Objective: Study of the histogenesis of skin in sheep and determine
the relation between developmental stages of fetuses and histological changes of their skin. Design: Developmental investigation on the skin in sheep at the
different stages of antenatal growth. Animals: A total of 75 apparently healty embryoes were collected from Urmia abatoir.
Procedure: Immediately after slaughter H&E of sheep, the embryoes
were taken out and their C.R lengths measured. The skin specimens were taken from face, neck, sholder, and forelimb of the fetuses. The specimens were fixed in 10% formaldehyde solution and
processed through routine paraffin embedding, cut at 5-71µ and staind with H&E, Van Giesson, and Verhoof methods, for study fibroblasts, collagen, and elastic fibers respectivelly.
Results: This study revealed that in second half of second month
of antenatal life the epidermis consisted of 1-2 cuboidal epithelial cells, whereas at 6 1-65 days fetuses, it was made up of stratified squamous or cuboidal type of epithelium. The melanin contaning
cells were seen at the end of this stage. During this period clausters of epidermal cells accumulation were seen at epidermis, and more likely here were primordial hair follicles which were growing from
epidermis towards the dermis. Mesenchymal cells were gathering
around this structures. At the first half of third momth the collagen,elastic and reticular fibers, fibroblasts and leukocytes were
appeared between mesenchymal cells. At the second half of third
month the epidermis was apparently stratified squamous with the same degrees of cornifications. At first half of fourth month, an increase in thickness of epidermis was observed and at this time
the hair follicles were in the form of inverted cup. The sebaceous
and sweat glands were in bud froms around the hair follicles at 90- 95 and 115-120 days respectively. The developmental changes were
faster in sholder than the other regions.
Conclusion: This study showed that at first half of second month the epidermis of developing fetuses were containing simple cuboidal epithelial cells without apparent differentiations, whereas at the
end of this stage beginning of differentiation was observed. The
superficial layer of the two layered epidermis known as periderm. This cells were appaered in amniotic fluid at first half of prenatal
period. It presumed that, the mesenchymal tissue in vicinities of
epidermis has inductive role on the differentiation of hair follicles, sebaceous and sweat glands. However we conclude that the skin and its associated structures are differentiating from second half
of fourth month of antenatal life. J. Fac. Vet. Med. Univ. Tehran.
59, 3: 215-220, 2004.