Exam 2: Lecture 23: Ovulation, Luteinization, And Leutolysis Flashcards
Ovulation is ___ dependent
LH surge
How long does ovulation last?
-In most species, 24 hour event except in Mare it is 3-5 day elevation
-The bitch ovulates 2-3 days AFTER LH surge
When do most species ovulate?
-During estrus (except cow)
What happens to the ovulated follicle during ovulation?
-Collapses
-Fills with blood
-Becomes Corpus Hemorrhagicum (CH)
___ is critically important in ovulation b/c it sets in motions a series of biochemical events that lead to ovulation
Preovulatory LH surge
______ is a complicated process that involves purposeful destruction of follicular tissue
Ovulation
What brings on ovulation?
-Elevated blood flow
-Breakdown of connective tissue
-Ovarian contractions
What do induced ovulators require for ovulation to occur?
-Require stimulation of vagina, cervix, and/or uterus
What animals are induced ovulators?
-Cats
-Rabbits
-Minks
-Ferrets
-Giant Fruit Bats
-13-lined Ground Squirrel (Chipmunks)
-Sumatran Rhinos
-Camelids
What else do camelids require in addition to stimulation for ovulation?
-Also require a substance in seminal plasma for ovulation
-Ovulation inducing factor (OIF)
-Beta-Nerve growth factor (B-NGF)
Cats have a ___% ovulation rate if they are mated once
50%
What are the steps of induced ovulators?
- Copulation stimulates sensory nerves in vagina & cervix
- Impulses are then relayed to spinal cord
- Impulses are then relayed to surge center in hypothalamus
What is the Luteal Phase?
-Metestrus & Diestrus
What are the 3 main events of the luteal phase?
- Luteinization of follicular cells to luteal cells
- Growth & development of CL & production of Progesterone
- Luteolysis
When does the luteal phase begin?
-Immediately after ovulation
What happens during early luteal phase?
-CL develops (Luteinization) & progesterone increases
What happens during the mid luteal phase (diestrus)?
-CL is full functional & progesterone plateaus
What happens during the last 2-3 days of the luteal phase?
-Destruction of CL occurs (luteolysis) & luteal phase terminates & proestrus is initiated (follicular phase is resumed)
The corpus luteum originated from
-An ovulatory follicle
____ begins to breakdown as ovulation nears in the formation of the CL
Basement membrane
What happens in corpus hemorrhagicum?
-Small blood vessels rupture and the Theca and Granulosa cells mix
What is the “Functional Corpus Luteum (CL)”?
-Mixture of large luteal cells (LLC) originating from Granulosa cells & Small luteal cells (SLC) originating from Theca cells
In some cases, there is remnant of follicular antrum that forms small cavity in center of CL
What is luteinization?
-Transformation of Theca International & Granulosa cells (that produced Estrogen prior to ovulation) to Luteal cells producing Progesterone
Where does the corpus luteum originate and what does it produce?
-Originated from ovulatory follicle
-Both large & small luteal cells produce progesterone
-Other hormones produced by the CL include Oxytocin & Relaxin
What is shown here? (cow)
-Corpora Hemorrhagicum (CH)
What is shown here? (Cow)
-Developing Corpus Luteum
What is shown here? (Cow)
-Corpus Luteum during peak luteal phase & peak progesterone production
What is shown here? (Cow)
-Regressing Corpus Luteum
What is shown here? (Sow)
-Developing Corpora Lutea
What is shown here? (Sow)
-Corpora Lutea during high secretory activity
What is shown here? (Sow)
-Regressing Corpora Lutea
What is shown here? (Mare)
-Corpora Hemorrhagicum (CH)
What is shown here? (Mare)
-Developing Corpus Luteum does not protrude from the surface
What is shown here? (Mare)
-Inner tissue mass of the Corpus Luteum
-(Some have a cavity & some do not)
What is shown here? (Mare)
-Regressing Corpus Luteum
What is the physiologic effect of Progesterone on the hypothalamus?
Negative feedback
-Reduces basal GnRH amplitude & frequency
-Prevents behavioral estrus
-Stops preovulatory LH surge
What is the physiologic effect of Progesterone on the anterior pituitary?
-Negative feedback
What is the physiologic effect of Progesterone on the Uterus?
-Positive influence on uterine glands to secrete “uterine milk” for potential conceptus
-Reduces myometrial tone (except Mare)
What is the physiologic effect of Progesterone on the mammary glands?
-Prior to parturition causes final alveolar development
What is luteolysis?
-Destruction of the CL
-Essential in order to return to new follicular phase (disintegration of the CL, dramatic drop in blood progesterone)
What is the luteolytic agent in domestic animals?
-PGF2a
What are sources of PGF2a?
-Uterine endometrium in domestic animals is the MAJOR source
-Dog uterus appears not to be involved in luteolysis
-Human PGF2a is made by the ovaries
What happens during luteolysis?
-Cessation of progesterone secretion
-Structural regression to form a corpus albicans
-Removal of negative feedback by progesterone upon GnRH secretion resulting in new follicular phase
What is the pathway to luteolysis?
(Varies by species)
-Local countercurrent exchange of PGF2a from ipsilateral uterine vein & ovarian artery in ruminants
-Systemic pathway in the mare
-Combination of local & systemic in sow
What is the mechanism of luteolysis in ruminants?
-Vascular countercurrent exchange mechanism
-Low molecular weight substances in high concentrations in one vessel diffuse into adjacent vessel of lower concentration
-Allows PFG2a secreted by uterus to be transported directly to ovary & CL w/out dilution by systemic circulation
-Portion of PGF2a transported directly from utero-ovarian vein into ovarian artery where it has direct lytic effect on the CL
What is the mechanism of luteolysis in mares?
-Systemic pathway only
-CL is more sensitive to PGF2a
-PGF2a is metabolized less rapidly (low 1st pass dilution rate)
What is the mechanism of luteolysis in the sow?
-Systemic & countercurrent exchange pathways
-Medium 1st pass dilution rate (~40%)
-Corpora lutea are not responsive to pGF2a until at least Day 12 post ovulation
____ causes luteolysis during about 60% of the Estrous cycle in most species
Exogenous PGF2a
Luteolysis is most potent after day ___ post ovulation, therefore almost always causes luteolysis if administered after this time
Day 5
