Heart Contraction

Question 1

General Chain of events

Answer 1

1. Atrial Systole
2. Isovolumetric contraction
3. Rapid ejection
4. reduced ejection
5. isovolumetric relaxation
6. Rapid ventricular filling

Question 2

Atrial systole

Answer 2

• AV valves open; Pulmonary & aortic valves are closed
• elec. depolar of atria; atria has not yet contracted
• P WAVE ON EKG
• initiates contraction of atrial musculature
  1. As it contracts, pressure in chambers incr.
  2. causes rapid blood flow –> ventricles
• after contraction, atrial pressure decr.
• causes AV valves to begin to close (to prevent blood returning to atria)
• ventricular vol @ max

Question 3

Isovolumetric contraction

Answer 3

• all valves closed
• QRS complex of EKG (ventricular depolarization)
• myocytes contract
• incr. in intraventricular pressure
• causes AV valves to close as intravent. pressure > atrial pressure
• All valves closed, incr. intravent press. volume

Question 4

Rapid Ejection

Answer 4

• Aortic and pulmonic valves open. (forced open by V. depolar.)
• AV valves remain closed
• Intraventricular press. > aortic & pulmonic artery press.
• -> aortic & pulmonic valves open & push out blood in ventricles

Question 5

Reduced Ejection

Answer 5

• Aortic &pulmonic valves open, AV valves closed
• ~150-200msec after QRS complex, ventricular repol occurs (T wave)
• Ventricular emptying decr. as intravenous press. decr.
• atrial press incr. due to venous return

Question 6

Isovolumetric relaxation

Answer 6

• all valves closed
• press. in pulmonary artery & aorta > ventricles
• press. reversal —> A&P valves close
• vent. press decrease
• vol. remains constant b/c valves are closed
• Atrial press. con’t to incr.

Question 7

Rapid ventricular filling

Answer 7

• happens after atria contract
• AV valves open
• When vent. press < atrial press.
• AV valves open and ventricular filling begins