Lecture 71: Female Cyclicity

Question 1

What is the difference between estrUS and estrOUS?

Answer 1

EstrUS: behavioral heat
EstrOUS: The whole 28-day cycle in females

Question 2

What is anestrus?

Answer 2

Period of time when the female is not cycling

Question 3

What is estrual?

Answer 3

Used to identify a condition related to estrus

Question 4

Name the three types of estrous cycles and give a brief description of each

Answer 4

1) Polyestrus: have a uniform distribution of estrous cycles throughout the entire year (Cattle, swine, rodents)

2) Seasonally Polyestrus: Have “clusters” of estrous cycles that occur only during a certain season of the year
- Short day breeders: breed as the day length is decreasing in the fall- sheep, goats, deer, elk
- Long-day breeders: breed as the day length is increasing- mares

3) Monestrus: Have one cycle per year- dogs, wolves, foxes, bears (dogs typically have three cycles per 2 years, but are classified as monestrus)

Question 5

What are the two MAJOR phases of the estrous cycle? What are the dominating structures and hormones during each phase?

Answer 5

Follicular Phase: primary structure is a primary ovarian follicle, dominant hormone is Estradiol
- It is the period from CL regression to ovulaiton

Luteal phase: primary structure is the corpus luteum, dominant hormone is progesterone
- it is the period of time from ovulation to CL regression

Question 6

Briefly describe the proestrus stage of the estrous cycle

Answer 6

Proestrus begins when progesterone declines as a result of luteolysis and ends at the onset of estrus
- 2-5 days depending on species
- characterized by major endocrine transition (progesterone to estradiol)

Question 7

Describe the estrus stage of the estrous cycle

Answer 7

It is the period of female sexual receptivity (“standing heat”)
- characterized by visible behavioral symptoms so often the most recognizable stage
- peak estradiol secretion

Question 8

Describe the metestrus phase of the estrous cycle

Answer 8

Period of corpus luteum formation (luteinization)
- beginning of progesterone secretion
- transition from estradiol dominance to progesterone dominance

Question 9

Describe the diestrus phase of the estrous cycle

Answer 9

Sustained secretion of high levels of progesterone from the mature CL(s)
- longest stage of the estrous cycle (2/3 of the time)
- ends with luteolysis

Question 10

What domestic species does not have a lactational anestrus?

Answer 10

Cats

Question 11

What are some causes of anestrus

Answer 11

Pregnancy
Lactation (not cats)
Presence of offspring
Season (photoperiod)
Stress
Pathology

Question 12

What is gestational anestrus?

Answer 12

Normal condition brought about by inhibition of GnRH by progesterone during pregnancy
** Should ALWAYS be on a differential list for anestrus

Question 13

What does seasonal anestrus enable an animal to do?

Answer 13

• Carry the developing fetus during a favorable time
• Give birth during an advantageous time for newborn

Question 14

Define folliculogenesis

Answer 14

Defined as the process whereby immature follicles develop into more advanced follicles and become candidates for ovulation

Question 15

The follicular phase consists of which two phases?

Answer 15

Proestrus and Estrus

Question 16

What are the four significant events of the follicular phase?

Answer 16

1) Gonadotropin released from the anterior lobe of the pituitary
2) Follicular preparation for ovulation
3) Sexual receptivity
4) Ovulation (LH)

Question 17

Estrogen is the dominant hormone during the follicular phase of the cycle. What does it control?

Answer 17

Changes in the repro tract
Behavioral changes
Controls the onset of the preovulatory LH surge

Question 18

What role does the tonic center of the hypothalamus play in the follicular phase?

Answer 18

Releases small amplitude pulses of GnRH that stimulate release of FSH (mostly) and LH (small amount) from the anterior pituitary

Gonadotropins cause the growth and development of follicles on the ovaries

The follicles produce estrogen

Question 19

What role does the surge center of the hypothalamus play in the follicular phase?

Answer 19

Responds in a positive feedback fashion to the increasing levels of estrogen in the absence of progesterone

This positive feedback of estrogen on the hypothalamus causes a release of a LARGE quantity of GnRH

This large dumping of GnRH causes the release of the LH surge, resulting in ovulation

Question 20

Describe the hormone profile of the follicular phase

Answer 20

Declining progesterone: regression of the previous CL
Increasing estrogen: growing follicles
Increased FSH: recruits the next wave of follicles
Surge release of LH: low progesterone and high estrogen