Control of Stroke Volume
The strength of contraction of the heart depends on three factors:
- What force the heart has to pump against (afterload)
- How stretched the cardiac muscle is before it contracts (preload).
These are both properties of the muscle itself, they can be demonstrated in isolated strips of muscle, and are therefore described as intrinsic factors - The inotropic state of the muscle (contractility).
This is controlled by nerves and hormones, and can therefore be thought of as an extrinsic factor.
