3. Intrinsic Regulation (Autoregulation) - Continued

Thus factors which increase venous return (ventricular preload) will result in an increase in cardiac output as a result of this intrinsic mechanism. In the heart 'in vivo' this mechanism is relatively unimportant since the autonomic nervous system is the dominant regulatory mechanism.

Importance of the The Frank-Starling Response.

1. Maintaining the balance between the right ventricular and left ventricular outputs;
2. It is a rapid response i.e. regulation on a beat-to-beat basis.
3. The atrial booster pump - stretch of myocardial fibres in the atria results in increasing tension in the walls of these chambers when they contract which increase ventricular filling. This maybe important during exercise when the heart rate increases and the time available for filling is decreased.

ii) Homeometric Autoregulation

A second autoregulatory mechanism not dependent on change in myocardial fibre length. Under conditions of increased aortic pressure (increased afterload) myocardial contractility increases. Initially there is a Frank-Starling response but after a delay of about 30 seconds the contractility increases to maintain stroke volume at the same myocardial fibre length. This is known as the Anrep effect and may have little relevance in the intact heart.