FIGURE 5.

Structure of the human amniotic membrane. (A) Schematic representation of the structure of the human amniotic membrane and tissues underneath (chorion laeve and capsular decidua). Human amniotic membrane epithelial cells (hAEC) form, for the most part, a monolayer facing the amniotic fluid. The basement membrane underneath separates the epithelial layer from the avascular amniotic mesoderm including the compact layer devoid of cells in touch with the basement membrane and the fibroblast layer below it containing human amniotic membrane mesenchymal stromal cells (hAMSC). Between amniotic membrane and the vascular chorionic mesoderm there are slender, fluid filled clefts forming an intermediate spongy layer. A basement membrane separates chorionic mesoderm from extravillous trophoblast (hCL-EVT) (embedded in self-secreted matrix-type fibrinoid) which is in touch with maternal capsular decidua (hCD). (B) Histological image of human amniotic membrane stained with haematoxylin-eosin staining solution. Magnification: 40x. (C) Transmission electron microscopy image showing the ultrastructure of hAEC belonging to the central region of hAM (left panel) or the peripheral region of hAM. Green arrows point at surface microvilli; pale blue arrows point at nuclei; blue arrows point at the basement membrane below hAEC; red asterisks point at different types of granules; orange asterisks point at nucleoli; yellow triangle points at extracellular matrix of the compact layer. Magnification: 3000x.