Estrous Cycle

Question 1

Follicular phase (proestrus, estrus)

Answer 1

-Period from the regression of the CL to ovulation
-about 20% of estrous

Question 2

Luteal phase (metestrus, diestrus)

Answer 2

-Period from ovulation to CL regression
-80% of estrous

Question 3

Atresia

Answer 3

-Degeneration of oocytes
-Not ovulated

Question 4

Follicle recruitment

Answer 4

-Small follicles
-High FSH
-Low LH

Question 5

Follicle selection

Answer 5

-Decrease of FSH
-Increase in LH
-Atresia of some follicles
-Few follicles proceed

Question 6

Follicle dominance

Answer 6

-One (sometimes two) follicle dominates
-All others atresia
-high LH
-low FSH
-inhibin being produced: Limit FSH

Question 7

Metestrus

Answer 7

-First phase
-Corpus Luteum is developing
-Increasing progesterone concentrations

Question 8

Diestrus

Answer 8

-Second phase
-Maximum progesterone concentrations

Question 9

Proestrus

Answer 9

-Third phase
-Progesterone starts to decrease
-Goes until signs of estrus show

Question 10

Estrus

Answer 10

Period of sexual receptivity (heat)

Question 11

Estrus vs estrous

Answer 11

-Estrus: Heat
-Estrous: Cycle that females experience

Question 12

Anestrus/anestrous

Answer 12

-Without cyclicity
-Ovaries relatively inactive
-Not present: Ovulatory follicles and Corpora lutea

Question 13

Polyestrous

Answer 13

-Uniform distribution of estrous cycles
-Throughout the year

Question 14

Seasonally Polyestrous

Answer 14

-Clusters of estrous cycles
-Occur during certain season of the year

Question 15

Monoestrous

Answer 15

Only one cycle per year

Question 16

Know the 2-cell, 2-gonadotropin model of estradiol synthesis. (Long)

Answer 16

1. GnRH: Targets gonadotropes (LH, FSH) and Hypothalamus
2. LH & FSH: anterior pituitary
3. LH: Targets LHr (Theca cell)
4. Cholesterol: Converted to Pregnenolone (P450scc)
5. Pregnenolone: Converted to Progesterone (3BHSD) and Converted to Androstenedione (17a-hydroxylase)
6. Androstenedione:
   ~Converted to estradiol 17-B: P450 Aromatase (Granulosa cell) and Triggered by FSH
7. StARprotein: Transport protein, Moves cholesterol
   Into inner mitochondrial membrane

Question 17

Roles/functions LH

Answer 17

-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.

Question 18

Roles/functions FSH

Answer 18

-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

Question 19

Roles/functions Estradiol

Answer 19

-Produced by follicles: On ovary
-Sent to the hypothalamus: Surge center, Decrease FSH (Anterior Pituitary, Kills competition), Increase LH

Question 20

Roles/functions Progesterone

Answer 20

-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

Question 21

Know the characteristics of a follicular wave.

Answer 21

-Recruitment
-Selection
-Dominance

Question 22

Recruitment

Answer 22

-Transient wave of FSH incites recruitment of follicular cohort
-Cohort (group of follicles) of chosen initially
-Tertiary follicles

Question 23

Selection

Answer 23

-Some atresia
-Some develop LHr on granulosa: These are selected

Question 24

Dominance

Answer 24

-Dominant follicle emerges: Continued growth to preovulatory size
-Achieved at time of luteolysis: Ovulation

Question 25

Know how the ovarian structures and hypothalamus/pituitary communicate with each other to cause recruitment, selection & dominance.

Answer 25

-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

Question 26

Know how LH pulse frequency changes during the estrous cycle.

Answer 26

-During metestrus: LH pulse high frequency low amplitude
-During diestrus: less frequency higher amplitude
LH Surge before proestrus

Question 27

Know how all of the main reproductive hormones change during the estrous cycle. (Long)

Answer 27

-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.