On the factors which contribute to thinning of the villous membrane in human placentae at high altitude. II. An increase in the degree of peripheralization of fetal capillaries.
The contribution made by fetal capillary peripheralization to the thinning of the villous membrane seen in human placentae from high-altitude pregnancies is examined by stereological methods. Variables characterizing the shape of the villous core and the spatial relationships between trophoblast and capillaries are quantified. They shed light on the relative importance of dynamic versus mechanistic processes of villous membrane attenuation. Highland villi differ from lowland villi in several ways. On average, they possess a thinner barrier due to closer approximation of capillaries to overlying trophoblast; in consequence, the villous core is more irregular in outline and its surface (that of the inner aspect of the trophoblast) exceeds in area that of the outer aspect of the trophoblast. These results suggest that the dynamic process (protoplasmic streaming within syncytiotrophoblast) cannot alone explain thinning of the villous membrane. A mechanistic process (capillary peripheralization and obtrusion into the trophoblastic epithelium) is sufficient to account for the differences observed, although the possibility that both processes operate concurrently cannot be discounted. This report completes a study into factors contributing to villous membrane thinning at high altitude.
Jackson
M R
MR
Department of Anatomy, Marischal College, University of Aberdeen.
Mayhew
T M
TM
Haas
J D
JD
D000531:Altitude; D000704:Analysis of Variance; D001838:Bolivia; D002196:Capillaries / Q000033:anatomy & histology / Q000196:embryology; D002824:Chorionic Villi / Q000098:blood supply*; D005006:Ethnicity; D005260:Female; D006801:Humans; D008954:Models, Biological; D011247:Pregnancy; D012737:Sex Factors; D014327:Trophoblasts / Q000033:anatomy & histology