Blood flow to an organ system is regulated by the degree of vasomotor tone of small arteries and arterioles. Vascular constriction and dilation is under sympathetic, autonomic, and humoral control, which allows each organ to have its own unique physiological characteristics, For example, vigorous exercise causes sympathetic discharge, which results in dilation of the vessels that supply contracting muscle and in constriction of virtually all other vessels of the peripheral circulation

 

Circulation through the vascular bed of bone is essential for maintenance of osseous homeostasis, Normal growth, remodeling, and repair of bone require delivery of nutrients and oxygen through blood flow to bone, Under normal physiological conditions. bone receives 5 to 10 per cent of the cardiac output. The gross and microscopic anatomy of the vascular bed of bone has been studied extensively. The long bones receive their blood supply from nutrient, periosteal. epiphyseal, and metaphyseal vessels, The normal mature diaphyseal cortex and medullary canal are supplied primarily by the nutrient artery system. The nutrient artery enters bone through the nutrient foramen and divides into end-arterioles, which ascend and descend in the medullary canal. Arterial blood flow is centrifugal; blood is delivered to cortical bone through anastomosing medullary arteries, which arise as branches of the nutrient end-arterioles', Blood from the medullary artery system flows into cortical capillaries that traverse the haversian system, Cortical capillaries communicate with both periosteal capillaries and medullary sinusoids, which drain centripetally into the central venous sinus to the emissary veins.

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