Chapter 19: 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 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) 19.2 – Cardiac Muscle Metabolism ▪ Normally metabolism is entirely aerobic ▪ Heart cells have a lot of myoglobin ▪ Myoglobin stores oxygen in muscle cells 19.3 – Cardiac Cycle ▪ Begins at atrial contraction and ends with ventricular relaxation ▪ Systole – pumping blood into circulation ▪ Diastole – chambers are relaxed and filling with blood 19.3 – Cardiac Cycle Phases ▪ Start with atria and ventricles relaxed – blood flows into atria and through into ventricles (70% - 80%), semilunar valves are closed ▪ Atrial systole – atria contract from superior portion following depolarization (P wave), known as “atrial kick” ▪ Atrial diastole – muscles relax as ventricles begin to contract ▪ Ventricular systole – blood in ventricles is the end diastolic volume (EDV) or preload, it flows toward the atria forcing the atrioventricular valves to close (isovolumic contraction), pressure increases and forces the semilunar valves open 19.3 - Cycle ▪ Stroke volume – amount of blood pushed out by ventricles, normally 70 80 mL ▪ End systolic volume (ESV) – amount of blood left in ventricles after stroke volume is pushed out Ventricular Diastole – relaxation (T wave), semilunar valves close and atrioventricular valves are closed too (isovolumic ventricular relaxation phase). Second phase the atrioventricular valves open 19.3 – Heart Sounds ▪ Healthy heart has 2 audible sounds – S1 and S2 (lub dub) ▪ S1 – closing of atrioventricular valves ▪ S2 – closing of semilunar valves ▪ S3 – blood flowing into atria, sloshing in ventricle, or tensing of chordae tendineae ▪ S4 – blood being pushed into a stiff or hypertrophic ventricle, failure of left ventricle, will happen before other sounds ▪ Having both S3 and S4 is referred to as S7 19.3 19.3 - Murmur ▪ Heart murmurs are caused by turbulent blood flow ▪ Inhalation increases blood flow to the right side and may increase the amplitude of a right sided murmur ▪ Expiration partially restricts blood flow to the left side and may increase the amplitude of a left sided murmur 19.4 – Cardiac Physiology ▪ Cardiac Output (CO) – amount of blood pumped by each ventricle in 1 minute ▪ CO = HR * SV ▪ SV is normally calculated in an echocardiogram ▪ SV = EDV – ESV ▪ Normal CO is in a range of 4 – 8 L/min ▪ Ejection fraction – percentage of blood pumped (SV divided by EDV), normal range is 50% – 70% 19.4 - Exercise ▪ Activity can increase CO by 4 – 8 times ▪ Cardiac reserve – difference in max CO and resting CO ▪ Max HR – 220 minus age (fair, but not exact number) ▪ Exercise increases HR, which increases CO ▪ Eventually HR gets high so that there is little time for blood to fill and so SV decreases, next HR gets even higher so CO decreases ▪ Target heart rate – a range to keep CO high