Physiology 2- Force Generation by the Heart Flashcards
How are cardiac myocytes electrically coupled?
Gap junctions
Where does cardiac excitation reach?
All the myocytes
What is the contractile unit of a cardiac muscle?
Microfibril
What filaments do microfibrils contains?
Thick myosin and thin actin
What causes muscle tension?
Actin sliding on myosin
What is required for both contraction and relaxation of cardiac muscle?
ATP and calcium
What does troponin do?
Covers the myosin binding site on actin
What does calcium do to troponin?
Calcium binds to troponin which produces a conformational change to move the tropomyosin complex out of the way to allow actin and myosin to interact
When are where is calcium released in cells?
Sarcoplasmic reticulum when there is already calcium in the extracellular fluid- Ca++ induced Ca++ release
When actin and myosin can interact to allow contraction, what does this induce?
Ventricular systole
What is the refractory period?
The period following an action potential during which no ore action potentials can take place
Where does the refractory period take place?
Plateau phase in myocytes
When ventricular muscle contracts, it ejects what?
The stroke volume
What is the stroke volume defined as?
The volume of blood ejected by the each ventricle per heartbeat
How can you work out stroke volume?
End diastolic volume- end systolic volume
The diastolic length/end diastolic volume is defined as what?
The volume of blood within each ventricle at the end of diastole
What is the Frank Starling law in simplified terms?
Increasing end diastolic volume/venous return will increase stroke volume
What is afterload?
The resistance into which the heart is pumping- imposed after the heart has contracted
If an increased afterload is continuous, what does this result in?
Hypertrophy (from increased force of contraction)
What is an inotropic effect?
Something that affects the force of contraction
Ventricular myocytes are controlled by which nerves?
Sympathetic nerves
Force of contraction increases because of Ca++ influx which is mediated by what?
cAMP
What is the cardiac output?
The volume of blood pumped by each ventricle per minute (SV x HR)
What is the cardiac output approximately?
5l
