CVS

• How many ion channels in the heart?

  three

  calcium channels

  sodium channels

  potassium channels
• Cardiac cycle


  The sequence of events that occurs during one heartbeat
• The average cardiac cycle is about 0.8 seconds
• Cardiac cycle phases


  1. Mid to late ventricular diastole

  2. Isovolumetric contraction

  3. Ventricular systole

  4. Isovolumetric relaxation
• Ventricular diastole


  The heart is relaxing and filling with blood
• Blood flow during ventricular diastole

  • Blood flows into the right atrium from the superior vena cava, inferior vena cava, and coronary sinus
  • Blood flows into the left atrium from the pulmonary veins
• Atrial contraction


  Occurs after 70-80% of blood has passively flowed from the atria to the ventricles
• Atrial pressure is greater than ventricular pressure


  Causes the mitral and tricuspid valves to open further to allow blood to flow from the atria to the ventricles
• The ventricles are relaxed during diastole, so their pressure is close to 0 mmHg
• Arterial pressure is greater than ventricular pressure

  Causes the aortic and pulmonic semilunar valves to remain closed
• Atrial contraction is represented by the P wave on the ECG
• Isovolumetric contraction


  Ventricular contraction with no change in ventricular volume
• Ventricular pressure increases during contraction

  Becomes greater than atrial pressure, causing the mitral and tricuspid valves to close
• S1 heart sound


  Caused by the closing of the mitral and tricuspid valves
• Ventricular pressure increases during contraction


  But remains less than arterial pressure, so the aortic and pulmonic valves remain closed
• The QRS complex on the ECG represents ventricular depolarization during early contraction
• Ventricular pressure


  Less than arterial pressure
• Right ventricular pressure


  4 vs 10, less than arterial pressure
• Arterial pressure is greater than ventricular pressure
• Aortic and pulmonic valves

  Only open when ventricular pressure is greater than arterial pressure
• Aortic and pulmonic valves are closed
• Ventricular depolarization


  Early phases of QRS complex
• Ventricles are not in complete contraction yet as pressure is not high enough to overcome arterial pressure
• Mid to late ventricular systole

  1. Ventricles continuing contraction

  2. Ventricular pressure increases to 25 mmHg (right) and 120 mmHg (left)

  3. Arterial pressure is 80 mmHg (aorta) and 10 mmHg (pulmonary trunk)
• Atrial pressure is still zero, blood is filling the atria
• Mitral and tricuspid valves are closed
• Closing of mitral and tricuspid valves during isovolumetric contraction causes the first heart sound (S1)
• No additional heart sounds during mid to late ventricular systole
• Ventricular pressure


  Greater than arterial pressure
• Aortic and pulmonic valves open
• Late stages of QRS complex

  Ventricles are still contracting
• Isovolumetric relaxation


  1. Ventricular pressure decreasing but still greater than atrial pressure

  2. Mitral and tricuspid valves remain closed
• Ventricular pressure


  Decreasing but still greater than atrial pressure
• No additional heart sounds during isovolumetric relaxation
• Ventricular pressure


  Decreasing and becoming less than arterial pressure
• Aortic and pulmonic valves close, producing the second heart sound (S2)
• Ventricular repolarization


  Represented by the T wave on the ECG
• Heart


  • Located in the thoracic cavity, specifically in the mediastinum
  • Shifted about two-thirds to the left of the midsternal line
  • Weighs approximately 200-300 grams
  • Size of a fist
• Heart chambers


  • Atria (right and left)
  • Ventricles (right and left)
• Right atrium


  • Receives blood from inferior vena cava, superior vena cava, and coronary sinus
  • Contains fossa ovalis (remnant of foramen ovale)