Question

(a) Draw and discuss the ventricular function (end-diastolic volume versus stroke volume) curve to illustrate the Frank-Starling mechanism. (b) Explain how sympathetic stimulation, increased pre-load or increased after- load might affect this curve respectively

Answer 1

The increased stretch of the muscle fibers results in increased force of contraction because the myofibrils become more sensitive towards the calcium. So that, more actin-myosin cross bridges are formed, which results in more forceful contraction of the muscle, this is the physiological basis of Frank-Starling’s law.

The term “contractility” refers to the strength of cardiac muscle contraction observed at a constant fiber length (EDV), afterload, and heart rate. The cardiac contractility increases with increase in venous return as per the “Frank-Starling law.” This in turn increase the “CO.”

The Frank-Starling’s law of heart explains the force-length relationship of muscle fibers. The more the muscle fibers are stretched, the greater will be the contraction.

The term “preload” refers to the extent of ventricular stretch caused by the end diastolic volume. The stroke volume increases with increase in preload, and contractility of the muscle fibers, which ultimately increase the cardiac output.

For example, during exercise, the venous return is higher. The increased venous return causes more stretching of the ventricles, which triggers more forceful contraction of the ventricles and thus, the greater stroke volume. The increased stroke volume increases the cardiac output. Thus, the stroke volume increases during exercise despite the shorter time available for filling.