* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download File
Cardiac contractility modulation wikipedia , lookup
Management of acute coronary syndrome wikipedia , lookup
Coronary artery disease wikipedia , lookup
Heart failure wikipedia , lookup
Aortic stenosis wikipedia , lookup
Antihypertensive drug wikipedia , lookup
Hypertrophic cardiomyopathy wikipedia , lookup
Quantium Medical Cardiac Output wikipedia , lookup
Electrocardiography wikipedia , lookup
Artificial heart valve wikipedia , lookup
Myocardial infarction wikipedia , lookup
Cardiac surgery wikipedia , lookup
Mitral insufficiency wikipedia , lookup
Arrhythmogenic right ventricular dysplasia wikipedia , lookup
Atrial septal defect wikipedia , lookup
Lutembacher's syndrome wikipedia , lookup
Heart arrhythmia wikipedia , lookup
Dextro-Transposition of the great arteries wikipedia , lookup
Biology 12 10.3 The Human Heart The heart is a muscular organ about the size of a fist. • Myocardium: the major portion of the heart; consists of cardiac muscle tissue • Pericardium: a thick membrane within which the heart lies; secretes lubricating liquid • Endocardium: the inner surface of the heart; a membrane composed of connective and endothelial tissue Structure of the Heart The septum separates the heart into a right side and a left side. The heart has four chambers: • Two upper, thin-walled atria o Atria fill with blood returning from the body and lungs • Two lower, thick-walled ventricles o Ventricles receive blood from atria and pump it out to body and lungs The heart has four valves that direct the flow of blood and prevent its backward movement. • Two atrioventricular valves that are supported by strong fibrous strings called chordae tendineae o tricuspid valve: the valve on the right side o bicuspid (mitral valve): the valve on the left side • Two semilunar valves o pulmonary semilunar valve: lies between right ventricle and pulmonary trunk o aortic semilunar valve: lies between the left ventricle and aorta Biology 12 Path of Blood through the Heart 1. The superior vena cava and the inferior vena cava, which carry O2-poor blood, enter the right atrium. 2. The right atrium sends blood through the tricuspid valve to the right ventricle. 3. The right ventricle sends blood through the pulmonary semilunar valve into the pulmonary trunk and through the two pulmonary arteries to the lungs. 4. Four pulmonary veins, which carry O2-rich blood, enter the left atrium. 5. The left atrium sends blood through the bicuspid valve to the left ventricle. 6. The left ventricle sends blood through the aortic semilunar valve into the aorta and on to the rest of the body. Biology 12 • The heart is a double pump. o Right ventricle sends blood into the lungs o Left ventricle sends blood into the rest of the body − A stronger pump, since it has to pump blood to the body • Cardiac output is the volume of blood that the left ventricle pumps per minute. o Cardiac output is about 5.25 L of blood per minute in a person with an average heart rate of 70 beats per minute o The pulse is a wave effect that passes down the walls of the arteries when the aorta expands and recoils with each ventricular contraction; can be used to determine heart rate The Heartbeat Each heartbeat is called a cardiac cycle. When a heart beats: • The two atria contract at the same time, and the ventricles are relaxed and fill with blood • Then, the two ventricles contract at the same time • Then, all the chambers relax The heart beats about 70 times a minute; each heartbeat is 0.85 s. • Systole is the contraction of the heart muscle • Diastole is the relaxation of the heart muscle Intrinsic Control of Heartbeat The heart is able to contract and relax rhythmically due to the presence of nodal tissue, a type of cardiac muscle. Nodal tissue is located in two areas:: • SA (sinoatrial) node: initiates the heartbeat and sends out an impulse every 0.85 s; also called the pacemaker • AV (atrioventricular) node: transmits an impulse through specialized cardiac muscle fibres called the atrioventricular bundle (AV bundle), which send the signal to Purkinje fibres Extrinsic Control of Heartbeat The body also has extrinsic ways to regulate the heartbeat. Medulla oblongata (portion of the brain that controls internal organs) • Can alter heartbeat by the autonomic nervous system o Parasympathetic: decreases SA and AV nodal activity when inactive o Sympathetic: increases SA and AV nodal activity when active Epinephrine and norepinephrine (hormones) • Released by the adrenal medulla • Heart pumps faster and stronger due to sympathetic stimulation and release of epinephrine and norepinephrine Biology 12 The Electrocardiogram An electrocardiogram (ECG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle. Different types of abnormalities, known as arrhythmias can be detected by an ECG • Atrial fibrillation (AF): multiple, chaotic impulses are generated from the AV node, causing an irregular, fast heartbeat • Ventricular fibrillation (VF): uncoordinated contraction of the ventricles; can occur after a heart attack, injury, or drug overdose o Heart in VF is not pumping blood and must be defibrillated by applying an electrical current to reestablish heartbeat o Automatic external defibrillators(AEDs) can be used to administer an electrical current to the chest Figure 10.14 Conduction system of the heart. b. A normal ECG . c. Ventricular fibrillation produces an irregular electrocardiogram due to irregular stimulation of the ventricles.