An Overview of the Endometrium

ENDOMETRIUM 

Evaluation of the Endometrium

Evaluation is done through the endometrial biopsy. The evaluation performs several different functions.

·        It assesses the hormonal status of the patient to tell whether the woman is menopausal or not.

·        It provides a documentation of ovulation, commonly used for infertility work-up. However, these days, endometrial biopsies are performed less for infertility work-ups.

·        It searches for causes of abnormal bleeding.

o        This is the most common reason for endometrial biopsies.

·        It tells at which stage of the menstrual cycle the patient is in.

o        Proliferation stage occurs in the first half of the menstrual cycle. There is endometrial growth due to the effects of estrogen only.

o        Secretory stage occurs in the 2^nd half of the menstrual cycle. Although Dr. Heller didn’t mention this in lecture, in the secretory stage, the glands swell and become torturous, the endometrium further thickens, and spiral arteries near the surface. These changes are due to the effect of both estrogen and progesterone. 

This is an image of the ideal menstrual cycle, which no one apparently has. The menstrual cycle lasts for 28 days. Day 1 of the cycle is the 1^st day of a woman’s period (menses). The average length of a period is 5 days. Ovulation then occurs on day 14. At day 28, you start the whole cycle over.  

The variation in women’s menstrual cycles (you can have anywhere from 25-30 day cycles) occurs more often in the first half of the cycle. Once ovulation begins, menstruation usually occurs 14 days later.
 

Endometrium Anatomy

The endometrium has 2 layers – the basalis and the functionalis.

·         The basalis layer remains as part of the uterine wall during menstruation. If the basalis layer is sloughed off, the front and back of the uterus will stick together, resulting in Asherman’s Syndrome.

·         The functionalis layer sloughs off normally during menstruation. 

This is a histo-slide of the proliferative endometrium. The characteristic feature of this stage is that the glands look like tiny “blue” donuts. The estrogen secreted during this stage causes mitotic activity in the endometrium, causing it to grow, and pseudostratification of glandular cells. The glandular cell numclie are at different levels but every single cell touches the basement membrane.  

This is a histo-slide of the secretory endometrium. The characteristic feature of this stage is that the glands look like piano keys. The endometrium is preparing for implantation with the production of nourishing secretions (glycogen). The secretory vacuoles start in a subnuclear position and push the nuclei up. By day 17, all the glandular cell nuclei line up, and at this point, pathologists can definitively state that the patient has ovulated.  

The secretory vacuoles undergo a characteristic pattern of changes during the secretory stage. They migrate from a subnuclear location to supranuclear, and then into the lumen to nourish the implanting ovum by day 20, which is the middle of the secretory phase. The vacuoles are secreted, and the endometrium then undergoes secretory exhaustion, which results in saw-toothing of the glands. The glandular cells are not pseudostratified anymore. All the nuclei are at one level, and there are no mitoses taking place. 

If you do not become pregnant, the cycle begins all over again. Menstrual flow is the breakdown of the endometrium due to a drop of hormones. Cells undergo apoptosis. Most of the material expelled is tissue (s. functionalis) sloughing off. Most women lose only 1 tsp of blood.        

During menopause, the endometrium atrophies. The glands are small and inactive. There are no stratification of glandular cells or mitoses seen.

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