Female Reproductive Physiology

Question 1

when does meiosis in the female gamete begin?

Answer 1

during fetal development

Question 2

what are the two periods of physiologic arrest in female meiosis? describe

Answer 2

1. at birth:
   -during fetal development, oogonia (diploid, 2N stem cells) undergo oocytogenesis, a mitotic division, producing two 2N daughter cells each;
   -the 2N daughter cells will then meiotically replicate its DNA and arrest in prophase with a large 4N nuclei until sexual maturity);
   -these cells comprise nearly all the oocytes in ovarian follicles, and bitches and mares ovulate these PRIMARY follicles!
   -these follicles are highly vulnerable to environmental insults (temp, nutrition, etc.)
2. after ovulation at MII to await fertilization:
   -just prior to ovulation in all species except bitches and mares, secondary follicles complete their first meiotic division and the first 2N polar body is formed
   -this is immediately followed by a second meiotic division, but the division is not completed as the cell arrests in metaphase to await fertilization

if fertilization occurs, the second meiotic division is completed, and the second polar body is formed to make a (1N) haploid cell with room for the sperm (1N) to join and make a 2N zygote

Question 3

compare equine ovaries to everyone else’s ovaries in terms of germ cell location and site of ovulation

Answer 3

nonequine ovaries, germ cells reach the surface all over the ovary, can ovulate from anywhere on ovary

but in equines, germinal epithelium is internal, so germ cells reach the surface only at the ovulatory fossa, an indentation unique to equines that causes the ovary to assume a reniform shape at 5-7 months of age and will be invaded by mesovarium, blood vessels, and nerves

ovulatory fossa becomes exclusive site of ovulation, and since it is indented, only large follicles can be palpated and a CL is difficult to palpate

Question 4

what does post-natal, early folliculogenesis require? does it occur with gonadotropin support?

Answer 4

requires an oocyte/follicle to establish bidirectional communication with somatic ovarian cells

Question 5

what do pre-antral and antral follicles require for growth? when does this occur?

Answer 5

require gonadotropin support; occurs at onset of puberty

Question 6

describe the first stage of post-natal follicle growth: primordial follicles

Answer 6

this is the resting stage that is formed by day 1 post-natal, surrounded by a single layer of squamous follicular/pre-granulosa cells

GnRH INDEPENDENT

Question 7

describe the second stage of post-natal follicle growth: primary follicles

Answer 7

recruited on days 2-7 of life from the finite primordial follicle pool upon follicular activation; bidirectional communication with the oocyte is established via granulosa cells of the ovary

GnRH INDEPENDENT!

Question 8

describe the 3rd stage of follicular growth: secondary/pre-antral follicle

Answer 8

3-5 layers of granulosa cells, oocyte growth

Question 9

describe the 4th stage of follicular growth: tertiary/antral/graafian follicle

Answer 9

1. follicle forms a fluid filled cavity that is FSH-dependent
2. differentiation of mural granulosa cells in the follicle wall (oocyte/cumulus complex)

Question 10

what is a unique biological feature of canine ovarian follicles?

Answer 10

polyovular follicles, with 2-5 oocytes per follicle; oocytes are of different viability within follicle (can be in different stages of development)

Question 11

describe establishment of the E2 positive feedback loop at the onset of puberty (4)

Answer 11

1. at the onset of puberty, pulsatile secretion of GnRH begins
2. GnRH causes FSH and LH release from the adenohypophysis
3. FSH causes antral follicles to release estrogen (E2)
4. E2 establishes positive feedback, increasing GnRH release until E2 high enough to trigger a surge of LH and ovulation

Question 12

when does onset of puberty occur in horses, cows, and dogs? what occurs at the onset of puberty? (2)

Answer 12

horses: 12-18 months
cows: 8-12 months
dogs: 6-12 months

at onset:
1. pulsatile gonadotropin secretion
2. gametogenesis and steroidogenesis

Question 13

describe the 2-cell/2-gonadotropin model for estradiol synthesis

Answer 13

1. antral follicles contain theca cells external to the BM, and granulosa cells internal to the BM
2. theca cells secrete testosterone and granulosa cells secrete estradiol
3. FSH binds to granulosa cells and induces estradiol release (woohoo!) but that’s often not sufficient production of estradiol (boo) so
4. LH binds theca cells and induces secretion of testosterone, which leaks/diffuses across the basement membrane to the granulosa cells, which can aromatize testosterone to estradiol (woohoo!)

Question 14

how does LH induce ovulation? (2)

Answer 14

1. rupturing the basement membrane for follicular rupture and release of oocyte into oviduct
2. inducing resumption of meiosis of the oocyte (to kick out second polar body to make way for sperm)

Question 15

what happens at the site of ovulation following ovulation? (2)

Answer 15

1. a corpus hemorrhagicum forms: a bloody mess of leftovers of ovulation
2. CH become corpus luteum, which has large and small luteal cells that secrete progesterone; becomes functional 3-5 days post ovulation and drives the rest of the cycle

Question 16

what does return to estrus require? how is this accomplished?

Answer 16

requires destruction of the CL via luteolysis

mechanism: vascular countercurrent mechansim of PGF2alpha secretion

ovarian artery wraps around the utero-ovarian vein, so PGF2alpha from uterine endometrium (secreted when no embryo detected) can diffused from the uterine-ovarian vein into the ovarian artery and be transported directly to the ovary to induce luteolysis

(if pregnant, embryo suppresses PGF2alpha release in maternal recognition of pregnancy)

Question 17

what 3 things are combined in diagnosis of the stage of the estrous cycle?

Answer 17

1. behavior
2. what is observed on the ovaries
3. what is being released from the adenohypophysis

Question 18

what is the main goal of diagnostic ultrasound and when can this be used? (3)

Answer 18

to detect a corpus luteum (or not)

used in:
1. early detection of nonpregnant cows
2. mares with twin pregnancies (uh oh time to pinch one off)
3. to determine fetal viability/sex

Question 19

describe palpation of the ovaries in cow to determine pregnancy (4)

Answer 19

1. use the pelvic wall as a landmark to scoot forward and find the cervix
2. cervix has 3-5 rings and should be able to move freely up to 70 days of pregnancy (if not freely moveable = pregnancy or problem)
3. once find cervix, scoot forward and retract the uterus, find the central intercornual ligament and pull it to bring the tract up into the floor of the pelvis
4. hold cervix to pelvic floor using wrist to keep in place, then look for any of the 4 signs of pregnancy: fetal membrane slip (chorio-allantoic membranes), amniotic vesicle, fetus, or feto-placental placentomes

Question 20

describe the correlation between number of follicular waves and fertility in cattle

Answer 20

more follicular waves = higher fertility

Question 21

describe endocrine control of follicular waves

Answer 21

1. immediately after ovulation, there is slight FSH secretion to begin recruitment, where multiple follicles begin to grow at the same time
2. this is followed by deviation, where one follicle is selected to become dominant and the rest that were developing undergo atresia
3. the dominant follicle grows and matures in the dominance phase
4. if the CL is still present and progesterone is still high, the dominant follicle cannot ovulate!! it will undergo atresia instead
5. another wave of recruitment begins and the same pattern continues until the CL is lysed and enough estradiol can be produced by the dominant follicle to establish positive feedback with the hypothalamus to trigger the LH surge and ovulation

Question 22

describe turner syndrome as ovarian dysfunction in domestic animals

Answer 22

failure to segregate the X chromosome during meiosis results in a genotype missing the X chromosome, leading to primary infertility and gonadal hypoplasia

final diagnosis can only be made by karyotyping

Question 23

what are the 2 main types of ovarian cysts? describe the general info of them both (3)

Answer 23

follicular and luteal

1. major cause of repro failure in dairy cattle
2. disturbance of hypothalamo-hypophyseal-ovarian axis leads to a unresponsiveness to estrogen, meaning there is no LH surges and therefore no ovulation
3. failure to ovulate leads to follicular or luteal cysts

Question 24

describe follicular cysts (definition, duration, clinical signs, diagnosis, treatment)

Answer 24

1. fluid filled structures larger than 2.5cm with no functional CL present in either ovary
2. persist for longer than 10 days and then may be replaced by another cyst
3. clinical signs most commonly are constant estrus if granulosa cells are still producing E2, but rarely can actually be anestrus if a thin luteal cell layer begins to form inside the follicle with no PGF2alpha receptors and produces enough progesterone to prevent LH release
4. diagnosed by behavior, transrectal ultrasonography, palpation findings, and plasma or milk progesterone
5. can spontaneously recover, or may be treated first by administering GnRH (will NOT induce ovulation, but WILL induce luteal formation, making the follicle responsive to PGF2alpha, so the follicle can then by lysed and resolve) OR

if GnRH no work, can try the more expensive hCG and PGF2alpha for refractory cysts; hCG will induce LH activity to induce follicular luteal formation = responsive to PGF2alpha = lyse

Question 25

describe luteal cysts (definition and treatment)

Answer 25

1. induces anestrus due to high progesterone secretions
2. treat by administering PGF2alpha, triggering luteolysis and return to estrus within 8 days