Estrus Cycle

Question 1

Describe the estrous cycle.

Answer 1

Period of time from one estrus to the next

Question 2

What two phases make up the estrous cycle?

Answer 2

The follicular (regression of CL to ovulation) and luteal (ovulation to regression of CL) phase

Question 3

What are the dominant structures during each phase of estrus?

Answer 3

Preovulatory follicles produce E2 during follicular phase

CL produces P4 during the luteal

Question 4

Name the four stages of the estrus cycle.

Answer 4

Proestrus, estrus, metestrus and diestrus

Question 5

What is it called when the female will arch her back for mating?

Answer 5

Lordosis

Question 6

Name each species and the length of their estrous cycle.

Answer 6

Cow-18-24 days
Sheep- 14-19 days
Sow-18-22 days
Horse-16-24 days

Question 7

Length of Estrus for each animal

Answer 7

Cow-12-19 hours
Sheep-24-36 hours
Sow-48-72 hours
Mare- 2-11 days

Question 8

What is the longest stage of the estrus cycle?

Answer 8

Diestrus at 10-14 days

Question 9

What are the different types of Anestrus?

Answer 9

Seasonal, Nutritional, Lactational, Gestational

Question 10

What makes up the tonic GnRH center?

Answer 10

ME, ARC and VMN

Question 11

What makes up the surge center?

Answer 11

PON, AHA, SCN

Question 12

What life events can pause the estrous cycle?

Answer 12

Pregnancy, Lactation, season, inadequate nutrition and environmental

Question 13

What is the difference between polyestrous and seasonally polyestrous?

Answer 13

Polestrous- Regular cycles through the year, cattle and swine

Seasonally- cycles that occur only a certain season of the year, sheep and horse

Question 14

What stages of the estrous cycle are included in the follicular phase?

Answer 14

Proestrus and estrus

Question 15

What stages of the estrous cycle are included in the luteal phase?

Answer 15

Metestrus and Diestrus

Question 16

Describe the Proestrus phase.

Answer 16

Begins: P4 declines at lueolysis
Ends: Onset of estrus
2-5 days
Characterized by a transition from P4 and E2.

Question 17

Describe Estrus.

Answer 17

Begins-When the female will stand to be mounted
End-When female no longer stands to be mounted
E2 induces the behaviors

Question 18

Describe Metestrus.

Answer 18

Begin: Ovulation
End: Formation of the CL
2-5 days

Question 19

Describe Diestrus.

Answer 19

When CL is functional and P4 is highest. 10-14 days

Question 20

What is the main reason for all anesrus?

Answer 20

Insufficient release of GnRH

Question 21

Gestational anestrus occurs when?

Answer 21

Due to elevated P4 from the CL and Placenta which decreases GnRH

Question 22

Describe Silent Ovulation

Answer 22

When the female ovulates after a phase of anestrus without estrus

Question 23

Why don’t dairy cattle experience lactational anestrus?

Answer 23

It suggests that the presence of the calf may be necessary

Question 24

Describe the nutritional anestrus.

Answer 24

absence of GNRH pulses and inactive ovaries

It will prolong lactational anestrus

Question 25

What are the four significant events that take place during follicular phase.

Answer 25

- Ovulation - Sexual Receptivity - Follicular preparation for ovulation - Gonadotropin release from the AP

Question 26

What is the appropriate stimulus for the the preovulatory to stop releasing basal levels of GnRH?

Answer 26

Its the threshold level of E2 in the absence of P4

Question 27

Why does each of the GnRH pulses occur in the tonic center?

Answer 27

Due to simultaneous depolarizations of several GnRH neurons

Question 28

What does GnRH do?

Answer 28

Stimulates the release of FSH and LH from the AP causes the growth and development of the ovarian follicles

Question 29

Describe diestrus at a hormonal level.

Answer 29

P4 is high and E2 is low

Question 30

What is the difference between spontaneous and induced ovulators?

Answer 30

Spontaneous- ovulate with regular frequency and don't require copulation. Cow, Sow, Horse, Ewe, Human Induced- Require vagina stimulation and or cervix. Rabbit, Cats, Ferret

Question 31

What is tactile stimulation?

Answer 31

associated with copulation and is converted into action potentials that go from repro to the spinal cord and finally the hypothalamus

Question 32

What is required for hormonally induced ovulation?

Answer 32

Premature or controlled luteolysis

Question 33

How can premature or controlled luteolysis be accomplished?

Answer 33

administration of PGF2a

Question 34

How can progestational compounds be administered and what accompanies it?

Answer 34

Can be placed as a small capsule in the ear, an example is norgestamet. Usually administered with a shot of E2.

Question 35

When hormonally controlling the ovulation what does E2 and norgestamet do?

Answer 35

E2-induces luteolysis | Norgestamet- Prevents estrus and ovulation

Question 36

What happens when the norgestamet is removed?

Answer 36

It mimics luteolysis and ovulation is induced

Question 37

What is MGA?

Answer 37

A progestagen that can be fed and withdraw

Question 38

When does the luteal phase last?

Answer 38

Time of ovulation-luteolysis and includes metestrus and diestrus

Question 39

When is the maximum P4 production the CL reached?

Answer 39

Diestrus

Question 40

What happens when the CL is lysed?

Answer 40

Becomes a corpus albicans

Question 41

What happens to the theca interna and grulosa cells after ovulation?

Answer 41

They become luteinized

Question 42

Why can't the horses CL be palpated?

Answer 42

Because they are on the inside of the ovary

Question 43

What does the luteal tissue consist of and where do they originate?

Answer 43

Large cells- granulosa cells | Small cells- theca interna

Question 44

What do the large luteal cells in ruminants have?

Answer 44

The have dense secretory granules and they contain oxytocin during estrus and relaxin in pregnancy

Question 45

Do small luteal cells contain granules?

Answer 45

No

Question 46

Are both large and small luteal cells steriodogenic?

Answer 46

Yes

Question 47

What are the target organs for P4?

Answer 47

Hypothalamus, uterus and mammary gland

Question 48

P4 reduces the contractions in what species?

Answer 48

Ewe, Sow, Cow

Question 49

What affect does P4 have on the mammary glands?

Answer 49

Final alveolar development

Question 50

What feedback does P4 exert on the hypothalamus? And what does it do?

Answer 50

Exerts a strong negative feedback | Reduces the frequency of basal secretion of GnRH

Question 51

What behavior does P4 inhibit?

Answer 51

Inhibits estrual behavior and provide a positive priming effect on the brain

Question 52

What characterizes Luteolsis?

Answer 52

Dramatic drop in blood levels

Question 53

What two hormones control luteolysis? And what are they produced by?

Answer 53

Oxytocin produced by the CL | PGF2a produced by the endometrium

Question 54

Uterectomy prolongs the life of what?

Answer 54

The CL

Question 55

What is responsible for luteolysis ?

Answer 55

The uterus and is must physically be near the ovary

Question 56

Describe the tranportation process of PGF2a.

Answer 56

From the uterus it is carried to the ipsilateral ovary through the vascular countercurrent exchange mechanism

Question 57

Describe the countercurrent exchange system during the lysis of the Cl.

Answer 57

Two blood vessels where blood flows in opposite directions of the adjacent vessel

Question 58

What allows for PGF2a to be delivered in high concentrations?

Answer 58

PGF2a from the endometrium enters the uterine vein by the counter-currant exchange diffuses into the uterine vein.

Question 59

How much of the PGF2a is denatured in the lungs of the cow and the sow?

Answer 59

98-99% in the cow | 40% in the sow

Question 60

What species does the countercurrent system present in?

Answer 60

Cow Sow and Ewe | Not the Mare because it doesn't metabolize PGF2a to the same extent

Question 61

Describe the PG secretion cycle from the endometrium.

Answer 61

First half of the estrus cycle is is nonexistent. | During late luteal phase it is secreted in pulses

Question 62

Describe Phagocytic cells and give some examples

Answer 62

The produce intercellular mediators of the immune response called cytokines. Examples-TNF, interleukins, interferons

Question 63

What causes a local ischemia on the the CL.

Answer 63

PGF2a

Question 64

What will happen if we inject an animal during the late luteal phase?

Answer 64

Leads to rapid release of ovarian oxytocin which leads to the secretion of PGF2a

Question 65

What is the relationship of oxytocin and PGF2a?

Answer 65

Stimulate each other in a positive feedback

Question 66

How does P4 prevent the secretion of PGF2a?

Answer 66

Formation of oxytocin receptors