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Reproductive Cyclicity - The Luteal Phase - Coggle Diagram
Reproductive Cyclicity - The Luteal Phase
luteal phase
lasts from ovulation until luteolysis of the corpus luteaum (CL) which is near the end of the estrous cycle
includes metestrus
includes diestrus
consists of
luteolysis
synthesis and secretion of large quantities of progesterone
luteinization (formation of CL)
after ovulation the theca interna and granulosal cell of follicle undergo a dramatic transfermation
corpus hemorrhagicum
when follicle ruptures at ovulation
seen from the time of ovulation until about day 1 to 3 of the estrous cycle
corpus luteum
vigor depends on
number of luteal cells
degree to which the CL becomes vascularized
progesterone synthesis requires cholesterol and LH
pressence of basal (tonic) LH and cholesterol is necessary for progesterone to be secretedby luteal cell
progesterone is a major importance in the endocrine control of reproduction because it exerts a strong negative feedback on the hypothalamus
progesterone is an inhibitor because it
reduces myometrial tone (except in the mare)
stops the pre ovulatory LH surge
prevents behavioral estrus
reduces GnRH pulse frequency
ovariectomized (removal of ovaries)
Lysis of the corpus luteum must occur before the female can enter the follicular phase
luteolysis (loss of progeterone secretion by the CL followed by loss of luteal tissue mass)
process whereby the corpus luteum undergoes irreversible degeneration characterized by a dramatic drop of blood concentrations of progesterone
uterectomy (removal of the uterus)
uterus is required for successful luteolysis in many species
ipsilateral (on the same side) the corpus luteum is removed, the life-span of the corpus luteum is almost twice as long as the normal cycle
contralateral (opposite side) uterine horn is removed, there is little, if any effect on the effect on the life span of the corpus luteum
vascular countercurrent transport system ensures that PGF(2alpha) will reach the ovary in sufficient quantities to cause luteolysis in the ewe, cow and sow
what stimulates PGF(2alpha) during the late luteal phase?
progesterone
large luteal cells synthesize and secrete oxytocin
luteolysis results in
structural regression to form a corpus albicans
removal of negative feedback by progesterone upon. GnRH secretion resulting in a new follicular phase
cessation of progeterone secretion
immune system may be involved in regression of the corpus luteum
immune cells are present in the corpus luteum at the time of luteolysis, cells are capable of performing phagocytosis
lymphocytes secret cytokines, which are non-antibody proteins secreted by a variety of immune cells that activate macrophages that then phagocytize damaged dead luteal cells and cellular debris
cell death:
apoptosis
phenomenon know as "programmed cell death" its normal for cells throughout the body to die on a daily basis
done biochemical process
necrosis (by pathologic damage)
luteolysis in women is an intra ovarian event. Uterus is not required
uterectomy in the woman does not influence ovarian cyclicity
normal pattern of folliculogenesis, luteal development and luteolysis occurs in a rhythmic fashion about every 28 days after removal of the uterus
luteolusos is thought to be a local effect and therefore only small amounts of PFG(2alpha) are required to lyse the CL
administration of progesterone results in manipulation of estrous cycle
exogenous progesterone suppresses estrus and ovulation
when exogenous progesterone is removed or withdrawn, the animal will enter proestrus and estrus within two to three days after progesterone removal
intravaginal progestrone is effective at synchronizing estrus in cattle
CIDR is inserted into the vagina of the cow/heifer and remains there for 7 days
altrenogest is administed by placing hte appropriate dose on the posterior dorsal surface of the mares tongue or is applied to the grain ration
given daily for 15 consecutive days
exogenous prostaglandin F(2alpha) is a potent luteolysin and can synchronize estrus
synchronizes ovulation: ovsynch
when GnRH and PGF(2alpha) are used together in the proper timed-sequence, visual detection of estrus can be eliminated and timed artificial insemination(TAI) can vbe performed
basic strategy steps
cow can then be inseminated without detection of estrus 16 hours after the second GnRH injection
second injection of GnRH 48 hours later causes the cow to ovulate
an injection of PGF (2alpha) seven days after GnRH causes luteolysis and the cow will enter the follicular phase
GnRH us ubjected into cows that are eligible to be inseminated
if there is a dominant follicle on the ovary the cow will ovulate in response to GnRH.
A CL will form
if the cow does not have a dominant follucle, GnRH will promote continued follicular growth.
ther is a CL present from the previous ovulation
help minimize problems, a strategy has been develped called Presynch
program begins 26 day to the first GnRH is injected