OOGENESISOOGENESIS

DR.SHABANA ALI

LEARNING OBJECTIVESLEARNING OBJECTIVES

1 gross anatomy of female reproductive1.gross anatomy of female reproductive tract.

2 hormonal control 2.hormonal control Oogenesis Sructure of follicles

The Female Reproductive System

Ovaries or female gonads Ovaries or female gonads release 1 immature gamete (oocyte) per month produce hormones

Uterine tubes: carry oocytes to uterus

If sperm reaches oocyte: If sperm reaches oocyte: fertilization is initiated and oocyte matures into ovum

Uterus: encloses and supports developing bembryo

Vagina: connects uterus with exterior External genitalia External genitalia Accessory glands

Ovary FunctionsOvary Functions

1 Production of immature female gametes1. Production of immature female gametes (oocytes)

2 Secretion of female sex hormones2. Secretion of female sex hormones (estrogens, progestins)

3 S ti f i hibi f f db k t l3. Secretion of inhibin for feedback control of pituitary FSH

OogenesisOogenesis

Begins before birth pausesBegins before birth, pauses Continues at puberty

D t t ll l t til Does not actually complete until fertilization!

Ceases at menopause Ovarian Cycle Includes monthly oogenesis y y g

between puberty and menopause

Oogenesis

Primordial germ cell 2nd week Primordial germ cell_2nd week

Y lk t d l i d 4th k Yolk sac to developing gonads_4th week Mitosis_no. increase Germ cells undergo gametogenesis

1.meiosis2.cytodifferentiation

OOGONIA

TILL 3RD MONTH-MITOSISCLUSTERSSURROUNDED BY FOLLICLAR

CELLS.

FEW WILL UNDERGO MEIOSISFEW WILL UNDERGO MEIOSIS,ARREST AT PROPHASE ONEPRIMARY OOCYTE.

TILL 5TH MONTH _7 MILLION BY MITOSIS. CELL DEATH BEGINSOOGONIA AND P OOCYTE ATRETICOOGONIA AND P. OOCYTE_ATRETIC

By 7th month most cells degenerateBy 7 month most cells degenerate except fewer cells near the surface.

All primary oocytes entered prophase of All primary oocytes _entered prophase of first meiotic division.

d d b fl tsurrounded by flat cells.PRIMORDIAL FOLLICLE

Oogonia = females reproductive stem cells g p complete mitotic divisions before birth (not thought to

happen at all after birth) Between third and seventh months:Between third and seventh months:

primary oocytes begin meiosis but stop at prophase of meiosis I

At birth a baby girls ovaries have about 2 At birth, a baby girl s ovaries have about 2 million primordial follicles each containing a primary oocyte arrested in prophase I of

i imeisosis At puberty rising FSH triggers start of ovarian

cycley

near time of birth,prophase has beennear time of birth,prophase has been started,DIPLOTENE STAGE.

oocyte maturation inhibitionoocyte maturation inhibition factor

600 000 800 0000 at birth.600,000-800,0000 at birth..Most of them atretic during childhood.40 000 b t.40,000-near puberty.More than 500 _ovulated.

Every month 15-20 follicles are slectedEvery month,15 20 follicles are slected and they mature in three stages

1 primary/preantral 1.primary/preantral 2.secondary/antral-longest 3.preovulatory-37 hrs before ovulation

Primordial folliclePrimordial follicle

Primary follicle_flat cells_cuboidalstratified-granulosa cells.gtheca folliculizona pellucida

Secondary follicleVesicular follicle 25 mm in diametermm in diameter _fluid filled spaces b/w granulosa cells-ANTRUMANTRUM._cumulus oophorus

_theca interna and externa

Atretic follicle-With each ovarian cycle,only one matures,y , y ,other degenerate.

When secondary follicle matures LH fromWhen secondary follicle matures LH from anterior pitutary gland is secreted.

causes preovulatory growth of follicle-causes preovulatory growth of follicle-Meiosis one is completed,2 daughter cells of unequal size are formed.Each with 23 double structured chromosomes

Now cell enters second meiotic divisionNow cell enters second meiotic division

ARREST t h 3h b f l tiARRESTmetaphase 3hrs before ovulation.

Meiosis 2 is completed only if fertilization occur.

OTHERWISE cell degenerates after 24 hrs.

The Ovarian CycleThe Ovarian Cycle

Figure 2816 (1 of 2)

The Ovarian CycleThe Ovarian Cycle

Figure 2816 (2 of 2)

Gonadotropins, Hormones, and the Ovarian d Ut i C land Uterine Cycles

Pituitary-Ovarian AxisPituitary Ovarian Axis

Feedback Mechanisms in Ovarian FunctionFeedback Mechanisms in Ovarian Function

Establishing the Ovarian Cycle

During childhood, ovaries grow and secrete small amounts of estrogens that inhibit the h pothalamic release of GnRHhypothalamic release of GnRH

As puberty nears, GnRH is released; FSH and LH are released by the pituitary which act onLH are released by the pituitary, which act on the ovaries

These events continue until an adult cyclic ypattern is achieved and menarche occurs

i/u life primordial follicle ist meiotici/u life..primordial follicle.ist meiotic division(prophase)

At puberty ovulation 2nd meiotic At puberty.ovulation.2nd meiotic division..metaphasef tili ti i i l t fertilization,.meiosis complete

One primordial follicle one matureOne primordial follicle..one mature oocyte and 3 polar bodies