Cardiovascular system in action Flashcards
What does the cardiac cycle refer to?
the series of steps undergone by the heart during one heartbeat
During the cardiac cycle what do the different chambers of the heart go through?
periods of systole (contraction) and periods of diastole (relaxation)
What is the average heart beat lasts for?
around 0.8 seconds (although this can vary significantly)
How do stages of the cardiac cycle occur?
in the same order simultaneously in both sides of the heart.
Describe diastole?
Blood flows into the atria via vena cavae and pulmonary veins. The heart muscle is in a relaxed states with the valves of the heart closed until the pressure of the blood in the atria is greater than that in the ventricles and the AV valves are pushed open allowing the blood to enter the ventricles.
Describe atrial systole?
The left and right atria contract simultaneously to force the remaining blood from the atria into the ventricles. The ventricles, which are still in diastole, fill up with blood and the pressure increases (greater than the atria), causing the AV valves to snap shut/close to prevent the backflow of blood from the ventricles to the atria.
Describe ventricular systole?
The ventricles then contract and the pressure exerted forces open the semi-lunar valves, allowing blood to be pushed into the aorta and pulmonary artery. When the ventricles empties, the semi-lunar valves close and the heart can return to a diastolic state.
How long does atrial and ventricular diastole last?
0.4 seconds
How long does atrial systole and ventricular diastole last?
0.1 seconds
How long does atrial diastole and ventricular systole last?
0.3 seconds
What must the order of these steps remain?
constant although the rate at which they happen may fluctuate
What are the sounds of the heart beat caused by?
the closing of valves
What causes the initial lubb sound?
the closing of the AV valves
What causes the secondary dupp sound?
the closing of the semi-lunar valves
How can we remember the sequence of valve movements?
Closed AV valves
Open semi-lunar valves
Closed semi-lunar valves
Open AV valves
What is the cardiac cycle predominantly under the control of?
the nervous system
What is the sino-atrial node?
it is positioned over the right atrium and is the pacemaker of the heart. It functions by initiating electrical impulses that spread across the atria to make the cardiac muscle contract. The function of the SA node is independent of the rest of the nervous system (auto-rhythmic) and continues to send impulses even in the absence of nerves from the nervous system
What does the initial wave of excitation that spreads across the atria stimulate?
atrial systole
After atrial systole what does the initial wave of excitation also do?
passed to the atrio-ventricular node
What does the AV node do?
passes the signal down conducting fibres which branch left and right to stimulate ventricular systole from the base of the heart upwards