N.C. Wyeth Maine “The Giant”

Cardiac Muscle Coronary Arteries and Electrical Activity (ECG)

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

Cardiac Tissue: Three Layers: Epicardium (Visceral Pericardium): Squamous Epithelial tissue + CT + Adipose Myocardium: Cardiac Muscle Endocardium: S. epithelium + CT Heart Valves are Endocardium

Muscle Cells: Cardiac vs. Skeletal Striated Single Nucleus Short Cylinders Branching Autonomic Control GAP Junctions Striated Single Nucleus Long Cylinders Non-Branching Voluntary Control

Remember the Sarcomere? Myofibrils: Chains of Sarcomeres Sarcomeres: Bundles of myofilaments Myofiliaments: Muscle Contractile Proteins ACTIN and MYOSIN

Energy for Contraction: This muscle MUST RESIST FATIGUE ! ATP O 2 Mitochondria Blood Supply Capillary Coronary Arteries

Origin: Base of the Aorta ( Pressure/ O 2 ) Names: Left Coronary Artery Right Coronary Artery

Rt. Marginal Branch

Coronary Artery Bloodflow Regulation: Aortic Pressure is primary regulator Sympathetic: Net Increase in Bloodflow Parasympathetic: Maintain Bloodflow Metabolic: Bloodflow = VO 2

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

Fatty Arteries: Normal Coronary Artery Atherosclerotic Artery

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…

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 ?

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.

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

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

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”

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

Heart Conduction System ¤ A specialized conduction system sends signal throughout the heart ¤ Contraction across the ventricles is almost simultaneous. SA

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

Parasympathetic Nervous System ª “Maintenance” ª Vagus nerve innervates heart at the SA Node ª Causes reduced HR

Sympathetic Nervous System ¤ “Rescues” in homeostatic emergencies (like exercise) ¤ Increases HR ¤ Increases Systolic contractility (Increased BP) ¤ Increases Mental acuity (you are prepared for battle!)

Endocrine System ¤ The adrenal medulla (above kidney) secretes Catecholamines: ¤ Epinephrine ¤ Norepinephrine ¤ Mimics the Sympathetic Nervous System ¤ Slower/Longer acting

Final Question: In a Heart Transplant, the heart is “denervated” How does someone with a heart transplant exercise?