This page will describe the histological changes in the ovary throughout the course of the menstrual cycle. The human ovary consists of an inner medulla and outer cortex with indistinct boundaries. The medulla contains the blood vessels and nerves, while the cortex is occupied by developing follicles. A cross-section of an ovary will reveal follicles in various stages of development. The next sections will describe the histological features of each stage of follicular development and the major functional changes in the cells compose follicles.
An ovarian follicle progresses through several distinct phases before it releases its ovum. During the first five months of development, a finite number of primordial follicles form in the fetal ovary.
These follicles consist of oocytes surrounded by a single layer of squamous follicular cells. These primordial follicles remain in the process of the first meiotic division. At puberty, they begin to develop further and become primary follicles. At the start of each menstrual cycle a limited number of primordial follicles are triggered to develop. The first apparent histological stage is the early primary follicle that consists of a central oocyte surrounded by a single layer of follicular cells which have become cuboidal.
The zona pellucida is a thin band of glycoproteins that separates the oocyte and follicular cells. Proteins on the surface of sperm will bind to specific glycoproteins in the zona pellucida.
The late primary follicle stage is reached when the follicular cells proliferate into a stratified epithelium known as the zona granulosa. Can you identify the oocyte , theca interna and externa , follicular cells , and follicular fluid?
The primary follicle develops into a secondary follicle. The secondary follicles look very similar to primary follicles, except that they are larger, there are more follicular cells, and there are small accumulations of fluid in the intracellular spaces called follicular fluid nutritive fluid for the oocyte. These gradually coalesce to form an antrum.
The surrounding granulosa cells is called the cumulus oophorus greek for 'egg bearing heap'. The surrounding theca differentiates into two layers: the Theca interna rounded cells that secrete androgens and follicular fluid and a more fibrous Theca externa - spindle shaped cells.
The androgens are converted into oestrogen by the granulosa cells. Can you identify the antrum, membrana granulosa, cumulus oophorus, theca externa and theca interna in this image of a Graafian follicle?
The first meiotic division is now completed, and the oocyte is now a secondary oocyte, and starts its second meiotic division. After the first meiotic division, most of the cytoplasm goes into one of the two daughter cells.
The other becomes the polar body hard to see. The folicular fluid fills a single space, called the antrum , which is surrounded by the follicular cells - called the membrana granulosa.
The granulosa cells that surround the oocyte, and project into the antrum are called as the cumulus oophorus. There is a basement membrane between the granulosa cells and the theca interna. The fibrous theca externa merges with the surrounding stroma. Glands are absent from the uterine tube. External to the mucosa and muscularis is the serosa visceral peritoneum. Slide 98 Uterine tube, intrauterine. This slide contains the intrauterine intramural portion of the uterine tube.
It is within the wall of the uterus look for a small simple columnar-lined tube in the "sea" of muscle of the uterine wall. Slide 99 Fimbria and isthmus. This slide contains the fimbria and isthmus portions of the uterine tube. Note that the finger-like projections of the fimbria appear to be part of the mucosa "turned inside out" with the epithelium exposed to the peritoneal cavity.
The isthmus has less complicated mucosal folds and more muscle in the muscularis than the ampulla. Slide 18 Ampulla. The ampulla of the uterine tube is indicated by the complicated folding of the mucosa and small amount of muscle in the muscularis.
The endometrium mucosa of the uterus consists of simple columnar epithelium and lamina propria. Note also the thick myometrium composed of interconnecting bundles of smooth muscle arranged in four ill-defined layers. The uterus is covered by a serosa or adventitia. Compare slides 19, 20 and These slides represent different phases of the endometrial cycle. Compare the thickness of the mucosa and the shapes of the uterine glands. Slide 19 Uterus, proliferative stage uterine endometrium.
Oogonia are diploid cells. They increase their number by mitotic cell divisions to produce primary oocytes. A five months-aged fetus contains 7 million primary oocytes.
But at birth, only 2 million primary oocytes are left in the ovary. Primary oocytes undergo meiosis to produce haploid oocytes. After the first mitotic division, the primary oocyte is called the secondary oocyte. Meiosis I also produces a smaller cell called the polar body. Secondary oocytes are arrested at the meiotic division stage until puberty. After puberty, the second stage of meiotic division starts, developing the secondary oocytes into the ootids.
The splitting of the secondary oocyte by the mitotic division also produces a polar body. The ovulation occurs at the ootid stage. The final stage of maturation of the ootid into ovum occurs after the fertilization. Follicle is a small secretory cavity which surrounds the developing oocyte.
It occurs in the cortex of the ovary. After puberty, hormones cause the maturation of follicles along with the primary oocytes. The maturation of both follicle along with the ovum causes the ovulation where the mature ovum is released from the ovary.
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