Ovulation, Luteolysis, seasonal ovulation

recruitment

entry into gonadotropin sensitive pool

selection

ovulatory follicles emerge

dominance

final growth of ovulatory follicle(s) and inhibition of others

estradiol targets- caudal vagina

mucosa increases in thickness

estradiol targets + actions- cervix and cranial vagina

produce mucous

lubrication, flush out foreign material flowing copulation, sperm transport

estradiol targets + Actions- uterus

development of uterine glands

estradiol targets + actions- oviduct

increases secretory rate; cilia increase beat frequency

estradiol targets + actions- increased blood flow to all of reproductive tract

facilitates secretion → delivery of leukocytes to submucosa → edema of external genitalia → delivery of hormones and metabolites

spontaneous ovulators

species: farm animals and humans

regulated by events of estrous or menstrual cycle and not affected by copulation

occurs due to endogenous endocrine and neuroendocrine factors

induced (reflex) ovulators

species: rabbit, cat, ferret, and mink

copulation stimulates the surge of LH ovulation

ovulation occurs through neuroendocrine reflex

how does ovulation actually happen?

follicular fluid volume increases→ 7-fold increase in blood flow

basement membrane partially disintegrates

stigma (ovarian surface) of follicle begins to push outward & weaken

formation of corpus luteum

after ovulation, follicular wall collapses forming folds

luteinization→ transformation of follicular cells into luteal tissue

granulosa cells= large luteal cells

theca interna cells= small luteal cells

large luteal cells

20-70 micrometers

primarily undergo hypertrophy

majority of progesterone synthesis/secretion

rarely multiply after ovulation

increase in volume (hypertrophy)

contains LH receptors, but binding of LH to its receptor does not increase progesterone production from these cells

small luteal cells

less than 20 micrometers

primarily undergo hyperplasia

produce progesterone

increase in number (hyperplasia)

have LH receptors and respond to LH by increasing progesterone production

luteal phase

lasts from ovulation until regression of the corpus luteum (luteolysis)

progesterone is the primary hormone during the estrous cycle which maintains what?

maintains pregnancy

actions of progesterone

affect basal LH secretion and prevent preovulatory surge

prevents estrus

reduces myometrial tone

long day breeders

horses

short day breeders

ewes

more light leads to

less melatonin release

luteal regression (luteolysis)

cessation of function of the CL

occurs at the end of the luteal phase

the hormone responsible in domestic farm species is PGF2a from the uterus

relationship of oxytocin and PGF2a

oxytocin is released from the posterior pituitary gland

progesterone suppresses the population of oxytocin receptors in the uterus

general outline of luteolysis

1. P4 loses its ability to suppress the formulation of uterine oxytocin receptors

2. E2 binds to endometrial receptors to upregulate oxytocin receptors

3. oxytocin binds to receptors to stimulate PGF2a release

4. amongst other actions, PGF2a increases oxytocin release from CL

How does PGF2a reach the ovary?

countercurrent Exchange → uterine PGF2a is transported from the uterine vein into the ovarian artery

PGF2a is metabolized by the lungs