Force Generation By The Heart Flashcards
Cardiac myocytes are electrically coupled by
Gap junctions
What do the desmosomes do
In intercalated discs provide mechanical adhesion between adjacent cardiac cells
Ensure tension developed by one cell transmitted to the next
Each muscle fibre contains many
Myofibrils - contractile units
What is the structure of a myofibril
Thick and thin protein filaments
- actin thin
- myocyin thick
Arranges into sarcomeres
How is muscle tension produced
By sliding actin filaments on myocyin filaments
What does forever generation depend on
ATP dept interaction between thick and thin filaments
Atp is needed for both
Contraction and relaxation
What is needed to switch on the cross bridge formation
Calcium
How is calcium released from sarcoplasmic reticulum
Dependnt on presence of extra-cellular calcium
What does a long refractory period prevent
Generation of tetanic contraction
What is a refractory period
Period following an action potentail in which it is not possible to produce another action potentail
In plateaus sodium channels closed state and falling phase pottasium channels open
What is the stroke volume
The volume of blood ejected by each ventricle per heart beat
SV = EDV - ESV
How is the stroke volume regulated
By intrinsic and extrinsic mechanisms
Who are changes of stroke volume brought about
Changes in diastolic length of myocardial fibres
What determines the preload
The end diastolic volume
What determines the end diastolic volume
The venous return
What does the frank starling curve describe
Relationship between venous return, end diastolic volume,stroke volume
Stretch also increases the
Affinity of troponin for calcium
How is optimal length in cardiac muscle achieved
By stretching the muscle
What si the afterload
Resistance of heart pumping
If increased afterload continues to exist lead to
Ventricular muscle mass hypertrophy to overcome resistance
What is the extrinsic control of stroke volume
Nerves and hormones
Supplied by symp which increases force of contraction positive ionotropic effect
Neurotransmitter - noradrenaline
What so the effect of symp Stim on ventricular contraction
Force of contraction increases due to activation of calcium channels
Effect cAMP mediated
Peak ventricular pressure arises contractility of heart at a given EDV rises
Frank starling shifted to the left
Reduces duration of systole
What is the effect of parasymp nerves on ventricular contraction
Very little inv in ventricles so little if any effect on SV
Vagal Stim major for rate not force of contraction
