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N.C. Wyeth Maine “The Giant”
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Cardiac Muscle Coronary Arteries and Electrical Activity (ECG)
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So what’s the Problem with Joe? Injury to the pericardium has allowed bleeding into the pericardial space. The heart cannot fill with blood Cardiac Tamponade: Acute heart failure
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Cardiac Tissue: Three Layers: Epicardium (Visceral Pericardium): Squamous Epithelial tissue + CT + Adipose Myocardium: Cardiac Muscle Endocardium: S. epithelium + CT Heart Valves are Endocardium
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Muscle Cells: Cardiac vs. Skeletal Striated Single Nucleus Short Cylinders Branching Autonomic Control GAP Junctions Striated Single Nucleus Long Cylinders Non-Branching Voluntary Control
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Remember the Sarcomere? Myofibrils: Chains of Sarcomeres Sarcomeres: Bundles of myofilaments Myofiliaments: Muscle Contractile Proteins ACTIN and MYOSIN
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Energy for Contraction: This muscle MUST RESIST FATIGUE ! ATP O 2 Mitochondria Blood Supply Capillary Coronary Arteries
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Origin: Base of the Aorta ( Pressure/ O 2 ) Names: Left Coronary Artery Right Coronary Artery
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Rt. Marginal Branch
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Coronary Artery Bloodflow Regulation: Aortic Pressure is primary regulator Sympathetic: Net Increase in Bloodflow Parasympathetic: Maintain Bloodflow Metabolic: Bloodflow = VO 2
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Coronary Artery Disease: CAD When critical bloodflow to the heart muscle is compromised, The Heart Cannot “Rest” from its work! Atherosclerosis: The progressive incompetency of arteries to permit adequate blood flow to tissues
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Fatty Arteries: Normal Coronary Artery Atherosclerotic Artery
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Take “5”: Read: “Did You Know?” pg. 311 Answer: What is the primary cause of artery “lesions”? What is “Angina Pectoris”? Evaluate the medical treatment for CAD: Would you rather treat or prevent CAD? Explain…
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Think Again: The heart already extracts MOST of the O 2 in the blood (70%): How does it get more O 2 during exercise?!? How does CAD affect the exercising heart ?
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Electrical Activity: Excitation - Contraction To contract, cardiac muscle cells must depolarize and propagate an Action Potential The Conduction of Action Potentials and Contractions must be well coordinated to efficiently pump blood.
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Action Potentials: Skeletal vs. Cardiac Depolarization: Na + channels open Repolarization: Voltage Gated K + channels open / Na + channels close Depolarization Na + and Ca ++ Channels open Plateau: All but Ca ++ channels close Repolarization K + open and Ca ++ channels close
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Why the Plateau Phase and Calcium? Plateau Phase: Relative Refractory: Cannot be re-stimulated – permitting coordinated contraction of entire heart muscle. Calcium: Important in the automaticity of cardiac myocytes
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Heart Rate Control ª Each heart cell can contract independently and automatically ª The entire heart must not contract at the same time. ª Excitation-Contraction of the heart is coordinated from “top to bottom” ª The excitation-contraction pathway is called “The Conduction System”
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Heart Conduction System The Sino-Atrial node (SA) serves as the pacemaker for the heart. When the SA node fires, it causes both atria to contract The excitation- contraction signal is then “conducted” to the ventricles SA
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Heart Conduction System ¤ A specialized conduction system sends signal throughout the heart ¤ Contraction across the ventricles is almost simultaneous. SA
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Extrinsic Control of Heart Rate ª The SA node has an Intrinsic Rate of 90 bpm ª External controls modify the heart rate: both at rest and during exercise ª Controls: Parasympathic Nervous System, Sympathetic Nervous System, Endocrine System
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Parasympathetic Nervous System ª “Maintenance” ª Vagus nerve innervates heart at the SA Node ª Causes reduced HR
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Sympathetic Nervous System ¤ “Rescues” in homeostatic emergencies (like exercise) ¤ Increases HR ¤ Increases Systolic contractility (Increased BP) ¤ Increases Mental acuity (you are prepared for battle!)
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Endocrine System ¤ The adrenal medulla (above kidney) secretes Catecholamines: ¤ Epinephrine ¤ Norepinephrine ¤ Mimics the Sympathetic Nervous System ¤ Slower/Longer acting
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Final Question: In a Heart Transplant, the heart is “denervated” How does someone with a heart transplant exercise?
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