Estrus Cycle Flashcards
Describe the estrous cycle.
Period of time from one estrus to the next
What two phases make up the estrous cycle?
The follicular (regression of CL to ovulation) and luteal (ovulation to regression of CL) phase
What are the dominant structures during each phase of estrus?
Preovulatory follicles produce E2 during follicular phase
CL produces P4 during the luteal
Name the four stages of the estrus cycle.
Proestrus, estrus, metestrus and diestrus
What is it called when the female will arch her back for mating?
Lordosis
Name each species and the length of their estrous cycle.
Cow-18-24 days
Sheep- 14-19 days
Sow-18-22 days
Horse-16-24 days
Length of Estrus for each animal
Cow-12-19 hours
Sheep-24-36 hours
Sow-48-72 hours
Mare- 2-11 days
What is the longest stage of the estrus cycle?
Diestrus at 10-14 days
What are the different types of Anestrus?
Seasonal, Nutritional, Lactational, Gestational
What makes up the tonic GnRH center?
ME, ARC and VMN
What makes up the surge center?
PON, AHA, SCN
What life events can pause the estrous cycle?
Pregnancy, Lactation, season, inadequate nutrition and environmental
What is the difference between polyestrous and seasonally polyestrous?
Polestrous- Regular cycles through the year, cattle and swine
Seasonally- cycles that occur only a certain season of the year, sheep and horse
What stages of the estrous cycle are included in the follicular phase?
Proestrus and estrus
What stages of the estrous cycle are included in the luteal phase?
Metestrus and Diestrus
Describe the Proestrus phase.
Begins: P4 declines at lueolysis
Ends: Onset of estrus
2-5 days
Characterized by a transition from P4 and E2.
Describe Estrus.
Begins-When the female will stand to be mounted
End-When female no longer stands to be mounted
E2 induces the behaviors
Describe Metestrus.
Begin: Ovulation
End: Formation of the CL
2-5 days
Describe Diestrus.
When CL is functional and P4 is highest. 10-14 days
What is the main reason for all anesrus?
Insufficient release of GnRH
Gestational anestrus occurs when?
Due to elevated P4 from the CL and Placenta which decreases GnRH
Describe Silent Ovulation
When the female ovulates after a phase of anestrus without estrus
Why don’t dairy cattle experience lactational anestrus?
It suggests that the presence of the calf may be necessary
Describe the nutritional anestrus.
absence of GNRH pulses and inactive ovaries
It will prolong lactational anestrus
What are the four significant events that take place during follicular phase.
- Ovulation
- Sexual Receptivity
- Follicular preparation for ovulation
- Gonadotropin release from the AP
What is the appropriate stimulus for the the preovulatory to stop releasing basal levels of GnRH?
Its the threshold level of E2 in the absence of P4
Why does each of the GnRH pulses occur in the tonic center?
Due to simultaneous depolarizations of several GnRH neurons
What does GnRH do?
Stimulates the release of FSH and LH from the AP causes the growth and development of the ovarian follicles
Describe diestrus at a hormonal level.
P4 is high and E2 is low
What is the difference between spontaneous and induced ovulators?
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
What is tactile stimulation?
associated with copulation and is converted into action potentials that go from repro to the spinal cord and finally the hypothalamus
What is required for hormonally induced ovulation?
Premature or controlled luteolysis
How can premature or controlled luteolysis be accomplished?
administration of PGF2a
How can progestational compounds be administered and what accompanies it?
Can be placed as a small capsule in the ear, an example is norgestamet.
Usually administered with a shot of E2.
When hormonally controlling the ovulation what does E2 and norgestamet do?
E2-induces luteolysis
Norgestamet- Prevents estrus and ovulation
What happens when the norgestamet is removed?
It mimics luteolysis and ovulation is induced
What is MGA?
A progestagen that can be fed and withdraw
When does the luteal phase last?
Time of ovulation-luteolysis and includes metestrus and diestrus
When is the maximum P4 production the CL reached?
Diestrus
What happens when the CL is lysed?
Becomes a corpus albicans
What happens to the theca interna and grulosa cells after ovulation?
They become luteinized
Why can’t the horses CL be palpated?
Because they are on the inside of the ovary
What does the luteal tissue consist of and where do they originate?
Large cells- granulosa cells
Small cells- theca interna
What do the large luteal cells in ruminants have?
The have dense secretory granules and they contain oxytocin during estrus and relaxin in pregnancy
Do small luteal cells contain granules?
No
Are both large and small luteal cells steriodogenic?
Yes
What are the target organs for P4?
Hypothalamus, uterus and mammary gland
P4 reduces the contractions in what species?
Ewe, Sow, Cow
What affect does P4 have on the mammary glands?
Final alveolar development
What feedback does P4 exert on the hypothalamus? And what does it do?
Exerts a strong negative feedback
Reduces the frequency of basal secretion of GnRH
What behavior does P4 inhibit?
Inhibits estrual behavior and provide a positive priming effect on the brain
What characterizes Luteolsis?
Dramatic drop in blood levels
What two hormones control luteolysis? And what are they produced by?
Oxytocin produced by the CL
PGF2a produced by the endometrium
Uterectomy prolongs the life of what?
The CL
What is responsible for luteolysis ?
The uterus and is must physically be near the ovary
Describe the tranportation process of PGF2a.
From the uterus it is carried to the ipsilateral ovary through the vascular countercurrent exchange mechanism
Describe the countercurrent exchange system during the lysis of the Cl.
Two blood vessels where blood flows in opposite directions of the adjacent vessel
What allows for PGF2a to be delivered in high concentrations?
PGF2a from the endometrium enters the uterine vein by the counter-currant exchange diffuses into the uterine vein.
How much of the PGF2a is denatured in the lungs of the cow and the sow?
98-99% in the cow
40% in the sow
What species does the countercurrent system present in?
Cow Sow and Ewe
Not the Mare because it doesn’t metabolize PGF2a to the same extent
Describe the PG secretion cycle from the endometrium.
First half of the estrus cycle is is nonexistent.
During late luteal phase it is secreted in pulses
Describe Phagocytic cells and give some examples
The produce intercellular mediators of the immune response called cytokines. Examples-TNF, interleukins, interferons
What causes a local ischemia on the the CL.
PGF2a
What will happen if we inject an animal during the late luteal phase?
Leads to rapid release of ovarian oxytocin which leads to the secretion of PGF2a
What is the relationship of oxytocin and PGF2a?
Stimulate each other in a positive feedback
How does P4 prevent the secretion of PGF2a?
Formation of oxytocin receptors
