The Female Reproductive System and Oogenesis Process

THE FEMALE REPRODUCTIVE SYS.

The Womans reproductive system must produce sex hormones & functional gametes and also be able to protect & support a developing embryo & nourish the newborn infant. Principal organs of the female reproductive system are the ovaries, uterine tubes (Fallopian tubes or oviducts), the uterus, the vagina & external genitalia.

The paired ovaries are small, almond-shaped located near the lateral walls of the pelvic cavity & the ovaries: 1- Produce immature female gametes or oocytes. 2- Secrete female sex hormones (estrogens & progestins). 3- Secrete inhibin involved in the feedback control of pituitary FSH productions.

Oogenesis or ovum production:- This begins before woman s birth, accelerates at puberty & ends at menopause, Oogenesis occurs on a monthly basis as part of the ovarian cycle. The Oogonia (or stem cells) of females, complete the mitotic division before birth (between the third & seventh months of fetal development).

Daughter cells or primary oocytes, prepare to undergo meiosis & they proceed until meiosis I which is completed after puberty. So primary oocytes then remain in a state of suspended development until puberty.

At puberty rising levels of FSH starts the ovarian cycle ((each month therefore some of the primary oocytes will be stimulated to undergo further development)) not all primary oocytes produced in development survive until puberty, there are roughly 2 million primordial follicles in the ovaries at birth each contain a primary oocyte, by the time of puberty that number has dropped to about 400.000.

** The meiosis division in the ovaries are the same as those in the testes but the process differs in two important details= 1. The cytoplasm of the primary oocyte is unevenly distributed during the two meiotic divisions. (Oogenesis produces one functional ovum, which contain most of the original cytoplasm, & two or three polar bodies). 2. The ovary releases a secondary oocyte rather than a mature ovum. The secondary oocyte is suspended in meiosis II & meiosis will not be completed unless & until fertilization occur.

=Steps of the ovarian cycle= =step 1= Formation of the primary follicle: follicle formation is stimulated by FSH from the anterior pituitary & the ovarian cycle begins as the activated primordial follicles develop into primary follicles. in a primary follicle the follicular cells enlarge & undergo repeated divisions , these follicle cells are called granulosa cells.

=step 2= Formation of secondary follicles: The wall of the follicle thickens & the granulosa cells begin secreting small amounts of fluid. This follicular fluid accumulates & gradually expend & separates the inner and outer layers of the follicle, (only few primary follicles will proceed to become secondary follicles).

=step 3= Formation of tertiary follicle: eight to ten days after the start of the ovarian cycle, the ovaries generally contain only a single secondary follicle & by the 10thto 14thday of the cycle the follicle has formed a tertiary follicle (or mature Graafian follicle) creating a prominent bulge in the surface of the ovary.

((as tertiary follicle completes its development, LH levels begin rising. the primary oocyte completes meiosis I to produce a secondary oocyte & a small nonfunctional polar body. then the secondary oocyte inters meiosis II & stop to complete when fertilization occurs)).

=step 4= Ovulation: the secondary oocyte and the surrounding granulosa cells lose their connections with the follicular wall (this takes place at day 14 of the 28-day cycle). At ovulation the tertiary follicle releases the secondary oocyte into the pelvic cavity.

=step 5= Formation & degeneration of the Corpus Luteum CL: the empty tertiary follicle collapse & ruptured vessels bleed into the antrum. The remaining granulosa cells then invade the area proliferating to create an endocrine structure known as corpus luteum under LH stimulation.

=step 6= Formation of corpus Albicans :(unless pregnancy occurs) the CL begins to degenerate roughly 12 days after ovulation if there is no pregnancy. & progesterone & estrogen levels fall markedly. fibroblasts invade the nonfunctional CL producing a pale scar tissue called Corpus Albicans.

The Uterine tubes: 1. the infundibulum: the closest end to the ovary forms an expanded funnel (or infundibulum) with numerous finger like projections that expand into the pelvic cavity. ((The inner surfaces of the infundibulum are lined with cilia that beat toward the middle segment of the uterine tube)). 2. the ampulla: it s the middle segment. 3. the isthmus: a short segment connected to the uterine wall.

The Uterine Cycle: (Menstrual Cycle) 1.Menses: the uterine cycle begins with the onset of menses, marked by: the degeneration of the functional zone of the endometrium. its caused by constriction of the spiral arteries which reduce blood flow. the secretary glands & other tissue in the functional zone begin to deteriorate.

the arterial walls rupture & blood pours in the tissue of the functional zone). Blood cells & degenerated tissue then break away & enter the uterine lumen. the functional zone is affected because the deeper basilar zone is provided by straight arteries.

2.Proliferative phase: the basilar zone survives menses intact & epithelial cells of the glands multiply & spread across the endometrial surface. further growth & vascularization result in complete restoration of the functional zone. Stimulated by estrogen secreted by primary & secondary follicles in the ovary. at this time the endometrial glands are secreting a mucus rich in glycogen & the functional zone is highly vascularized.

3.Secretory phase: the endometrial glands enlarge accelerating rates of secretion & the arteries elongate & spiral through the tissue of the functional zone. (secretory phase is under the combined stimulatory effect of progestins & estrogens from the corpus luteum).

Defenitions *Menarche: is the first menstrual period at puberty at age of 11-12 years. *Menopause: is the last uterine cycle at age of 45-55 years old. **Amenorrhea: is a condition in which either menarche dose not appear by age 16 or the normal uterine cycle of an adult woman becomes interrupted for 6 months or more, there are 2 types: -primary amenorrhea= is the failure to initiate menses. This condition may indicate developmental abnormalities, such as nonfunctional ovaries, absence of the uterus, or endocrine or genetic disorder. -secondary amenorrhea= may be caused by several physical or emotional stresses, e.g. weight-reduction programs, anorexia, severe depression.

#Hormones & the follicular phase = * Follicle development begin under FSH stimulation. Each month some of the primordial follicles begins to develop into primary follicles, as follicles enlarge they begin to secrete Estrogen (estradiol, estrone, estriol).

* Estrogens have many functions : stimulate muscle & bone growth. maintaining female secondary sex characteristics such as body hair distribution & location of adipose tissue deposits. affecting CNS activity. maintaining functional accessory reproductive glands & organs. initiating repair & growth of the endometrium.

Pulse frequency *Early in the follicular phase estrogen levels are low & the GnRH pulse frequency is 16-24/day at this pulse frequency FSH is the dominant hormone released by the anterior pituitary gland & the estrogen released by the developing follicles inhibit LH secretion. As secondary follicle develop, FSH levels decline due to the negative feedback effect of inhibin.

*A tertiary follicle begins forming & the concentration of circulating estrogens rises & the GnRH pulse frequency increase to 36/day which stimulate LH secretion, at day 10 of cycle. (effect of estrogen on LH secretion changes from inhibition to stimulation). The result is massive secretion of LH from the anterior pituitary which due to: 1.completion of meiosis I by primary oocyte. 2.rupture of the follicular wall. 3.ovulation.

#Hormones & the luteal phase = High LH levels that stimulate ovulation also promote progesterone secretion & formation of corpus luteum (CL). ((As progesterone levels rise & estrogen levels fall, GnRH pulse frequency decline sharply 1-4/day this stimulate LH secretion more than FSH, & LH maintain the structure & secretion of the CL.)) Progesterone is the main hormone of the luteal phase its primary function is to: -continue preparation of the uterus for pregnancy by promoting blood supply to the functional zone. -stimulate secretion of endometrial glands.

*if pregnancy dose not occur the CL degenerate (12 days after ovulation CL becomes nonfunctional) progesterone & estrogen levels fall & blood supply to the functional zone is restricted & the endometrial tissue begin to deteriorate. And GnRH pulse frequency increase & stimulate FSH secretion & the cycle begins again.

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