cardiovascular physiology Flashcards
what is stroke volume?
volume of blood pumped by one ventricle per contraction
~ 75ml
what is cardiac output?
volume pumped per ventricle per minute
~ 5L/min
what is venous return?
volume of blood returning to the heart
correlation between CO and VR?
should be equal
where does electrical activity originate in the heart?
sinoatrial SA node
how does the electrical activity spread?
via gap junction
role of annulus fibrosis?
non-conducting layer between atria and ventricles electrically insulates/isolates chambers
what does the P wave show?
atrial depolarisation
what is the Q interval?
P-R
interval between start of excitation of atria and ventricles
what is the QRS complex?
ventricular depolarisation
atrial repolarisation occurs but is obscured
what is the ST segment?
all ventricular tissue depolarised, contraction
what is the QT interval?
contraction occurring but includes ventricular repolarisation
what is the T wave?
ventricular repolarisation
how does activation of sympathetic nerves effect heart rate?
- release of noradrenaline, binds to B1 receptors
- increased opening of HCN channels
- opens Ca2+ channels
- increased phase 4 slope
- increased heart rate
how does activation of parasympathetic nerves effect heart rate?
- release of Ach, binds to muscarinic receptors
- decreased opening of HCN channels
- slowed opening of Ca2+ channels
- opens additional K+ channels
- reduces slope of phase 4
- heart rate decreases
normal value for intrinsic rate of firing of SA node?
~ 100-110 APs per min
what is preload ?
degree of stretch in ventricles due to end diastolic pressure
what is the heterometric (intrinsic) mechanism of regulating force of contraction?
starlings law of the heart
- force of contraction is proportional to the INITIAL fibre length in diastole / number of cross bridges possible
effect on muscles of low preload (almost empty chamber)?
- actin and myosin overlap isn’t optimal
- reduced ability to contract
effect on muscles of high preload (full ventricle)?
stretching of muscle
optimal cross bridges available
increased affinity of troponin C to Ca2+
maximal force
effect on muscles of heart failure(overfull heart)?
actin and myosin physically separated
prevents interaction
reduced force
effects of sympathetic nerve stimulation on homeometric (extrinsic) mechanism?
increased stroke volume without change in initial fibre length
increased contractility (positive ionotropic)
effect of catecholamines in extrinsic mechanism?
produces more forceful but shorter contraction
