L13 Q&A
What are the 4 determinants of cardiac output? - (correct answer)heart rate, preload,
afterload and
contractility
Define preload - (correct answer)The load on the muscle BEFORE contraction is
initiated. The preload stretches the muscle length and therefore generates passive
tension on the muscle. In the heart, preload is dependent on ventricular filling (end-
diastolic volume
Define afterload - (correct answer)The load on the muscle AFTER contraction is
initiated. Afterload is any force that resists muscle shortening. Normally, arterial
pressure is the force that resists left ventricle contraction (muscle shortening).
Define contractility - (correct answer)- The inherent ability of actin and myosin to form
cross-bridges and generate contractile force. Contractility is INDEPENDENT of preload
and afterload. Contractility is
primarily determined by intracellular [Ca2+]. In cardiac muscle, the active tension curve
rises steeply in relation to changes in muscle length.
Define isometric contraction - (correct answer)Contraction without shortening (no
change in length). If a muscle is unable to generate enough force to meet the afterload,
then the contraction is isometric (no muscle shortening)
Define isotonic contraction - (correct answer)Contraction with shortening and constant
force (no change in force). If a muscle is able to generate enough force to meet the
afterload, then the contraction is isotonic (muscle shortens).
An increase in resting cardiac muscle length will (increase or decrease) contraction
strength. - (correct answer)increase
What are the 4 determinants of cardiac output? - (correct answer)heart rate, preload,
afterload and
contractility
Define preload - (correct answer)The load on the muscle BEFORE contraction is
initiated. The preload stretches the muscle length and therefore generates passive
tension on the muscle. In the heart, preload is dependent on ventricular filling (end-
diastolic volume
Define afterload - (correct answer)The load on the muscle AFTER contraction is
initiated. Afterload is any force that resists muscle shortening. Normally, arterial
pressure is the force that resists left ventricle contraction (muscle shortening).
Define contractility - (correct answer)- The inherent ability of actin and myosin to form
cross-bridges and generate contractile force. Contractility is INDEPENDENT of preload
and afterload. Contractility is
primarily determined by intracellular [Ca2+]. In cardiac muscle, the active tension curve
rises steeply in relation to changes in muscle length.
Define isometric contraction - (correct answer)Contraction without shortening (no
change in length). If a muscle is unable to generate enough force to meet the afterload,
then the contraction is isometric (no muscle shortening)
Define isotonic contraction - (correct answer)Contraction with shortening and constant
force (no change in force). If a muscle is able to generate enough force to meet the
afterload, then the contraction is isotonic (muscle shortens).
An increase in resting cardiac muscle length will (increase or decrease) contraction
strength. - (correct answer)increase
