CHAPTER 12

• Heart


  Muscular organ that pumps blood
• Healthy adult heart pumps approx. 5L of blood / minute at rest
• Heart


  • Two pumps in one
  • Right side: Pulmonary circulation
  • Left side: Systemic circulation
• Functions of the heart

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


  • Size - fist size
  • Weight - less than 1lb
  • Location - between lungs in thoracic cavity
  • Orientation - apex (bottom) towards left side
• Pericardium


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


  • Fibrous pericardium - helps hold the heart in place
  • Serous pericardium - reduces friction as the heart beats
• Layers of serous pericardium

  • Parietal pericardium - membrane around heart's cavity
  • Visceral pericardium - membrane on heart's surface
  • Pericardial cavity - space around heart filled with pericardial fluid which lubricates the heart as it moves
• Layers of the heart wall

  • Epicardium - superficial layer, thin serous membrane
  • Myocardium - thick middle layer of cardiac muscle cells, responsible for contraction
  • Endocardium - deep layer, simple squamous epithelium over connective tissue, covers heart valves
• Heart wall


  • Pectinate muscles - muscular ridges in the auricles
  • Crista terminalis - ridge separating right atrium from larger, smooth portions of atrial wall
  • Trabeculae carneae - larger, muscular ridges and columns in the interior of the ventricles
• External anatomy of the heart

  • Auricles - flaplike extensions of the atria
  • Coronary sulcus - extends around heart, separating atria from ventricles
  • Interventricular sulci - grooves indicating division between right and left ventricles
  • Superior and inferior vena cava - carry blood to right atrium
  • Pulmonary veins - carry blood from lungs to left atrium
  • Pulmonary trunk - carries blood from right ventricle to lungs
  • Aorta - carries blood from left ventricle to body
• The chambers of the heart allow complete separation of oxygenated and deoxygenated blood
• Atria


  Superior and receiving chambers, small and thin walls, contract minimally to push blood to ventricles
• Ventricles


  Inferior and pumping chambers, have much thicker myocardium, contract forcefully to eject blood out of heart and to great arteries
• Heart valves


  • Atrioventricular valves - tricuspid valve, bicuspid (mitral) valve
  • Semilunar valves - pulmonary semilunar valve, aortic semilunar valve
• Papillary muscles


  Cone-shaped, muscular pillars in each ventricle
• Chordae tendineae


  Strong connective tissue strings that attach papillary muscles to free margins of atrioventricular valve cusps
• Control of heart valves

  When ventricles contract, papillary muscles contract and pull on chordae tendineae to prevent atrioventricular valves from opening into atria
• Cardiac muscle contractions


  Produce pressure changes within heart chambers, responsible for blood movement
• Route and 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
• Coronary arteries


  Supply blood to heart wall, originate from base of aorta
• Coronary arteries


  • Left coronary artery - 3 branches, supplies anterior heart wall and left ventricle
  • Right coronary artery - originates on right side of aorta, supplies right ventricle
• Cardiac veins


  Drain blood from cardiac muscle, parallel to coronary arteries, most drain into coronary sinus then into right atrium
• Cardiac skeleton


  Fibrous plate of connective tissue between atria and ventricles, consists of fibrous rings around valves to provide support, also serves as electrical insulation and attachment site for cardiac muscle
• Cardiac muscle


  • Elongated, one centrally located nucleus
  • Branching cells
  • Rich in mitochondria
  • Striated (actin and myosin - responsible for contraction)
  • Ca2+ and ATP used for contractions
  • Intercalated disks connect cells
  • Desmosome and gap junction
• Components of the conduction system

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


  In right atrium, where action potential originates, functions as pacemaker, has large number of Ca2+ channels
• Atrioventricular node


  In lower right atrium, action potentials from SA node sent here, action potentials spread slowly to allow atria to complete contraction before reaching ventricles
• Action potential path through the heart

  Originates in SA node, travels to AV node, through AV bundle to left and right bundle branches, then to Purkinje fibers which carry it to ventricular walls
• Stimulation of the heart

  Atria contract first, pushing blood into ventricles, then ventricles contract, pushing blood into great arteries
• Cardiac muscle action potential

  • Changes in membrane permeability produce action potentials and pacemaker potentials
  • Depolarization phase - voltage-gated Na+ channels open, K+ channels close, Ca2+ channels begin opening
  • Early repolarization and plateau phase - Na+ channels close
• Cardiac muscle contractions


  1. Atria contract first, followed by ventricles

  2. Heart is at rest and all chambers are relaxed

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

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

  5. 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

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

  Changes in membrane permeability are responsible for producing action potentials and called pacemaker potential
• Phases of cardiac muscle action potential

  1. Depolarization phase (rapid)

  2. Early repolarization & plateau phase

  3. Final repolarization phase

  4. Refractory period effect on tension
• Plateau phase prolongs action potential by keeping Ca2+ channels open
• In skeletal muscle action potentials take 2 msec, in cardiac muscle they take 200 to 500 msec
• Autorhythmicity of cardiac muscle

  The heart is said to be autorhythmic because it stimulates itself (auto) to contract at regular intervals (rhythmic)
• Electrocardiogram (ECG/EKG)


  • Record of electrical events in heart
  • Diagnoses cardiac abnormalities
  • Uses electrodes
  • Contains P wave, QRS complex, T wave
• Hypertrophy


  Increase of muscle mass
• Atrophy


  Loss of muscle mass