Estrous Cycle Flashcards
estrous cycle (4)
- the period between two estrous/ovulation episodes
- ovarian cycle with regular duration
- variable among species, breeds, and individuals
- can be affected by multiple factors or pharmaceutically controlled with hormones
describe the summary of events leading up to ovulation (6)
- FSH initiates follicle recruitment
- follicles all grow and begin to produce estradiol, which reduces FSH
- follicle selection and growth
- selected follicle acquires LH receptors and becomes LH dependent
- estradiol reaches a threshold that stimulates GnRH to produce an LH surge
- ovulation
follicular wave (4)
- recruitment
- growth
- selection
- either ovulation or atresia
describe summary of events after ovulation if no pregnancy (5)
- corpus luteum develops and produces progesterone, which inhibits LH
- follicular wave begins to occur
- lack of LH surge will prevent ovulation and selected follicle will undergo atresia
- uterus endometrium produces PG to kill CL
- once CL is reduced and progesterone levels decrease, the next follicular wave can undergo ovulation
describe summary of events after ovulation if pregnant (4)
- corpus luteum develops and produces progesterone, which inhibits LH
- follicular wave begins to occur
- lack of LH surge will prevent ovulation and selected follicle will undergo atresia
- corpus luteum will be maintained and sustain high levels of progesterone so that ovulation will continue to not occur
what happens to the selected follicle if the follicular wave is under high progesterone levels
- no ovulation and follicle atresia
what happens to the selected follicle if the follicular wave is under low progesterone levels
- ovulation of selected follicle
what are the feedback loops present in the estrous cycle (3)
- E2 inhibits FSH
- P4 inhibits LH
- PG inhibits P4
what produces estradiol
- follicles
what produces progesterone
- corpus luteum
what produces GnRH, LH, and FSH
- the brain/hypothalamus
what produces prostaglandin
- uterus endometrium
luteolysis (3)
- structural and functional degradation of corpus luteum
- determines length of diestrus phase and the estrous cycle
- sign of the end of a cycle or the end of pregnancy
what is the major luteolytic agent in most species (4)
- agent
- synthesis
- delivery
- inhibition
- prostaglandin
- synthesized by the uterus in the endometrium
- delivered to ovaries through counter-current transfer in the plexiform structure
- inhibited by conceptus in pregnant animals
what do follicle cells rearrange into in the corpus luteum (3)
- large luteal cells
- small luteal cells
- fibrocytes (epithelial cells)
how does PG act on the CL (2)
- PG membrane receptors present on luteal cells
- binding of PG to receptors triggers pathway with G protein coupled receptor and kinases
what affects does the PG induced pathway have on the CL (3)
- anti-angiogenesis affect: no new blood vessels
- cell apoptosis: CL shrinks into a scar
- shut down of steroidogenesis enzymes to halt P4 synthesis
phases of estrous cycle of the follicular phase (2)
- proestrus
- estrus
phases of estrus cycle of the luteal phase (2)
- metestrus
- diestrus
what is proestrus defined by (2)
- high estradiol
- low progesterone
what are the characteristics of proestrus (2)
- preparation of mating
- development of ovulatory follicle
what is estrus defined by (2)
- highest estradiol
- low progesterone
what are the characteristics of estrus (4)
- acceptance of the male for mating and when mating occurs
- visible behaviors of estrus
- presence of large graafian follicle
- ovulation occurs after estrus ends
what is metestrus defined by (2)
- low estrogen
- low progesterone
what are the characteristics of metestrus (3)
- first few days after estrus
- formation of the corpus luteum
- bleeding
what is diestrus defined by (2)
- low estrogen
- high progesterone
what are the characteristics of diestrus
- lasts until luteolysis
- functional corpus luteum
- associated with follicle turnover/atresia
what are the phases of the estrus cycle (5)
- proestrus
- estrus
- metestrus
- diestrus
- anestrus
anestrus (3)
- period of reproductive incompetence with no ovulation or corpus luteum formation
- follicular waves DO occur, but all follicles undergo atresia/turnover
- no expression of estrus behaviour
anestrus (3)
- period of reproductive incompetence with no ovulation or corpus luteum formation
- follicular waves DO occur, but all follicles undergo atresia/turnover
- no expression of estrus behavior
what situations would the estrous cycle be in anestrus (3)
- post-partum anestrus
- seasonal anestrus
- pseudopregnancy
post-partum anestrus (3)
- period of no ovulation after pregnancy so body/uterus can recover and focus resources on newborn
- involution; uterus size recovery and shrinking
- suckling effect from mammary glands sends negative neuro-endocrine signals to GnRH
seasonal anestrus
- light exposure alters melatonin levels in seasonal breeding animals, which affects GnRH and ovulation
pseudopregnancy (2)
- bitches can act pregnant due to high progesterone (no luteolysis)
- no ovulation will occur during this period
monoestrus
- animals with only one estrus cycle per year
polyestrus
- animals with multiple estrus cycles per year
monotocous
- ovulation of ONE follicle
polytocous (2)
- ovulation of MANY follicles
- amount varies between species and litters
induced ovulators
- ovulation depends on act of mating/copulation and not increased estradiol levels
spontaneous ovulators
- ovulation is hormonally driven
what is the average length of estrus cycle (2)
- about 3 weeks
- determined by luteolysis
what is the average duration of estrus (2)
- 20 hours to 72 hours typically
- some animals have 4-8 days on average, variable
what is the average time of ovulation relative to estrus
- 24 to 48 hours from start of estrus
puberty: male
- age with high testosterone and functional gametes
puberty: female (2)
- age at first estrus followed by ovulation
- initiation of complete estrus cycles can be irregular (poor signs of estrus) at first, and then transition to become regular after a few cycles
what occurs before puberty in females
- follicular waves don’t complete due to GnRH blocking
puberty variation (2)
- varies among species, breeds, and individuals
- depends on a variety of factors
puberty endocrinology
- hypothalamus and gonad control
puberty endocrinology: female (3)
- strong negative feedback on estradiol is reduced
- rapid increase in steroidogenesis: estradiol for ovulation
- timing is more related to body weight than age
puberty endocrinology: male (3)
- maturity of gonads (Leydig and sertoli cells in males)
- gametogenesis becomes functional
- rapid increase in steroidogenesis: testosterone for spermatogenesis
LH pulse frequency before puberty (7)
- lots of E2 receptors on hypothalamus/pituitary; strong negative feedback on E2
- strong feedback inhibits follicle recruitment and growth; leads to lots of recruitment and atresia
- E2 receptors are reduced over time, weakening the negative feedback on E2
- recruited follicles are gradually able to grow more before atresia
- increased E2 induced GnRH to stimulate LH pulses
- follicle develops until it is close to normal cycle and close enough to trigger ovulation
- more frequent and larger pulses lead up to a LH surge, which triggers ovulation and puberty
factors affecting initiation of puberty (4)
- hormonal
- genetics
- nutrition
- environmental
factors affecting initiation of puberty: hormonal (4)
- reduced GnRH release
- reduced pituitary response
- reduced ovarian response
- pineal gland stimulus from melatonin
factors affecting initiation of puberty: genetics (3)
- inbreeding delays, while crossbreeding hastens (genetic diversity is better)
- certain breeds vary
- smaller breeds reach puberty faster than larger breeds as they reach mature body faster
factors affecting initiation of puberty: nutrition (3)
- underfeeding leads to a delay
- optimum feeding will hasten
- growth hormone, insulin and insulin growth factors will affect GnRH
factors affecting initiation of puberty: environmental (5)
- feed availability (nutrition)
- temperature and humidity changes during seasons
- confinement leads to delays
- presence of male may hasten
- cortisol and adrenaline will affect GnRH
early induction of puberty
- economic advantage for
