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SC BIOL 244 - The Heart

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BIOL 244 1st Edition Lecture 7Outline of Last Lecture I. Cardiovascular System II. HeartIII. Coverings of the HeartIV. Anatomy of the HeartV. Circuits of the HeartOutline of Current Lecture I. Valves of the HeartII. Cardiac CycleIII. Cardiac Muscle FibersIV. Cardiac Muscle ContractionV. Self-excitable Cardiac CellsVI. Autonomic Innervation of the HeartVII. ElectrocardiogramVIII. HeartbeatCurrent LectureI. Valves of the Heart: 4 valves, 2 setsa. Right atrioventricular valves (AKA right AV, Tricuspid valve)i. Valves between the right atrium and right ventricle ii. Has 3 flaps of tissue1. When flaps press up against each othera. Valve closesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Left atrioventricular valves (AKA left AV, Mitral valve)i. Valves between the left atrium and left ventricle ii. Has 2 flaps of tissue 1. Prevents improper flow of blood c. Semilunar valvesi. Valves between a ventricle and a great arteryii. Pulmonary semilunar valve 1. Valve between right ventricle and pulmonary trunkiii. Aortic semilunar valve1. Valve between left ventricle and the aortaII. Cardiac Cycle a. Ventricle fills with blood and starts to contracti. Pressure builds within the ventricleii. Pushes blood up against the flaps1. Forces cusps together and closes the valves iii. Prevents blood within ventricle from being pushed into the atriumb. At one moment, all of the valves are closedc. The pressure within the pulmonary trunk and in aorta gets higher when ventricles start to relaxi. Blood presses against semilunar valves, closes flap so that blood doesn’t flow backwards III. Cardiac Muscle Fibersa. Similarities to skeletal muscle fiber i. Striated: striped appearance ii. Thin filaments and thick filaments 1. For muscle contractioniii. T-tubulesiv. Calcium: binds to troponin 1. Tropomyosin shifts away from myosin binding sights b. Differences to skeletal muscle fiber i. A lot of calcium that is necessary for contraction to occur comes from outside the cellii. The shape of the cells1. Individual cardiac muscle fibers are shorter and branched iii. Connections between adjacent cells 1. Joined by intercalated discs a. Gap junctionsi. Ions can flow from one cell to the next 1. Don’t have to be individually stimulated by the nervous system ii. Electrically couple all of the cells within the heart1. Heart is one contractile unit b. Desmosomes (Anchoring junctions)i. Mechanically lock adjacent cells next to each other1. Helps cells and tissues to stay together while undergoing stress IV. Cardiac Muscle Contractiona. 1% are self-excitablei. Capable of autorhythmacy1. Capable of depolarizing themselves without any influence from the nervous system a. Nervous system controls the rate of contraction, but the heart will contract with no functioning nervous system ii. Lead to contraction of the entire heart b. The rest are contractile muscle fibersi. Require a stimulus outside of themselves (which are the self-excitable cells)c. Has a long muscle refractory periodi. Sodium channels are either open or are inactivated and cannot open again for a whileii. Cannot generate sustained, complete tetanus (long, sustained muscle contraction)1. The heart has to relax and contract to do its job (heart is not in complete tetanus- if it were it would cause death)d. Depolarization opens voltage-gated fast Na channelsi. Decreases membrane potential ii. Causes sarcoplasmic reticulum (SR) to release calcium into muscles iii. Opens calcium channels to allow calcium to come in from outside 1. Calcium increases inside celle. Repolarizationi. Potassium rushes out of cell ii. Calcium exits and is being taken back up by SR V. Self-excitable Cardiac Cellsa. Distributed in specific locationsb. Intrinsic cardiac conduction systemc. Establish the basic rhythm of the heartd. Sinoatrial nodei. Causes heart rate to be about 75 beats per minute1. Nervous system adjusts this e. Atrioventricular nodei. Above right atrioventricular valvef. Atrioventricular bundlei. Right and left bundle branches1. Give rise to purkinje fibers VI. Autonomic Innervation of the Hearta. Medulla oblongata: 2 cardiac centersi. Cardio-acceleratory center1. Sympathetic division2. Stimulates SA node, AV node, heart muscle (myocardium), cardiac vesselsa. Accelerates heart rateii. Cardio-inhibitory center1. Parasympathetic division2. Primarily innervating AV node and SA node VII. Electrocardiograma. 3 major wavesi. P Wave1. Depolarization spreading from SA node across the atria 2. Atria depolarizing: atrial contraction ii. Q-R-S Complex1. Ventricular contraction iii. T Wave 1. Repolarization spreads through ventricles VIII. Heartbeat a. Systole i. Contractionii. At the end of ventricular diastole, atrial systole occurs1. Push more blood into ventriclesiii. Then ventricle systole occurs1. Increase the pressure within the ventricles2. AV valves close iv. Isovolumetric contraction phase1. All valves are closed although the ventricles are contractingv. Ventricular ejection phase1. Continued contraction of ventricles eventually causes semilunar valves to open 2. Blood pushed out into pulmonary and systemic circuitb. Diastole i. Relaxationii. Ventricular diastole 1. When the ventricles are relaxed, they are capable of filling with blood 2. Initially, the AV valves are open as the blood is moving from the atria to the ventricles passively, and the atria and ventricles are in diastole c. EDV: end diastolic volume i. What is the volume of blood in the ventricles at the end of diastoled. ESV: end systolic volumei. What is the volume of blood in the ventricles at the end of


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SC BIOL 244 - The Heart

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