Follicular Phase Flashcards
Follicular Phase
Proestrus
oestrus
Follicles dominant structure
Lutelolysis
Marks onset of follicular phase
-Causes CL to become non functional
=no progesterone
=no negative feedback =increasd GnRH (LH and FSH) and promotes eostradoil release too
4 phases of oocyte maturation
Mitotic and meiotic divisions occur prenatally
Nuclear arrest of primary oocyte
Cytoplasmic growth
Resume meiosis at puberty
LH surge resumes meiosis
Nucleus of oocyte migrates towards the periphery of the plasma membrane
First polar body fromed just before ovulation
4 major events of follicular phase
- Increased Gonadotrophin release from anterior pituitary
- Follicle growth, maturation and preparation for ovulation
- Sexual receptivity and behaviour
- Ovulation
Steps leading to Preovulatory LH surge
Decrease P4 from CL Increased GnRH Inc FSH and LH Proestrual follicular development Inc Estradiol to threshold Preovulatory LH surge Ovulation
What control GnRH release
Tonic and surge center (LH surge)
Increased level of oestradiol
Has positive feedback on hypothalamus = secretion of large GnRH leading to preovulatory LH surge
Increased progesterone
during dioestrus creates negative feedback on preovulatory center = decreased gnrh
Dynamics of antral follicles
Always follicules are being secreted, not just during follicular phase due to basal FSH and LH
- Recruitment (emergence)
- Selection
- Dominance
- Atresia (degeneration)
Recruitment
Cohort of small anral follicles begin to grow and secrete eatradoil
High FSH
Low LH
Low Inhibin
Low Estrogen
Selection
Some undergo atresia, some selected and become dominant
Low FSH
Mod LH
Low Inhibin
Mod oestrogen
Dominance
Continue to grow and secrete more estradiol
Low FSH
High LH
High inhibin
High oestrogen
Antral follicle inhibits what?
Secretes inhibin which keeps secretion FSH low
Folliculogenesis
Continuous atresia (destruction of follicles)
First wave
Follicles arent exposed to appropriate endocrine conditions for continued development and undergo atresia, progesterone is either increasing or at its highest
luteolysis
CL regression, foolicles if second wave become preovulator follicle
Where does LH Bind
Theca interna cell of developing follicle
Converts colesterone to testosterone
This si secreted out and enters granulosa cell
Granulosa Cells
has FSH receptors
Converts testosterone to estradiol
2 cell, 2 gonadotrophin pathway
Conversion of cholesterone to testosterone in theca interna cell
Testosterone conversion to estradoil in Granulosa cell
continues until levels of eostrogen increase to threshold to induce preovulatory LH surge
=Reptoductive tract effects, behaviour (lordosis)
Effects of Eostradoil on Repro tract
Increased blood flow
genital swelling
Leukocytosis
Increased mucosal secretion
Initiation of uterine gland growth
Elevated myometrial tone
How is ovulation brought about
Elevated blood flow
Breakdown of connective tissue
Ovarian contractions
Post LH surge affect on theca interna cells
Produces progesterone not testosterone
LH surge causes:
e2 is synthesised and secreted by the ovary
Ovulation causes
DOminant follicle produces p4 before ovulation. this stimulate enzymes to breakdown connective tissue (collagenase)
Volumes of follicular fluid increasesand puts the “stigma “ (apex of follicle) under pressure
Prostaglandin causes smooth muslce contractions to increase pressure further
Types of ovulators
Spontaneous
- Ovulate with regular frequence and dont need copulation
- In response to hormones (cows, ewe, sow, mare, woman)
Reflex
- Required stimulation of vagina/cervix
- Rabbits, ferrets, camels
Induced ovulation
Neuroendocrine reflex
Copulation stimulates sensory nerves in vagina
Impulses relayed to spinal cord
Impulses relayed to surge center in hypothalamus
GnRH released
Finally LH released and ovulation occurs
Zona Pellucida
Primary ocytes accumulate in large volumes around the ctyoplams
