HEART

• Cardiovascular system


  Consists of the heart, blood vessels, and blood
• The heart of a healthy adult, at rest, pumps approximately 5 liters (L) of blood per minute
• The heart is actually two pumps in one
• Heart


  • Pumps blood through the body
  • Essential for life
• Pulmonary circulation


  The heart's right side pumping blood to the lungs and back to the left side of the heart through vessels
• Systemic circulation


  The left side of the heart pumps blood to all other tissues of the body and back to the right side of the heart through vessels
• Functions of the heart

  • Generates blood pressure
  • Routes blood
  • Ensures one-way blood flow
  • Regulates blood supply
• Heart characteristics


  • Size: size of a fist and weighs less than 1 lb (less than 500 grams)
  • Location: between lungs in thoracic cavity
  • Orientation: apex (bottom) towards left side
• Pericardium


  Double-layered sac that anchors and protects heart
• Parietal pericardium


  Lines the fibrous pericardium
• Visceral pericardium


  Covers heart's surface
• Pericardial cavity


  Fluid-filled space around heart
• Heart external anatomy


  • Coronary sulcus extends around the heart, separating the atria from the ventricles
  • Two grooves, or sulci, which indicate the division between the right and left ventricles, extend inferiorly from the coronary sulcus
  • The anterior interventricular sulcus extends inferiorly from the coronary sulcus on the anterior surface of the heart
  • The posterior interventricular sulcus extends inferiorly from the coronary sulcus on the posterior surface of the heart
  • The superior vena cava and inferior vena cava carry blood from the body to the right atrium, and four pulmonary veins carry blood from the lungs to the left atrium
  • Two arteries, often called the great vessels or great arteries, carry blood away from the ventricles of the heart
• Pulmonary trunk


  Arising from the right ventricle, splits into the right and left pulmonary arteries, which carry blood to the lungs
• Aorta


  Arising from the left ventricle, carries blood to the rest of the body
• Atria


  • Superior chambers
  • Small, thin walled
  • Receive blood from veins
  • Contract minimally to push blood into ventricles
  • Interatrial septum: separates right and left atria
• Ventricles


  • Inferior chambers
  • Pump blood out of heart to arteries
  • Thick, strong walled
  • Contract forcefully to propel blood out of heart
  • Interventricular septum: separates right and left ventricles
• Tricuspid valve


  AV valve between RA and RV, 3 cusps
• Bicuspid valve (mitral)


  AV valve between LA and LV, 2 cusps
• Pulmonary semilunar valve


  Between RV and pulmonary trunk
• Aortic semilunar valve


  Between LV and aorta
• Cardiac skeleton


  • A plate of connective tissue, sometimes called fibrous skeleton
  • Consists mainly of fibrous rings that surround the AV and SL valves and give them solid support
  • Also serves as electrical insulation between the atria and the ventricles
  • Provides a rigid attachment site for cardiac muscle
• Left coronary artery


  Originates on left side of aorta, supplies blood to left ventricle
• Right coronary artery


  Originates on right side of aorta, supplies blood to right ventricle
• Cardiac veins


  Drain blood from the cardiac muscle, most of the veins drain blood into the coronary sinus
• Heart wall


  • Epicardium: surface of heart (outside)
  • Myocardium: thick, middle layer composed of cardiac muscle
  • Endocardium: smooth, inner surface
• Cardiac muscle


  • One centrally located nucleus
  • Branching cells
  • Rich in mitochondria
  • Striated (actin and myosin)
  • Ca2+ and ATP used for contractions
  • Intercalated disks connect cells
• Stimulation of the heart

  1. Atria contract first, followed by ventricles

  2. Cardiac muscle cells in the atrial wall are stimulated as action potentials spread across the atrial wall and towards the ventricles

  3. Cardiac muscle cells in the atrial wall contract, pushing blood into the ventricles

  4. Cardiac muscle cells in the ventricular wall are stimulated as action potentials spread across the ventricular wall from the apex of the heart towards its base

  5. Cardiac muscle cells in the ventricular wall contract, pushing blood into the great arteries
• Pacemaker potential


  Changes in membrane permeability are responsible for producing action potentials
• Cardiac muscle action potentials

  1. Depolarization phase: Na+ channels open, Ca2+ channels open

  2. Plateau phase: Na+ channels close, some K+ channels open, Ca2+ channels remain open

  3. Repolarization phase: K+ channels are open, Ca2+ channels close
• In skeletal muscle action potentials take 2 msec, in cardiac muscle they take 200 to 500 msec
• Conduction system of the heart

  • Includes the sinoatrial node, atrioventricular node, atrioventricular bundle, right and left bundle branches, and Purkinje fibers
  • All the cells of the conduction system can produce spontaneous action potentials
• Sinoatrial node (SA node)


  In Right Atrium where action potential originates, functions as pacemaker, large number of Ca2+ channels
• Atrioventricular node (AV node)

  Located in the lower portion of the right atrium, action potentials from SA node sent to this node, action potentials spread slowly through it, slow rate of action potential conduction allows the atria to complete their contraction before action potentials are delivered to the ventricles
• Atrioventricular bundle


  Action potentials from AV node travel by the AV bundle to the ventricles, AV bundle divides into a left and right bundle branches to left and right ventricles
• Purkinje Fibers


  At the tips of the left and right bundle branches, action potentials are rapidly delivered to all the cardiac muscle of the ventricles
• Electrocardiogram (ECG/EKG)


  Record of electrical events in heart, diagnoses cardiac abnormalities, uses electrodes, contains P wave, QRS complex, T wave
• P wave


  Depolarization of atria
• QRS complex


  Depolarization of ventricles, contains Q, R, S waves
• T wave


  Repolarization of ventricles