OOGENESIS
DR.SHABANA ALI
LEARNING OBJECTIVES
• 1
1.gross
gross anatomy of female reproductive
tract.
• 2.hormonal
2 hormonal control
• Oogenesis
• Sructure of follicles
The Female Reproductive
System
• Ovaries or female gonads
– release 1 immature gamete (oocyte) per month
– produce hormones
• Uterine tubes:
– carry oocytes to uterus
• If sperm reaches oocyte:
– fertilization is initiated and oocyte matures into ovum
• Uterus: encloses and supports developing
embryo
b
• Vagina: connects uterus with exterior
• External genitalia
• Accessory glands
Ovary Functions
1 Production of immature female gametes
1.
(oocytes)
2 Secretion of female sex hormones
2.
(estrogens, progestins)
3 Secretion
3.
S
ti off inhibin
i hibi ffor ffeedback
db k control
t l
of pituitary FSH
Oogenesis
• Begins before birth
birth, pauses
• Continues at puberty
• Does
D
nott actually
t ll complete
l t until
til
fertilization!
• Ceases at menopause
• Ovarian Cycle
y
Includes monthly
y oogenesis
g
between puberty and menopause
Oogenesis
• Primordial germ cell
cell_2
2nd week
• Y
Yolk
lk sac tto d
developing
l i gonads_4
d 4th week
k
• Mitosis_no. increase
• Germ cells undergo gametogenesis
1.meiosis
2.cytodifferentiation
OOGONIA
• TILL 3RD MONTH-MITOSIS
CLUSTERS
SURROUNDED BY FOLLICLAR
CELLS.
FEW WILL UNDERGO MEIOSIS,
MEIOSIS
ARREST AT PROPHASE ONE
PRIMARY OOCYTE.
TILL 5TH MONTH _7 MILLION BY MITOSIS.
CELL DEATH BEGINS
OOGONIA AND P.
P OOCYTE_ATRETIC
OOCYTE ATRETIC
• By 7th month most cells –degenerate
degenerate
except fewer cells near the surface.
• All primary oocytes _entered
entered prophase of
first meiotic division.
surrounded
d db
by flflatt
cells….PRIMORDIAL FOLLICLE
• Oogonia
g
= females reproductive
p
stem cells
– complete mitotic divisions before birth (not thought to
happen at all after birth)
• Between third and seventh months:
– primary oocytes begin meiosis but stop at prophase
of meiosis I
• At birth,
birth a baby girl’s
girl s ovaries have about 2
million primordial follicles each containing a
primary oocyte arrested in prophase I of
meisosis
i
i
• At puberty rising FSH triggers start of ovarian
cycle
y
• near time of birth,prophase has been
started,…DIPLOTENE STAGE.
oocyte maturation inhibition
factor
.600,000-800,0000
600 000 800 0000 at birth
birth.
.Most of them –atretic during childhood.
.40,000-near
40 000
puberty
b t
.More than 500 _ovulated.
• Every month
month,15
15-20
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 follicle
• Primary follicle_flat cells_cuboidal
g
cells.
stratified-granulosa
theca folliculi
zona pellucida
Secondary follicle
Vesicular follicle – 25
mm in diameter
_fluid filled spaces b/w
granulosa cellsANTRUM.
ANTRUM
_cumulus oophorus
_theca interna and
externa
• Atretic follicle-With each ovarian cycle,only
y , y one matures,,
other degenerate.
• When secondary follicle matures –LH
LH from
anterior pitutary gland is secreted.
-causes
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 division
ARREST t h
ARRESTmetaphase
3h b
3hrs
before
f
ovulation.
l ti
Meiosis 2 is completed only if fertilization
occur.
OTHERWISE cell degenerates after 24 hrs.
The Ovarian Cycle
Figure 28–16 (1 of 2)
The Ovarian Cycle
Figure 28–16 (2 of 2)
Gonadotropins, Hormones, and the Ovarian
and
d Ut
Uterine
i C
Cycles
l
Pituitary-Ovarian
Pituitary
Ovarian Axis
Feedback 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 GnRH
hypothalamic
• As puberty nears, GnRH is released; FSH and
LH are released by the pituitary
pituitary, which act on
the ovaries
y
• These events continue until an adult cyclic
pattern is achieved and menarche occurs
• i/u life
life…..primordial
primordial follicle
follicle….ist
ist meiotic
division(prophase)
• At puberty
puberty….ovulation….2
ovulation 2nd meiotic
division…..metaphase
• fertilization,….meiosis
f tili ti
i i complete
l t
• One primordial follicle
follicle…..one
one mature
oocyte and 3 polar bodies