M6(7) Correlation b/w Anterior Pituitary and Ovarian Cycle, Uterine Cycle

Anterior Pituitary and Ovarian Cycle Interaction

1. Anterior Pituitary Starts Follicle Growth

2. Rising Estrogen

3. High Estrogen

4. LH surge

5. Corpus Luteum Shutdown

6. If No Pregnancy

Anterior Pituitary Starts Follicle Growth

The anterior pituitary (stimulated by GnRH from FSH and LH)

• Releases FSH and LH

Ovarian Follicle Effect:

• FSH → granulosa cells

  • stimulates follicle growth

  • produces estrogen

• LH → theca cells

  • produces androgens

  • granulosa cells convert these → estrogen

follicles grow → vesicular (antral) follicles form

Rising Estrogen

• Estrogen:

  • inhibit hypothalamus + pituitary

  • ↓ FSH

Ovarian Follicle Effect:

• only the dominant follicle survives

• others undergo atresia

High Estrogen

When estrogens reach a critical threshold

• feedback flips to positive

• stimulates hypothalamus + pituitary

→ massive LH surge

LH Surge

• LH causes:

  • completion of meiosis I

  • follicle rupture → ovulation

  • formation of corpus luteum

Ovarian Follicle Effect:

• follicle → corpus luteum (major shift in tissue function)

Corpus Luteum Shutdown

Corpus Luteum releases:

• Progesterone

• Estrogen

• Inhibin

Effects:

• Strong negative feedback on hypothalamus and anterior pituitary

  • ↓ GnRH

  • ↓ FSH

  • ↓ LH

Structural effect:

• prevents new follicles from developing

• maintains luteal structure temporarily

If No Pregnancy

• Corpus luteum degenerates

• Hormones drop

👉 Result:

• inhibition removed

• FSH rises → new cycle begins

Uterine Cycle

Menstrual Phase (Day 0-4)

Proliferative Phase (Day 5-14)

Secretory Phase (Day 15-28)

Menstrual Phase (Day 0-4)

Ovarian hormones (estrogen + progesterone) are low

• Hormone-dependent functional layer of endometrium is no longer supported → breaks down and sheds

• Bleeding for 3-5 days

• By day 4, the growing ovarian follicles start to produce more estrogens

Proliferative Phase (Day 5-14)

Driven by estrogen from developing follicles

• Functional layer of endometrium is rebuilt and thickens

  • Glands enlarge

  • Spiral arteries increase in number

  • Endometrial cells synthesize progesterone receptors

• Ovulation occurs at the end of this stage in response to the LH surge

Secretory Phase (Day 15-28)

Driven by progesterone from corpus luteum

Endometrium becomes functional and implantation-ready

• Progesterone causes:

  • Endometrial glands to enlarge and coil

  • Spiral arteries develop

  • Converts functional layer to secretory mucosa

  • Nutrients sustain the embryo until it has implanted in the blood-rich endometrial lining

• Rising progesterone (and estrogen) levels inhibit LH release by anterior pituitary

If No Fertilization

Corpus luteum degenerates

• ↓ progesterone + estrogen

• blood supply collapses → endometrium breaks down

👉 This triggers:

• next uterine/menstrual cycle