Question

1.) How is a pre-loaded muscle able to sustain high tension with increasing loads while an after-loaded muscle does not? Explain in physiological terms

2.) Explain why the rate of contraction is faster in a pre-loaded muscle compared to an after-loaded muscle? Explain in physiological terms

Thank you!

Answer 1

1. Preload - The pre - load is the degree of which the myocardium is stretched before it contracts.it occurs during diastole.

The relationship between the extent of pre - load and tensions developed in cardiac muscle gives the Frank - starling law . The pre - load muscle have higher tension that of after - load muscle.

After - load - it is the resistance against which ventricles pump the blood.It occurs during systole.

according to frank - starling law higher tension is seen in pre - load muscle.

2. The pre load is one of heterometric regulation of cardiac output.

Preload is directly proportional to EDV( end - diastolic volume).Amount of blood in ventricles at end of diastole. Pre load muscle has faster rate of contraction .It depends on and increased by -

a. Increase in EDV (end - diastolic volume)

b.increase in pump action.

c.increase in venous return.