The endometrium is divided into basal layer and functional layer. The basal layer is not affected by the changes of ovarian hormones during menstrual cycle, and does not fall off during menstrual period; The functional layer changes periodically under the influence of ovarian hormones, and the menstrual period is necrotic and exfoliated. Therefore, the thickness of endometrium is not a fixed value, it will change periodically with the menstrual cycle. We take the 28-day menstrual cycle as an example. The periodic change of endometrial thickness can be divided into three periods:
1. Proliferating period: from the 5th day of menstrual cycle to 14, which is equivalent to the mature stage of follicular development. Under the action of estrogen in follicular phase, endometrial glands and interstitial cells are in a state of proliferation.
The proliferation period is divided into early stage, middle stage and late stage.
① Early proliferative phase: the 5th to 7th day of menstrual cycle. The hyperplasia and repair of intima began in menstrual period. At this stage, the intima is very thin, only L-2mm. The glandular epithelial cells are cubic or low columnar. The stroma is dense and the cells are star-shaped. The arterioles in the stroma are straight and thin.
② Mid-proliferation: Day 8- 10 of menstrual cycle. This stage is characterized by obvious interstitial edema; The number of glands increases and grows in a curved shape; The glandular epithelial cells proliferate actively, with columnar cells and mitotic images.
③ Late proliferative phase: menstrual cycle 1 1- 14 days. At this stage, the intima thickens to 3-5mm, and the surface is uneven and slightly wavy. Epithelial cells are high columnar, glandular epithelium continues to grow, mitotic images increase, and glands become longer and curved. Interstitial cells are star-shaped and combine with each other to form a network; Tissue edema is obvious, arterioles are slightly curved and lumen is enlarged.
2. Secretion period: After corpus luteum is formed, the endometrium is secreted under the action of progesterone. The secretory phase is also divided into three stages: early, middle and late.
① Early secretory phase: the first 15- 19 day of menstrual cycle. At this stage, the endometrial glands are longer and the flexion is more obvious. Glycogen vesicles, called subnuclear vacuoles, began to appear under the nucleus of glandular epithelial cells, which was the histological feature of early secretion.
② Secretion metaphase: the 20th to 23rd day of menstrual cycle. The intima is thicker and serrated than before. The membrane at the top of glandular endocrine epithelial cells is broken, and the glycogen in the cells is discharged into the glandular cavity of human body, which is called apocrine. During this period, the parenchyma was highly edema and loose, and the spiral arterioles proliferated and curled.
③ Late secretory stage: the 24th to 28th day of menstrual cycle. This period is premenstrual. The endometrium is thickened and spongy. The opening of endometrial gland faces the official cavity, glycogen and other secretions overflow, and the stroma is loose and edema. The matrix under the surface epithelial cells differentiated into hypertrophic decidual cells. At this stage, the spiral arterioles grow faster than the intima thickness, and become more curved, and the vascular lumen also expands. In the later stage of secretion, the thickness of endometrium is about 5 ~ 6 mm
3, menstrual period: the first day of the menstrual cycle. At this time, the level of estrogen and progesterone decreased, which activated the synthesis of prostaglandin in intima. Prostaglandins can stimulate the contraction of myometrium, resulting in continuous spasm of spiral arterioles in the functional layer of endometrium and decreased blood flow in endometrium. The area of damaged ischemic necrosis tissue gradually expanded. Tissue degeneration, necrosis, increased permeability of blood vessel wall, leading to blood vessel rupture, leading to the formation of hematoma at the bottom of intima, promoting tissue necrosis and shedding. The degenerated and necrotic intima is mixed with blood and discharged to form menstrual blood. The thickness of endometrium can reach 8-10 mm.