Oogenesis

1
Oogenesis
Oogonia complete mitosis before birth

• Make female gametes
• Monthly ovarian cycle
• Occurs in ovarian follicles
• 2 million primary oocytes at birth
• Puberty 400,000

1 oocyte (primordial follicle) at birth
Arrested in diplotene of prophase I until
puberty as primary follicle
At puberty grow resumes Meiosis I now
called secondary follicle
Finish Meiosis I form 2 oocyte within mature
Graafian follicle, freezes in Metaphase II
Ovulation secondary oocyte in mature Graafian
follicle
Fig 27.13
2
Ovarian Cycle

• FSH LH stimulate follicle development
• Before or at birth
• 1 oocyte within follicular cells ? primordial
  follicle
• Suspended in prophase I until puberty as primary
  follicle

Fig 27.12
3
Ovarian Cycle

• Primordial ? 1 follicle
• FSH several layers of follicular cells to
  develop around 1 oocyte
• LH causes 1 oocyte to develop
• Has zona pellucida (transparent jelly-like stuff)
• Follicle cells now called granulosa cells
• Adjacent stromal cells form thecal cells around
  follicle
• These and granulosa cells release estrogen...

4
Estrogen

• Stimulates bone and muscle growth
• Maintains female sex characteristics
• Maintains function of reproductive organs and
  glands
• Initiates repair and growth of endometrium of
  uterus

5
Ovarian Cycle

• Puberty 1 follicle ? 2 follicle
• Grow resume Meiosis I
• Follicular cells secrete liquor folliculi
• ? 2 follicle
• Still 1 oocyte!
• Basically once this fluid is secreted, its
  called a 2 follicle

6
Ovarian Cycle
Graafian Follicle

• 8-10 days later
• More fluid, bigger ? mature Graafian follicle
• Bulges ovarian wall
• Completes meiosis I
• 2 oocyte and polar body formed
• Corona radiata and cumulus oophorous
• Frozen in metaphase II (completes at
  fertilization)
• If fertilization finish meiosis II ? ovum and
  polar body
• Ovum is short-lived b/c zygote is being formed