Reproductive Cyclicity in the Female
Reading
Estrous Cycles
Terminology
- Estrus vs. Estrous
- Oestrus and Oestrous
- Estrus and heat are synonymous
- Anestrus
- Polyestrus
- Seasonally Polyestrus
- Monoestrus
Hormonal and Ovarian Changes During the
Estrous Cycle
Follicular Phase
- Follicles the dominate ovarian structure
- Estrogen the dominate hormone
Luteal Phase
- Corpora lutea the dominate ovarian structure
- Progesterone the dominate hormone
The 4 Stages of the Estrous Cycle
- Proestrus
- follicle enlarges
- estrogen increases
- vasularity of the female reproductive tract increases
- endometrial glands begin to grow
- estrogen levels peak
- Estrus
- allows male to mount
- estrogen decreases
- LH surge occurs
- ovulation 24-48 hr after surge of LH
- uterine motility high with contractions moving toward oviduct
- sperm transport is optimal
- cervical mucus volume increases
- Metestrus
- estrogen low
- corpus hemorrhagicum present
- ovulation in cow
- uterus
- contractions subside
- endometrial glands continue to grow and become coiled
- in cattle bleeding occurs
- FSH increases, triggering growth of follicles
- Diestrus
- progesterone high
- FSH low but increases at some point to cause growth of pre-ovulatory follicle
- Uterus
- secrets fluid but the volume of fluid decreases over time
- contraction stop
- corpus luteum regresses at the end of this period if female is not
pregnant
|
Cow |
Ewe |
Sow |
Mare |
Estrous cycle (d) |
21 |
17 |
21 |
21 |
Proestrus (d) |
3-4 |
2-3 |
3-4 |
2-3 |
Estrus (hr) |
12-18 |
24-36 |
48-72 |
4-8 |
Metestrus (d) |
3-4 |
2-3 |
2-3 |
2-3 |
Diestrus (d) |
10-14 |
10-12 |
11-13 |
10-12 |
Estrous Cycles in the Dog and Cat (Figure 2)
- Dog
- Anestrus - has an FSH increase that triggers follicular growth
- Proestrus - estradiol increase and peaks at end, also bloody discharge begins
- Estrus - estradiol declines, LH surge, ovulation, progesterone increases even before ovulation
- Metestrus I - 20 days, progesterone high, increase in estradiol
- Metestrus II - 70 days, progesterone declines, estradiol declines, prolactin increases and then declines
- Patterns the same in pregnant and non-pregnant bitch
- Psuedo-pregnancy occurs in non-pregnant bitch because of increases in prolactin.
- Cat
- Estrus 9 days, Proestrus 8 days, repeats until mating occurs, estrus when estradiol present, progesterone is low throughout
- After mating, LH surge induced, progesterone increases then decreases, estrus returns after parturition when progesterone goes back down.
Causes of Anestrus
- Pregnancy
- Presence of offspring
- season
- stress
- pathology
Specific Types of Anestrus
- Gestational
- Normal
- corpus luteum present during pregnancy
- progesterone has negative feedback effects on GnRH
- LH and FSH don't surge
- estrogen remains low to moderate
- estrogen has negative feedback effects in the presence of progesterone
- corpus luteum regresses before parturition but hypothalamus still does
not increase GnRH pulse frequency and amplitude for a while
- due to long inhibition of hypothalamus during gestation
- useful to allow for uterine involution prior to the first postpartum
estrous cycle
- Seasonal
- horses are long day breeders and sheep are short day breeders
- anestrus to estrus - like entering puberty
- first ovulation slient
- progesterone needed to prime hypothalamus so that when exposed to estrogen the animal will express estrus behavior
- effect of light
- light sends signals via hypothalamus, superior cervical ganglion to the pineal gland
- Melatonin released at night and not during the day
- Long days = short nights = low melatonin
- short days = long nights = high melatonin
- melatonin effects are Kiss neurons and then impact GnRH release
- Low Melatonin
- in mare, low melatonin stimulates GnRH release and leads to cyclicity
- in ewes, low melatonin inhibits GnRH release and leads to anestrus
- High Melatonin
- in mare, high melatonin inhibits GnRH release and leads to anestrus
- in ewes, high melatonin stimulates GnRH release and leads to cyclicity
- Lactational
- Females suckling young experience anestrus
- Sow - completely suppresses estrus
- Cow - suppressed for up to 60 days
- suckling frequency (need at least 2 / day)
- not due to teat stimulation
- visual, olfactory or possibly auditory encounter
- potential role for prolactin
- prolactin inhibits GnRH release
- major infertility problem in non-lactating women
- Nutritional
- Negative energy balance can trigger anestrus
- similar to puberty in that inhibit GnRH pulse frequency because insufficient
energy available
- remember effects of 2 deoxyglucose infusion in that it inhibits GnRH
release
- problem in primiparous females with combined requirements of lactation
and growth
Menstrual Cycle in Human Females (Figure
6) (Concept Tutor on Menstrual
Cycles)
- Average cycle length is 28 days from start of menstruation until start
of next menstruation
- Ovarian events
- Follicular wave starts day 1 -2 with recruitment followed
by selection and dominance
- Ovulation occurs on day 14
- CL forms and lasts 12- 14 days
- luteolysis is not dependent on the uterus
- CL is programed to last only 12 - 14 days and regresses
if the female
is not pregnant
- Ovarian steroids
- As follicles begin to grow during selection and dominance,
estradiol is secreated by tertiary follicles. This estradiol
has negative feedback effects initially on the hypothalamus and
anterior pituitary to inhibit GnRH release and its effects on
the anterior pituitary. Around day 10, the estradiol begins to
have positive feedback on the hypothalamus and anterior pituitary.
This triggers the GnRH and LH surges that cause ovulation.
- The Cl in primates produces both estradiol and progesterone
- luteolysis causes a drop in both estradiol and progesterone
and initiates menses
- Gonadotropins
- FSH increases initiate the follicular wave at days 1-2 and LH is
low at this time.
- FSH then declines
- Positive feedback of estradiol causes the LH to rise around day
10 and the surge occurs on day 13 with ovulation on day 14.
- Both LH and FSH then decline and remain low through the remainder
of the cycle
- Uterine events
- on day 1, menses begins and involves loss of uterine endometrial
tissue
- as menses ends, the uterine endometrium begins to proliferate
under the influence of estradiol from growing follicles
- after ovulation and formation of the CL, estradiol and progesterone
from the CL cause the uterine endometrium to further proliferate
- Luteolysis on day 25-27 results in a drop of both estradiol and
progesterone causing first a constriction of blood vessels to the
uterine edometrium followed by dilation. Lack of oxygen and nutrients
from the blood vessels results in endometrial tissue death and
then blood vessels bleed. Blood clots and then liquifies. Menstrual
flow consists of both serum and endometrial tissue debris.
- Portions of the cycle,
for an average cycle
(Figure 7 )
- Menses - 5 days
- Follicular phase - 9 days
- Luteal phase - 14 days
- Variation in cycle length (Figure 8 )
- Characteristics
- menses does not change, approx. 5 days
- luteal phase does not change, approx. 14 days
- follicular phase can be variable
- 6 days for a 25 day cycle
- 9 days for a 28 day cycle
- 16 days for a 35 day cycle
- breast tenderness occurs 5 - 7 days before menses
- effect of progesterone and estradiol
on development of breast tissue
- lactation does not occur due to low prolactin levels
- Effect of age
- Length (average)
- 35 days for 15 - 19 year olds
- 30 days for 30 year olds
- 28 days for 35 year olds
- Variation
- more in teenagers
- less for women in peak reproductive years
- Effect of lactation on postpartum menstrual cycles
- Not Lactating, 50% cycling by 8 months, 90% cycling by 12 months
- Lactating (for 24 months), 30% cycling by 12 months, 70% cycling by 24 months