Lesson 4: Oogenesis

Question 1

Gamete Formation -
Eggs

Answer 1

This process is called
oogenesis

Takes place in the ovary of
the female

The process begins with
diploid cells called the
oogonia, which are the
germinal epithelial cells
within the ovaries.

Oogonia divide by
mitosis to produce more
diploid cellsThe oogonia enlarge to form the primary oocytes, which are also diploid.

Primary oocytes begin meiosis but stop at prophase I, leaving the primary
oocyte surrounded by follicle cells in a structure known as the primary
follicle.

At puberty, the development of primary follicles continues.

Question 2

Follicle Development

Answer 2

During each menstrual cycle a few follicles
continue meiosis I, however, just one will
complete it producing two haploid cells.

The division of the cytoplasm is uneven at
the end of meiosis I.

The larger cell is called the secondary
oocyte and the smaller one is called a polar
body.

The polar body degenerates and does not
develop further.

The secondary oocyte begins meiosis II but stops
in prophase II. The follicle cells also divide and
produce a fluid that causes the follicle to swell.
Which at ovulation causes the follicle to rupture
and release the secondary oocyte.After fertilization the
secondary oocyte will
complete meiosis II to
become a mature ovum. It
expels another polar body in
the process.

The empty follicle develops
into the corpus luteum
which produces
progesterone.

The unequal division of the
cytoplasm during oogenesis
is to provide the ovum with
enough nutrients to support
the developing zygote for a
few days after fertilization

Question 3

Hormones and the Menstrual
Cycle

Answer 3

The menstrual cycle is approximately 28 days.

The menstrual cycle is regulated by hormones produced by the
pituitary gland.Follicle – stimulating hormone
(FSH) from the pituitary gland
stimulates the follicle inside the
ovary to develop

This developing follicle secretes
estrogen

The estrogen secreted by the
developing follicle stimulates the
lining of the uterus to thicken.

Estrogen also stimulates the
pituitary gland to produce
luteinising hormone (LH).

The release of LH causes
ovulation.

Question 4

The Corpus Luteum

Answer 4

The corpus luteum
produces both
progesterone and estrogen.

Progesterone increases the
uterine lining and causes
FSH and LH to drop.

This drop in FSH and LH
prevents the release of
another egg until
progesterone decreases
again.

Question 5

If the egg is not fertilized

Answer 5

The corpus luteum will break down causing the levels of
progesterone to drop.

This drop in progesterone causes the uterine lining to break down
and menstruation to occur.

Menstruation continues for 4 – 7 days until progesterone reaches a
certain level, which causes the release of FSH by the pituitary, and
the cycle starts again.

Question 6

If the egg is fertilized – Pregnancy

Answer 6

When sperm is deposited
into the female cervix, they
travel up the uterus into
the oviduct.

Fertilization occurs in the
oviducts when one sperm
enters the mature egg and
their nuclei fuse to form a
zygote