Endometrium

The endometrium (from the scientific Latin endometrium) is the mucosa that lines the inside of the uterus and consists of a simple columnar epithelium with or without cilia, glands and a stroma. It is rich in connective tissue and is highly vascularized. Its function is to house the zygote or blastocyst after fertilization, allowing its implantation. It is the place where the placenta develops and undergoes cyclical alterations in its glands and blood vessels during the menstrual cycle in preparation for implantation of the human embryo.

Menstrual cycle

The drop in estrogen levels determines a decrease in water content, collapse and contraction of arterioles —branches of the uterine artery— with consecutive ischemia of the functional epithelium of the uterus. The fall in progesterone levels determines the release of relaxin from endometrial granulocytes, which leads to dissolution of the endometrial reticulum and desquamation.

• Days 1 to 3: menstruation and repeating.
  • Day 1: hemorrhages in the surface stroma, even secretion foci in collapsed glands.
  • Day 2: hematic material, leukocytes and remains of glands and stroma.
  • Day 3: regeneration. Repeating is done from the glandular funds and from the isthmus and uterine horns.

Follicular phase

During the proliferative or follicular phase (days 4 to 14) the endometrium proliferates as a consequence of the secretion of estrogen, an anabolic hormone. The follicular phase ends with ovulation.

• Days 4-14: endometrial of the estrogenic phase (proliferative). Estrogen (of developing follicles) stimulates glandular proliferation.
  • Early proliferative phase (days 4-7): low endometrial, corresponds to the re-epitulated basal. Few glands, straight, narrow lumen. Low epithelium, oval cores, lax stroma.
  • Average proliferative phase (days 8-10): higher endometrial, longer glands (greater than endometrial thickness: mild tortuosity), higher cylindrical glandular cells, mytosis in glands and stroma, edema of stroma, larger stroma cells.
  • Late proliferative phase (days 11-14): greater tortuosity of glands, higher epithelial cells, with pseudo-stratetization of nuclei. Alargated nicles (in cigar), hyperchromatic. Edema-free, densely cellular.

• Day 14 or 15 of the cycle, counted from the first day of menstruation: Ovulation occurs

Luteinizing phase

During the secretory or luteinizing phase (days 14 to 28) the endometrium differentiates under the influence of progesterone, this being the most receptive period for the blastocyst, especially between days 20 and 23. Tissue can even be observed decidual in menstruation due to the catabolic influence of progesterone.

• Days 15 or 16 to 28: endometrial of the progestative phase (secretor). Secret changes occur by the action of the progesterone of the luteum body.
  • Day 15: no change. It takes 36 hours for progesterone to produce morphological changes.
  • Day 16: at least 50% of the glands with infranuclear vacuolas in the epithelial cells.
  • Day 17: 100% of the glands with infranuclear vacuolas. Nucleos ordered in a row, displaced towards the middle third of the cell by the vacuolas.
  • Day 18: Infranuclear and supranuclear vacuolas. Few mitosis.
  • Day 19: cores returned to the base, rounded, vesicles, in a row. Few vacuolas. Absence of mytosis.
  • Day 20: beginning of lumen secretion, cells with apical depenachment.
  • Day 21: maximum free secretion in the lumen. Eedema incipient of the stroma.
  • Day 22: maximum edema of the stroma. Enlargement of stroma cells, still fused.
  • Day 23: prominent arterioles (grow 5 times in length and endometrial, 2 times in thickness: enrollment of arterioles). Rounding and increased stroma cell size around arterioles.
  • Day 24: Stroma cells are transformed into predictable cells (increase of cytoplasm, eosinophilic, rounded nuclei, vesicles) around arterioles. Stroma cells are recognized with hyperchromatic, irregular and cytoplasmic nucleus with granulocytes endometriales.
  • Day 25: Predecidual surface transformation (initial part: discontinue).
  • Day 26: Continuous compact. First signs of retraction of endometrial (at the beginning of luteal body involution).
  • Day 27: Retraction of endometrial: collapse of glands, internal glandular edges in serrucho teeth. When the decrease of progesterone allows the activation of NFkB routes.
  • Day 28: disintegration of the estroma reticle: disintegration of the estroma. Delight of the endometrial. Appearance of detritus in glandular lumens. Edema and conscription of immune system cells is generated that continue with the activation of MMP (metaloproteases) that achieve the tissue detachment.

Pregnant endometrium

During pregnancy, the corpus luteum does not involute, this happens when the levels of β-hCG (beta-human chorionic gonadotropin) increase by the embryo, and thus the secretion of progesterone persists in the first trimester of pregnancy. After the first trimester, the placenta is sufficiently developed and synthesizes progesterone on its own, degenerating the corpus luteum. The endometrial glands show increased secretion and hyperchromatic nuclei, the predecidual cells become decidual (with more organelles), with abundant cytoplasm., net limits and epitheloid arrangement, which constitutes the decidua (from Latin, decidere: to fall). Decidual cells control the degree of invasion of the trophoblast. The endometrium may show the Arias-Stella phenomenon: glands with hypersecretion and atypical nuclei (large, irregular, hyperchromatic).

Alterations of the proliferative phase

1. Atrogenic stimulation deficit: atrophy (e.g., orthoatrophy of postmenopausal women).
2. By excess strogenic stimulation: diffuse or extensive hyperplasia.

partly proliferative, partly secretory): areas that do not respond to progesterone.

1. Endometrio secretr defasado, sincrónico: con secreción delayed (retardo de más de 2 días) en forma homogénea en todo el endometrio. It is usually due to biphasic cycle (ovulatory) with late ovulation.
2. Disadvantaged, asynchronous secretive endometrium: with differences corresponding to more than 2 days between different areas of the endometrial. It is due to insufficiency of the luteum body or different response of endometrial areas.
3. Endometrial secretr with irregular and prolonged decamation (menorragia). The decamation, instead of being completed in 48-72 hours, lasts longer. Endometrial loins in dissolution alternate with other secretive integrity. It occurs due to delay in the involution of the luteum body (luteal body) or local factors (leiomiomas, polyps, and others).
4. Dissociated endomerium: atrophic glands and extensive predecidual reaction. It occurs in the prolonged administration of combined oral contraceptives.

Hyperplasia of the endometrium

• Endometrial polyp (focal hyperplasia)

Endometrial polyps are common; usually, sessile. In 20% of cases they are multiple. They occur around menopause. They are usually asymptomatic, but they can bleed. They are developed by prolonged estrogenic stimulation in areas of endometrial refractory to progesterone. As a rule the rest of the endometrial is proliferative.

• Hyperplasia (difuse)

It corresponds to an increase in volume of endometrial by increase of both the glandular and the stroma component. The glands are proliferative, but with greater nuclear stratification and more mitosis. Endometrial can be normal macroscopically or be thickened and irregular. It usually occurs around menopause and occurs by protractedly high levels of estrogen with absence or decrease of progestative activity. It gives rise to metrorrhage. Basically there are two forms of endometrial hyperplasia: the normotypic and the atypical.

• Normotypical hyperplasia

It can be interpreted as the normal endometrial response to high and maintained estrogenic stimulation. This form can be simple or cystic, the latter has glandular dilations sometimes so accentuated that they look like Swiss cheese (Fig. 6-8).

• Atypical hyperplasia

It can be interpreted as an abnormal endometrial response to high and maintained estrogenic stimulation. The glands are irregular; the stroma is scarce. Nuclear atypia is given by rounded nuclei, large, with clear chromatin and prominent nuclei, unlike the proliferative endometrium, which has nuclei, hyperchromatic, elongated, in cigar. Atypical hyperplasia is a precancerous lesion. The risk of developing a carcinoma is higher in hyperplasias with nuclear atyps.

Metaplasia is frequently found in endometrial hyperplasia: squamous in 25% of cases, tubal in 100% of cases; others are mucinous, clear cell, and eosinophilic. All of them seem to be secondary to estrogen hyperstimulation.

Ailments of the endometrium

• Endometriosis
• Endometritis
• Endometrial cancer