Where does most of the blood supply in cortical bone come from?

The periosteum plays a crucial role in supplying blood to the cortical bone. It is a dense layer of vascular connective tissue that surrounds the outer surface of bones, except at the surfaces of joints. The periosteal blood vessels penetrate the bone through Volkmann's canals, providing essential nutrients and oxygen to the cortical bone. This vascularization is important for maintaining the health and integrity of the bone, facilitating metabolic activities, and contributing to the repair process in case of injury.

While internal marrow spaces and cancellous bone vasculature also contribute to the overall blood supply to the bone, they primarily nourish the trabecular regions rather than the cortical bone itself. Systemic circulation certainly provides blood throughout the body, but it is the specific vascularization provided by the periosteum that is essential for supplying the cortical bone directly.