3B Estrous cycle phases review

Which phase is described …?

Ovarian structure: CL

Steroid hormone produced: P4

Stages: metestrus & diestrus

Luteal phase

Which phase is described …?

Ovarian structure: dominant follicle

Steroid hormone produced: estradiol (E2)

Stages: proestrus & estrus

Follicular phase

What denotes day one of the estrous cycle?

Ovulation

When does the luteal phase occur?

Ovulation to initial CL regression

(Metestrus & diestrus)

When does the follicular phase occur?

Initial CL regression to ovulation

(Proestrus & estrus)

Which estrous cycle stage is described…?

Longest stage, “opposite of estrus”

Ovarian structures: CL

Steroid hormone produced: P4

Diestrus

Which estrous cycle stage is described…?

“Prior to estrus”

Ovarian structures: regressing CL + dominant follicle

Steroid hormone produced: decreasing P4, increasing E2

Proestrus

Which estrous cycle stage is described…?

“Standing heat”

Ovarian structures: preovulatory dominant follicle

Steroid hormones produced: E2

Estrus

Which estrous cycle stage is described…?

“After estrus”

Ovarian structures: developing CL

Steroid hormones produced: increasing P4

Metestrus

What is initiated at the end of diestrus, stimulated by prostaglandin F2a?

Luteolysis

Which cells produce prostaglandin F2a?

Uterine endometrial cells (within the cell membrane)

Which cells express the receptors for prostaglandin F2a?

Only luteal cells of mature CLs

Who is prostaglandin F2a not required for luteolysis in humans, dogs, & cats?

Humans: Cl regresses unless “rescued” by hCG

Dogs/cats: CL regresses in ~2 months

Ovulation is stimulated by a dramatic increase of what hormone?

LH

Which estrous cycle stage is being described …?

Increased [E2]

• inhibits GnRH secretion from tonic center

• Inhibits FSH & LH secretion

• Stimulates inhibin secretion from granulosa cells

• Stimulates uterine blood flow, mucous secretion, & myometrial contractions

Proestrus

Which estrous cycle stage is being described …?

Increased [E2]

• inhibits GnRH secretion from tonic center

• Stimulates GnRH secretion from the surge center

• Inhibits FSH & LH secretion

• Stimulates inhibin secretion from granulosa cells

• Stimulates uterine blood flow, mucous secretion, & myometrial contractions

Estrus

Which estrous cycle stage is being described …?

Increased [P4]

• inhibits GnRH secretion from tonic & surge centers

• Inhibits FSH & LH secretion

• Stimulates uterine endometrial gland secretion, inhibits myometrial contractions

Metestrus

How does vaginal/cervical stimulation promote ovulation in induced ovulators?

1. Mechanical stimulation during copulation

2. APs travel from sensory neurons to CNS neurons

3. Afferent neurons synapse on hypothalamic neurons

4. Surge center neurons release GnRH bolus

5. LH surge

How long does the CL stay present in a cat after ovulation, regardless of pregnancy status?

60 days

What causes polyestrous species to enter anestrus?

Insufficient GnRH release from hypothalamus

How is lactational anestrus maintained in cows?

Auditory, visual, &/or olfactory stimuli associated with the dam’s own calf nursing.

In increase in day length, thus increase in light reaching retinal neurons, will ultimately do what to melatonin secretion levels?

Decrease