Question

Briefly define the following terms:

1. Preload
2. Afterload
3. Starling’s law of the Heart

Answer 1

Preload is the passive muscle stress due to the filling pressure of the blood in the ventricle at the onset of contraction. In Cardiac physiology, preload is the end diastolic volume that stretches the right or left ventricle of the heart to its greatest dimensions under variable physiologic demand.it is the initial stretching of the cardiomyocytes prior to contraction; therefore it is related to the sarcomere length at the end of diastole. parameters such as ventricular end diastolic volume or pressure are used to measure preload.

Afterload is the pressure against which the heart must work to eject blood during systole.it is the end load against which the heart contracts to ejects blood. it can also be described as the pressure that the chambers of the heart must generate in order to eject blood out of the heart and thus is a consequence of the aortic pressure ( for the left ventricle) and pulmonic pressure or the pulmonary artery pressure (for the right ventricle). the pressure in the ventricles must be greater than the systemic and pulmonary pressure to open the aortic and pulmonic valves, respectively. as afterload increases, cardiac output decrease.

Frank -starling law of the heart states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart ( the end diastolic volume) when all other factors remain constant.

As a larger volume of blood flows into the ventricle, the blood will stretch the walls of the heart, causing a greater expansion during diastole, which in turn increases the force of the contraction and thus the quantity of blood that is pumped into the aorta during systole.