Progesterone increases the number of peg cells, while estrogen increases their height and secretory activity.

Interspersed between the ciliated cells are peg cells, which contain apical granules and produce the tubular fluid.

A peg cell is a non-ciliated epithelial cell within the uterine tube (oviduct or Fallopian tube).

Also, standard PEG cell fusion is poorly reproducible and different types of cells have have various fusion susceptibilities.