heart

• Heart


  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
• Heart


  Two pumps in one, with the right side pumping blood to the lungs and the left side pumping blood to all other tissues of the body
• 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 thoracic cavity
  • Apex (bottom) towards left side
• Pericardium


  Double-layered sac that anchors and protects heart
• Parts of the pericardium

  • Parietal pericardium (membrane around heart's cavity)
  • Visceral pericardium (membrane on heart's surface)
  • Pericardial cavity (space around heart)

  
• Heart external anatomy


  1. Coronary sulcus (separates atria from ventricles)

  2. Anterior interventricular sulcus (on anterior surface)

  3. Posterior interventricular sulcus (on posterior surface)

  4. Superior vena cava and inferior vena cava (carry blood to right atrium)

  5. Pulmonary veins (carry blood from lungs to left atrium)

  6. Pulmonary trunk (carries blood from right ventricle to lungs)

  7. Aorta (carries blood from left ventricle to body)

  
• Heart chambers


  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle
  • Coronary sulcus (separates atria from ventricles)
  • Interatrial septum (separates right and left atria)
  • Interventricular septum (separates right and left ventricles)

  
• Atria


  Superior chambers that receive blood from veins, small and thin-walled, contract minimally to push blood into ventricles

  
• Ventricles


  Inferior chambers that pump blood out of heart to arteries, thick and strong-walled, contract forcefully to propel blood out of heart
• Atrioventricular heart valves


  • Tricuspid valve (between right atrium and right ventricle)
  • Bicuspid valve (mitral valve, between left atrium and left ventricle)

  
• Control of heart valves

  Papillary muscles (cone-shaped, muscular pillars) contract and pull on chordae tendineae (connective tissue strings) to prevent atrioventricular valves from opening into atria during ventricular contraction

  
• Semilunar heart valves


  • Pulmonary valve (between right ventricle and pulmonary trunk)
  • Aortic valve (between left ventricle and aorta)

  
• Cardiac skeleton


  Plate of connective tissue that surrounds and supports the heart valves, provides electrical insulation between atria and ventricles, and serves as attachment site for cardiac muscle

  
• 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

  
• Blood supply to the heart

  1. Coronary arteries (originate from base of aorta, supply blood to heart wall)

  2. Left coronary artery (3 branches, supplies anterior heart wall and left ventricle)

  3. Right coronary artery (supplies right ventricle)

  4. Cardiac veins (drain blood from cardiac muscle, most drain into coronary sinus, then into right atrium)

  
• Heart wall


  • Epicardium (surface, outside)
  • Myocardium (thick, middle layer 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. Action potentials spread across atrial wall, stimulating atrial contraction

  3. Action potentials spread across ventricular wall from apex to base, stimulating ventricular contraction

  
• Cardiac muscle action potentials

  • Depolarization phase (Na+ and 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
• 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 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

  • Sinoatrial node
  • Atrioventricular node
  • Atrioventricular bundle
  • Right and left bundle branches
  • Purkinje fibers

  
• Sinoatrial node (SA node)

  Where action potential originates, functions as pacemaker, large number of Ca2+ channels
• Atrioventricular node (AV node)

  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
• Action Potential Path through Heart

  1. SA node

  2. AV node

  3. AV bundle

  4. Right and Left Bundle branches

  5. Purkinje fibers
• Electrocardiogram (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, the heart is a two sided pump, with the atria being primers for pumps and the ventricles being the actual pumps

  
• Atrial systole


  Contraction of atria