Search

Histological structure of adrenal gland is studied in four age groups of the harp seal: in adults, in two juvenile groups (6 and 1-1.5 months), and in newborns (1-1.5 days). Development of the adrenal gland in this species is analogous to that of terrestrial mammals, but also has some peculiarities of its own. Differentiation of the definitive cortex occur in the prenatal development. In the newborns it is, though weakly developed, clearly differentiated into arched, fascicle and reticular zones. The foetal cortex is discovered in newborns, which further develops in juveniles and is present (without any signs of involution and degeneration) in adults. Adrenal gland persistence was previously known in horses only, but in that case the foetal cortex was partly degenerated in adults. Chromaffin cells undergo differentiation in embryonic development, as newborns already possess two types of such cells. The final differentiation ends in juvenile of 1.5 months old.

The harp seal adrenal gland studied is alike that of terrestrial mammals, but has some peculiarities. Firstly, this is presence of the fetal cortex in the adrenal gland without any signs of involution and degeneration in adult animals. This phenomenon has been previously described only for the horse adrenal gland. The glomerular zone of the cortex peculiar for the adrenals in the terrestrial mammals in the species studied has the form of arches. This property is also characteristic only to the horse gland. The absence of intermediate and juxtamedullary zones also differs the harp seal adrenal gland from that of terrestrial mammals.