Adaptation of arterioles to moving capillaries

The capillary network of the enamel organ of the continuously growing mandibular incisor of the rat is supplied by a series of arteries which, after penetrating the bone, are disposed in a row in the periodontium along the tooth and linked together by anastomoses. The branches from these arteries are subjected to adaptive changes consistent with a forward movement of the capillaries in relation to the arteries. The mechanism which renders this movement possible appears to be the following: Each artery in the row supplies a section of the passing plexus by coupling and uncoupling short-lived arterioles, which go through a cycle of proliferation, elongation and degeneration. Proliferation takes place at the posterior end of the section, where new arterioles replace discarded arterioles from the preceding artery. By growing in length, the arterioles keep pace with the migrating capillary network. When the capillaries are within reach of the next artery, the arterioles disconnect. Thereafter they become obliterated and die in the intermediate zone of the periodontium, to which they have been gradually displaced by proliferation of the inner-tooth-related layer of the periodontal connective tissue.