Basic Anatomy and Physiology 1 Cardiovascular System Topic 5.2: Heart PDF

Basic Anatomy and Physiology1 Cardiovascular system Topic 5.2 : Heart Prepared by: Madam Leong Yee Leng 1 LEARNING OUTCOME At the end of this session, student will be able to : ▪ state description of the heart ; ▪ state the function of the heart ;...

Basic Anatomy and Physiology1 Cardiovascular system Topic 5.2 : Heart Prepared by: Madam Leong Yee Leng 1 LEARNING OUTCOME At the end of this session, student will be able to : ▪ state description of the heart ; ▪ state the function of the heart ; ▪ explain the macroscopic structure of the heart ; ▪ explain the microscopic structure of the heart ; ▪ describe the blood circulation through the heart and whole body; ▪ describe the components and function of the heart; ▪ list 3 stages of cardiac cycle; ▪ identify the waves or deflections of an electrocardiogram; ▪ understand how the heart sound is produced; ▪ define cardiac output and stroke volume; 2 DESCRIPTION OF THE HEART The heart is a roughly cone- shaped hollow muscular organ. It is about 10cm long and weighs about 225g in women, 310g in men. 3  FUNCTIONS OF THE HEART 1. Supply oxygen, nutrients and other essential substances to the tissues of the body. 2. Remove carbon dioxide and other metabolic end products from the tissues. 3. Generating blood pressure which is responsible for moving blood through the blood vessels. 4. Ensuring one-way blood flow. The valves of the heart ensure a one-way flow of blood through the heart and blood vessels. 5. Regulating blood supply. 4  MACROSCOPIC STRUCTURE OF THE HEART 1. Heart Position 2. Organs associated with the heart 5  POSITION OF THE HEART Heart is muscular organ situated in between the two lungs in the mediastinum. Slightly more to the left of the chest. Apex is about 9cm to the left midline at the level of the 5th intercostal space The base extends to the level of the 2nd rib 6 Anatomical Position 7 Anatomical Position Inferiorly- apex ,rest on the central tendon of diaphragm Superiorly-the great blood vessels ,i.e. the aorta, superior vena cava, pulmonary artery Posteriorly-the oesophagus, trachea, left and right bronchus, descending aorta Laterally-the lungs, the left lung overlaps the left side of the heart Anteriorly- the sternum 8  MICROSCOPIC STRUCTURE OF THE HEART Heart consist of : 1. Three layers of heart wall 2. Four Heart chambers 3. Four Heart Valves 9  LAYERS OF THE HEART LAYERS OF WALL OF THE HEART Heart is made up of three layers of tissues 1. Outer pericardium 2. Middle myocardium 3. Inner endocardium 10  LAYERS OF THE HEART PERICARDIUM Is the outer covering of the heart. It is made up of two layers. The outer fibrous layer and inner serous layer. 1. The outer fibrous layer continues as the tunica adventitia of the large blood vessels. ✓It is attached with diaphragm below. ✓Because of the fibrous nature, it protects the heart from overstretching. 2. The inner serous layer is a membranous sheath and it is made up of two layers namely the outer parietal pericardium and inner visceral pericardium. 11  LAYERS OF THE HEART PERICARDIUM (cont.) The parietal pericardium lines the fibrous layer. The visceral pericardium is also known as epicardium. In between the parietal and visceral pericardium, there is a thin space called pericardial space - lined by the fluid secreted by epithelial cells. The fluid allows the smooth movement of the heart when it contracts and relaxes. 12  LAYERS OF THE HEART MYOCARDIUM The middle layer of the wall of the heart Constituted by three types of cardiac muscle fibers. i. The muscle fibers forming the contractile unit of the heart ii. Ther muscle fibers forming pacemaker which initiates the impulses for contraction iii. The muscle fibers forming the conductive system through which the impulses are conducted. 13  LAYERS OF THE HEART The contractile unit of the heart are striated and are more or less similar to the skeletal muscles in structure Cardiac muscle is involuntary Muscle fibers is bound by sarcolemma It has a nucleus which lies in the center of the cell. Myofibrils are embedded in the sarcolemma. 14 LAYERS OF THE HEART ENDOCARDIUM The inner most layer of the heart wall. Thin and smooth and glistening membrane. To minimize the surface friction It is formed by a single layer of endothelial cells lining the inner surface of the heart. Endocardium continues as endothelium of the blood vessels. 15  CHAMBERS OF THE HEART FOUR HEART CHAMBERS 1. Two superior receiving chamber called right and left atrium 2. Two inferior pumping chamber called right and left ventricles. 16  CHAMBERS OF THE HEART RIGHT ATRIUM - Received blood from three veins superior vena cava, inferior vena cava and coronary sinus - Septum – a thin partition between right and left atrium LEFT ATRIUM - Receives blood from the lungs through pulmonary veins - Same thickness as the Right Atrium with a smooth posterior wall. 17  CHAMBERS OF THE HEART RIGHT SIDE OF THE HEART Right atrium got the pace maker known as sinoatrial node (SA) that produces cardiac impulses and atrioventricular nodes (AV) that conducts these impulses to the ventricles. 18 CHAMBERS OF THE HEART RIGHT SIDE OF THE HEART (CONT.) Right atrium communicates with the right ventricle through the tricuspid valve. Venous blood from the right atrium enters the right ventricle through tricuspid valve. From right ventricle, pulmonary artery arises- carries venous blood to lung. Right ventricle contain a series of ridges formed by raised bundle of cardiac muscle called trabeculae carneae- help with forceful ejection of blood from the ventricles. 19  CHAMBERS OF THE HEART LEFT SIDE OF THE HEART Left atrium separated from left ventricle through the mitral valve (bicuspid valve). Left atrium empties the arterial blood into the left ventricle through this valve. Left ventricle pumps the arterial blood to different parts of the body through systemic aorta. 20  SEPTUM OF THE HEART SEPTUM OF THE HEART The two atria of the heart are separated from one another by a fibrous septum called interatrial septum. The interventricular septum separates the two ventricles. The upper part of this septum is a membranous structure, the lower part of it is muscular in nature. 21  VALVES OF THE HEART VALVES OF THE HEART Valves of the heart permit the flow of blood through the heart in only one direction. There are four valves in the human heart. Two of the valve between atria and ventricles called atrioventricular valves (AV). 22  VALVES OF THE HEART VALVES OF THE HEART (cont.) TWO semilunar valves, placed at the opening of blood vessels arising from the ventricles. 23  VALVES OF THE HEART ATRIOVENTRICULAR VALVES Also known as mitral valves or bicuspid valve Formed by two valvular cusps The right AV valve is known as tricuspid valve and it is formed by three cusps. The brim of AV valve is attached to the AV ring, which is the fibrous connection between the atria and ventricles. The cusps of the valve are attached to the papillary muscles by means of chordae tendinea. Papillary muscle-prevent the back flow of blood from ventricle to atria during ventricular contraction. 24  VALVES OF THE HEART SEMILUNAR VALVES present at the opening of systemic aorta and pulmonary artery i. Pulmonary valve ii. Aortic valve Half moon shape-semilunar valve Each one has three flaps Open towards the aorta and pulmonary artery and prevent back flow of blood into the ventricles. 25  BLOOD VESSELS OF THE HEART RIGHT SIDE OF THE HEART It receives venous (deoxygenated) blood via, i. Superior vena cava that returns the venous blood from the head, neck and upper limbs ii. Inferior vena cava that returns the venous blood from lower parts of the body iii. Coronary Sinus that returns the venous blood from the heart 26  BLOOD VESSEL OF THE HEART In the lungs, the deoxygenated blood gets oxygenated and is returned to left atrium as arterial blood through pulmonary veins. 27  BLOOD VESSEL OF THE HEART Right and left coronary arteries- supply heart with arterial blood. 1. Right Coronary Artery 2. Left Coronary Artery i. Left Circumflex Artery ii. Left Anterior Descending Artery It is branch from the aorta immediately distal to the aortic valve. 28  BLOOD CIRCULATION 1. Pulmonary Circulation 2. Systemic Circulation 3. Coronary Circulation 29  CIRCULATORY SYSTEM 1.PULMONARY CIRCULATION Superior and inferior vena cava empty the blood into the right atrium Blood ejected into right ventricle via tricuspid valve Blood is pumped from right ventricle via pulmonary valve to the lungs through pulmonary artery. The exchange of gases occurs between blood and alveoli of the lungs through pulmonary capillary membrane. The oxygenated blood returns to left atrium through the pulmonary veins.  CIRCULATORY SYSTEM 2. SYSTEMIC CIRCULATION Four pulmonary veins from the lung carry oxygenated blood back to the left atrium The blood which is pumped from left ventricle passes through the mitral valve then into aorta and arterial system and reaches the tissues. The blood vessels of arterial system are aorta, larger arteries, smaller arteries and arterioles. The arterioles branch into the capillaries. The capillaries are responsible for exchange of various substances between blood and the tissues.  CIRCULATORY SYSTEM SYSTEMIC CIRCULATION (cont.) After exchange of materials at the capillaries, the blood enters the venous system and returns to right atrium of the heart. The blood vessels of the venous tree or venous system are the venules, smaller veins, larger veins and vena cava. From right atrium, blood enters the right ventricle. Through the systemic circulation, the oxygenated blood or arterial blood is supplied from heart to the tissues The venous blood returns to the heart from the tissues.  CIRCULATORY SYSTEM 3. CORONARY CIRCULATION Coronary arteries branch from the aorta and encircle the heart Left coronary artery passes inferior and divides into left anterior descending artery and left circumflex branches Right coronary artery supplies blood to the right atrium 34  PHYSIOLOGY OF THE HEART The function of the heart is to pump blood to the lungs through the pulmonary circulation & the rest of the body through systemic circulation. Accomplished by systemic contraction & relaxation of the cardiac muscle (myocardium) Effective contraction of the heart are coordinated by the conduction system of the heart. 35  CONDUCTING SYSTEM OF THE HEART Heart has got a specialized conductive system by which, the impulse from SA node spreads to the different part of the heart. The conductive system is formed by modified cardiac muscle fibers. 36 CONDUCTING SYSTEM OF THE HEART Conduction through the Heart SA node (pacemaker) Travels through atria by inter nodal pathway Spreads to AV node Travels through AV bundle (Bundle of His) Distributed throughout ventricles by Purkinje fiber 37  Pacemaker (SA node) Pacemaker is defined as the part of the heart from which the impulses for heartbeat are produced normally. SA node is a small strip of modified cardiac muscle situated in the superior part of lateral wall of right atrium, just below the opening of superior vena cava. The fibers of this node do not have contractile elements. These fibers are continuous with fibers of atrial muscle, so that the impulse from SA node can spread rapidly through atria. Even though other parts of heart like AV node, atria, and ventricle can produce the impulses, SA node is called the pacemaker because, the rate of production of impulse is more. 38  Atrioventricular Node (AV node) Located at the wall of atrial septum near the atrioventricular valves Secondary pace maker Conduct impulse more slowly to allow time for the atria to finish their contraction phase before the ventricles begin contracting Initiates impulses 40-60 per min 39  Atrioventricular Bundle (bundle of His) Originate from AV node The AV bundle crosses fibrous ring that separates atria & ventricles Divides into right & left at the end of ventricular septum Together with bundle of branches & purkinje fibers – convey the electrical impulses from AV node to the apex 40  Purkinje Fibers Conveys electrical impulses to the apex of the myocardium. It cause the ventricles to contract causing the blood from the ventricles to enter into the pulmonary artery and aorta. 41  CONDUCTION SYSTEM OF THE HEART The beating of the heart is regulated by the intrinsic conduction (nodal) system Its function is to ensure that the chambers of the heart contract in the proper rhythm and sequence: The two atria should contract first and at the same time After that the two ventricles should contract, both at the same time The main center is the sinoatrial (SA) node, located in the right atrium The atrioventricular node is located at the junction of the atria and the ventricles 42 CONDUCTION SYSTEM OF THE HEART the atrioventricular (AV) bundle (bundle of His) is located in the interventricular septum the Purkinje fibers are located inside the walls of the ventricles the SA node is called the pacemaker of the heart, because it generates the impulse 43  CLINICAL APPLICATION Pace Maker Commonly used artificial pacemaker is the demand pacemaker which monitors the heart activity and takes control only when the heart rate falls. 44  HEART SOUND Four heart sound, each corresponding to a particular event in the cardiac cycle. The first sound “lub” is fairly loud- closure of atrioventricular valves. This corresponds with the start of ventricular systole. The second sound “dup” is softer and is due to the closure of the aortic and pulmonary valves. This corresponds with ventricular diastole. 45 ELECTRICAL ACTIVITY IN THE HEART Electrocardiogram (ECG) ECG shows the spread of the electrical signal generated by the SA node as it travels through the atrial, the AV node and ventricles. 46 ELECTRICAL ACTIVITY IN THE HEART The normal ECG tracing shows 5 waves- P,Q,R,S,and T P wave represents the impulse from the SA node sweeping over atria (atrial depolarisation) QRS complex represents the ventricular depolarization, followed immediately by ventricular systole. 47 ELECTRICAL ACTIVITY IN THE HEART The ST segment -the time the heart muscle is completely depolarised and contraction normally occurs. The T wave represents ventricular depolarization. Atrial repolarisation occurs during ventricular contraction. 48 ELECTRICAL ACTIVITY IN THE HEART The ECG described beside represent normal heart rhythm originating from SA node and so called sinus rhythm. Normal heart rate 60-100bpm, a heart rate over 100bpm is called tachycardia, and below 60bpm is bradycardia. 49  CARDIAC OUTPUT Cardiac output is the amount of blood pumped from each ventricle every minute. It means left ventricular output through aorta into various organs of the body. Stroke volume is defined as the amount of blood pumped out by each ventricle during each beat. Normal value is 70ml (60ml to 80ml) when heart rate is normal. Cardiac output (L/min) = stroke volume x heart rate Example: 70ml x 60 bpm = 4200ml/min =4.20L/min 50  CARDIAC OUTPUT Stroke volume is determined by the volume of blood in the ventricles immediately before they contract, the ventricular end diastolic volume, some times is call preload. Increase preload leads to stronger myocardial contraction and more blood is expelled, increasing stroke volume and cardiac output. 51  CARDIAC OUTPUT Factor affecting cardiac output Cardiac output= stroke volume x heart rate Factor affecting stroke volume i. Ventricular end-diastolic volume (VEDV-preload) ii. Venous return: position of the body, skeletal muscle pump, respiratory pump iii. Strength of myocardial contraction iv. Blood volume. 52  CARDIAC OUTPUT Arterial blood pressure Affects the stroke volume, ads it creates resistance to blood being pumped from the ventricles into the great arteries. This resistance (sometimes call afterload)is determined by the distensibility , or elasticity, of the large arteries and the peripheral resistance of arterioles. Increasing afterload increases the workload of the ventricles because it increases the pressure against which they have to pump. This may reduce stroke volume if systemic blood pressure becomes significantly higher than normal. 53  CARDIAC OUTPUT Blood volume This is normally kept constant by the kidneys. Should blood volume fall, e.g. through sudden haemorrhage, this can cause stroke volume , cardiac output and venous return to fall. 54  CARDIAC OUTPUT Venous return Major determinant of cardiac output and the heart normally pumps out all blood returned to it. Systemic venous pressure is much lower than arterial blood pressure, as the pressure wave from the heart is lost as blood flows through capillaries at low pressure. The blood returns to the heart, assisted by venous valves, despite opposition from gravity but helped by the contraction of skeletal muscles and the respiratory pump. 55  CARDIAC OUTPUT Heart rate Is a major determinant of cardiac output. Heart rate rises=cardiac output increase Heart rate falls= cardiac output falls too. Factor determining heart rate are: i. Autonomic nervous system Sympathetic nervous system activity increases heart rate. Parasympathetic activity decreases it ii. Circulating chemicals- hormones adrenalin have sympathetic stimulation iii. Position- heart rate faster when a person sit upright than lying down iv. Gender- heart rate is faster in women than men. v. Age –small children heart rate is more rapid than older children and adult vi. Temperature- heart rate rises and falls with temperature vii. Baroreceptor reflex 56 CARDIAC CYCLE Cardiac cycle is defined as the succession of coordinated activities, which take place during every heartbeat. Every heartbeat consist of two major periods called systole and diastole. During systole, there is contraction of the cardiac muscle and pumping of blood from the heart. During diastole, there is relaxation of cardiac muscle and filling of blood. Various changes occur in different chambers of the heart during each heartbeat. 57 CARDIAC CYCLE At rest, the healthy adult heart is likely to beat at a rate of 60-90 beats per min. Factors affecting heart: i. Autonomic activity ii. Circulating hormones iii. Activity and exercise iv. Gender v. Age vi. Temperature vii. Baroreceptor reflex viii. Emotional states 58 CARDIAC CYCLE Stages of cardiac cycle 1. Atrial systole- contraction of atria 2. Ventricular systole- contraction of ventricles 3. Complete cardiac diastole-relaxation of the atria and ventricles 59 60 CARDIAC CYCLE Stages of cardiac cycle 1. Atrial are filling with blood from superior and inferior vena cava (into the right atrium) and the pulmonary vein (into the left atrium) 2. As pressure rises in atria, the AV valves are pushed open and blood flow passively into the ventricles, helped by gravity. 3. Up to 70% of ventricular filling can be accomplished without any atrial contraction at all. 4. SA node triggers a wave of contraction that spreads over the myocardium of both atria, emptying the atria and completing ventricular filling. 61 CARDIAC CYCLE Stages of cardiac cycle 5. When the electrical impulse reaches the AV node, it is slowed down, delaying AV transmission. 6. The delay means that the mechanical result of atrial stimulation, atrial contraction, lags behind the electrical activity by a fraction of a second. 7. This allow atria to finish emptying into ventricles before the ventricles begin to contract. 8. After this brief delay, the AV node triggers its own electrical impulse which quickly spread to ventricular muscle via AV bundle, then bundle branches and Purkinje fibres. 62 CARDIAC CYCLE Stages of cardiac cycle 9. This results a wave of contraction that sweeps upwards from apex of the heart and across the walls of both ventricles, pumping the blood into the pulmonary artery and the aorta 10. The high pressure generated during ventricular contraction forces the atrioventricular valves to close, preventing backflow of blood into atria 11. Contraction of ventricles is followed by complete cardiac diastole, a period of 0.4 second, when atria and ventricles are relaxed. 12. During this time, the myocardium recovers, ready for next heartbeat, and the atria refill, ready for the next cycle. 63  CARDIAC CYCLE Stages of cardiac cycle 13. The valve of the heart and those of the great vessels open and close, according to the pressure within the chambers of the heart. 14. The AV valves open during atrial filling and systole because pressure in the atria is higher than in the ventricles. 15. When ventricles contract, there is a rapid increase in ventricular pressure, and when it rises above atrial pressure, the AV valve close. 16. When ventricular pressure rises above that in the pulmonary artery and in the aorta, the pulmonary and aortic valves open and blood flows into these vessels. 64 CARDIAC CYCLE Stages of cardiac cycle 17.When the ventricle relax and the pressure within them falls, the reverse process occurs.. 18.First the pulmonary and aortic valves close, then the atrioventricular valves open and the cycle begins again. 19.This sequence of opening and closing valves ensures that the blood flows in only one direction. 65 CONCLUSION 1. describe the structure of the heart and its position within the thorax; 2. the circulation of the blood through the heart and the blood vessels of the body; 3. The conducting system of the heart; 4. relate the electrical activity of the cardiac conduction system to the cardiac cycle; 5. main factors determining heart rate and cardiac output. 66 This Photo by Unknown Author is licensed under CC BY-SA-NC 67 This Photo by Unknown Author is licensed under CC BY-NC 68