Exam 4: Animal Repro Final

Reproductive cyclicity

-Provides females with repeated opportunities to become pregnant:

- Estrous cycle

- Menstrual cycle

Estrous Cycle

Consists of the physiologic events that occur between successive periods of sexual receptivity and ovulations

Follicular Phase

- Dominated by estradiol from follicles

- Initiates changes in the tract (increase in muscle contraction/tone, increase mucus production lubrication) and initiates sexual receptivity

Luteal Phase

When we have CL on ovaries.

- Dominated by progesterone from the corpus luteum

- Prepares the tract for pregnancy - job of progesterone

Anestrus

- Period of time when the estrous cycle ceases

Reasons: Pregnancy, season , lactation, stress, or pathology

Estrus

- Noun: Period of sexual receptivity

Estrous

Adjective:

Describes the reproductive cycle

Estrual

Adjective;

Used to identify a condition related to estrus

Polyestrous

Uniform distribution of estrous cycles throughout the year

- Cow, Pig, and Rodents

Seasonal Polyestrus

Cluster of estrous cycles that occur only during certain seasons of the year.

- Shortday breeders: (fall winter) Sheep

- Longday breedings: (spring summer) Horses

Monoestrous

-One cycle per year

- Estrus lasts several days to increase opportunity to become pregnant

(Dogs, wolves, goxes, and bears)

- Domestic canids - 3 cycles every 2 years

Follicular phase Details

- Follicle development, maturation, and ovulation

- Estradiol is the dominant hormone

- Accounts for 20% of the cycle

Luteal Phase Details

- Primary structure is the corpus luteum

- Progesterone is the predominant hormone

- Accounts for 80% of they cycle

What are the four stages of the estrous cycle?

Proestrus : Transition periods

Estrus: Follicular Phase

Metestrus:

Transition periods

Diestrus : Luteal phase

Proestrus

-Precedes estrus

-Begins when P4 declines due to luteolysis

-Lasts 2 to 5 days

-Decreasing P4 and increasing E2

-Follicles are recruited for ovulation (increaseing amount of LH and FSH)

Estrus Phase is what?

Period of sexual receptivity and mating

- Estradiol is the dominant hormone

- Characterized by:

1. Increased locomotion

2. Phonation

3. Nervousness

4. Attempts to mount others

5. Standing to be mounted (primary sign )

What happens as estrus progresses?

The females willingness to accept the male for mating

- Standing estrus

- Lordosis: Characteristic mating posture/arching of the back

Metestrus

- Period between ovulation and formation of a functional CL

- E2 and P4 are relatively low (transition period)

- Oulatory follicle undergoes luteinization

- Two to five days before CL produces significant progesterone

Diestrus

- Longest stage of the estrus cycle

- CL is fully functional and P4 is high

- Ends when the CL is destroyed

- High P4 prompts the uterus to prepare a suitable environment for early embryo development

True Anestrus

Cuased by insufficient hormonal Stimuli

- Not enought GnRH being secreted so not enough stimulation to cycle

Apparent Anestrus

Failure to detect estrus or failure to recognize that a female is pregnant.

Female is cycling or is pregnant but notit is not noticed.

To eliminate true anestrus one must:

- Improve nutrition

- Remove offspring to terminate lactation

- Eliminate Stress

- Eliminate pathological factors (uterine infection, persistent CL, mummified fetus)

To eliminate apparent anestrus one must:

- Improve detection of estrus or detection of pregnancy

- Lack of cycicity is a major clue that a female is pregnant

- P4 from the Cl/placenta exert negative feedback on GnRH neurons (less LH & FSH)

- Low incidence of behavioral estrus during pregnancy (cows and ewes 3-5%)

Seasonal anestrus:

- Controlled by photoperiod

- Allows females to conceive when ambient temp is lower (fall and spring)

- Give birth in the spring when nutritional conditions favor lactation and growth of the young

Silent Ovulation

- Ovulation not preceded or accompanied by behavioral estrus

- First ovulation in the ewe after seasonal anestrus is silent

- For maximal expression of behavioral estrus, progesterone must be present for a certain period of time prior to exposure to estrogen

Silent ovulation: P4 from the first CL after anestrus does what?

"primes" the brain so that sensitivity to E2 is optimized

Onset of Seasonal Cyclicity

-Similar to onset of puberty

-Characterized by hypothalamic dormancy in regard to GnRH secretion (Not sufficient to cause sufficient release of LH and FSH)

-Cyclicity is influenced by photoperiod and temperature (Photoperiod much more important)

-Melatonin stimulates release of GnRH (Only synthesized and released during night hours)

-Daylight prevents secretion of melatonin by the pineal gland

Cyclicity is influenced by

Photoperiod (more important) and temperature.

Hormone associated with photoperiod is Melatonin which stimulates?

The released of GnRH.

- Only synthesized and relased during night hour

Daylight prevents secretion of what by the what gland?

SEcretion of melatonin by the pineal gland

Lactational Anestrus

- Occurs in almost all mammals nursing young

- Varies in length

- Cyclicity can be delayed by as much as 60 days after parturition:

1. influenced by the degree of suckling

2. Greating than two suckling sessions per day tend to cause anestrus

Cyclicity is completely suppressed by what in the sow?

Lactation

Is mammary stimulation totally responsible for lactational anestrus?

Not completely.

During suckling is LH low or high?

Quite low

Factors other than teat stimulation that are responsible for inhibition of GnRH

- Visual encounters with offspring

- Olfactory encounters with the offspring

- Auditory encounters with the offspring

Menstrual Cycle

Physiological events that occur between successibe menstrual periods.

- Averages 28 days in women (24-25 day range)

- Each cycle consists of 3 distinct phases

PHases of menstrual cycle: Menses

- Period of endometrial sloughing

- This is the beginning/end of the menstrual cycle

- Lasts 2 to 5 days

Menstrual cycle phases: Follicular Phase

- Endometrium begins to grow and thicken

- Follicles develop and ovulation occurs

(dominant hormone is E2)

- Last about 9 days

(Half of menstrual cycle)

Menstrual Cycle Phases: Luteal Phase

- Dominated by the CL that produces P4 and E2

- Endometrium continues to increase in thickness (prepares for secretory acitivity for embryo environment)

- After the 28th day, the endometrium is sloughed

- Last about 14 days

Menstrual cycle differs from estrous cycle because:

- Period of endometrial sloughing called menses

- Timeline begins and ends with menses, not ovulation or estrus

- Follicular phase and luteal phase are of equal length

- No defined period of sexual receptivity

Menopause

- Analogous to anestrus

- Caused by a depletion of follicles

Amenorrhea

- Absence of menses in Women of reproductive age

- Negative energy balance

- Lactational amenorrhea (high prolactin causes a decrease in GnRH secreation and Lactation can be considered a form of contraception when nutrition is limiting)