cardio

• Heart


  A transport system consisting of two side-by-side pumps
• Pulmonary circuit


  Right side of heart receives oxygen-poor blood from tissues and pumps it to lungs to get rid of CO2 and pick up O2

  
• Systemic circuit


  Left side of heart receives oxygenated blood from lungs and pumps it to body tissues

  
• Receiving chambers of heart

  • Right atrium receives blood returning from systemic circuit
  • Left atrium receives blood returning from pulmonary circuit

  
• Pumping chambers of heart

  • Right ventricle pumps blood through pulmonary circuit
  • Left ventricle pumps blood through systemic circuit

  
• Size of heart


  Approximately the size of a fist, weighs less than 1 pound
• Location of heart


  In mediastinum between second rib and fifth intercostal space, on superior surface of diaphragm, two-thirds to left of midsternal line, anterior to vertebral column, posterior to sternum

  
• Orientation of heart


  Base (posterior surface) leans toward right shoulder, apex points toward left hip, apical impulse palpated between fifth and sixth ribs, just below left nipple
• Pericardium


  Double-walled sac that surrounds heart, made up of fibrous pericardium and serous pericardium (parietal layer and visceral layer/epicardium) with fluid-filled pericardial cavity

  
• Layers of heart wall

  • Epicardium, myocardium (with cardiac skeleton), endocardium

  
• Cardiac skeleton


  Crisscrossing, interlacing layer of connective tissue that anchors cardiac muscle fibers, supports great vessels and valves, and limits spread of action potentials to specific paths

  
• Internal features of heart

  • Four chambers (two atria, two ventricles), interatrial septum, interventricular septum

  
• Surface features of heart

  Coronary sulcus, anterior interventricular sulcus, posterior interventricular sulcus

  
• Atria


  • Small, thin-walled receiving chambers that contribute little to propulsion of blood, with auricles to increase volume, right atrium receives deoxygenated blood, left atrium receives oxygenated blood
• Ventricles


  • Larger, thicker-walled pumping chambers, right ventricle pumps blood into pulmonary trunk, left ventricle pumps blood into aorta, with trabeculae carneae and papillary muscles

  
• Heart valves


  Ensure unidirectional blood flow, two major types: atrioventricular (tricuspid and mitral) and semilunar (pulmonary and aortic)

  
• Function of atrioventricular (AV) valves

  Prevent backflow into atria when ventricles contract, with chordae tendineae anchoring valve cusps to papillary muscles
• Function of semilunar (SL) valves


  Prevent backflow from major arteries into ventricles, open and close in response to pressure changes
• Incompetent valve


  Blood backflows so heart repumps same blood over and over
• Valvular stenosis


  Stiff valve flaps that constrict opening, requiring heart to exert more force to pump blood
• Pathway of blood through heart

  Right side: superior vena cava, inferior vena cava, coronary sinus -> right atrium -> tricuspid valve -> right ventricle -> pulmonary semilunar valve -> pulmonary trunk -> pulmonary arteries -> lungs

  Left side: four pulmonary veins -> left atrium -> mitral valve -> left ventricle -> aortic semilunar valve -> aorta -> systemic circulation

  
• Pulmonary circuit


  Short, low-pressure circulation
• Systemic circuit


  Long, high-friction circulation
• Defective valve


  Can be replaced with mechanical, animal, or cadaver valve
• Pathway of Blood Through Heart

  1. Right side of the heart

  2. Superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary trunk → Pulmonary arteries → Lungs

  3. Left side of the heart

  4. Four pulmonary veins → Left atrium → Mitral valve → Left ventricle → Aortic semilunar valve → Aorta → Systemic circulation

  
• Pathway of Blood Through Heart

  • Equal volumes of blood are pumped to pulmonary and systemic circuits
  • Pulmonary circuit is short, low-pressure circulation
  • Systemic circuit is long, high-friction circulation
  • Left ventricle walls are 3x thicker than right to pump with greater pressure

  
• Coronary Circulation


  1. Coronary arteries arise from base of aorta and supply arterial blood to heart

  2. Coronary arteries encircle heart in coronary sulcus

  3. Coronary veins collect blood from capillary beds and empty into coronary sinus

  
• Heart receives 1/20th of body's blood supply
• Coronary arteries contain many anastomoses (junctions) that provide additional routes for blood delivery but cannot compensate for coronary artery occlusion

  
• Angina pectoris


  Thoracic pain caused by fleeting deficiency in blood delivery to myocardium
• Myocardial infarction (heart attack)

  Prolonged coronary blockage leading to areas of cell death repaired with noncontractile scar tissue

  
• Cardiac muscle cells


  • Striated, short, branched, fat, interconnected
  • One central nucleus (at most, 2 nuclei)
  • Contain numerous large mitochondria that afford resistance to fatigue
  • Rest of volume composed of sarcomeres
• Intercalated discs


  Connecting junctions between cardiac cells that contain desmosomes to hold cells together and gap junctions to allow ions to pass from cell to cell, electrically coupling adjacent cells
• Cardiac muscle cells are a functional syncytium, a single coordinated unit
• Tetanic contractions cannot occur in cardiac muscles
• Intrinsic Cardiac Conduction System

  1. Sinoatrial (SA) node

  2. Atrioventricular (AV) node

  3. Atrioventricular (AV) bundle

  4. Right and left bundle branches

  5. Subendocardial conducting network (Purkinje fibers)

  
• Heart depolarizes and contracts without nervous system stimulation, although rhythm can be altered by autonomic nervous system
• Coordinated heartbeat is a function of the intrinsic cardiac conduction system
• Defects in intrinsic conduction system may cause arrhythmias, uncoordinated atrial and ventricular contractions, and fibrillation
• Defibrillation interrupts chaotic twitching, giving heart "clean slate" to start regular, normal depolarizations