Ultrastructural Studies on Cyclic Changes in the Human Endometrium

Abstract

In the present study, to clarify the effects of steroid hormone on the endometrium and the relationships between the endometrium and implantation of the ovum, histological and ultrastructual investigations were performed with regard to changes of the endometrium and the endocervix of the uterus in women with regular menstrual cycles and postmenopausal women.
The following conclusions were obtained.
1) The endometrial epithelium h a s two different cell types: a ciliated type and a nonciliated type. The latter is dominant. These cells show cyclic changes.
2) In the endometrial epithelial non-ciliated cells, as s hown by TEM, ribosomes gradually increase in number, and the cytoplasmic organelles develop in the early to middle proliferative phase. At the end of the proliferative phase, further development of intracellular organelles is observed, and accumulation of glycogen is found in the basal part of the cells. At the early to middle secretory phase, cytoplasmic organelles enlarge, and vacuoles are also formed. Cytoplasmic organelles reach their maximum size at the middle secretory phase, and thereafter, show degenerative changes. A large number of ribosomes are recognized at the early secretory phase, but they gradually decrease in number from the middle to end secretory phase.
The cytoplasma of the ciliated cells show little change during menstru a l cycle.
3) In the endometrium, as shown by SEM, the surface of the non-ciliated cells is convex like a dome at the early proliferative phase, and protrusion of their surface becomes most prominent from the middle to end secretory phase. Apocrine or microapocrine like secretion is also observed at this stage. The microvilli, at the early proliferative phase, are short and small, and then, become swollen from the end proliferative phase to early secretory phase. Their number and size decrease from the middle to end secretory phase.
The ciliated cells gradually increase in number at t h e proliferative phase, reaching a peak at the end of the proliferative phase. The cilia are short and immature at the early proliferative phase. They gradually become elongated, reaching full maturity at the end of the proliferative phase, and again shorten at the middle to end secretory phase.
4) Fewer ciliated cells are present in the endocervix than in the endometrium, and they remain unchanged during the menstrual cycle. In the non-ciliated cells, cytoplasmic organelles most increase and secretory granules and vacuoles accumulate in the ovulatory phase.
5) The endometrium is sharply demarcated from the endocervical epithelium at the level of the histological internal os, with no transitional type of cells found between the two epithelia.
6) Atrophic changes are prominent in the endometrium after menopause. The number of ciliated cells decreases, and size and height of cilia are reduced. Non-ciliated cells become flat, and are intermingled with cells coated with dense or thin microvilli.
7) Remarkable differences are found in the distributio n of ciliated cells between the uterine body and cervix, whereas no differences are apparent between any parts of the endometrium of the uterine cavity.
8) In conclusion, it is speculated that not only the number and/or distribution of ciliated cells in the endometrium but also the mobility of the cilia as well as the biological response of the endometrium against the fertilized ovum also play a role in the implantation of the ovum.