Estrous Cycle Flashcards
Follicular phase (proestrus, estrus)
-Period from the regression of the CL to ovulation
-about 20% of estrous
Luteal phase (metestrus, diestrus)
-Period from ovulation to CL regression
-80% of estrous
Atresia
-Degeneration of oocytes
-Not ovulated
Follicle recruitment
-Small follicles
-High FSH
-Low LH
Follicle selection
-Decrease of FSH
-Increase in LH
-Atresia of some follicles
-Few follicles proceed
Follicle dominance
-One (sometimes two) follicle dominates
-All others atresia
-high LH
-low FSH
-inhibin being produced: Limit FSH
Metestrus
-First phase
-Corpus Luteum is developing
-Increasing progesterone concentrations
Diestrus
-Second phase
-Maximum progesterone concentrations
Proestrus
-Third phase
-Progesterone starts to decrease
-Goes until signs of estrus show
Estrus
Period of sexual receptivity (heat)
Estrus vs estrous
-Estrus: Heat
-Estrous: Cycle that females experience
Anestrus/anestrous
-Without cyclicity
-Ovaries relatively inactive
-Not present: Ovulatory follicles and Corpora lutea
Polyestrous
-Uniform distribution of estrous cycles
-Throughout the year
Seasonally Polyestrous
-Clusters of estrous cycles
-Occur during certain season of the year
Monoestrous
Only one cycle per year
Know the 2-cell, 2-gonadotropin model of estradiol synthesis. (Long)
- GnRH: Targets gonadotropes (LH, FSH) and Hypothalamus
- LH & FSH: anterior pituitary
- LH: Targets LHr (Theca cell)
- Cholesterol: Converted to Pregnenolone (P450scc)
- Pregnenolone: Converted to Progesterone (3BHSD) and Converted to Androstenedione (17a-hydroxylase)
- Androstenedione:
~Converted to estradiol 17-B: P450 Aromatase (Granulosa cell) and Triggered by FSH - StARprotein: Transport protein, Moves cholesterol
Into inner mitochondrial membrane
Roles/functions LH
-Produced by gonadotropes: Anterior pituitary
-Stimulates the theca interna
-Grow follicle
-Increases in estradiol, Feedback to decrease the FSH from the anterior (LH dominates), Inhibin is produced, Feedback to decrease FSH (Increase LH)
-The amounts of estradiol continually increase until the dominant follicle is ovulated or dies.
Roles/functions FSH
-Produced by gonadotropes: Anterior pituitary
-Grows the follicle
-Stimulates the granulosa cells
-Increases in estradiol, Feedback to decrease the FSH from the anterior (LH dominates), Inhibin is produced, Feedback to decrease FSH (increase LH)
-The amounts of estradiol continually increase until the dominant follicle is ovulated or dies
Roles/functions Estradiol
-Produced by follicles: On ovary
-Sent to the hypothalamus: Surge center, Decrease FSH (Anterior Pituitary, Kills competition), Increase LH
Roles/functions Progesterone
-Produced by the CL: On ovary (Postovulatory)
-At high levels until luteolysis / proestrus: Decreases to allow for ovulation.
-Suppresses ovulation: Prevents estrus (Stop the preovulatory surge of LH)
-Affects basal LH secretion
-Reduces myometrial tone: Except mares
Know the characteristics of a follicular wave.
-Recruitment
-Selection
-Dominance
Recruitment
-Transient wave of FSH incites recruitment of follicular cohort
-Cohort (group of follicles) of chosen initially
-Tertiary follicles
Selection
-Some atresia
-Some develop LHr on granulosa: These are selected
Dominance
-Dominant follicle emerges: Continued growth to preovulatory size
-Achieved at time of luteolysis: Ovulation
Know how the ovarian structures and hypothalamus/pituitary communicate with each other to cause recruitment, selection & dominance.
-GNRH from Hypothalamus (Surge center) Stimulates gonadotropes
-FSH & LH from Gonadotrope cells, Stimulates Theca & Granulosa cells
-Estradiol from Theca & Granulosa cells Stimulates Hypothalamus and Inhibits FSH production
-Inhibin from Theca & Granulosa cells, Stimulates Gonadotropes and Inhibits FSH production
Know how LH pulse frequency changes during the estrous cycle.
-During metestrus: LH pulse high frequency low amplitude
-During diestrus: less frequency higher amplitude
LH Surge before proestrus
Know how all of the main reproductive hormones change during the estrous cycle. (Long)
-Estradiol is produced from follicles on the ovary and is sent to the hypothalamus (surge center).
-Increases in estradiol send signals to decrease the FSH from the anterior.
-As FSH decreases and LH increases inhibin is produced and sent back to the anterior further reducing FSH and increasing LH.
-The amounts of estradiol continually increase until the dominant follicle is ovulated or dies.
-Progesterone is at high levels up until proestrus when it decreases to allow for ovulation.
-Ovulation occurs after luteolysis, or when progesterone starts to decrease at the end of diestrus and start of proestrus.
-Ovulation occurs at the end of estrus and also marks the start of the next cycle.
