4

what are the 4 phases of the cardiac cycle

1. ventricular filling

2. contraction / systole

3. ejection

4. relaxation/ diastole

what are the two stages during ventricular filling

atrial diastole and atrial systole

what happens during the atrial diastole phase of ventricular filling

the heart is relaxed

mitral valve is open

blood flows passively into the ventricle

semilunar valve closes

what happens during the atrial systole phase of ventricular filling

• ventricle remains in systole

• atrium contracts

• blood is forced into the ventricle to complete ventricular filling

what happens during contraction / systole

• atrial systole ends and ventricular systole begins

• intraventricular pressure rises

• av valve rises

what happens during ejection

• ventricle continues to contract

• semilunar valves open

• atrium is relaxed and filling with blood

• intraventricular pressure surpasses pressure in aorta

what happens during relaxation / diastole

• ventricular diastole starts

• atrial pressure increases above intraventricular pressure AV valve opens

what happens during phase 1 of the cardiac cycle

atrial diastole and atrial systole

what happens during phase 2 of the cardiac cycle

contraction

what happens during phase 3 of the cardiac cycle

ejection / ventricular systole

what happens during phase 4 of the cardiac cycle

relaxation / diastole

how to calculate stroke volume

End diastolic volume - End systolic volume

how to calculate the ejection fraction

(EDV - ESV) / EDV x 100

what could effect the stroke volume

• preload, afterload and connectivity

what is preload

before cardiac muscle cells are stretched just before they contract

what happens as the greater the end diastolic volume

the greater preload

what is afterload

pressure the ventricles must overcome to ejecct

what is contractability

contractile strength achieved at a certain muscle length

what does increased preload do to the stroke volume

increase it

what does increased afterload do to the stroke volume

decrease the stroke volume

what does increased contractability do to the stroke volume

increases it

how to calculate blood pressure

Blood pressure = cardiac output x peripheral resistance

BP = CO x TPR

what is resistance

the tendancy of the cardiovascular system to oppose blood flow

what are 3 factors that affect resistance

• radius of tube

• length of tube

• viscosity of fluid

what is venous return

when blood return from peripherial veins to the heart through to the right side of the heart

what happens to venous return on exercise

it increases because of the respiratory pump and skeletal pump

what is the respiratory pump

when pressure changes in the thorax and abdomen

what is the skeletal muscle pump

skeletal muscles contract in lower limbs

what encourages venous return

sympathetic renoconstriction

what else can increase venous return on exercise, that isnt respiratory pump or skeletal pump?

ANS induced venoconstriction leads to an increased preload, which leads to an increased stroke volume so an increased cardiac output