024 Jesus is Lord 48 Figure 6: Conducting cell action potential Jesus is Lord 49 6/20/2024 Phases of Action Potentials of Conducting Cells contd. If the rate of phase 4 depolarization increases, threshold is reached more quickly, the SA node will fire more action potentials per time, and heart rate will increase. Conversely, if the rate of phase 4 depolarization decreases, threshold is reached more slowly, the SA node will fire fewer action potentials per time, and heart rate will decrease. 6/20/2024 Jesus is Lord 50 Phases of Action Potentials of Conducting Cells contd. Thus, the pacemaker potential provides the SA node with automaticity, the capacity for spontaneous, rhythmic self-excitation. The rate of this activity can however be modified significantly by external factors such as i. autonomic nerves ii. Hormones iii. Drugs iv. ions, and v. ischemia/hypoxia 6/20/2024 Jesus is Lord 51  Latent Pacemakers The cells in the SA node are not the only myocardial cells with intrinsic automaticity; other cells, called latent pacemakers, also have the capacity for spontaneous phase 4 depolarization. Latent pacemakers include the cells of the AV node, bundle of His, and Purkinje fibers. Although each of these cells has the potential for automaticity, it normally is not expressed. The rule is that the pacemaker with the fastest rate of phase 4 depolarization controls the heart rate. 6/20/2024 Jesus is Lord 52  Read About the following 1. Conduction velocity 2. Excitability 3. Refractory period 6/20/2024 Jesus is Lord 53  Effects of Autonomic Nervous System on the Cardiovascular System The autonomic nervous system is an involuntary system that controls and modulates the functions primarily of visceral organs. It has two major divisions: 1. Sympathetic division 2. Parasympathetic division Both divisions often complement each other in the regulation of organ system function. 6/20/2024 Jesus is Lord 54  Effects of Autonomic Nervous System on the Cardiovascular System contd. The autonomic nervous system has effects on 1. heart rate, 2. conduction velocity, 3. myocardial contractility, and 4. Vascular smooth muscle 6/20/2024 Jesus is Lord 55 Table 1 : summarizes the effects of the autonomic nervous system on the heart and blood vessels AV, Atrioventricular; EDRF, endothelial-derived relaxing factor; M, muscarinic. Jesus is Lord 56 6/20/2024  Autonomic Effects on Heart Rate The effects of the autonomic nervous system on heart rate are called chronotropic effects. Positive chronotropic effects are increases in heart rate. Negative chronotropic effects are decreases in heart rate. Sympathetic stimulation increases heart rate and parasympathetic stimulation decreases heart rate. 6/20/2024 Jesus is Lord 57  Figure 7: Effect of sympathetic and parasympathetic stimulation on the SA node action potential. A, The normal firing pattern of the SA node is shown. B, Sympathetic stimulation increases the rate of phase 4 depolarization and increases the frequency of action potentials. C, Parasympathetic stimulation decreases the rate of phase 4 depolarization and hyperpolarizes the maximum diastolic potential to decrease the frequency of 3/22/2023 action potentials. 58 6/20/2024 Jesus is Lord. Autonomic Effects on Conduction Velocity in the Atrioventricular Node The effects of the autonomic nervous system on conduction velocity are called dromotropic effects. Positive dromotropic effects increases conduction velocity. Negative dromotropic effects decreases conduction velocity. Sympathetic stimulation increases conduction velocity. 6/20/2024 Jesus is Lord 59 Autonomic Effects on Conduction Velocity in the Atrioventricular Node contd. The most important physiologic effects of the autonomic nervous system on conduction velocity are those on the AV node. This effect alters the rate at which action potentials are conducted from the atria to the ventricles. 6/20/2024 Jesus is Lord 60  Autonomic Effects on myocardial contractility The effects of the autonomic nervous system on myocardial contractility are called inotropic effects. Positive inotropic effects increases myocardial contractility. Negative inotropic effects decreases myocardial contractility. Sympathetic stimulation increases myocardial contractility. 6/20/2024 Jesus is Lord 61  Autonomic Effects on Systemic Blood Vessels Most systemic blood vessels, especially those of the abdominal viscera and skin of the limbs, are constricted by sympathetic stimulation. Under some conditions, the beta (β) function of the sympathetics causes vascular dilation instead of the usual sympathetic vascular constriction, but this dilation occurs rarely. Parasympathetic stimulation has almost no effects on most blood vessels. 6/20/2024 Jesus is Lord 62 Table 1 : summarizes the effects of the autonomic nervous system on the heart and blood vessels AV, Atrioventricular; EDRF, endothelial-derived relaxing factor; M, muscarinic. Jesus is Lord 63 6/20/2024  ANY QUESTIONS PLEASE 6/20/2024 Jesus is Lord 64  REMEMBER: The best time to start reading was yesterday but the next best time to start reading is “TODAY” 05/03/2018 Jesus is Lord 65  MAKE GOOD USE OF THE REST OF TODAY AND THE WEEK 05/03/2018 Jesus is Lord 66  THANK YOU FOR LISTENING 6/20/2024 Jesus is Lord 67  THE END 6/20/2024 Jesus is Lord 68