The purpose of this study was to gain more information on the structure of different layers of renal artery
and comparing these structures in post-natal male and female sheep. To do so, right and left renal arteries of
6 adult and 6 newborn animals were dissected; the middle parts of arteries were only collected. After tissue
processing using paraffin embedding method, 5–6-μm sections were cut and stained with haematoxylin and
eosin, green Masson’s trichrome and Verhoeff’s elastic fiber methods. Three layers were identified in the
wall of artery in both sexes. In tunica media the number of rows of circular smooth muscle cells was 15–25
rows in newborn and 30–40 in adult sheep. External elastic membrane was visible in adult and was
structurally thinner than the internal membrane. Tunica adventitia was visible in all samples and collagen
fibers and smooth muscles bundle were distinguished. The existence of these muscle bundles in external
layer of renal artery was not reported previously in domestic animals and regarded as a new finding in the
present study. These muscle bundles were thicker in adult than in newborn animals and probably have a
relationship with the function of kidney’s vascular system. It was concluded that these bundles may
potentiate the tunica media muscle cells to prevent hypertension crisis | 