Autoregulatory neural and endocrine mechanisms activate after blood loss to compensate for the loss and restore homeostasis.
Neural mechanisms involve blood pressure and blood chemistry. Cardiac centers and vasomotor centers may increase the blood flow and cardiac output (sympathetic) or decrease the blood flow and cardiac output (parasympathetic). Peripheral vessels are also constricted and nor epinephrine decreases flow in the arteries and decreases the flow in the veins.
Endocrine control acts in the renal and adrenal organs, the brain and heart. RBCs, renin/angiotensiogen/aldosterone, catecholamines, antidiretic hormone, atrial natriuretic hormone regulate blood volume and blood pressure by keeping the fluids in the cardiovascular system. It also initiates vasoconstrictors or vasodilators.