THE CARDIOVASCULAR SYSTEM THE HEART INTRODUCTION The cardiovascular

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THE CARDIOVASCULAR SYSTEM THE HEART

THE CARDIOVASCULAR SYSTEM THE HEART

INTRODUCTION • The cardiovascular system is composed of blood, blood vessels and the heart.

INTRODUCTION • The cardiovascular system is composed of blood, blood vessels and the heart. • Our heart beats nearly 100, 000 times daily. • Blood vessels are fractionated into a pulmonary circuit and systemic circuit. • Artery: vessels that carry blood away from the heart. Usually oxygenated • vein: vessels that carry blood towards the heart. Usually deoxygenated. • Capillaries: a small blood vessel that allow diffusion of gases, nutrients and wastes between plasma and interstitial fluid.

HEART ANATOMY • The human heart, which is about the size of a clenched

HEART ANATOMY • The human heart, which is about the size of a clenched fist, is located obliquely within the mediastanium of the thorax. • The heart is located within a double sac made up of the outer fibrous pericardium and the inner serous pericardium (parietal and visceral layers). • The pericardial cavity contains the thymus, esophagus and trachea. The pericardium may be divided into the visceral and parietal pericardium. The cavity is space between the pericardium and epicardium. • The cavity contains a fluid called the pericardial fluid.

Layers of the heart wall • Layers of the heart wall, from the interior

Layers of the heart wall • Layers of the heart wall, from the interior out are the endocardium, the myocardium and the epicardium. Epi. Lines the heart surface, the myo. Makes up the largest portion of the heart and endo. The innermost layer of the heart’s wall. • The heart has four chambers- two superior atria and two inferior ventricles. Functionally the heart is a double pump. • Entering the right atrium are the superior vena cava, the inferior vena cava, and the coronary sinus. Four pulmonary veins enter the left atrium. • The right ventricle discharges blood into the pulmonary trunk and the left ventricle pumps blood into the aorta.

The Heart • The heart has four valves, two AV valves : bicuspid and

The Heart • The heart has four valves, two AV valves : bicuspid and tricuspid- and two semilunar valves-aortic and pulmonic. • The tricuspid and bicuspid are located between the atria and ventricles and these valves are anchored by fibers called Chordae Tendinae. • These serve as one way door to keep blood flowing in one direction. • The heart cannot pump unless an electrical stimulus occurs. • SA--> AV--> Purkinje fibers.

Pathway of blood through the heart • The right heart is the pulmonary circuit

Pathway of blood through the heart • The right heart is the pulmonary circuit pump. Oxygen-poor systemic blood enters the right atrium, passes into the right ventricle, through the pulmonary trunk to the lungs, and back to the left atrium via the pulmonary veins. • The left heart is the systemic circuit pump. Oxygen-laden blood entering the left atrium from the lungs flows into the left ventricle and then into the aorta, which provides the functional supply of all body organs. Systemic veins return the oxygen -depleted blood to the right atrium.

Innervation of the Heart • The sympathetic and parasympathetic divisions of the ANSS provide

Innervation of the Heart • The sympathetic and parasympathetic divisions of the ANSS provide innervation to the heart through the cardiac plexus. • The vagus nerve carries PS preganglionic fibers to small ganglia in the cardiac plexus. Both ANS divisions innervate the SA and AV nodes and atrial muscle cells. • Stimulation of the cardioaccedlaratory center activates the necessary sympathetic neurons; the nearby cardioinhibitory center governs the activity of the PS neurons. • The baroreceptors and chemoreceptors innervated by NIX and NX are monitored by cardiac center.

Coronary Circulation • The coronary circulation includes the right and left coronary arteries. These

Coronary Circulation • The coronary circulation includes the right and left coronary arteries. These ensure a continuous flow of blood to meet the demands of active cardiac muscle and cardiac veins. • Right cornary artery supplies blood to the rt. Atrium, portion of both ventricles and portions of the SA and AV nodes. • The left coronary artery-to the left ventricle, left atrium and IV septum. • Venous blood, collected by the cardiac veins (great, middle and small), is emptied into the coronary sinus.

Cardiac Veins • The great cardiac vein begins on the anterior surface of the

Cardiac Veins • The great cardiac vein begins on the anterior surface of the ventricles. Then it reaches the level of the atria and then curves around the left side of the heart within the coronary sulcus. • The vein empties into the coronary sinus which then communicates with the right atrium near the base of the inferior vena cava. • Other cardiac veins are: posterior cardiac vein, the middle cardiac vein and small and anterior cardiac veins. They all empty into the great cardiac vein or coronary sinus.

Cardiac Muscle Fibers • Cardiac muscle cells are branching, striated, generally uninucleate cells. They

Cardiac Muscle Fibers • Cardiac muscle cells are branching, striated, generally uninucleate cells. They contain myofibrils consisting of typical sarcomeres. • Adjacent cardiac cells are connected by intercalated discs containing desmososmes and gap junctions, which convey the force of contraction from cell to cell and conduct action potentials. • Cardiac muscle has abundant mitochondria and depends primarily on aerobic respiration to form ATP.

Mechanism and events of contraction • Action-potential generation in the contractile cardiac muscle mimics

Mechanism and events of contraction • Action-potential generation in the contractile cardiac muscle mimics that of skeletal muscle. Membrane depolarization causes opening of sodium channels and sodium entry which is responsible for the rising phase of the action potential curve. • Depolarization also opens slow calcium channels. -creates the plateau. the actin potential is coupled to sliding of the myofilaments by ionic calcium released by the SR and entering from the extracellular space. • Compared to skeletal muscle, cardiac muscle has a longer refractory period that prevents tetanization.

Heart Physiology • Certain noncontractile cardiac muscle cells exhibit automaticity and rhythmicity and can

Heart Physiology • Certain noncontractile cardiac muscle cells exhibit automaticity and rhythmicity and can independently initiate action potentials. • Such cells have an unstable resting potential called a pacemaker potential that gradually depolarizes drifting toward threshold for firing. • These cells comprise the intrinsic conduction system of the heart. • Defects in the intrinsic conduction system can cause arrhythmia, fibrillation ands heart block.

Electrical Events • Autorhythmicity: heart contracts without help of hormonal or neuronal stimulation. •

Electrical Events • Autorhythmicity: heart contracts without help of hormonal or neuronal stimulation. • The conduction or nodal system of the heart consists of the AV and SA nodes, the AV bundle and bundle branches and Purkinje fibers. • This system coordinates the depolarization and ensures the heart beats as one. • The SA acts as the heart’s pacemaker and sets the sinus rhythm.

Impulse pathway • SA node sends stimulus->reaches AV node-->internodal pathways->atrial contraction->IV septum->bundle branches, Purkinje

Impulse pathway • SA node sends stimulus->reaches AV node-->internodal pathways->atrial contraction->IV septum->bundle branches, Purkinje fibers, papillary muscles->Purkinje relay to ventricular myocardium->ventricular contraction>blood pushed to aortic and pulmonary trunks. • Conduction deficit problems that happen when the conducting pathways are damaged. The rhythm of heart will be disturbed. • Ectopic pacemaker: an abnormal cell generates action potential which overrides those of SA or AV nodes. Disrupts timing of ventricular contraction. Heart efficiency is reduced.

Electrical events • The heart is innervated by the ANS. • Autonomic cardiac centers

Electrical events • The heart is innervated by the ANS. • Autonomic cardiac centers in the medulla include the cardioaccelaratory center, which projects to the T 1 -T 5 region of the spinal cord, which in turn projects to the cervical and upper thoracic chain ganglia. • The PS cardioinhibitory center exerts influence via the vagus nerve which project to the heart wall. Most PS nerves serve the SA and AV nodes.

ECG • A recording of electrical activities in the heart is an Electrocardiogram or

ECG • A recording of electrical activities in the heart is an Electrocardiogram or ECG. • Important landmarks of an ECG include P wave, QRS complex and the T wave. • The P wave reflects atrial depolarization. • The QRS complex indicates ventricular depolarization. • T wave indicates ventricular repolarization. • ECG analysis is especially useful in diagnosing cardiac arrhythmias, abnormal patterns of cardiac electrical activity.

Mechanical Events: Cardiac Cycle • Cardiac cycle refers to events occurring during one heartbeat.

Mechanical Events: Cardiac Cycle • Cardiac cycle refers to events occurring during one heartbeat. It contains periods of atrial and ventricular systole (contraction) and diastole (relaxation). • When the heart beats the two ventricles eject equal volumes of blood. • The closing of valves and rushing of blood through the heart causes characteristic heart sounds which can be heard during auscultation.

Cardiac Cycle • During mid-to-late diastole, the ventricles fill and atria contract. • Ventricular

Cardiac Cycle • During mid-to-late diastole, the ventricles fill and atria contract. • Ventricular systole consists of the isovolumetric contraction phase and the ventricular ejection phase. • During early diastole, the ventricles are relaxed and are closed chambers until increasing atrial pressure forces the AV valves open and the cycle begins again. • At a normal heart rate of 75 beats/min, a cardiac cycle lasts 0. 8 s. • pressure changes promote blood flow and valve opening and closing.

CARDIAC OUTPUT • Cardiac output which is typically 5 L/min is the amount of

CARDIAC OUTPUT • Cardiac output which is typically 5 L/min is the amount of blood pumped out by each ventricle in one minute. • Stroke volume is the amount of blood pumped out by a ventricle with each contraction. • Cardiac output=heart rate X stroke volume

CARDIAC OUTPUT • Stroke volume depends to a large extent on the degree of

CARDIAC OUTPUT • Stroke volume depends to a large extent on the degree of stretch of cardiac muscle by venous return. • This is approx. 70 m. L and is the difference between the EDV(end diastolic volume) and ESV (end systolic volume). Anything that influences heart rate or blood volume influences venous return and hence stroke volume. • Activation of the SNS increases heart rate and contractility; parasympathetic activation decreases heart rate and contractility.

CARDIAC OUTPUT • Chemical regulation of the heart is effected by hormonesepinephrine and thyroxine-

CARDIAC OUTPUT • Chemical regulation of the heart is effected by hormonesepinephrine and thyroxine- and ions (Na, K, Ca). Imbalances in the ion severely impair heart activity. • Other factors influencing heart rate are age, sex, exercise and body temperature. • Congestive heart failure occurs when the pumping of the heart is inadequate to provide normal circulation to meet body needs. • Right heart failure leads to systemic edema and left to pulmonary edema.

Factors Affecting Heart Rate • The cardioaccelaratory center in the medulla oblongata activates sympathetic

Factors Affecting Heart Rate • The cardioaccelaratory center in the medulla oblongata activates sympathetic neurons; the cardioinhibitory center governs the activities of the parasympathetic neurons. These in turn receive inputs from higher centers and from the baroreceptors and chemoreceptors. • The basic heart rate is established by pacemaker cells of the SA node. • Sympathetic activity produces more powerful contractions and parasympathetic stimulation slows the heart.