Download Meiosis in the Oocyte

All female structures
are analogous to male
structures and must
perform the similar
functions.
• Produce gametes
• Deliver gametes
• Provide environment
for organism to
develop if fertilization
occurs
A female is born with all the egg cells that she will ever have.
They are immature primary oocytes and only develop into
mature egg cells when the woman enters sexual maturity.
From puberty (around age 12) until
menopause (around age 50) a female will
release 1 egg per 28 days (on average) unless
fertilization occurs.
Eggs are stored and
mature in the ovary.
They travel down the
fallopian tube
(oviduct) to the uterus
Oogenesis: The formation of Eggs
This begins in the developing ovaries of the female fetus
By the 3rd month of fetal development primary oocytes are formed. They
stop at the prophase of meiosis I
At birth over 2 million primary oocytes are already in place, no
new ones are formed.
Many primary oocytes die each day so that by puberty only about
400,000 remain.
This is more than enough to produce 1 egg every month from
puberty till menopause
How many is that if a woman comes into puberty at 13 and
menopause at 50?
Surrounding each oocyte is a layer of smaller cells which secrete
female hormones and nourish the developing oocyte.
The follicle secretes
the hormone estrogen.
Once a month pituitary
hormones stimulate the
development of several
follicles.
The oocytes and these
cells are called the
follicle.
Meiosis in the Oocyte
The polar bodies are left over
chromosomes
The follicle ruptures and releases
the secondaary oocyte and the
fimbriae move it into the oviduct.
The egg starts to move down the Oviduct (fallopian tube).
The follicle remains and turns into the Corpus Luteum.
The corpus luteum secretes both estrogen and progestrone.
If fertilization does not occur the corpus luteum breaks down
If the egg meets a sperm cell and is fertilized during its 3 day
journey down the oviduct, it will plant itself on the uterine
lining and begin to gain nutrients from the endometrium of
the uterus so that it can grow.
If the egg does not meet a sperm,
the egg will be discarded along
with the nutrient-rich
endometrium that is primed for its
arrival. This is called
menstruation and occurs once
every 28 days or so unless the egg
is fertilized.