Ovaries and Ovarian Cycle

Question 1

Functions of ovaries?

Answer 1

1. Produce immature female gametes (oocytes)
2. Secrete female sec hormones (oestrogens + progestins)
3. Secrete inhibin (feedback control of pituitary FSH production)

Question 2

Which ligaments stabilise the ovary?

Answer 2

• Mesovarium
• Ovarian ligament (uterus to medial surface of ovary)
• Suspensory ligament (lateral surface of ovary to pelvic wall) - contains major BV of ovary
• Broad ligament (mesentery enclosing ovaries, uterine tubes + uterus, continuous with parietal peritoneum)

Question 3

Which BV supply + drain ovary?

Answer 3

Ovarian artery
Ovarian vein
- ovarian hilum

Question 4

Describe the tissue structure of the ovaries?

Answer 4

Visceral peritoneum covering ovaries (layer of columnar epithelial cells), overlies dense CT layer called tunica albuginea
- cortex + medulla

Question 5

What stages of oogenesis occur from before birth to puberty?

Answer 5

• Begins before birth, accelerates at puberty, ends at menopause
• Monthly basis as part of ovarian cycle
• Mitosis of stem cells happens before birth
• In fetus, primary oocytes prepare for meiosis + proceed as far as prophase of meiosis I
• Remain dormant until puberty, rising FSH levels trigger start of ovarian cycle
• Not all primary oocytes produced during development survive until puberty, primordial follicles each containing a primary oocyte degenerate in process called atresia

Question 6

What are the stages of the ovarian cycle?

Answer 6

1. Formation of primary follicles
2. Formation of secondary follicles
3. Formation of tertiary follicle
4. Ovulation
5. Formation and degeneration of corpus luteum
6. Unless fertilization occurs, the corpus luteum begins to degenerate roughly 12 days after ovulation

Question 7

What are ovarian follicles?

Answer 7

Specialized structures where oocyte growth + meiosis I occur

- located in cortex of ovary

Question 8

Describe the formation of primary follicles.

Answer 8

• Stimulated by FSH from ant pituitary gland
• Primordial follicle (primary oocyte surrounded by single squamous layer of follicular cells) develop into primary follicles
• Follicular cells enlarge + divide into several layers of cells called granulosa cells
• Microvilli from granulosa cells intermingle with microvilli of primary oocyte (this region is called zona pellucida)
• Thecal cells form around follicle in ovarian stroma

Question 9

Describe the formation of the secondary follicles

Answer 9

• Many primordial follicles become primary follicles, but only a few will develop into 2ndary follicles
• Wall of follicle thickens + granulosa cells secrete fluid
• This follicular fluid accumulates, expands, separates inner + outer layers of follicle and causes follicle to expand
• Secondary follicle

Question 10

Describe the formation of the tertiary follicle

Answer 10

• Now only a single secondary follicle ready for development
• 10th-14th day - tertiary follicle/ Graafian follicle
• spans width of ovarian cortex, bulge in ovary
• oocyte projects into antrum (expanded central chamber of follicle containing fluid, surrounded by granulosa cells)
• LH levels rising, primary oocyte complete meiosis I and produces a secondary oocyte + non-functional a polar body
• Secondary oocyte enters meiosis II + stops at metaphase (only completed at fertilisation)
• Day 14-28 - sec oocyte + surrounding granulosa cells lose connections with follicular wall
• Now free within antrum + granulosa cells known as corona radiata

Question 11

Describe ovulation.

Answer 11

• Graafian follicle ruptures + releases secondary oocyte (+ corona radiata)
• Remains stuck to surface of ovary by sticky follicular fluid
• Projections of uterine tube + fluid currents transfer oocyte along tube

Question 12

Describe the formation + degeneration of corpus luteum

Answer 12

• Ruptured vessels bleed into antrum of empty follicle
• Remaining granulosa cells invade area + proliferate to create endocrine structure corpus luteum (due to LH stimulation)
• Lipids within are used to make steroid hormones - mainly progesterone and some oestrogen
• Function to prepare uterus for pregnancy by stimulating maturation of uterine lining + secretion of uterine glands

Question 13

What happens when the corpus luteum degenerates as no fertilisation has occurred?

Answer 13

• Progesterone + oestrogen levels drop
• Corpus luteum becomes corpus albicans (scar tissue)
• end of ovarian cycle