An Antagonistic Relation Between Wound Contraction and Regeneration - Tissue and Organ Regeneration in Adults - page 209

larva

adult frog

Fig. 8.1 Wounds close partly by contraction and regeneration in the tadpole; however, they close
by contraction and scar formation in the adult frog. Photos of healing of full-thickness excisional
skin wounds (defects) in tadpoles and frogs are from the study described in Fig. 8.2 and in the text.
(Yannas et al. 1996) Top left : Full-thickness skin defect in tadpole, day 1. Top right : Although the
tadpole wound contracted significantly, it closed partly by regeneration. Area enclosed with broken
line in tadpole : The regenerated skin has spots that are native to the skin of this species (North
American bullfrog). Day 97. Bottom left : Full-thickness skin defect in adult frog, day 0. Bottom
right : The frog wound closed partly by contraction and partly by scar formation. Area enclosed
with broken line in adult frog : Contracted and scarred wound. Day 150. Identification of tissues as
regenerated skin or scar was based on histological views (Yannas et al. 1996)

closure by regeneration correspondingly decreased from 59.2 ± 6.8 to 9.9 ± 2.3 during
the same period. The data are shown in Fig. 8.2 and have been entered numerically in
Table 4.4 in connection with the practice of the defect closure rule (see Chap. 4).
Since scar formation was first observed after metamorphosis to the frog, contrac-
tion and regeneration were the only mechanisms for wound closure in the tadpole.
In this model, contraction and regeneration appeared to be in a directly antagonistic
relation in skin defect closure during development; contraction increased continu-
ously at the expense of regeneration (Fig. 8.2 ) (Yannas et al. 1996).

8.2.2 Anatomical restriction to wound contraction during healing

of the rodent ear by regeneration

In the rabbit, a sharp difference in healing outcome of dermis-free defects has been
observed between two anatomical sites: the dorsal region and the ear. While the
defect in the dorsal region closes by vigorous contraction and synthesis of scar, the