Luteal Phase Lecture Notes Flashcards
What is ovulation?
A series of events that culminate in the evacuation of antral contents of a follicle including, its mature cumulus-oocyte complex and the initiation of development of a corpus luteum
What are the two classifications based on ovulation?
Spontaneous ovulators: ovulation occurs at regular intervals and depends upon the circulating estradiol (Human, sheep, cattle, horse, pigs, and most rodents)
Induced/Reflex ovulators: ovulation is associated with coitus (rabbits, ferrets, cats, and camelids)
What are the steps in the pathway of induced ovulation?
- Copulation stimulates sensory nerves in the vagina and cervix
- Impulses are then relayed to the spinal cord
- Impulses are then relayed to the surge center in the hypothalamus
- The hypothalamus causes an LH surge which induces ovulation
What is the site of ovulation in a mare vs. in all other female animals?
Mare: ovulation fossa
All other species: anywhere. on the surface of the ovary
What are the stages in the luteal phase?
Metestrus and diestrus
What is the dominant ovarian structure in the luteal phase?
Corpus luteum
What is the dominant hormone in the luteal phase?
Progesterone
What are the 3 major processes of the luteal phase?
- Luteinization: transformation of follicular cells into luteal cells after ovulation
- Synthesis and secretion: growth and development of the corpus luteum accompanied by increasing quantities of progesterone
- Luteolysis: regression of the corpus luteum
What hormone is luteinization regulated by?
LH
What is the difference between large luteal cells (LLC) and small luteal cells (SLC)?
LLC originate from granulosa cells and secrete progesterone and oxytocin.
SLC originate from the cells of the theca interna and secrete progesterone
What are the four types of corpus luteum found in mammals (differing in lifespan and steroidogenic output)?
1) Cycle (CL spurium): does not exist in induced ovulators
2) Pseudopregnancy: does not form in primates
3) Pregnancy (CL verum): present in all mammalian species
4) Lactation: only in species that ovulate after parturition
What are the steps in LH stimulating progesterone synthesis?
- cholesterol uptake
- LH binds to its receptor
- LH/LHR signaling pathway activation
- cAMP formation
- Activation of PKA
- mitochondrial enzymes are responsible for converting cholesterol to pregnenolone (PREG)
- PREG leaves mitochondria and is converted to progesterone (PROG) in the smooth ER
What are the two mechanisms of progesterone action?
Genomic or slow response: uterine gland secretion
Non-genomic or fast response: ion channel inhibition to reduce myometrial contractions
What are the functions of progesterone?
Prepares the endometrium for implantation by increasing activity of secretory glands in the endometrium.
Maintenance of pregnancy by inhibiting the motility of the myometrium.
Acts synergistically with estrogens to induce behavioral estrus.
Inhibits estrus and the ovulatory surge of LH at high levels.
Develops the secretory tissue (alveoli) of the mammary glands.
What is luteolysis?
The process whereby the corpus luteum undergoes irreversible degeneration characterized by a dramatic drop in blood concentration of progesterone.
What is PGF2alpha?
luteolytic agent secreted by the uterine endometrium (farm animals) and by the ovary (primates)
Which part of the uterus affects corpus luteum lifespan?
The part ipsilateral to the CL
In which species is PGF2alpha transported directly to the ovary? In which species does it travel through systemic circulation?
Direct to ovary: cow, ewe, sow
Systemic circulation: mare
