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The larger ovarian follicles consist of an external fibrovascular coat, connected with the surrounding stroma of the ovary by a network of blood vessels, and an internal coat, which consists of several layers of nucleated cells, called the membrana granulosa. It contains numerous granulosa cells.
Section of vesicular ovarian follicle of a cat. X 50. Membrana granulosa labeled at upper left. In the development of the urinary and reproductive organs, the oogonia become invaginated in the gonadal ridge. The embryological origin of granulosa cells remains controversial.
The anterior pituitary complex and hypophyseal portal system, where FSH and LH are released. Theca cells are responsible for synthesizing androgens, providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures.
The outer layer is the ovarian cortex, consisting of ovarian follicles and stroma in between them. Included in the follicles are the cumulus oophorus, membrana granulosa (and the granulosa cells inside it), corona radiata, zona pellucida, and primary oocyte. Theca of follicle, antrum and liquor folliculi are also contained in the follicle.
Folliculogenesis is continuous, meaning that at any time the ovary contains follicles in many stages of development. The majority of follicles die and never complete development. A few develop fully to produce a secondary oocyte which is released by rupture of the follicle in a process called ovulation .
Theca interna cells express receptors for luteinizing hormone (LH) to produce androstenedione, which via a few steps, gives the granulosa the precursor for estrogen manufacturing. [ 1 ] After rupture of the mature ovarian follicle , the theca interna cells differentiate into the theca lutein cells of the corpus luteum .
The cumulus oophorus (discus proligerus) is a cluster of cells that surround the oocyte both in the ovarian follicle and after ovulation. In the antral follicle, it may be regarded as an extension of the membrana granulosa. The innermost layer of these cells is the corona radiata. [1]
Ovarian stroma differs from typical connective tissue in that it contains a high number of cells. The stroma cells are distributed in such a way that the tissue appears to be whorled. Stromal cells associated with maturing follicles may acquire endocrine function and secrete estrogens. The entire ovarian stroma is highly vascular. [1]