Female Reproduction Flashcards by Sarah L

What do ovaries (female gonads) do?

produce gametes (ova) by oogenesis, and two sex steroid hormones – estrogen (estrodyl E2), and progesterone

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What are the 3 parts of the reproductive tract?

oviducts (Fallopian tubes)
uterus
vagina

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What do the oviducts (Fallopian tubes) do?

receive ovulated ova – site of fertilization

fimbriae at end of tubes catch fertilized egg

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What is the uterus?

site of menstrual bleeding, and embryonic and fetal development

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What does the vagina do?

connects uterus to external environment – site of sperm deposition

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Production of Ova by Ovary

How is oogenesis in females different than spermatogenesis in males?

total supply of eggs is determined at birth (while sperm is produced only after reaching puberty)
eggs are released in monthly cycles from puberty until menopause (age ~51 in Canada)

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Production of Ova by Ovary

When do oogonia?

appear during early prenatal development, divide by mitosis and are diploid

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Production of Ova by Ovary

Before Birth

~400,000 of oogonia enlarge in each ovary to form primary oocytes
these enter meiosis, but become arrested in early stages (prophase) of first meiotic division

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Production of Ova by Ovary

At Birth

each primary oocyte is surrounded by single layer of cells to form primordial follicle (primary oocyte + follicular cell)

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Production of Ova by Ovary

What is a primordial follicle composed of?

primary oocyte + follicular cell

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Production of Ova by Ovary

What is an ovary reserve?

number of primordial follicles in ovaries at time of birth

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Production of Ova by Ovary

Between Birth and Puberty

no new oocytes are produced

- primordial follicles either remain quiescent or undergo atresia

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Production of Ova by Ovary

What is atresia?

degeneration due to apoptosis or programmed cell death

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Production of Ova by Ovary

After puberty

pools of 40-50 primordial follicles are ‘recruited’ to enter monthly ovarian cycles
each cycle results in single ‘dominant’ follicle that releases its oocyte during ovulation
recruitment continues until ovarian pool of primordial follicles is exhausted at menopause
only ~400 follicles ovulate during reproductive life of woman
remaining 99.9% undergo atresia

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Production of Ova by Ovary

What do recruited primordial follicles do?

form primary follicles surrounded by single layer of cube-shaped granulosa cells (GCs)

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Production of Ova by Ovary

What do primary follicles become?

become secondary follicles as they begin to accumulate multiple layers of GCs, and acquire

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Production of Ova by Ovary

What do secondary follicles develop into?

develop into tertiary (Graafian) follicles as a result of rapid growth and formation of fluid-filled antrum (fluid-filled space)

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Production of Ova by Ovary

What happens to tertiary follicles during each ovarian cycle?

one of the tertiary follicles becomes dominant and ovulates, and remaining follicles undergo atresia

Production of Ova by Ovary

What does the primary oocyte of dominant follicle do just before ovulation?

completes first meiotic division, and is no called secondary oocyte (large secondary oocyte and first polar body are formed)
secondary oocyte becomes arrested at one of the early phases of 2nd meiotic division

Production of Ova by Ovary

What does the primary oocyte of dominant follicle do following ovulation?

released ovum enters oviduct and (if sperm are present) may be fertilized there

Production of Ova by Ovary

How is haploid mature oocyte produced?

when 2nd meiotic division is completed, only after haploid sperm has crossed ovum’s cell membrane

Production of Ova by Ovary

What is folliculogenesis?

follicle growth

Production of Ova by Ovary

What are the 2 phases of folliculogenesis?

preantral or gonadotropin-independent phase

- antral or gonadotropin-dependent phase

Production of Ova by Ovary

What occurs in the first stage (preantral or gonadotropin-independent phase) of folliculogenesis?

growth and differentiation of follicles (primordial follicles to secondary follicles)

Production of Ova by Ovary What controls the first stage (preantral or gonadotropin-independent phase) of folliculogenesis?

controlled by locally produced growth factors through autocrine/paracrine mechanisms

Production of Ova by Ovary What happens in the second stage (antral or gonadotropin-dependent phase) of folliculogenesis?

additional growth of few follicles, followed by selection of single dominant follicle which releases its oocyte as a result of ovulation

Production of Ova by Ovary What controls the second stage (antral or gonadotropin-dependent phase) of folliculogenesis?

controlled by FSH, LH, estrogen and growth factors

Production of Ova by Ovary After Ovulation

remnants of dominant follicle in wall of ovary transform into corpus luteum (CL)

Ovarian Cycle What are the 3 critically important events?

- selection and development of dominant follicle - ovulation - formation of CL

Ovarian Cycle What is the average length of ovarian cycle?

28 days

Ovarian Cycle What are the two phases?

(days 1-14) follicular phase (days 15-28) luteal phase

Ovarian Cycle What is the follicular phase (days 1-14) characterized by?

presence of maturing follicles – culminates in ovulation (days leading to ovulation)

Ovarian Cycle What is the luteal phase (days 15-28) characterized by?

presence of CL – culminates in menstruation, UNLESS ovulated egg has been fertilized corpus luteum is formed

Ovarian Cycle What is the cycle controlled by?

complex hormonal interactions

Ovarian Cycle What does estrogen do?

estrogen (E) regulated changes in hypothalamic GnRH pulse frequency control release of FSH and LH from anterior pituitary

Ovarian Cycle Process

1. early in follicular phase: low E levels produced by maturing follicles maintain low frequency of GnRH pulses (release) in hypothalamus: - this favours release of FSH over LH - at this stage: low E has negative feedback effect on GnRH secreting neurons 2. at roughly day 10 of cycle: very high concentration of E produced by dominant follicle reaches threshold to induce very high GnRH pulse frequency (release) in hypothalamus - this now favours release of LH over FSH - at this stage: very high E has positive feedback effect on GnRH secreting neurons 3. LH peak observed on about day 13 of cycle triggers the following events: - completion of meiosis I by oocyte (inducing transition of primary oocyte → secondary oocyte) - rupture of follicular wall - ovulation - formation of CL 4. CL begins to secrete high levels of progesterone (P) and moderate amounts of estrogen (E) - high concentration of both ovarian steroids inhibits GnRH release from hypothalamus, resulting in inhibition of LH and FSH release from anterior pituitary - high E and P have strong negative feedback effect on GnRH secreting neurons 5. P and E levels remain high for about a week – then, unless pregnancy occurs, CL begins to deteriorate and stops producing P and E 6. new cycle begins (back to step 1)

Ovarian Cycle What do hormonal changes associated with the cycle have significant effects on?

uterus

Ovarian Cycle What does the uterine (menstrual) cycle consist of?

repeating changes in structure of uterine lining or endometrium

Ovarian Cycle What are the 3 phases of the uterine (menstrual) cycle?

- proliferative - secretory - menstrual

What is the proliferative phase of the uterine (menstrual cycle) caused by?

stimulated and sustained by increasing levels of E produced by rapidly developing follicles and involves development of endometrial glands and vascularization of lining - as a result, by the time of ovulation, the so-called ‘functional zone’ of endometrium is several mm thick, glands secrete mucus rich in glycogen, and numerous spiral arteries are present

What is the secretory phase of the uterine (menstrual cycle) caused by?

begins at ovulation, as endometrial glands enlarge and produce large amounts of secretions under combined stimulatory effects of P and E from CL - secretory activities peak at about day 12 after ovulation and then decline as CL begins to degenerate - as a result of rapidly decreasing P and E levels, spiral arteries constrict, reducing blood flow to endometrium and causing rapid degeneration of its functional zone

What is the menstrual phase of the uterine (menstrual cycle) caused by?

weakened arterial walls rupture, blood and degenerating lining enter uterine lumen and are discharged from vagina - sloughing off of endometrial tissue continues for several days until rising E levels produced by next batch of developing follicles stimulate repair and regeneration of lining

Ovarian Cycle What are endocrine activities in ovary regulated by?

hypothalamic-pituitary-ovarian axis