Cardiac cycle Flashcards
What does the SVC drain?
SVC drains blood from head, neck, upper limbs and chest.
What does the IVC drain?
IVC drains blood from the lower limbs.
How do left ventricular valves work?
LV closes, backward P gradient pushes blood backwards, mitral valve opens with forward pressure- prevents blood going backwards. Mitral valve has papillary muscles- they pull the valves inwards towards the V to prevent them bulging towards the atria when the V contracts. When V contracts get a huge pressure so stops the valves going backwards.
What do the two sounds in a normal heart beat mean?
Heart sound 1 – systole
Heart sound 2 – beginning of diastole
Normal heart sound- first sound caused by closing of the atrioventricular valves (mitral and tricuspid valves) and second sound is caused by closing of the semilunar valves (aortic and pulmonary valves).
What are the phases of the cardiac cycle?
Diastole and systole
What is diastole?
- Isovolumetric ventricular relaxation
- Rapid ventricular filling
- Slow ventricular filling
- Atrial contraction
What is systole?
- Isovolumetric ventricular contraction
- Ejection
What are the mechanical events of the cardiac cycle?
Late diastole- both sets of chambers are relaxed and ventricles allow blood passively by gravity.
Atrial systole- atria contract and forces a small amount of blood into ventricles- sometimes called the atrial kick
Isovolumic ventricular contraction- First phase of ventricular contraction- blood pushes AV valves closed, not enough pressure as ventricles start to contract to open up the semi-lunar valves
Ventricular ejection- as ventricles pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood id ejected
Isovolumic ventricular relaxation- Ventricles then relax and pressure falls and blood falls back into cusps of semi lunar valves and snaps them shut.
What is the name for filling the heart with blood?
Diastole
What is the name for contraction of myocardium an ejection of blood?
Systole
How long does one cardiac cycle last?
0.8 seconds
What is the electrical activation of the cardiac cycle?
P wave- depolarisation of atria in response to SA node triggering
PR interval- delay of AV node to allow filling of ventricles
QRS complex- depolarisation of ventricles, triggers main pumping contractions
ST segment- beginning of ventricle repolarisation
T wave- ventricular repolarisation
Definition of SV
Stroke Volume (SV)-volume of blood ejected from the left ventricle with each cardiac cycle (resting: 70 ml)
Definition of CO
Cardiac Output (CO)- volume of blood ejected from the left ventricle each minute (resting 5.0 l/ min)
Formula for CO
CO = HR x SV
