Changes in Placental Morphology and their Association with Embryonic Skin Development

Histogenesis and organogenesis in mammals normally transpires in a hypoxic environment. Oxygen diffusing capacity is dependent on diffusion distance, which may vary with the thickness of placental barrier and with the level of tissue vascularity. Since the epidermis is avascular, its development fully depends on dermal blood vessels. Despite the large number of studies focusing on uteroplacental circulation and embryogenesis, it is clear that the current knowledge of how placental changes in pregnancy contribute to skin development is incomplete. The aim of this study was to evaluate the association between structural changes in the placental barrier and development of the integumentary system, with special reference to dermal angiogenesis. The study included specimens of six embryos and ten foetuses from 5 to 24 developmental weeks, and 21 specimens of placental tissue 6–40 weeks gestational age. The panel of antibodies used was S- 100, SMA, CD31, CD34, AE1/AE3 (PCKT), CKRT7, CD 56 and hCG. During the first trimester, maternal blood flow to the placenta appears to be initially restricted by trophoblast plugs. Natural killer cells appear in great abundance in subendothelium of decidual blood vessels, potentially stimulating extensive angiogenesis. By the end of the first trimester, new capillary beds organise to supply the developing epidermal derivatives. During the second trimester, the placental barrier becomes progressively thinner, and uteroplacental circulation is established due to dissolution of endovascular trophoblast plugs. Progression of the formation of skin appendages, hypodermal adipose tissue, demarcation of papillary and reticular dermis, and keratinisation of interfollicular epidermis in the second trimester strongly accompanies the dermal angiogenesis and placental maturation.