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Ovarian and menstrual cycles
Published in David M. Luesley, Mark D. Kilby, Obstetrics & Gynaecology, 2016
After the release of the oocyte–cumulus complex the follicular antrum is filled with blood and new blood vessels forms. The theca-lutein cells become full of cholesterol (luteinised) and the resulting structure is called a corpus luteum. The corpus luteum produces oestrogen, progesterone (P4) and inhibin A in response to LH pulses. These in turn suppress FSH and LH secretion by the pituitary. In the face of declining FSH and LH levels the corpus luteum functions for only about 10 days, with peak activity at about 7 days after ovulation (mid-luteal peak of progesterone on day 21 of a 28-day cycle). It then enters into an apoptosis and regression phase of about 4 days if pregnancy does not occur. In the absence of pregnancy, the corpus luteum has a fairly predictable life span of 14 days. The falling oestradiol and progesterone levels lead to apoptosis and shedding of the endometrium. The falling ovarian steroid levels release the hypothalamus and pituitary from the negative feedback effect, with a subsequent increase in FSH levels and ensuring a new cycle of recruitment of secondary follicles. The luteo-follicular transition phase is characterised by increasing FSH levels, low oestradiol and progesterone levels and high inhibin B secreted by the granulosa cells of recruited follicles.3,4
Follicular fat-soluble vitamins as markers of oocyte competency
Published in Systems Biology in Reproductive Medicine, 2020
Patrycja Skowrońska, Michał Kunicki, Ewa Pastuszek, Lucyna Konieczna, Tomasz Bączek, Krzysztof Łukaszuk
Current methods of embryo selection such as morphological assessment, timelapse imaging and preimplantation genetic testing that attempt to define the development potential of oocytes and obtained embryos are not optimal (Revelli et al. 2009). New methods of embryo development prediction are still needed. In the last few years, there has been a tendency to look for markers of oocyte quality among molecules found in the follicular fluid (FF) (Revelli et al. 2009). FF fills the follicular antrum and surrounds the oocyte in the ovarian follicle (Revelli et al. 2009). Its composition is the result of the transfer of blood plasma constituents that cross the blood follicular barrier and the secretory activity of granulosa and thecal cells (Fortune 1994). Improvements in analytical techniques allow for a move from the research of single molecular markers to more complex analyses that allow researchers to study large numbers of metabolites in FF (Revelli et al. 2009).
Regulation of follicle growth through hormonal factors and mechanical cues mediated by Hippo signaling pathway
Published in Systems Biology in Reproductive Medicine, 2018
Ikko Kawashima, Kazuhiro Kawamura
Secondary follicles have multilayered granulosa cells together with a theca cell layer with a blood vessel network [Young and McNeilly 2010]. To support rodent granulosa cell survival, theca cells secrete BMP7 [Erickson and Shimasaki 2003; Lee et al. 2001], whereas oocytes secrete BMP15 and GDF9 [Dong et al. 1996; Galloway et al. 2000]. At the end of secondary follicle development, follicular antrum is formed in the granulosa cell layer [Hussein 2005]. The follicular antrum is filled with fluid and thus its expansion requires an influx of fluids. This process includes derivation of fluid from thecal vasculature via aquaporin into follicular antral cavity [Rodgers and Irving-Rodgers 2010]. Aquaporin is a fluid transporter shown to express in granulosa cells of mouse, rat, and human follicles [McConnell et al. 2002; Thoroddsen et al. 2011; West-Farrell et al. 2009]. However, the roles of aquaporin as a fluid transporter are not fully elucidated. A bovine study revealed that accumulation of hyaluronan into the follicle exerted an osmotic gradient [Clarke et al. 2006]. Because large molecule hyaluronan is unable to pass through aquaporin channels, solution influx from thecal vasculature into follicular antrum increases in antral follicles [Clarke et al. 2006; Rodgers and Irving-Rodgers 2010].