The physiology of blood circulation in bone is discussed. Despite the clinical need for knowledge in this area, this subject has received no attention in the standard textbooks of physiology, probably because available knowledge has not been adequately formulated. I hope that this lecture will stimulate future studies.

The available data indicate that the rates of blood flow in various bones in the rat, rabbit, dog, and man are about five to twenty milliliters per minute per 100 grams of wet bone. The rates of flow in the entire skeleton in the rat, rabbit, dog, and man are estimated to be 4 to 10 per cent of the resting cardiac output. The nutrient artery of a long bone in the rabbit is found to be responsible normally for about two-thirds of the blood supply of the diaphysis and for about one-third of the blood supply of each metaphysis.

Accumulated evidence strongly indicates that bone circulation is controlled by neural, hormonal, and metabolic mechanisms. Stimulation of the sympathetic nerves decreases bone-blood flow, as does administrations of vasopressor hormones such as adrenaline, noradrenaline, and pitressin. Metabolic factors, such as acid metabolites, low pH, and high carbon dioxide and low oxygen tensions of blood increase bone-blood flow.

In addition to these three control mechanisms, many other systemic, regional, and local factors apparently affect bone-blood flow. Local and regional factors have been studied far more extensively than systemic factors.

Some of the functions of bone-blood flow, particularly in osteogenesis, maintenance of bone vitality, bone growth, and fracture healing are discussed by relating experimental findings to clinical practice.