CVS - Heart part 1 PDF

By Doaa Samy Professor of Physiology  Anatomical organization of the cardiovascular system It consist of: 1- The heart: 2 atria , 2 ventricles and 4 valves. 2- The blood vessels: arteries, arterioles, capillaires, veinules, viens. The heart...

By Doaa Samy Professor of Physiology  Anatomical organization of the cardiovascular system It consist of: 1- The heart: 2 atria , 2 ventricles and 4 valves. 2- The blood vessels: arteries, arterioles, capillaires, veinules, viens. The heart  Four chambers & Four Valves Atrio-ventricular valves (A-V): - Tricuspide valve: between the right atrium and right ventricle - Mitral valve: between the left atrium and left ventricle Semilunar Valves: - The Pulmonic Valve: between the right ventricle and pulmonary trunk - The ortic Vlave: between left ventricle and aorta  Blood Flow through the Heart Right atrium (RA) - receives deoxygenated blood from two sources PA PA – superior vena cava (SVC) PT – inferior vena cava (IVC) Right ventricle (RV) – receives blood from RA RA – pumps blood to lungs via pulmonary arteries (PA) RV  Blood Flow through the Heart Pulmonary arteries – Carry deoxygenated blood from the heart to the lungs PA PA for gas exchange – blood gives up CO2 and PT picks up O2 in the lungs Pulmonary veins (PV) transmit the oxygenated RA blood from the lungs to the left atrium RV Pulmonary Circulation  Blood Flow through the Heart Left atrium – receives oxygenated blood from PV Aortic – Pumps blood to left arch ventricle PV LA PV Left ventricle (LV) – Pumps oxygenated blood to the body via the aorta LV Circulations in the body l Systemic or “greater” circulation: start from the left ventricle to right atria. (arterial blood ➔ ➔ venous blood) l Pulmonary or “lesser” circulation: start from the right ventricle to left atria. (venous blood ➔ ➔ arterial blood) Properties of the cardiac muscle Properties of Cardiac Muscle Contractility Rhythmicity Conductivity Excitability  1- Contractility Definition: It is the ability to convert chemical energy into mechanical work (contraction and relaxation) , thus acting as a pump to push blood into the blood vessels. Contraction of the heart is called systole while its relaxation is called diastole.  Inotropism: influence on contractility +ve inotropic effect is one which increases myocardial contractility. e.g sympathetic supply, digitalis. -ve inotropic effect is one which decreases myocardial contractility. e.g vagus nerve, toxins. FACTORS AFFECTING CONTRACTILITY OF THE HEART 1- AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC increases the force decreases the force of contraction of of contraction of the both atria and atria, but not the ventricles ventricles  FACTORS AFFECTING CONTRACTILITY OF THE HEART 2- Frank-Starling law It states that: “the strength of cardiac contraction is directly proportional to the initial length of its fibers (or the end-diastolic volume) provided the fibers are not excessively stretched above their elastic limit”  Frank Starling Law of the Heart = Increased blood volume = increased stretch of Increased force to pump blood out. myocardium Cardiac muscle is like a rubber band Like a rubber band on increasing the initial length the force of contraction increases but within limits  FACTORS AFFECTING CONTRACTILITY OF THE HEART 3- ELECTROLYTES Calcium Potassium promotes systole, so, excess promotes diastole , so, calcium (hypercalcemia) excess potassium prolongs the period of systole (hyperkalemia) prolongs and the heart may stop in the period of diastole spastic contraction called and the heart becomes calcium rigor. dilated and flaccid.  2- Rhythmicity (automaticity) The ability of cardiac muscle to beat [contract and relax] at regular intervals. Does not depend its nerve supply It is MYOGENIC IN NATURE The conducting system of the heart These are specialized cardiac tissues concerned with the formation (rhythmicity) and propagation (conductivity) of cardiac impulse. It involves: sino-atrial node (SAN), Atrio-ventricular node (AVN), Atrio-ventricular bundle or bundle of His (AVB), Right and left bundle branches Purkinje fibers that end into the ventricular wall. The conducting system of the heart RHYTHMICITY IN DIFFERENT CARDIAC FIBRES SA node =100-105/min AV node and bundle = 45-60 b/min Purkinje & Ventricles= 25-40 b/min  Pacemaker of the heart If the SAN stopped SA-node for any reason AV-node normal pacemaker ectopic pacemaker 105 impulse/min 45-60 impulse/min Sinus rhythm Nodal rhythm If the AVN stopped for any reason Purkinje System & ventricles Inhibitory vagal ectopic pacemaker tone 25-40 impulse/min Idioventricular rhythm The normal pace maker of the heart: is SAN because it has the highest rate of discharge of cardiac impulses i.e highest rhythmicity. Vagal tone: At rest, Parasympathetic effect exceeds the sympathetic effect at the SAN, causing decrease in the heart rate from the intrinsic rate of the SA node (100-105) to the resting heart rate= 70-75 b/min Chronotropism: influence on rhythmicity = heart rate +ve chronotropic effect is one which increases heart rate. -ve chronotropic effect is one which decreases heart rate. FACTORS AFFECTING RHYTHMICITY OF THE HEART 1- AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC Increases the Decreases the rhythmicity of the rhythmicity of the SAN, AVN, AVB and SAN, AVN but not AVB Purkinje fibers or Purkinje fibers Increases heart rate Decreases heart rate FACTORS AFFECTING RHYTHMICITY OF THE HEART Physical and chemical factors Temperature Hypoxia Fever Increases heart Moderate changes rate increase, while severe Each 1ºC change ➔ changes decrease 15 B/min heart rate  3- Conductivity It is the ability to transmit the cardiac impulse generated in the SA node to the rest of the heart  3- Conductivity Cardiac cells are electrically coupled via gap junctions, excitation of one cell results in the spread of action potential throughout the heart. Conducting system of the heart  How it happens?? PURKINJE Rt & Lt FIBREs bundle BUNDLE OF HIS branches AV NODE SA NODE Conduction speed Atrial pathway= 1m/s AV node= 0.05m/s Bundle of His= 1m/s Purkinje fibers= 4m/s Ventricle= 1m/s The conducting system of the heart The slowest conduction of impulses occurs at AVN to allow complete emptying of atria before ventricular systole start. The fastest conduction of impulses occurs at Purkinje fibers to allow simultaneous contraction of all ventricular muscle fibers at the same time (as one unit). Dromotropism: influence on conductivity +ve dromotropic effect is one which increases conductivity. -ve dromotropic effect is one which decreases conductivity (heart block).  FACTORS AFFECTING CONDUCTIVITY OF THE HEART 1- AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC Increases the Delays the conduction conduction at the at the AVN & AVB AVN, AVB and Increases the AVN delay Purkinje fibers If severe >>>>> Heart block  4- Excitability Definition: Ability of the heart to respond to a stimulus Once the heart is stimulated, excitability is completely lost (absolute refractory period), then excitability is gradually recovered (relative refractory period) Excitability changes during cardiac activity Absolute Refractory Period (ARP) Complete loss of excitability Whole systole and early part of diastole. No stimulus whatever strong can excite the cardiac tissue Value of this long ARP: to prevent tetanus of the heart. Relative Refractory Period (RRP) Excitability is partially restored. It occupies the late part of diastole If a strong stimulus is applied during the RRP, it would produce a new systole “extrasystole” BUT a stronger stimulus is required to give a response. Bathmotropism: influence on excitability +ve bathmotropic effect is one which increases excitability. -ve bathmotropic effect is one which decreases excitability..  FACTORS AFFECTING EXCITABILITY OF THE HEART 1- AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC Increases the Decreases the excitability of the excitability of the heart heart May cause extrasystole Cardiac Properties Parasympathetic (Vagal) Sympathetic Supplies the atria, SA Supplies all cardiac tissue node, AV node & AV including the ventricles bundle+ coronaries but not + coronaries the ventricles (ventricular escape) Rhythmicity Slowing due to depression Acceleration due to ↑ of of SA node SA node Excitability ↓ ↑ AV conduction ↓ (heart block) ↑ Contractility Depressed in atria Stimulated in atria and ventricles neurotransmitter acetylcholine Norepinephrine Epinephrine receptor Muscarinic B1- adrenergic Coronary blood flow ↓ ↑ CARDIAC CYCLE  Cardiac cycle= one beat It is the cardiac systole and diastole and the accompanying changes in pressure and volume of different cardiac chambers.  CARDIAC CYCLE TIME Average heart rate= 75/minute. cardiac cycle= 60/75= 0.8 sec. Three Phases 1) Atrial systole 2) Ventricular systole 3) Diastole of the whole heart systole diastole total Atria 0.1 0.7 0.8 sec. Ventricles 0.3 0.5 0.8 sec.  Atrial Atrial systole diastole ventricular ventricular diastole diastole Atrial v ar Atrial diastole di e systole n ventricul diastole a tri stole cu lar sys cular ve iast ntr ole e Atrial d tol tri icu Atrial ven diastole lar diastole ventricular ventricular diastole systole Atrial Atrial diastole diastole  During atrial systole, the A-V valves are open and the ventricles are in diastole to receive the blood. During ventricular systole, the A-V valves close and the semilunar valves open. The atria are in diastole Atrial and ventricular diastoles occur at the same time during the diastole of the whole heart, which lasts for 0.4 sec. The A-V valves are open, and the semilunar valves are closed. The diastole of ventricles is important for filling of the ventricles & filling of the coronary arteries with blood. 75% of ventricular filling occurs by pressure gradient, while the remaining 25% by atrial systole  Heart sounds Two classical sounds of the heart, first and second sounds. The first heart sound. Cause: - sudden closure of the A-V valves. It occurs at the beginning of systole The Second heart sound. Cause: - sudden closure of the semilunar valves. It occurs at the beginning of diastole 49 THANK YOU