Lecture 27 3/22/24 Flashcards
What is the estrous cycle?
interval between two ovulations
What are the phases of the estrous cycle, based on dominant structure?
-follicular phase
-luteal phase
What are the primary behavioral events during estrus?
-sexual receptivity
-copulation
What are the characteristics of the follicular phase?
-period from regression of CL to ovulation
-relatively short
-primary structures are growing dominant follicles
-follicles produce estradiol
What are the characteristics of the luteal phase?
-period from ovulation until CL regression
-longer phase
-dominant structure is corpora lutea
-CL produces progesterone
What are the stages of the estrous cycle?
-proestrus
-estrus
-metestrus
-diestrus
Which stages occur during the follicular phase?
-proestrus
-estrus
Which stages occur during the luteal phase?
-metestrus
-diestrus
What are the characteristics of proestrus?
-begins when progesterone declines
-terminates at onset of estrus
-follicle development and rise in estradiol
What are the characteristics of estrus?
-most recognizable stage
-peak of estradiol
-sexual receptivity and mating
-ovulation occurs
What is standing estrus?
the female’s willingness to accept a male for mating
What are the characteristics of metestrus?
-between ovulation and formation of functional corpora lutea
-initial development of CL
-transition from estradiol to progesterone
What are the characteristics of diestrus?
-mature phase of CL
-progesterone dominance
-period of maximum luteal function
-longest stage of estrous cycle
-ends when CL is destroyed
How does the estrous cycle compare to the menstrual cycle?
Estrous:
-interval between ovulations
-short follicular phase
-ovulation to begin cycle
Menstrual:
-interval between menses
-long follicular phase
-ovulation mid-cycle
What occurs during the proliferative and secretory phases of the menstrual cycle?
changes in endometrial thickness
What are the major events that occur during the follicular phase?
-elevated gonadotropins
-follicular growth
-preparation for ovulation
-sexual receptivity
-ovulation
What are the characteristics of ovulation?
-after luteolysis and absence of progesterone
-dominant follicle secretes large amount of estrogens
-feedback to surge center leads to LH peak
What happens after the surge center causes LH to peak?
-increase in PGE2 and blood flow
-increase in PGF2a
-increase in intrafollicular pressure
-disruption of connective tissue of follicle/weakening of follicle wall
-change from estradiol to progesterone
-removal of meiotic inhibition
-1st meiotic division
What are the roles of granulosa and theca cells?
-luteinization
-switch from estrogen to progesterone
What is the role of LH?
induction of ovulation
What is the role of luteotropin?
essential for maintaining CL
What are the characteristics of progesterone?
-prepares uterus for initiation/maintenance of pregnancy
-negative feedback with hypothalamus and pituitary
-stimulates endometrial secretion
-reduces myometrial motility
-poor progesterone synthesis/secretion can lead to repro. failure
What are the characteristics of the corpus luteum lifespan?
-lifespan is preprogrammed
-luteolysis occurs if animal is not pregnant
-maternal recognition of pregnancy prolongs CL lifespan
Which hormones control luteolysis?
-oxytocin
-progesterone
-PGF2a
What is maternal recognition of pregnancy?
mechanism that prevents PGF2a secretion and produces a luteotropic hormone that stimulates/prolongs CL
How does the uterus control the duration of the CL lifespan?
-PGF2a production
-expression of oxytocin receptors
What are the clinical uses of PGF2a?
-break CL and return animal to heat
-estrous synchronization
-short cycle
-abortion
How does progesterone prevent PGF2a secretion during the first half of the estrous cycle?
by blocking the formation of oxytocin receptors
How do spontaneous ovulators differ from induced ovulators?
-spontaneous ovulators have endocrine triggers
-induced ovulators have gonadotropin release in response to copulation
Which animals exhibit polyestrus?
-cow
-cat
-pig
-rodent
Which animals exhibit seasonal polyestrus?
-horse
-cat
Which animals exhibit monoestrus?
dog
What is polyestrus?
uniform distribution of cycles regularly throughout the year
How do long day breeders differ from short day breeders in seasonal polyestrus?
-long day breeders are in heat in spring and summer
-short day breeders are in heat in fall and winter
What are the steps of the estrus cycle in the bitch?
-anestrus
-proestrus
-estrus
-diestrus
Why is there a delay between ovulation and fertilization in the bitch?
primary oocytes are ovulated and fertilization cannot occur for 48-72 hours after ovulation
Why is there no luteolysis or maternal recognition of pregnancy in dogs?
the estrus cycle is long enough that this step does not need to occur
How long does it take for ovulation to occur in dogs after the LH peak?
3 days
What is postestrus?
an interestrus period in cats that follows estrus in which there was no mating, no ovulation, no CL development, and thus no diestrus
What are the characteristics of anestrus?
-lack of cyclicity
-lack of ovarian activity/no follicles or CLs
-insufficient GnRH from hypothalamus to stimulate gonadotropin secretion
What causes anestrus?
-age
-pregnancy
-lactation
-nutrition
-season
-stress
-pathology
How can anestrus be diagnosed?
-ultrasound of ovaries
-progesterone determination
-previous records of GnRH or progesterone supplementation
How does true anestrus differ from pseudoanestrus?
-in true anestrus, the ovaries are small and inactive
-in pseudoanestrus, the ovaries are active, and there are other factors causing anestrus
Which tests can be done to properly time insemination?
-vaginal cytology
-endocrine levels
How are progesterone levels used to determine breeding day?
-measure progesterone levels every 1-2 days once vaginal discharge begins
-follow progesterone increase
-breed two days post ovulation (typically two insemination times)
What is galactorrhea?
spontaneous development of mammary glands with secretions
What are the characteristics of pseudopregnancy in dogs?
-occurs at end of diestrus
-associated with decline in progesterone
-decrease in progesterone triggers increase in prolactin
-prolactin causes clinical signs
-typically resolves with no intervention
-can occur following ovariohysterectomy
