Flashcards in Cardiovascular (Dr Rohit) Deck (88)
what function does the heart serve
- demand and supply
- biochemical processes need energy which creates a demand for oxygen (demand)
- Heart generates pressure and creates a pressure gradient (critical for supply)
Cardiac output =
heart rate x stroke volume (~80mL/beat)
= amount of blood ejected per unit time
ventricular blood volume unchanged. All 4 valves closed.
percentage of blood pumped out of a full ventricle
Blood volume after atrial systole and ventricular diastole
at rest, cardiac output =
volume of blood returning to the heart from the vasuclature every minute (linked to CO)
difference between maximum cardiac output and cardiac output at rest
Frank-starling law of the heart
the more the heart fills with blood (during diastole), the more the ventricular myocytes stretch, and the greater the force of contraction (systole)
- degree of stretch of the myocardial fibres, at the end of diastole, before they contract
- preload is proportional to end-diastolic volume (the greater the EDV, the more forceful the next contraction)
force of contraction, of ventricular myocytes, at any given preload
pressure that must be exceeded before ejection of blood from the ventricles can occur
a healthy heart pumps out all the blood that has entered its chambers during the previous diastole TRUE/FALSE
draw a stroke volume loop
(check it on page 73)
two mechanisms by which stroke volume is regulated
1. intrinsic regulation of the force of contraction - governed by the degree of stretch of the myocardial fibre (end of diastole)
2. extrinsic regulation - determined by activity of autonomic nervous system and levels of certain hormones
increase in filling pressure leads to...
increase in end-diastolic volume and increase in stroke volume
work done by the heart
change in pressure x change in volume
area of the 'pressure-volume loop'
how does pressure in the ventricle change during filling
pressure falls at first due to suction effects of relaxation, then it rises as the volume increases
how does a positive inotrope effect contractility?
increases force of contraction by promoting Ca2+ inflow
effect of the calcium store, in the sarcoplasmic reticulum, on the membrane potential of the myocyte
excitation is initiated by specialised cells in the _________ ______ which lies close to the point of entry of the ______ _______ into the _____ atrium. A ______ ___ ________ is then conducted throughout the myocardium of the _____. The cells of the ____ ____ have an _______ resting potential. Between successive APs there is a ______ ________ due to the slow ___ inflow. This is the _______. When _______ is reached (-40mV) an AP is triggered to initiate a ________.
excitation is initiated by specialised cells in the _sinoatrial_ _node_ which lies close to the point of entry of the _vena_ _cava_ into the _right_ atrium. A _wave_ _of_ _depolarisation_ is then conducted throughout the myocardium of the _atria_. The cells of the _SA_ _node_ have an _unstable_ resting potential. Between successive APs there is a _progressive_ _depolarisation_ due to the spontaneous _Na+_ inflow. This is the _pacemaker_. When _threshold_ is reached (-40mV) an AP is triggered to initiate a _heartbeat_.
what do the action potentials of the atria, ventricles and conducting system have in common?
fast initial upstroke followed by a plateau phase of depolarisation before repolarisation.
what causes the plateau phase?
inward movement of calcium ions through L-type Ca2+ channels
what is the importance of the long plateau phase?
- the action potential lasts almost as long as the contraction of the cell
- enough time for efficient contraction (if it was just a twitch that would be poor)
- ensures unidirectional excitation of the myocardium
when does repolarization of myocardial occur
when voltage-dependent calcium channels inactivate
slows the AP, which allows time for atrial systole
AV bundle/bundle of His
conducts from the AV node to the purkinje fibres i.e. carries the wave of depolarisation from the right atrium, through the insulating fibrous skeleton, to the ventricles