Female Reproduction Flashcards
What do ovaries (female gonads) do?
produce gametes (ova) by oogenesis, and two sex steroid hormones – estrogen (estrodyl E2), and progesterone
What are the 3 parts of the reproductive tract?
- oviducts (Fallopian tubes)
- uterus
- vagina
What do the oviducts (Fallopian tubes) do?
receive ovulated ova – site of fertilization
fimbriae at end of tubes catch fertilized egg
What is the uterus?
site of menstrual bleeding, and embryonic and fetal development
What does the vagina do?
connects uterus to external environment – site of sperm deposition
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)
Production of Ova by Ovary
When do oogonia?
appear during early prenatal development, divide by mitosis and are diploid
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
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)
Production of Ova by Ovary
What is a primordial follicle composed of?
primary oocyte + follicular cell
Production of Ova by Ovary
What is an ovary reserve?
number of primordial follicles in ovaries at time of birth
Production of Ova by Ovary
Between Birth and Puberty
- no new oocytes are produced
- primordial follicles either remain quiescent or undergo atresia
Production of Ova by Ovary
What is atresia?
degeneration due to apoptosis or programmed cell death
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
Production of Ova by Ovary
What do recruited primordial follicles do?
form primary follicles surrounded by single layer of cube-shaped granulosa cells (GCs)
Production of Ova by Ovary
What do primary follicles become?
become secondary follicles as they begin to accumulate multiple layers of GCs, and acquire
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)
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
- 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 - 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 - 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 - 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 - P and E levels remain high for about a week – then, unless pregnancy occurs, CL begins to deteriorate and stops producing P and E
- 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
