Adaptation of Arterioles to Moving Capillaries

Abstract

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.

Enamel

“…It is commonly as deep as it is wide in human enamel, but it may be much deeper than it is wide in many other mammalian species, the much-studied rat incisor enamel being a good case in point (REITH 1961(REITH , 1963FRANK 1968;KATCHBURIAN and HOLT 1972;KURAHASHI and MOE 1969;RONNIIOLM 1962;SASASKI and HIGASHI 1983;SASAKI 1983, 1981;WAKITA and HINRICHSEN 1980 ;WAKJTA and KOBAYASHI 1983 ;W EI NSTOCK and LEBLOND 1971 ;SK OBE et al 1981 ;WARSHAWSKY 1968;WARSHAWSKY et al 1981). Thus, in the most common form of ameloblast, which has a fla ttish face on one side of Tomes' process (in human enamel roughly perpendicular to the prism di rection within the rorming tissue), this is a major secretory site.…”

“…(Although it is. in which two extreme morphologies can be recognised (REITH and COTTY 1962;REITH 1963;KALLENBACH 1968KALLENBACH , 1970KALLENBACH , 1974KALLENBACH , 1980KURAHASHI and MOE 1969;GARANT 1972;ROBINSON et al 1977ROBINSON et al , 1981SMITH and WARSHAWSKY 1977;JOSEPHSEN and FFJERSKOV 1977;BOYDE 1975 ;BOYDE and REITH 1976, 1977, 1978, 1981, 1982IWAKu and OZAWA 1979;TAKANO and OZAWA 1980;TAKANO et al 1982a, b;TAKANoetal. In the case of human pennanent leeth, the ameloblasts may be in this functional position for a period of years after secretion as such has stopped .…”

“…clear that there is a point at which ameloblasts produce no more mineralisable matrix , recent studies have shown that maturation ameloblasts still produce matrix proteins even in the maturation zone; these, however, are not assembled to make a n extra layer of enamel (GRAVER et al 1978 ;NANCI et al 1984NANCI et al , 1988]. 1982;REITH and BOYDE 1981a, b, 1983, 1985HODDE et al 1982;JOSEPHSEN 1984;GARANT et al 1983;GOLDBERG and SASAKI 1985;MOE 1971MOE , 1981REITH et al 1982REITH et al , 1984SASAKJ et al 1983SASAKJ et al , 1984SUGA et al 1970 ;TAKANO and OZAWA 1984;TAKANO et al 1982;NISKIKAWA and JOSEPH-SEN 1987;SASAKI and GARANT 1987). During maturation, tbe concentration of amelogeni ns in the enamel is greatly reduced.…”

Progressive Involution and Physiological Death of Smooth Muscle Cells of Rat Incisal Arterioles

“…However, if changes in the functional parameters are sustained, structural adaption of the vessels may take place. This is seen, for example, in chronic hypertensive states [Folkow, 1978;Mulvany et al, 1978;Folkow, 1983] and in situations where collateral circulation devel ops [Borgers et al, 1970;Schaper et al, 1971], Both proliferative and degenerative changes may be involved in the adaptive pro cess [Fischer-Dzoga, 1979;Moe et al, 1979;Weber, 1980;Moe, 1981], However, the de generative phenomena are known only in broad outline. The explanation may be that the processes are diversified, proceed rela tively rapidly and are rarely seen frequently enough to be understood coherently.…”