Download Luteal Phase Corpus Luteum corpus hemorrhagicum (ovulation till

Luteal Phase
Corpus Luteum
corpus hemorrhagicum (ovulation till day 1 to 3)
o CL becomes more recognizable by day 3 to 5
production of progesterone
o size of CL corresponds with its progesterone production
luteolysis
o regression of CL
o change in structure as well as ability to secret progesterone
o the CL becomes the corpus albicans
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Corpus Luteum Formation
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in response to LH surge, granulosa and theca cells of preovulatory follicle
luteinize
basement membrane disintergrates
at ovulation the walls of the follicle collapse
theca and granulosa cells mix
basement membrane becomes the connective tissue network of CL
breakage of small blood vessels leads to the blood clot seen in the corpus
hemorrhagicum
CL structure and Function
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large luteal cells from granulosa
o contain secretory granules
 during estrous cycle contain oxytocin
 during pregnancy contain relaxin
small luteal cells from theca interna
o do not contain secretory granules
both small and large luteal cells make progesterone
increase in CL size due to
o large luteal cells increase in size (hypertrophy)
o small cells increase in number (hyperplasia)
vascularization of CL
insufficient luteal function important factor in reproductive failure
Targets of Progesterone Action
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hpothalamus
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negative feedback on GnRH amplitude and frequency
prevents behavioral estrus
stops preovulatory LH surge
uterus
endometrium
 stimulates endometrial gland secretion which supports
development of conceptus prior to implantation
o myometrium
 decreases muscle contraction (motility)
mammary gland
o stimulates development of alveoli
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Progesterone Synthesis
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Cholesterol ester is importated into the cell bound to LDL
LH via its binding to its receptor increases cAMP and PKA
PKA causes
o increase internalization of the cholesterol-LDL molecule
o activates cholesterol esterase
o increased cholesterol uptake by mitochondria
o probably a role in regulating pregnenolone conversion to progesterone in
smooth ER
Luteolysis
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uterus required
o hysterectomy prevents luteolysis
o partial hysterectomy
 ipsilateral
 prevents luteolysis
 contralateral
 no effect on luteolysis, occurs at normal time
o transplant ovary to neck
 prevents luteolysis
o uterus needed for luteolysis and must be near ovary to have effect
PGF is luteolysin
o counter current exchange between uterine vein and ovarian artery
 present in cow, ewe, sow
 important as PGF is destroyed in peripheral circulation as it
passes through the lungs
 not present in mare
PGF gets to ovary after going through the general
circulation
 mare ovary is more sensitive to PGF than other species
o sensitivity of CL to PGF
 cow, ewe only after day 5-6 of cycle
 sow not until day 12-14 of cycle
oxytocin
o produced by CL (large luteal cells)
o receptors in uterus decline after ovulation as progesterone increases
o after 10-12 days progesterone, uterine oxytocin receptors again begin to
increase
o in response to oxytocin binding to its receptor in the uterine
endometrium, PGF is released
o PGF triggers release of oxytocin from CL to intiate a positive feedback
loop
o oxytocin can also come from posterior pituitary
intracellular mechanisms of luteolysis
o ischemia (decreased blood flow to CL)
o apoptosis
 increase in intracellular calcium
 protein kinase C inhibits progesterone synthesis
the immune system
o macrophages and lymphocytes are present in luteal tissue and increase at
the time of luteolysis
 can perform phagocytosis of luteal cells
 cytokines are released and cause
 cell death
 stop progesterone production
 apoptosis
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