Unit 4 - Cardiac Contraction and Relaxation Flashcards
Explain the excitation-contraction coupling reaction.
In response to the action potential, Ca enters the cell across the sarcolemma from the extracellular space Ca binds to the cisternae Ca is released from the sarcolemma ATP is hydrolyzed Cross bridges between actin-myosin forms the myosin head flexes
What is the excitation-contraction coupling reaction also known as?
physiologic systole
Explain the process of relaxation.
longitudinal tubules of the SR accumulate Ca which removes it from the site of interaction with contractile proteins
Once Ca is removed, cross bridge formation ceases
the sarcomere returns to its resting length
What is relaxation of the myocyte also known as?
physiologic diastole
What is afterload?
the amount of work needed to eject blood
What is the major component of afterload for the left ventricle?
systolic aortic pressure
What is the major component of afterload for the right ventricle?
systolic pulmonary artery pressure
If aortic pressure is increased, how does this affect afterload and stroke volume?
afterload will increase, stroke volume will decrease
How does decreasing afterload effect velocity and length by which the muscle contracts?
it increases the velocity and the length
What is preload?
preload is the end diastolic volume that stretches the right or left ventricle of the heart to its greatest dimensions under variable physiologic demand.
What does preload determine?
the amount of muscle stretch before contraction
What does increasing the preload of an isolated muscle cause?
an increased force on contraction
When does preload occur?
during diastole
How is the resting muscle fiber length determined?
by ventricular end-diastolic pressure or volume
How does increasing preload affect stroke volume or work?
it increases it
What is the Frank-Starling relationship related to?
the resting length of the sarcomeres
What does the Frank-Starling relationship describe?
the relation between energy output and ventricular diastolic size
What is increased contractility characterized by?
increased velocity of contraction and an increase in peak tension development
What does increased contractility generally mean (in relation to Ca and systolic rate)?
increase in systolic rate and increased peak cytosolic Ca
What increases Ca flow?
sympathetic stimulation, catecholamines, thyroid hormone and some other drugs
What decreases Ca flow?
beta blockers and Ca entry blocker drugs
What determines contractility at the cellular level?
cytosolic Ca, contractile proteins, sensitivity to Ca ions present
What does increased contractility lead to in relation to stroke volume and ESV?
increased stroke volume and smaller ESV
