Heart

• Right Atrium


  Receives blood from 3 veins: Superior vena cava, Inferior vena cava, Coronary sinus
• Right Atrium

  • Pectinate muscles
  • Interatrial septum has fossa ovalis
  • Remnant of foramen ovale
  • Tricuspid valve
• Right Ventricle


  Forms anterior surface of heart
• Right Ventricle

  • Trabeculae carneae
  • Tricuspid valve connected to chordae tendinae connected to papillary muscles
  • Interventricular septum
  • Pulmonary semilunar valve
• Left Atrium

  About the same thickness as right atrium, Receives blood from the lungs through pulmonary veins, Bicuspid valve (mitral valve or left AV valve)
• Left Ventricle

  Thickest chamber of the heart, Forms apex
• Left Ventricle

  • Chordae tendinae attached to papillary muscles
  • Aortic valve
• The Heart has 4 Chambers: 2 atria - receiving chambers, 2 ventricles - pumping chambers
• Pulmonary circuit

  Right side of heart, carries blood to lungs for gas exchange
• Systemic circuit

  Left side of heart, supplies blood to all organs of the body
• The right side pumps into the pulmonary circuit, the left side pumps into the systemic circuit
• Path of blood flow through the cardiovascular system

  1. Systemic circuit: Left side of heart, Receives blood from lungs, Ejects blood into aorta, Systemic arteries, arterioles, Gas and nutrient exchange in systemic capillaries, Systemic venules and veins lead back to right atrium

  2. Pulmonary circuit: Right side of heart, Receives blood from systemic circulation, Ejects blood into pulmonary trunk then pulmonary arteries, Gas exchange in pulmonary capillaries, Pulmonary veins takes blood to left atrium
• Coronary circulation

  Myocardium has its own network of blood vessels, Coronary arteries branch from ascending aorta, Anastomoses provide alternate routes or collateral circuits, Coronary capillaries, Coronary veins collect in coronary sinus and empty into right atrium
• Cardiac Cycle

  One complete contraction and relaxation of all 4 chambers of the heart, Atrial systole, Ventricular diastole, Atrial diastole, Ventricular systole, Quiescent period
• Operation of Semilunar Valves

  1. Ventricles relax, pressure drops, semilunar valves close, AV valves open, blood flows from atria to ventricles

  2. Ventricles contract, AV valves close, pressure rises, semilunar valves open, blood flows into great vessels
• Operation of Atrioventricular Valves

  1. Ventricles relax, pressure drops, semilunar valves close, AV valves open, blood flows from atria to ventricles

  2. Ventricles contract, AV valves close, pressure rises, semilunar valves open, blood flows into great vessels
• Valvular prolapse


  Abnormal condition where a heart valve does not close properly
• Cardiac Muscle Tissue and the Cardiac Conduction System

  • Autorhythmic fibers - self-excitable, repeatedly generate action potentials that trigger heart contractions, Act as pacemaker, Form conduction system
• Structure of Cardiac Muscle

  • Short, branched cells, one central nucleus, Sarcoplasmic reticulum, large T-tubules, Intercalated discs join cardiac myocytes end to end, interdigitating folds - large surface area, mechanical junctions tightly join myocytes, electrical junctions - gap junctions allow ions to flow
• Atrial syncytium


  Network of interconnected atrial muscle cells
• Ventricular syncytium

  Network of interconnected ventricular muscle cells
• Cardiac muscle is myogenic (heartbeat originates within heart) and autorhythmic (regular, spontaneous depolarization)
• Cardiac Conduction System

  1. SA node: pacemaker, initiates heartbeat, sets heart rate

  2. Fibrous skeleton insulates atria from ventricles

  3. AV node: electrical gateway to ventricles

  4. AV bundle: pathway of signals from AV node

  5. Right and left bundle branches: divisions of AV bundle that enter interventricular septum

  6. Purkinje fibers: upward from apex spread throughout ventricular myocardium
• ECG

  • P wave: SA node fires, atrial depolarization, atrial systole
  • QRS complex: ventricular depolarization (atrial repolarization and diastole - signal obscured)
  • ST segment: ventricular systole
  • T wave: ventricular repolarization
• Ventricular fibrillation

  The normal path of electrical activity is broken, The cells of the ventricle are all contracting but they're each on their own, Each cell is working very hard but they are NOT coordinated so they do not create a wave of contraction, No wave of contraction = NO blood being pumped!
• Absence of a P wave in a patient's ECG would indicate a problem with the SA node, absence of atrial systole, or fibrillation of the ventricles
• To test how well the heart works, we need to know how much blood the heart can pump in a minute
• Echocardiography


  Technique to visualize the structure and function of the heart
• End-diastolic volume


  Amount of blood in a ventricle as it begins to contract
• End-systolic volume

  Amount of blood left in a ventricle after it has contracted
• Stroke volume

  Amount of blood ejected from one ventricle in one heartbeat
• Cardiac Output (CO)

  The volume of blood ejected from one ventricle in one minute, calculated as Heart Rate x Stroke Volume
• Cardiac Output is about 4 to 6L/min at rest, and can increase to 21 L/min for a fit person and up to 35 L/min for a world class athlete during vigorous exercise
• Ejection fraction

  The percentage of the end-diastolic volume that is ejected in a single ventricular contraction
• Cardiac reserve

  The difference between a person's maximum CO and their CO while resting, should be 4 to 5 times resting
• The output of the two ventricles must balance, as the pulmonary and systemic circulations are connected in series
• Both ventricles must eject the same amount of blood and have the same stroke volume
• Regulation of stroke volume

  • Preload, Contractility, Afterload
• Preload


  Degree of stretch on the heart before it contracts, Proportional to the end-diastolic volume (EDV), The pressure found in the vena cava and pulmonary veins during atrial diastole, Greater preload increases the force of contraction (Frank-Starling law of the heart)
• Contractility

  Strength of contraction at any given preload, Positive inotropic agents increase contractility, Negative inotropic agents decrease contractility