Luteal Cycle Flashcards
at what stage does the preovulatory LH surge occur?
estrus
define ovulation
ovulation is a series of events that ends with
- the follicle expelling the mature cumulus-oocyte complex (among other contents)
- the begining of CL develoopment
The preovulatory LH surge directly causes 5 things…
- increase in PGE2
- increase in PGF2
- shift from E2 to P4 by dominant follicle
- breakdown between granulosal cells and oocyte
- changes on the surface epithelium
ovulation is mechanically caused by
- an increase in folliular pressure
- weakening of follicle walls
in spontaneous ovulators
ovulation occurs at regular intervals depending upon the circuation of estradiol
(ex. human, sheep, cattle, horses, pigs, most rodents)
in induced ovulators
ovulation is associated with sex
(ex. rabbits, ferrets, cats, camelids)
pathway of induced ovulation
- stimulation of sensory nerves in vagina and cervix
- impulses relayed through spinal cord to surge center
site of ovulation
in mares, the ovulation fossa
in other female animals, anywhre on the surface of the ovary
time peroid of luteal phase
ovulation to luteolysis (mestrus and diestrus in between)
3 Major Process of Luteal Phase
- luteinization (transformation of follicular cells into luteal cells after ovultion)
- synthesis and secretion (growth and development of CL due to increasing progesterone)
- luteolysis (regression of CL)
what occurs during the luteinization phase?
After ovulation…
the follicular (theca interna and granulosa) cells are transformed into the corpus luteum (luteal cells)
what occurs during luteolysis?
- regression/damage of Corpus Luteum
- dramatic drop in blood progesterone
Corpus Hemorrhagicum is defined as
the process in which the corpus luteum forms
How does Luteinization mechanically occur?
ovulation causes the follicular structure to collaspe which mixes theca and granulosa cells and transforms them into luteal cells
large luteal cells (LLC)
- originate from granulosa cells
- secrete progesterone and oxytocin
small luteal cells (SLC)
orginate from the theca interna cells and secrete progesterone
the types of CL differ in
their lifespan and steroidogenic output
name the types of CL’s
- cycle (CL spurium)
- pseudopregnancy
- pregnancy (CL verum)
- lactation
the CL of pregnancy is
only found in mammalian species
the CL of the cycle
doesn’t exist in induced ovulatiors
the CL of pseudopregnacy
doesn’t form in primates
the CL of lactation
only occurs in induced ovulators
in rodents
all four types of CL can be found
LH stimulates…
Progesterone synthesis
progesterone is derived from
chlolesterol
genomic or slow progesterone response
causes uterine gland secretion
Non-genomic or fast progesterone response causes
ion channel inhibition to reduce myometrial contractions
Functions of Progesterone
- prepares endometrium for implantation
- maitence of pregnancy by inhibiting myometrium motility
- (along with estrogens) induces behavioral estrus
- inhibits estrus and the ovulatory surge of LH at high levels
- develops secretory tissue (alveoli) of the mammary glands
Luteolysis is triggered by ___ hormone
PGF2delta which is secreted by the uterine endomtrium in farm animals (ovary in primates)
effect of urerextomy on ewe
- with a total uterectomy, the CL lifespan is similar to a normal gestation length
- a partial uterectomy contralateral to the CL will lead to a lifespand similar to a normal cycle
- a partial uterectomy ipsilateral to the CL will cause the CL to have a lifespan longer than normal
transport of PGF2a im cow, ewe, and sow
- it is secreted by the uterus and transported directly to the ovary, which avoids diluting PGF2a in systemic circulation
- PGF2a is then metabolized in the lungs and quickly eliminated through breathing
in mares, PGF2a
IS released into systemic circulation, meaning that it isn’t metabolized as quickly and the CL is more sensitive to it (in comparison to ewes, cows, etc)
PGF2a is derived from
pnospholipids, meaning it binds to receptors on the outer mitochondrial membrane
change in PGF-M during late diestrus and proestrus
increases
During the Early Luteal Phase
- progesterone blocks oxytocin receptors in the endometrium which prevents the secretion of PGF2a
- causes continous secretion of progesterone by CL
During the late luteal phase
- progesterone loses its ability to block oxytocin receptors
- therefore oxytocin initiates the synthesis of PGF2a in the endometrium
- PGF2a acts on CL to release luteal oxytocin which causes endometrial oxytocin receptors to amplify the relese of PGF2a from the endometrium
- closed loop system is formed, both oxytocin and PGF2a are produced to inhibit progesterone secretion until the completion of luteolysis
The Loss of Progesterone Secretion from Luteal Cells Occurs Because…
- PGF2a binds to receptors on membrane of luteal cells
- influx of Ca+ occurs which causes an apoptotic effect
- Activation of PKC that ultimetly inhibits progesterone synthesis
luteoysis and cyclicity
luteolysis is the driving force for continued cyclicity
hormone that destroys the CL
PGF2a
