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Mammalian Transport System Ch. 8 Part 4 Heart Function Structures to Know • • • • • • • • Atria (Atrium) or auricle • Upper chambers • Receive blood from veins Ventricles • Lower chambers • Blood flows into from the atria and out through arteries Aorta Pulmonary artery Venae cavae (vena cava) Pulmonary veins Coronary arteries • Bring oxygenated blood back to the heart Septum • Wall of muscle that separates chambers on the right side of the heart from the chambers on the left side of the heart • Blood cannot pass through Valves and Nodes to know • Atrioventricular valves (between the atrium and the ventricle) • Mitral/bicuspid valve (LEFT SIDE OF HEART) • Tricuspid valve (RIGHT SIDE OF HEART) • Semilunar valves • Pulmonary Valve • Aortic Valve • Sinoatrial node (SAN) • Patch of specialized muscle fibers in RIGHT ATRIUM • Pacemaker • Atrioventricular node (AVN) • Patch of conducting muscle fiber located in upper septum • Purkyne tissue • Conducting muscle fibers running down septum, along the right and left ventricles Valves • Atrioventricular valves (between the atrium and the ventricle) • Mitral/bicuspid valve (LEFT SIDE OF HEART) • Tricuspid valve (RIGHT SIDE OF HEART) • Semilunar valves • Pulmonary Valve • Aortic Valve Important!!!! • Heart is myogenic does NOT need outside nerve impulses to initiate heart beat • Valves in heart do NOT actively open and close • Valves open and close due to PRESSURE changes in chambers Closing of valves create thump-thump of heartbeat Structure of Heart • Atrium walls thin, muscular walls • Low pressure exerted • Ventricle walls thick and muscular • Right ventricle small force needed to push blood to lungs • Left ventricle large force needed to push blood all over body • VERY MUSCULAR • Greater pressure developed in left ventricle than left atria The Cardiac Cycle • Sequence of events that make up 1 heart beat • Heart beats about 70x a minute • 3 stages of the cycle 1. Atrial systole 2. Ventricular Systole 3. Ventricular Diastole Systole Contraction Diastole Relaxation Atrial Systole • Heart filled with blood • Muscle in atrial walls (very thin) contract • Not a lot of pressure from this contraction • Enough pressure to force blood in atria through ATRIOVENTRICULAR VALVES (AV) into ventricles • No back flow of blood into pulmonary veins or vena cava b/c of semilunar valves Ventricular Systole • Ventricles contract 0.1 s after atria contracts • Thick, muscular ventricle walls push blood out (exert high pressure) • AV valve shut when pressure in ventricles exceeds pressure in atria • Semilunar valves open • Blood rushes up into aorta & pulmonary artery • Lasts for 0.3 seconds Ventricular Diastole • After 0.3 seconds, ventricular muscle relaxes • Ventricle pressure decreases • Semilunar valves shut, preventing backflow of blood • Blood only fills in cusps of valves • Blood from veins flow into the 2 atria • Blood is at low pressure • Walls of atria expand to accommodate blood (very little resistance) • Some blood trickles into ventricles through AV valve • Atria contracts and cardiac cycle begins again Control of the Heart Beat • Myogenic muscles • Naturally contracts and relaxes • No nerve impulses required • Sinoatrial Node (SAN) • Set out rhythm for all other muscle cells to contract • SAN contraction rhythm slightly faster than the rest of the heart • SAN contracts wave of excitation (depolarization) sent across all of the atria & muscles of atria contract Things NOT to say when describing nodes: • “Signal” • “Wave” alone • “Pulse” • “Message” • “Nerve impulse” You SHOULD describe the function of SAN using: • “Wave of excitation” • “depolarization” • “impulse” Ventricle contraction • SAN causes contraction of all atria muscles • Ventricle muscles delayed due to band of fibers between the atria and ventricles that does NOT conduct electric impulses • Only path for impulses to reach ventricles is through path of conducting fibers in septum called ATRIOVENTRICULAR NODE (AVN) • AVN receive excitation from atria, delays it 0.1s and then passes it to another bunch of conducting fibers called the PURKINJE FIBERS or PURKYNE TISSUE • Wave of excitation is sent up ventricle walls— bottom-up Fibrillation • When muscular walls of heart flutter rather than contract and relax as a whole • Rapid, irregular, unsynchronized contraction of muscle cells • Atrial fibrillation (non fatal) Afib • Can lead to stroke • Ventrical fibrillation (fatal) Vfib • Faint, cardiac arrest • Caused by: • Electric shock or damage to large areas of muscle in walls of heart • Miss firing of electric impulse from atria • Instead of electrical impulse going from atria to AVN to Purkinje tissue in the ventricle, all muscle cells in ventricle get excited in all directions Electrocardiograms (ECGs) • Graph plotting voltage vs. time • Records electrical potentials of heart over time • Place electrodes over opposite sides of heart • P= wave of excitation over atrial walls • Q, R, S= wave of excitation over ventricle walls • T = recovery of ventricle walls • Contraction time = time b/t Q and T • Filling time = time b/t T and Q • EKG paper is a grid where time is measured along the horizontal axis. • Each small square is 1 mm in length and represents 0.04 seconds. • Each larger square is 5 mm in length and represents 0.2 seconds. • Voltage is measured along the vertical axis. • 10 mm is equal to 1mV in voltage. How To Read an ECG Calculating Heart from ECG 1. Determine rate of strip • Time of strip is given; measure strip with ruler and divide length by sec of strip or… • May be given 20mm * s-1 2. Measure distance of one cardiac cycle • Beginning of one P to the beginning of the next P