Cardiovascular System: The Heart PDF

The Cardiovascul ar System: The Heart CHAPTER 19 19.1 – Heart Anatomy ▪ The heart is a muscle that pumps 5.25 L of fluid per minute ▪ It is located between lungs in a space called the mediastinum ▪ The heart is separated from other structures by the pericardium – a tough membrane ▪ The heart sits in...

The Cardiovascul ar System: The Heart CHAPTER 19 19.1 – Heart Anatomy ▪ The heart is a muscle that pumps 5.25 L of fluid per minute ▪ It is located between lungs in a space called the mediastinum ▪ The heart is separated from other structures by the pericardium – a tough membrane ▪ The heart sits in the pericardial cavity ▪ The base of the heart is superior and medial to the apex ▪ The great veins (superior and inferior vena cava) and arteries (aorta and pulmonary trunk) attach at the base ▪ Cardiac notch – a depression of the inferior lobe of the left lung 19.1 - Heart ▪ A typical heart is about the size of your fist, athletes are larger ▪ 4 chambers in the heart – 2 atria and 2 ventricles ▪ Atria are superior, collect blood, and push it into lower chambers ▪ Ventricles are inferior and pump blood out to the body or lungs ▪ 2 circuits – pulmonary and systemic ▪ Right ventricle connects to the pulmonary trunk and left ventricle connects to the aorta ▪ CO2 leaves and O2 enters in the pulmonary capillaries 19.1 - Heart ▪ Pulmonary artery is the only artery to carry deoxygenated blood ▪ Pulmonary vein is the only vein to carry oxygenated blood 19.1 – Heart Membranes and Layers ▪ Two layers – Fibrous and Serous Pericardium ▪ Serous layer has 2 sub layers – parietal and visceral layers separated by pericardial cavity ▪ Cavity filled with lubricating fluid ▪ Visceral layer is called epicardium and produces fluid 19.1 – Heart Features ▪ 2 auricles – thin walled structures that can hold blood and empty into atria ▪ Sulci – fat filled grooves that contain coronary blood vessels 19.1 - Layers ▪ Epicardium – most superficial ▪ Myocardium – middle thickest layer, muscle cells, nerve fibers, and blood vessels. Muscles on the left side are thicker ▪ Endocardium – innermost layer, lines the chambers filled with blood, covers heart valves, the cells are continuous with the lining of the blood vessels, cells are called endothelium ▪ Endothelium releases endothelins which are strong vasoconstrictors and may regulate growth patterns of cardiac muscle cells 19.1 – Internal Structures ▪ Septum – divides the heart into chambers, physical extensions of myocardium, 3 septa in the heart ▪ Fossa ovalis – a depression in the interatrial septum, was a foramen ovale (opening) while a fetus ▪ Atrioventricular valves – separate atria from ventricles, tricuspid on right and mitral or bicuspid on left ▪ Semilunar valves – separate ventricles from blood vessels, pulmonary and aortic valves 19.1 - Chambers ▪ Right atrium – receives deoxygenated blood from systemic circulation (superior and inferior vena cava, coronary sinus), contains pectinate muscles, and has a small contractile phase ▪ Right ventricle – has chordae tendineae connected to 3 papillary muscles that close the tricuspid valve, has trabeculae carneae and moderator band (muscles for cardiac conduction), receives deoxygenated blood from the right atrium ▪ Left atrium – receives oxygenated blood from the pulmonary veins, no pectinate muscles, small contractile phase (20%) ▪ Left ventricle – thicker muscle, no moderator band, has chordae tendineae connected to 2 papillary muscles to close the mitral valve, receives oxygenated blood from the left atrium, it pushes blood into the aorta 19.1 - valves ▪ Valves ensure unidirectional blood flow ▪ Semilunar valves have no muscular attachments, but make an audible sound as they close ▪ Tricuspid and mitral valves close due to papillary muscles ▪ Valve disorders are usually caused by inflammation ▪ Altered blood flow produces a heart murmur during auscultation 19.1 – Coronary Circulation ▪ Coronary circulation is cyclical and not continuous (it nearly ceases during heart contraction) ▪ Arteries branch off the aorta just superior too semilunar valve ▪ Coronary arteries bring blood to the myocardium and other components ▪ Anastomosis - blood vessel interconnections to allow blood to flow even if there is a partial blockage in another branch ▪ Coronary veins bring the deoxygenated blood back to the right atrium 19.2 – Cardiac Muscle and Electrical Activity ▪ Autorhythmicity – cardiac muscle can initiate an electrical potential at a fixed rate ▪ Myocardial conducting cells – 1%, initiate and propagate the action potential through the heart ▪ Myocardial contractile cells – 99%, conduct impulses and contract to pump blood through the body ▪ Cardiac muscle cells – shorter and narrower than skeletal muscles, have striations, T tubules are found only at Z discs so there are half as many, sarcoplasmic reticulum stores little Ca++, lots of mitochondria, and most have 1 nucleus 19.2 ▪ Cardiac muscle cells branch freely ▪ 2 cells adjoin at an intercalated disc ▪ Desmosomes stop the cardiac muscle cells from ripping apart ▪ Gap junctions allow ions to travel between cells to keep the proper contractile rhythm ▪ Cardiac muscle cells have a long refractory period (prevent tetany) and a short relaxation period (heart refills with blood) 19.2 - Conduction ▪ Sinoatrial (SA) node – in the superior and posterior wall of the right atrium, sets normal cardiac rhythm, known as the pacemaker ▪ Atrioventricular (AV) node – impulse comes from SA node through the intermodal pathways, inferior portion of right atrium, it slows the impulse and forces the atrioventricular septum to contract ▪ Max efficient contraction rate is 220 BPM 19.2 - Conduction ▪ Bundle of His – receives impulse from AV node and flows down the interventricular septum, it branches into right and left bundle branches ▪ Purkinje fibers – additional fibers to spread the impulse around the ventricles, they start at the apex and flow toward the atrioventricular septum ▪ Total time from initial impulse to ventricle depolarization is about 225 ms 19.2 – Membrane Potentials ▪ Cardiac conductive cells have Na+ channels that allow a slow influx to create the spontaneous depolarization, they repolarize similar to a skeletal muscle cell ▪ Cardiac contractile cells depolarize as an impulse reaches them, then they plateau before repolarizing ▪ Plateau – at +30mV Na+ channels close, Ca++ channels are open, and few K+ channels are open. At 0mV Ca++ channels close and K+ channels open for typical repolarization. ▪ This long refractory period prevents premature contractions 19.2 – Calcium ions ▪ Slow Ca++ channels allow for the plateau ▪ Ca++ binds to troponin to allow the myosin and actin cross bridge 19.2 – Comparative Conduction ▪ SA node would fire 80 – 100 times per minute if not for endocrine control ▪ AV node would fire 40 – 60 times per minute ▪ Atrioventricular bundle would fire 30 – 40 times per minute ▪ The bundle branches would fire 20 – 30 times per minute ▪ Purkinje fibers would fire 15 – 20 times per minute ▪ Lowest recorded HR is 28 BPM, pro cyclist 19.2 - Electrocardiogram ▪ Electrodes on the body to record electrical signals of the heart ▪ Abbreviated ECG or EKG ▪ 3, 5, or 12 leads. More leads means more info ▪ The prominent points : ▪ P wave – depolarization of the atria ▪ QRS complex – depolarization of ventricles and it masks the repolarization of the atria ▪ T wave – repolarization of ventricles 19.2 – Electrical Problems ▪ AED’s are designed to correct fibrillations ▪ Heart block – interruption in the normal conduction pathway ▪ Artificial pacemaker – delivers electrical impulses to ensure effective heart contractions (some have built in defibrillators)