Scanning electron microscopy of the endometrium during the secretory phase.

Scanning electron microscopy was used to study the surface morphology of the rabbit endometrium during the secretory phase of the oestrous cycle. The free surfaces of ciliated and of inactive active secretory cells are described. Changes in secretory cell surface morphology resulting from accumulation and secretion of material involve the apparent retraction of microvilli and the formation of one or more bulbous protrusions of the cell's apical surface. These protrusions may be relatively smooth surfaced or exhibit long slender micro-extensions. The protrusions grow in size and are eventually pinched off. Loss of the bulbous protrusions often leaves behind crater-like invaginations of the cell's surface. Secretory cells adjacent to the endometrial glands are the first to exhibit signs of mucin accumulation and secretion. The single cilium of a secretory cell is not apparently affected by the secretory process. Signs of ciliated and secretory cell degeneration, and possible sloughing, are also described.