Reproductive System II (copy)

What separates in meiosis I?

What separates in meiosis II?

Compare the differences in
gametogenesis in males and
females.

Homologous Chromosomes

- Sister Chromatid

• Spermatogenesis: Continuous
• Oogenesis: Cyclical and have arrest point:

1) Prophase I

2) Metaphase II

The Hypothalamic-Pituitary-Gonadal Axis (HPG axis)

• Hypothalamus → GnRH( Gonadotropin Releasing Hormone pulses) → Anterior pituitary → secretes FSH (Follide Stimulating Hormone) and LH ( Luteinzing Hormone)

• FSH/LH act on gonads (testes or ovaries) → sex hormones → feedback loops

• Key idea: “GnRH drives FSH and LH, which drive follicle development and ovulation.”

Overview of Ovarian Follicles

• Definition: follicle = oocyte + surrounding support cells
• Role: protects, nourishes, and secretes hormones (help it develop)

Primordial Follicle (Resting/Waiting)

Present at birth

Single layer of squamous (sometimes call flat cells) cells around a primary oocyte (arrested in Prophase I)

Resting pool for future cycles (ready to go into oogenesis and cause ovalution)
- Most never develop
- Atresia (if it not dominant follicle)

Primary Follicle

FSH activates the follicle

Cuboidal granulosa cells appear - Granulosa cells begin producing estrogen precursors
(FSH become a primary hormone at this step)

Zona pellucida (layer of glocoprotein) forms around oocyte

Key Point: oocytes from being dormant to active

Secondary Follicle

LH → Theca Cell → Androgen → Granolosa → Estrogen

• Granulosa layers multiply
• Theca cells form around follicle → respond to LH → make androgens → converted to estrogen by granulosa cells
• Follicular fluid begins to accumulate

Mature (Graafian) Follicle

• Large antrum filled with fluid
• Oocyte on a stalk of granulosa cells
• High estrogen output (positive feedback)
• Triggers LH surge

Ovulation

Triggered by LH surge (positive feedback from rising estrogen)

LH Surge:

1) Ovulation

2)Finish Meiosis I

• Follicle ruptures → oocyte enters uterine tube
• Secondary oocyte released, arrested in Metaphase II

Corpus Luteum Formation

• Remaining follicle cells transform into corpus luteum
• Secretes progesterone (and some estrogen)
• Prepares endometrium for possible implantation

1) Prepare Uteres from pregnancy

2) Preven another ovulation

a) Negative food back of hypothela → decrease GnRH

b) Negative Anteriole pit gland decrease FSH and decrease LH

If no fertilization occurs...

• Corpus luteum degenerates → corpus albicans
• Progesterone & estrogen drop → menstruation begins
• FSH rises to start new cycle

Hormonal Regulation in Females

• FSH: stimulates follicle growth & granulosa (turn antrogen → Estrogen) activity
• LH: stimulates theca (androgen → turn antrogen → estrogen) cells, triggers ovulation
• Estrogen: promotes growth of endometrium; positive feedback for LH surge
• Progesterone: stabilizes endometrium, inhibits GnRH/FSH/LH post-ovulation

Key Ideas

Hormone Level Graph

• Estrogen levels rise as follicle grows
• High estrogen → LH Surge
• Day 14: LH surge → ovulation
• Luteal phase: progesterone peak
• Drop in hormones → menstruation

Male Hormonal Regulation

• Same HPG framework:
• GnRH → FSH & LH
• LH → Leydig cells → testosterone
• FSH → Sertoli cells → ABP & sperm support
• Negative feedback: testosterone & inhibin

Comparing Male vs. Female Feedback Loops

Hormone Disruption

• Low body fat / stress → ↓ GnRH → amenorrhea → ability to menstructe
• Polycystic ovary syndrome (PCOS): excess androgens, anovulation:
• Testosterone therapy in males → ↓ FSH/LH → low sperm count

Summary

• Follicles develop from primordial → Graafian → ovulation → corpus luteum → regression (if no fertilization)
• HPG axis controls the process
• Hormone feedback ensures only one ovulation per cycle (progesterone “hypothalamus” → anter pit)
• Males use same axis but maintain constant gamete production

What triggers ovulation?

LH Surge

What hormone peaks after ovulation?

Progesteron

Which cells make estrogen?

Granolosa

Which hormone provides negative feedback on FSH?

Progesteron/ Inhibin

What would happen if two follicles mature in one cycle?

Fraterial twin

Predict what happens to FSH, LH, estrogen, and progesterone if
the corpus luteum fails to form

1) Progesterone → plumnets

2) Estrogen → drop

3) FSH→ increase alot

4) LH → Increase