Female Reproductive System Overview

Female Reproductive System Development

• Male and female reproductive systems develop from similar embryonic tissues.
• In the absence of anti-mullerian hormone, female reproductive organs develop.
• In the presence of anti-mullerian hormone, male reproductive organs develop.

Female Reproductive System Functions

• Production of ova.
• Providing suitable conditions for embryo implantation, fetal growth, development, and birth

Regulation

• Regulated by the hypothalamic-pituitary-ovarian axis.
• The ovarian cycle results in changing patterns of hormone production.
• This regulation operates on a negative feedback loop.

Female Reproductive Organs

• Ovaries
• Fallopian tubes
• Uterus
• Vagina
• External genitalia (vulva)

Oogenesis

• Females produce a finite number of egg cells.
• During fetal development, germ cells migrate to the ovaries and differentiate into oogonia.

Oogenesis: Before Birth

• Oogonia divide by mitosis to create 1-2 million primary oocytes in the embryo.
• Primary oocytes begin meiosis I.
• Meiosis I is arrested in prophase I until puberty.

Primordial Follicles

• Support cells surround the oocyte in the ovary.
• Around 2 million primordial follicles are present at birth.
• 400,000 primordial follicles remain at puberty.

Oogenesis: After Puberty

• Hormones stimulate several follicles to develop each month.
• Primary oocytes resume meiosis I.
• The cell divides into a secondary oocyte and a polar body.
• The secondary oocyte begins meiosis II but stops in metaphase II.
• The secondary oocyte is ovulated.
• Meiosis II is completed only if fertilization occurs.

Oogenesis: Oogonia to Oocytes

• Germ cells from the yolk sac migrate to the ovary and become oogonia.
• Most oogonia degenerate.
• Remaining oogonia develop into primary oocytes.
• Around 2 million primary oocytes are present at birth and 400,000 remain at puberty.
• Only 400 oocytes mature during a woman’s reproductive lifespan.
• Hormones cause meiosis I to resume, leading to ovulation.
• Each month, 20 primary oocytes become secondary oocytes, but typically only one is ovulated.
• Fertilization triggers the final stages of meiosis.

Ovary

• Female gonads.
• Paired organs located in the peritoneal cavity.
• Suspended by the suspensory ligament.

Ovary - Follicle Development

• Each follicle contains an immature egg called an oocyte.
• Surrounding the oocyte are:
  • Follicle cells (one cell layer thick)
  • Granulosa cells (when more than one layer is present)
  • Thecal cells (cells in the ovarian stroma)
• Granulosa cells, stimulated by FSH, mature.
• Thecal and granulosa cells work together to produce estrogen.
• A protective layer of glycoprotein called the zona pellucida forms around the egg.

Ovary - Follicle Development: Continued

• The ovary contains oocytes enclosed within follicles.
• These follicles contain theca and granulosa cells; endocrine cells that produce ovarian hormones.
• Follicles start to develop further after the first menstrual cycle.
• Each cycle, several follicles develop into Graafian follicles.
• The Graafian follicle is characterized by increased granulosa and theca cells.
• The outer layer develops a vascularized structure, supplying blood-borne substances like LH and FSH.
• Around day 5-7 of the menstrual cycle, one follicle becomes dominant, grows rapidly, and releases the oocyte.
• The rest of the follicle becomes the corpus luteum.
• The corpus luteum produces hormones essential for implantation and early development of a fertilized ovum.
• If no conception occurs, the corpus luteum regresses approximately 14 days later, becoming the corpus albicans.

Ovary - Follicle Development

• Primordial Follicle: one layer of squamous-like follicle cells surrounds the oocyte.
• Primary Follicle: two or more layers of cuboidal granulosa cells enclose the oocyte.
• Secondary Follicle: has a fluid-filled space between granulosa cells that coalesces to form a central antrum.
• Graafian Follicle: the most mature stage of the secondary follicle, which bulges from the surface of the ovary.

Primordial Follicle

• Undeveloped follicles.
• Inactive structures that await stimulation from FSH to re-enter their developmental pathway.
• The most numerous follicle type in the cortex.
• Consists of a primary oocyte surrounded by a single layer of flattened follicular cells.
• The primary oocyte has a large nucleus, dispersed chromatin, a prominent nucleolus, and little cytoplasm.
• The primary oocyte is in prophase I of the first meiotic division.
• Further meiotic activity is arrested.

Primary Follicle

• FSH stimulates primordial follicles to develop into primary follicles.
• Follicular or granulosa cells enlarge.
• A single layer of cuboidal cells forms.
• The follicle increases in size.
• A glycoprotein layer called the zona pellucida develops around the oocyte.

Primary Multilaminar Follicle

• The primary follicle oocyte enlarges.
• Follicular cells multiply via mitosis and become cuboidal.
• The cells are now called granulosa cells.
• A zona pellucida layer develops between the oocyte and the granulosa cells.

Secondary Follicle

• The zona granulosa continues to proliferate.
• Fluid-filled spaces form between the granulosa cells.
• These spaces fuse to form the follicular antrum.
• The oocyte nearly reaches full size and becomes situated eccentrically within the zona granulosa.
• The zona pellucida can also be seen.
• The antrum contains hormone-rich fluid.

Secondary Follicle: Continued

• Stroma around the developing follicle differentiates into thecal cells.
• The theca folliculi develops two layers:
  • Theca interna (TI) is made up of several layers of rounded cells.
  • Theca externa(TE) is less distinct and merges with surrounding stroma.

Graafian Follicle

• This is the mature follicle.
• It develops just before ovulation.
• The oocyte reaches its full size.
• The oocyte is now called the secondary oocyte.
• The follicular antrum is enlarged.
• The zona granulosa forms a layer around the follicle.
• The Graafian follicle reaches 1.5 - 2.5 cm in diameter.
• The cumulus oophorus diminishes, and the oocyte is surrounded by the corona radiata.

Corpus Luteum

• Following ovulation, the ruptured follicle collapses and fills with a blood clot to form the corpus luteum.
• The blood clot is surrounded by granulosa lutein cells, penetrated by septa containing blood vessels.
• A thin zone of theca lutein cells can be observed peripherally.
• The corpus luteum provides hormones necessary for implantation and early development of a fertilized ovum.

Corpus Luteum: Hormones

• The corpus luteum secretes:
  • Progesterone, which completes preparation of the uterine lining.
  • Estrogens, which work with progesterone.
  • Relaxin, which relaxes uterine muscles and the pubic symphysis.
  • Inhibin, which decreases FSH and LH secretion.
• Corpus luteum hormones inhibit pituitary LH and FSH, preventing ovulation of other follicles.

Corpus Luteum: Continued

• If pregnancy occurs, the corpus luteum continues to produce progesterone to maintain the uterine wall during early development (4-5 months). This is stimulated by placental human chorionic gonadotropin (HCG).
• If fertilization does not occur, the corpus luteum degenerates, regresses, and becomes the corpus albicans.
• The corpus albicans is inactive fibrous tissue and a scar left behind after the corpus luteum dies.

Explore the development, functions, and regulation of the female reproductive system in this comprehensive quiz. Learn about the female reproductive organs, oogenesis, and the hormonal regulation involved in the ovarian cycle. Test your knowledge on the complexities of female reproductive health.