Humoral regulation refers to the effect of hormones in the heart and how hormones that are released into the bloodstream under certain physiological states may regulate cardiac function. Catecholamines released from the adrenal medulla increase the dP/dt of the heart. This effect is potentiated by steroid hormones. Calorigenic hormones like insulin, glucagon and thyroxine also increase cardiac contractility. Thyroxine produces a permissive effect on the action of catecholamines. In hypothyroidism the effect of catecholamines in the heart is depressed by the absence of thyroxine.
Addis Ababa University Collage of Health Science Department of Physiology By : Robel Abay September 19 09/30/11 Regulation of cardiac out put
Heart is not the primary controller of cardiac output.
Instead, factors of the peripheral circulation affecting venous return, are the primary controllers.
The main reason peripheral factors are usually more important than the heart itself in controlling cardiac output is that the heart has a built-in mechanism that normally allows it to pump automatically whatever amount of blood that flows into the right atrium from the veins.