Properties of the Cardiac Muscle, Valves & Blood Vessels.pdf

Properties of the Cardiac Muscle, Valves & Blood Vessels By Prof. Lutfi & Dr. Ramaze What are the main functions of the cardiovascular system? Functions of the CVS • Transport functions: – Nutrients e.g. Glucose, A.A , F.A, vitamins, … ect. – Gases e.g. O2, CO2. – Waste products. – Hormones. –...

Properties of the Cardiac Muscle, Valves & Blood Vessels By Prof. Lutfi & Dr. Ramaze What are the main functions of the cardiovascular system? Functions of the CVS • Transport functions: – Nutrients e.g. Glucose, A.A , F.A, vitamins, … ect. – Gases e.g. O2, CO2. – Waste products. – Hormones. – Heat. How can the functional organization of the heart and blood vessels helps in maintaining cardiovascular functions? Cardio vascular System Cardio-vascular The Heart Heart Veins Arteries Venules Arterioles Capillaries Exchange Vessels Resistance Vessels Capacitance Vessels * Made of 2 atria + 2 ventricles * Valves maintain unidirectional flow The blood vessels Functional Organization of the Heart 1. Cardiac muscle proper. 2. Special tissues: – Pacemaker: generate action potential (cardiac impulse). – Conductive system: transmit impulses from pacemaker to cardiac muscle proper. Functional Organization of the Heart 3. Fibrous tissues: – Separate atria from ventricles. – Make the valves. 4. Endocardium and pericardium: – Cover the inner and out sides of the myocardium. Cardiac Muscle Proper Special Tissues – The Conducting System Inter-atrial Tracts Sino-atrial Node Anterior, Middle and Posterior Inter-nodal Tracts Purkinje fibers Atrio-ventricular Node Bundle of His Right and Left Bundle Branch Fibrous Tissues of the Heart 1. Separate the atria from the ventricles Fibrous Tissues of the Heart 2. Make the valves Opening of the Atrio-Ventricular Valves Closure of the Atrio-Ventricular Valves Opening of the Semi-Lunar Valves Closure of the Semi-Lunar Valves Endocardium Vs. Pericardium Functional Organization of the Blood Vessels Blood Vessels What is the importance of the pre-capillary sphincters? Greater Vs Lesser Circulations Lesser (Pulmonary) Circulation Greater (Systemic) Circulation Distribution of the Cardiac Output Autonomic Control of the CVS Functions Organ Sympathetic Parasympathetic Action Receptor Action Receptor SA node, heart rate ↑ β1 ↓ M AV nodal conduction ↑ β1 ↓ M Contractility ↑ β1 ↓ (atria only) M Skin; splanchnic Constricts α1 Skeletal muscle Skeletal muscle Endothelium Dilates Constricts β2 α1 Releases EDRF M 1. Heart 2. Vascular Smooth Muscle Properties of the Cardiac Muscle 1. Contractility 2. Rythmicity 3. Excitability 4. Conductivity Cardiac Muscle Proper Cardiac Muscle Proper 1. Contractility • Cardiac muscle is striated due to the presence of actin + myosin filaments • Intercalated discs allow cardiac muscle to function as a syncytium. Why? • There are two syncytia (atrial + ventricular) separated by fibrous tissue. • Cardiac muscle contraction needs Ca++ and ATP. • ATP is derived from aerobic metabolism → adequate O2 supply is essential for cardiac muscle contraction. 1. Contractility • Positive inotropic factors = ↑ cardiac muscle contraction. • Positive chronotropic factors = ↑ heart rate. • Cardiac muscle contraction = systole. • Cardiac muscle relaxation = diastole. What are the differences between cardiac and skeletal muscles contraction? Skeletal Muscle Contraction Cardiac Muscle Contraction Factors Influencing Heart Contractility – ↑ Venous return → ↑ end diastolic volume Cardiac Contractility 1. Frank Starling law: → stretch of the cardiac muscle fibres Venous Return → ↑ cardiac muscle contractility Factors Influencing Heart Contractility 2. Autonomic innervation: – Sympathetic → +ve inotropic effect. – Parasympathetic → -ve inotropic effect. 3. Humoral factors and drugs: – Catecholamines, digitalis, alkalis and Ca++ → +ve inotropic effect. – Acetylcholine, chloroforms, acids, K+ and some bacterial toxin e.g. diphtheria toxin → -ve inotropic effect. Factors Influencing Heart Contractility 4. Physical factors: – Warmth → +ve inotropic effect. – Cold → -ve inotropic effect. 5. O2 supply: – Hypoxia → -ve inotropic effect. Factors Influencing Heart Contractility 6. Heart rate: – ↑ HR → +ve inotropic effect (treppe). – Premature heart contraction (extrasystole) → +ve inotropic effect (post-extrasystolic potentiation). ↑ Force of contraction Bowditch Staircase (Treppe) ↑ Rate of stimuli • If a number of stimuli of the same intensity are sent into the muscle after a quiescent period, the first few contractions of the series show a successive increase in amplitude (strength). Bowditch Staircase (Treppe) • Treppe occurs as a result of increased heart rate because: – Increasing availability of Ca++ in the sarcoplasm – Heat production by contracting muscles: → The enzymes become more efficient. → The muscle becomes more pliable. Postextrasystolic Potentiation • The tension developed on the extrasystolic beat is less than normal, however, the next beat exhibits increased tension. • Due to increased availability of Ca++ in the sarcoplasm from the previous extrasystolic contraction. Indicates time of regular contraction 2. Rythmicity (automaticity) • Rythmicity = self-generation of action potential → muscle contraction. • Autonomic fibers only modify rate and force of contraction. • The normal pacemaker is SA node. Why? What are the differences between nerve and pacemaker action potentials? 1. Ca ++ channels close 2. K+ channels open ↓ Ca ++ permeability Na+ influx K+ efflux RMP 1. K+ leak channels 2. Gibb’s-Donnan Effect 3. Na+-K+ ATPase Pump ↑ K+ permeability RMP Hyperpolarization Nerve Action Potential Ca + channels open Prepotential 1. K+ channels close 2. Slow Na + channels open Pacemaker Potential Threshold Pacemaker Action Potential Autonomic modulation of the Prepotential Effect of sympathetic stimulation Effect of parasympathetic stimulation (Positive chronotropic effect) (Negative chronotropic effect) ↑Na+, ↑Ca++ and ↓K+ permeability ↓Na+, ↓Ca++ and ↑K+ permeability Factors Influencing Rhythmicity 1. Autonomic innervation: – Sympathetic → +ve chronotropic effects – Parasympathetic → -ve chronotropic effects 2. Physical factors: – Warmth → +ve chronotropic effects – Cold → -ve chronotropic effects Factors Influencing Rhythmicity 3. Humoral factors and drugs: – Catecholamines, thyroid hormones→ +ve chronotropic effects – Acetylcholine, digitalis → -ve chronotropic effects 4. O2 supply: – Hypoxia → -ve chronotropic effects Factors Influencing Rhythmicity 5. Effects of ions: – Sodium: • Hyponatremia slows SA node depolarization → -ve chronotropic effects • Hypernatremia depress the cardiac activity → -ve chronotropic effects Factors Influencing Rhythmicity 5. Effects of ions: – Calcium: • Hypocalcemia shorten the plateau of ventricular action potential → +ve chronotropic effects • Hypercalcemia prolong the plateau of ventricular action potential → -ve chronotropic effects. Factors Influencing Rhythmicity 5. Effects of ions: – Potassium • Hypokalemia enhances repolarization → activation of Na+ and Ca++ channels → increases the slopes prepotential and depolarization → +ve chronotropic effects • Hyperkalemia → -ve chronotropic effects. 3. Excitability • Excitability is the ability of cardiac muscle to respond to adequate stimuli by generating an action potential. • The action potential of the cardiac muscle is different from that of the pacemakers. What are the differences between nerve and cardiac muscle action potentials? K+ efflux Ca + + influx Na+ influx K+ efflux RMP 1. K+ leak channels 2. Gibb’s-Donnan Effect 3. Na+-K+ ATPase Pump Na+ influx RMP RMP K+ efflux RMP Hyperpolarization Nerve Action Potential Cardiac Muscle Action Potential What are the differences between pacemaker and cardiac muscle action potentials? Action Potential of Different cardiac Tissues Absolute Vs Relative Refractory Periods Absolute Refractory Period • Prolonged compared with both nerves and skeletal muscles. • Occupies the whole period of systole. • Corresponds to depolarization and most of the repolarization. • Excitability becomes zero. → no stimulus, whatever strong can induce contraction. → cardiac muscle cannot be tetanized. Relative Refractory Periods • Occupies part of the diastole. • Corresponds to the late part of the repolarization. • A strong enough stimulus can induce contraction. • Can be modified by the heart rate, body temperature, autonomic fibres stimulation and bacterial toxins and drugs. What are the factors that affect cardiac excitability? 4. Conductivity Inter-atrial Tracts Inter-atrial Tracts CV = 1 m/s Sino-atrial Node CV = 0.05 m/s Anterior, Middle and Posterior Inter-nodal Tracts CV = 1 m/s Purkinje fibers CV = 4 m/s Sino-atrial AV Node Node CV = 0.01 m/s Bundle of His CV = 1 m/s Right and Left Bundle Branch CV = 4 m/s Vagal Tone • Although SA nodal rhythm is approximately 90 discharge/min, the heart contracts at a rate about 70 beat/min. • This is due to the effect of the vagus → vagal tone. 70 mph 50 mph 30 mph What are the factors that affect the conducting system of the heart?