Cardiovascular system Flashcards
What is the Cardiac conduction system?
Heart is myogenic- creates own electrical impulse, forcing walls to contract.
Sino-atrial Node (SAN) - initiates impulse across left and right atrial walls causing them to contract.
Atrio-ventricular Node (AVN)- impulse reaches AV node in right atrium, causing 0.1 sec delay.
Bundle of HIS- passed down from AV node, impulse passes into septum of the heart.
Purkinje fibres- bundle of HIS splits into 2 different branches, spreading the impulse down the bottom of the heart and up and around the walls of the ventricle.
This causes the ventricles to contract and then relax, the cycle then starts again.
What is the Cardiac Cycle?
Sequence of events involved in a single heartbeat.
1 cycle takes approx. 0.8 seconds to complete.
Diastole- relaxation of cardiac muscle.
Systole- contraction of cardiac muscle.
SAN, Atrial systole, AVN, BofH, Purkinje fibres, Ventricular systole.
Atrial diastole- atrial fills with bloods, AV valves closed, atria blood pressure rises above ventricular pressure.
Atrial systole- AV valves open and blood passes into both ventricles via contraction of atria.
Ventricular diastole- Ventricles fill with blood, semilunar valves remain closed.
Ventricular systole- contraction of the ventricles increases ventricular pressure, aortic and pulmonary valves forced open, AV valves closed. Blood forced out into the aorta and to the body/tissues.
