Reproductive Cycles Flashcards
when does the reproductive cycle occur?
between periods of sexual receptivity (estrus or heat) and/or ovulations
types of reproductive cycles
estrous cycle (domestic animals)
menstrual cycle (primates)
ovulatory cycle (birds)
types of estrous cycles
- Polyestrous
- Seasonally polyestrous
- monoestrus
polyestrous cycle
- uniform distribution of estrous cycle throughout the year
seasonally polyestrous cycle
clusters of estrous cycle that occur only during a certain season of the year
monoestrus cycle
having only one cycle per year
phases of estrus cycle
follicular and luteal
follicular phase is characterized by
1) development of follicle
2) ovulation
luteal phase is characterized by
formation and function of corpus luteum
Hormonal Regulation of Estrous Cycle (4 steps)
1) Hypothalamus releases GnRH
2) Pituitary releases FSH and LH
3) Ovary releases estrogen and progesterone
4) Estrogen and progesterone enter reproductive tract
Describe the Events Ocurring During the Follicular Phase
1) steady release of GnRH from the tonic center of the hypothalamus
2) GnRH acts of gonadotrophs of the anterior pituitary to secrete gonadotropins- FSH and LH
3) FSH and LH act on ovary, induce follicular development and maturation
4) Low level of estradiol from the follicle exerts negative feedback on hypothalamus and pituitary to reduce FSH secretion
5) High levels of estradiol exerts positive feedback on the surge center resulting in the preovulatory surge of LH
Ovulation is caused by ____ and results in ____
caused by: preovulatory surge of LH acting on the follicle
results in: rupture and release of oocyte
Events Occuring at Luteal Phase
1) Formationand maturation of corpus luteum
2) High progesterone (secreted by mature CL) suppress FSH and LH synthesis (negative feedback)
3) Regression of corpus luteum (luteolysis)
4) Progesterone secretion decreases
5) Release of negative feedback of progesterone on hypothalamus and pituitary
proestrus is _ begins when ___
Period before estrus
Begins when progesterone declines as a result of luteolysis/ destruction of the corpus lutem (from the previous estrus)
proestrus is characterized by ____ this is due to _____
shift from progesterone dominance to estradiol dominance, due to FSH and LH
During Proestrus, the increased secretion of _____ causes what changes?
The increased secretion of estradiol causes:
- ovulatory follicles to mature in preperation for ovulation
- reproductive system to prepare for estrus and mating
What is the most recognizable stage of the estrus cycle, characterized by visible behavioral symptoms such as sexual receptivity, female allows copulation?
estrus
What is the most dominant hormone during estrus?
estradiol, which both changes behavior and causes major physiological changes in reproductive tract
Signs of estrus
increased locomotion, phonation (vocal expression), nervousness, attempts to mount other animals
Standing estrus is the
willingness of female to accept male for mating
Lordosis
characteristic arching of the back in preparation for mating
During Metestrus
1) transition from estradiol dominance to **progesterone dominance **
2) ovulation (release of egg from ovaries)
3) Corpora lutea becomes fully functional (due to the cellular and structural remodeling of the ovarian follicle)
Diestrus is the
Longest stage of the estrous cycle
and the period of maximum luteal function
during diestrus
- High progesterone secretion prompts the uterus to prepare a suitable environment for embryo implantation and successful pregnancy
- Ends when the CL is lysed (luteolysis)
diestrus is characteriszed by
the substained secretion of progesterone (high amounts of progesterone)
the luteal phase includes
metestrus and diestrus
what is the major ovarian structure of the follicular phase?
the follicle
what is the major ovarian structure of the luteal phase?
the corpus luteum
what is the major hormone of the follicular phase?
estradiol
what is the major hormone of the luteal phase?
progesterone
sexual receptivity occurs in what stage
the follicular phase, not the luteal
Changes in OVIDUCT due to estradiol and progesterone
Estradiol
- Increase in: spontaneous muscular activity, fluid secretion, epithelial cell height
- Ciliation of epithelial cells
Progesterone
- Generally causes inactivity
- Epithelial cells regress and atrophy (decreased cell height and partial de-ciliation)
- Some mucous secretion
Changes in UTERUS due to estradiol and progesterone
Estradiol
- Preparation for transport and survival of spermatozoa
- Congestion and edema of the uterine mucosa with mostly columnar epithelial cells
- increase in epithelial, glandular, and stromal cell division
- Sensitivity and amplitude of myometrial contractions (resulting in firm/erect uterus)
- Infiltration of leucocytes
Progesterone
- High progesterone prompts the uterus to prepare a suitable environment
- Reduced congestion and edema of the mucosa
- Increased cell differentiation and glandular secretions (Histotroph-Uterine milk)
- Flaccid uterus. Reduced myometrial tone (quiescence)
Infiltration of leukocytes reduced
Changes in CERVIX due to Estradiol and Progesterone
Estradiol
- Relaxation of the cervical folds
- Congestion and edema
- Increased cell proliferation
- Increase in secretion of mucus through vulva
Progesterone
- Cervical canal tightly closed
- Reduced congestion and edema
- Increased cell differentiation
- Thick and tenacious mucus
Changes in VAGINA due to estradiol and progesterone
Estradiol
Congestion and edema
Increased cell proliferation
Keratinization of the epithelium
Marked increase in the glandular secretion of the clear viscid mucus discharged through vulva
Progesterone
Reduced congestion and edema
Increased cell differentiation
Reduced keratinization
Reduced secretions
long photoperoid leads to
low melatonin
Transition from anestrus to cylicity in ewe (during breeding season) is due to
- an increase in progesterone during the luteal phase of the estrus cycle
- this enables the preovulatory GnRH surge
in cats
the reproductive cycle continues unless there is mating, mating disrupts the cycle and is necessary for ovulation
Vaginal Epithelial Changes in Bitch
Anestrus (A): vaginal epithelium is thin and underlying stroma is compact
Proestrus (P): vagina becomes thicker and cornified, stroma and smooth muscle also start to thicken and there is both stromal congestion and edema
Estrus (E): the vagina is thick and heavily cornified
Diestrus (D): vagina is much thinner (three to four cell layers) and loses its cornification
high/low hormones during diestrus
peak progesterone
low estradiol, LH, and FSH
high/low hormones during proestrus
progesterone decreasing
estradiol increasing
LH and FSH increasing
high/low hormones during estrus
peak estradiol, LH, and FSH
low progesterone
high/low hormones during metestrus
increasing progesterone
low estradiol, LH, and FSH
