When I lectured on female reproductive histology on Tuesday, I began with slide 32, thinking that I was picking up where we left off the week before – but actually, we had stopped at slide 21! So here’s a summary of the important points on the slides we didn’t cover in lecture.
Slides 21-23 cover ovulation. At around day 12 of the menstrual cycle, estrogen (produced by the developing ovarian follicles) reaches its peak. This triggers release of massive amounts of LH (the “LH surge“) from the anterior pituitary. LH causes the Graafian follicle to move to the surface of the ovary and release its little oocyte into the world. This oocyte release is called ovulation, and it happens around the midpoint of the cycle (about day 14).
Slides 24-28 cover the corpus luteum. After it releases its oocyte, the Graafian follicle is called the corpus luteum. Under the influence of LH (we’re still in the LH surge), its granulosa and theca interna cells turn into granulosa lutein and theca lutein cells, respectively – and both cell types make estrogen and progesterone. The progesterone is particularly important because it stimulates growth of uterine glands, so that if the oocyte is fertilized, it has a nice cushy uterine lining to land on.
The corpus luteum hangs around for the remainder of the menstrual cycle, and if no fertilization occurs, it involutes (shrinks) and becomes a tiny white scar, called the corpus albicans. If fertilization does occur, the corpus luteum sticks around for the first trimester of the pregnancy, and then hangs it up and becomes the corpus albicans.
Slides 29-31 cover the endometrium. The uterus is composed of two layers:
- Myometrium: smooth muscle, makes up the bulk of the uterus
- Endometrium: glandular tissue, forms the lining of the uterus
The endometrial glands are divided into two zones:
- Functionalis (at the top): glands in this region change during the menstrual cycle (they become longer and more tortuous during the second half of the cycle), and if no fertilization occurs, they become necrotic and are sloughed off during menstruation.
- Basalis (at the bottom): glands in this region don’t change during the menstrual cycle; their job is to replenish the functionalis after menstruation.
That’s about it! Let me know if you have questions.