05 Estrous

Question 1

Estrous cycle

Answer 1

consists of a follicular phase and luteal phase with no menstruation occurring. Begins with one period of estrus and ends with the next period of estrus

Question 2

Menstrual cycle

Answer 2

consists of three phases: menses(endometrial sloughing), a proliferative phase, and a secretory phase. Only in humans and primates

Question 3

Monoestrus

Answer 3

one cycle per year. Usually prolonged since they only get one opportunity.
wolves, foxes, bears, dogs

Question 4

Polyestrus

Answer 4

have repeated estrous cycles that are uniformly distributed throughout the year
cattle, swine, rodents

Question 5

Seasonally polyestrus

Answer 5

have repeated estrous cycles but their cyclicity is limited to only part of the year and is predominantly determined by photoperiod and to a lesser degree temperature.
horses, sheep, goats, cats

Question 6

Anestrus

Answer 6

a term used to describe a time period when the female does not exhibit estrous cycles. Ovaries are generally inactive during this period. Reasons could be: seasonal, pregnancy, lactation, stress, pathology.

Question 7

Seasonal anestrus

Answer 7

time period when seasonally polyestrus animals do not cycle.

Question 8

Reproductive cyclicity is driven by the secretion of hypothalamic and ___________ hormones

Answer 8

pituitary

Question 9

Relationship between melatonin and darkness

Answer 9

More darkness-more melatonin

Less darkness-less melatonin

Question 10

In short day breeders (sheep and goat), cyclicity occurs during fall month when daylight hours decrease. Why?

Answer 10

When day length shortens in the fall there is little inhibition of the pineal gland, and more melatonin secreted. Melatonin stimulates the secretion of GnRH and promotes cyclicity. In the spring when daylight increases, less melatonin is secreted so less less GnRH is secreted.

Question 11

Short day breeder(sheep and goats)
Increased daylight
Decreased daylight

Answer 11

Inc light=dec melatonin= decrease GnRH=anestrus

Dec light=inc melatonin=increase GnRH=cycle

Question 12

Long day breeder (horses)
Increased daylight
Decreased daylight

Answer 12

Inc light=dec melatonin= increase GnRH=cycle

Dec light=inc melatonin=decrease GnRH=anestrus

Question 13

Two phases of the estrous cycle are

Answer 13

luteal phase, follicular phase

Question 14

Follicular phase

Answer 14

Dominated by estrogen. Takes up about 20% of the estrous cycle. Subdivided into proestrus and estrus

Question 15

Luteal phase

Answer 15

dominated by progesterone secreted from the corpus luteum. Lasts for about 80% of the estrous cycle. Subdivided into metaestrus and diestrus

Question 16

Proestrus

Answer 16

Begins when progesterone declines following luteolysis. During proestrus, follicles are recruited for ovulation and the female reproductive tract is preparing for estrus and mating.

Question 17

Estrus

Answer 17

Characterized by behavioral receptivity and mating. The dominant hormone is estrogen which is responsible for both receptive sexual behavior and changes in the reproductive tract. In most species ovulation occurs during estrus.

Question 18

Metestrus

Answer 18

Period of transition from ovulation to formation of functional corpus luteum. During metestrus both estrogen and progesterone are low, but progesterone increases over the first few days following ovulation as the corpus luteum matures and secretes increasing amounts of the hormone.
Female not receptive

Question 19

Diestrus

Answer 19

Maximum progesterone secretion. Last 10-14 days ends with destruction of the corpus luteum through actions of PGF2a if the female fails to become pregnant. If the female does become pregnant the corpus luteum is not destroyed and diestrus is prolonged
Female refuses male

Question 20

GnRH

Answer 20

gonadotropin releasing hormone.
Released from hypothalamus and acts on AP to stimulate release of FSH and LH.
It is inhibited by high concentration of progesterone

Question 21

FSH

Answer 21

Promotes follicular development
glycoprotein hormone secreted from the AP
stimulated by GnRH.
Inhibited by inhibin

Question 22

Estrogen

Answer 22

produced by the growing dominant follicle and peaks around the time of ovulation. Responsible for sexual receptivity to mating. Involved in both + and - feedback depending on concentration.

Question 23

While estrogen is responsible for sexual receptivity to mating it is important to note that behavioral sexual receptivity also requires the absence of ___________

Answer 23

progesterone

Question 24

Low levels of estrogen feedback __________ on pituitary (FSH) and hypothalamus (GnRH)

Answer 24

negatively

Question 25

High levels of estrogen ___GnRH and ___LH

Answer 25

Increase GnRH which increases LH leading to ovulation

Question 26

LH

Answer 26

from AP
stimulated by GnRH
inhibited by progesterone
causes ovulation

Question 27

Progesterone

Answer 27

Produced by the corpus luteum. Dominant hormone during diestrus. Essential for the maintenance of pregnancy early embryonic growth and development, preparation of the endometrium for early pregnancies and placentation. Inhibits estrus behavior even in presence of estrogen.

Question 28

Progesterone feedbacks _______ on the hypothalamus to inhibit GnRH and on the pituitary to inhibit LH secretion

Answer 28

negatively

Question 29

Prostaglandin F2a (PGF2a)

Answer 29

is released from the endometrium and is responsible for luteolysis (destruction of CL). Luteolysis is triggered in late diestrus in absence of pregnancy and allows female to return to estrus. Also causes uterine contractions.

Question 30

The follicular phase is initiated after luteolysis consequent to the decline in ____________

Answer 30

progesterone