Physiology of Cardiovascular System Flashcards
4 chambers of heart & 4 main valves
R & L atrium and ventricles
tricuspid
pulmonary
mitral
aortic
coronary vessels
arterial blood supply to the myocardium is via R and L coronary arteries and their branches
venous drainage is mostly via coronary veins into R atrium
describe the heart conducting system
R + L atria contract 1st then the ventricles this is achieved by conducting system
SA node natural pacemaker to define cardiac rhythm
Electrical stimulation of upper R side of right atrium initiates contraction of both atria
Electric signal travels to AV node which delays transmission of electrical signal giving time for atria to contract and fill both ventricles
Signal then travels though R and L bundle of His to apex of heart and initiates ventricle contraction through purkinje fibres
innervation of the heart
Innervation from both sympathetic and parasympathetic
Para - neurotransmitter is acetylcholine slow down pacemaker & increase delay hence reducing conduction velocity which is described as negative chronotropic and dromotropic effect
Symp - neurotransmitter is noradrenaline. Increased heart rate, conduction and velocity in this case as well as contractility. Effect on myocytes increases rate of relaxation
cardiac cycle
Ventricular systole
1st contraction - isovolumetric as there is no change in volume in ventricular chamber
Closure of respective valve from respective atrium which filled the ventricle
Ejection - contraction pushes blood out of the ventricle
Ventricular diastole
1st - allows respective atrioventricular valve to open by relaxing ventricle without changing the volume
2nd - valve opens and blood flows from atrium to ventricle
3rd - contraction of respective atria for active filling
Requires pressure changes & timing, volumes, mechanical events (valves) and electrical events to work
p wave
atrial depolarisation
qrs complex
ventricular depolarisation
t wave
ventricular repolarisation
coronary blood flow
blood flow greatest during ventricular diastole
coronary arteries are compressed during systole
coronary blood flow is decreased by
- increased HR
- low aortic diastolic BP
to calculate blood pressure
BP = CO x TPR
BP = mean arterial bp
CO = cardiac output
TPR = total peripheral resistance
to calculate cardiac output
CO = stroke volume x HR
venous return
blood returning to right atrium
push forces:
- momentum from systole
- muscle pump; limb muscles & venous valves
pull forces:
- thoracic pump; negative intrathoracic pressure
stroke volume preload
tension in heart wall as a result of filling
determined by end diastolic volume
starling’s law of heart; increased EDV leads to increased stroke volume
length - tension relationship (overlap of actin & myosin filaments
starling’s law
the stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction
stroke volume & contractility
increase contractility & positive inotropic effect
decrease contractility e.g. heart failure
