Force Generation by the heart Flashcards
What is the structure of cardiac muscle?
- Striated
- cardiac myoctes (cells) are electrically coupled by gap junctions
- chromosomes within intercalated discs provide mechanical adhesion between adjacent cardiac cells
What is the “all or none law of the heart”
Gap junctions form electrical communication pathways between neighbouring myocytes which allows excitation to reach all cardiac myocytes
What are myofibrils made up of?
- Myosin: thick - causes darker appearance
2. Actin: thin - causes lighter appearance
What produces muscle tension?
sliding of actin filaments on myosin filaments
How does excitation of cardiac cells cause contraction?
When relaxed: regulatory proteins troponin and tropomyosin cover the binding site on actin for myosin
When excited: Ca++ binds to T&T and the binding site opens
How does Ca+ influence Ventricular systole?
- during plateau phase the Ca+ enters the myocytes and stimulates release of more Ca+ from sarcoplasmic reticulum
- This creates the action potential (systole)
How does Ca+ influence Ventricular diastole?
When there is not enough extracellular supply of Ca+ the heart muscle relaxes
What is the importance of a long refractory period?
PREVENTS MYOCARIDAL INFARCTION
- by the time the action potential is over the tension developed by muscle fibres is also over
What is a refractory period?
period following an action potential in which it is not possible to produce another action potential
Define Stroke Volume
the volume of blood ejected by each ventricle per heart beat
What does SV= ???
SV= End Diastolic Volume - End Systolic Volume
What is the Frank-Starling Mechanism?
The more the ventricle is filled with blood during diastole (EDV) the greater the volume of ejected blood will be during systolic contraction (stroke volume)
How is Stroke Volume of the right and left ventricles matched?
If venous return to the right atrium increases, the EDV of the right ventricle increases and Stroke Volume to the pulmonary artery increases.
The same is for the left but the SV into the aorta increases.
What is afterload?
the resistance into which the heart is pumping
- extra load is imposed after the heart has contracted
How does afterload affect SV?
If afterload increases, the EDV increases as the heart cannot eject the full SV. Therefore force of contraction increases.
