Heart

• The heart


  A muscular organ that is essential for life because it pumps blood through the body
• 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
• For most people, the heart continues to pump at approximately that rate for more than 75 years
• The heart


  Two pumps in one, with the heart's right side pumping blood to the lungs and back to the left side of the heart through vessels of the pulmonary circulation, and the left side of the heart pumping blood to all other tissues of the body and back to the right side of the heart through vessels of systemic circulation
• Functions of the heart

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


  • Size of a fist and weighs less than 1 lb
  • Located between lungs in the thoracic cavity
  • Apex (bottom) towards the left side
• Pericardium


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


  Membrane around heart's cavity
• Visceral pericardium


  Membrane on heart's surface
• Pericardial cavity


  Space around heart
• External anatomy of the heart

  • Coronary sulcus
  • Anterior interventricular sulcus
  • Posterior interventricular sulcus
  • Superior vena cava
  • Inferior vena cava
  • Pulmonary veins
  • Pulmonary trunk
  • Aorta
• Heart chambers


  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle
• Coronary sulcus


  Separates atria from ventricles
• Atria


  Superior chambers, receive blood from veins, small and thin walled, 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 and strong walled, contract forcefully to propel blood out of heart
• Interventricular septum


  Separates right and left ventricles
• Atrioventricular heart valves


  • Tricuspid valve
  • Bicuspid valve (mitral)
• Papillary muscles


  Cone-shaped, muscular pillars in each ventricle, attached by chordae tendineae to the free margins of the cusps of the atrioventricular valves
• Semilunar heart valves


  • Pulmonary valve
  • Aortic valve
• Blood flow through the heart

  1. Right Atrium

  2. Tricuspid valve

  3. Right Ventricle

  4. Pulmonary semilunar valve

  5. Pulmonary trunk

  6. Pulmonary arteries

  7. Lungs

  8. Pulmonary veins

  9. Left Atrium

  10. Bicuspid valve

  11. Left Ventricle

  12. Aortic semilunar valve

  13. Aorta

  14. Body
• 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. Heart at rest and all chambers relaxed

  2. Cardiac muscle cells in atrial wall stimulated, contract and push blood into ventricles

  3. Cardiac muscle cells in ventricular wall stimulated, contract and push blood into great arteries
• Cardiac muscle action potentials

  • Changes in membrane permeability responsible for producing action potentials and called pacemaker potential
  • Depolarization phase: Na+ channels open, Ca2+ channels open
  • Plateau phase: Na+ channels close, some K+ channels open, Ca2+ channels remain open
  • Repolarization phase: K+ channels open, Ca2+ channels close
  • Plateau phase prolongs action potential by keeping Ca2+ channels open
  • In cardiac muscle action potentials take 200 to 500 msec
• Conduction system of the heart

  • Sinoatrial node
  • Atrioventricular node
  • Atrioventricular bundle
  • Right and left bundle branches
  • Purkinje fibers
• 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 lower portion of right atrium, action potentials from SA node sent to this node, action potentials spread slowly through it, slow rate of action potential conduction allows atria to complete contraction before action potentials delivered to ventricles
• Atrioventricular bundle


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


  At tips of left and right bundle branches, pass to apex of heart and then extend to cardiac muscle of ventricle walls, action potentials rapidly delivered to all cardiac muscle of ventricles
• Action potential path through heart

  1. SA node

  2. AV node

  3. AV bundle

  4. Right and Left Bundle branches

  5. Purkinje fibers
• 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
• Cardiac cycle


  Summative description of all the events that occur during one single heartbeat, with atria being primers for pumps and ventricles being the actual pumps
• Heart chamber contractions


  Cardiac muscle contractions produce pressure changes within heart chambers, blood moves from areas of high to low pressure