Role of Hormones in Regeneration
Several neurosecretory effects in regeneration are integrated into a neuroendocrine feedback system. It is frequently difficult to distinguish hormonal from neural affects during regeneration, specifically in invertebrates, although the two influences are easily distinguished in vertebrates. In amphibians, the hormones of the three glands that are pituitary, adrenal and thyroid come out to affect limb regeneration. These hormones control different phases of the regeneration process hence the mechanism of their action is till not very clear. Furthermore the hormonal response changes with the age of animal. For example, larval urodeles regenerate limb in total nonexistence of pituitary hormone, whereas the adult is completely dependent upon the pituitary gland for limb regeneration, a dependence attained during metamorphosis. The role of the pituitary gland and its hormones in regulating regeneration has been worked out along with great difficulty by means of various experiments.