Oogenesis
Summary
TLDRThis script explores oogenesis, the intricate process of female gamete formation. Beginning in the fetal stage, it details the meiotic events leading to the production of haploid cells and the development of the follicle. The script explains how primary oocytes are reduced in number and how, at puberty, they continue meiosis to form secondary oocytes. It also covers the transformation of follicle cells into the corpus luteum and the importance of the menstrual cycle in this process, offering a comprehensive look at the biological journey from oocyte to ovum.
Takeaways
- 🌱 Oogenesis is the process of female gamete formation, beginning during the fetal stage.
- 🔬 The process includes two main events: meiosis and follicle development.
- 🧬 Meiosis consists of two divisions, meiosis I and II, which reduce the chromosome number by half.
- 📉 Primary oocytes are numerous at fetal development but many undergo atresia, reducing their numbers over time.
- 🔄 Meiosis I is initiated but halts at prophase I until puberty, when it resumes and completes.
- 🌟 The result of meiosis I is two haploid cells: a secondary oocyte and a first polar body.
- 🌐 Meiosis II begins but stalls at metaphase II until fertilization occurs.
- 🌿 Follicle development involves the growth of the primary oocyte surrounded by follicle cells into various stages of follicles.
- 🌕 The Graafian follicle, containing the secondary oocyte, is the mature form ready for ovulation.
- 🌱 If fertilized, the secondary oocyte completes meiosis II to become an ovum; otherwise, it degenerates.
- 🔄 The remnants of the follicle after ovulation develop into the corpus luteum, which produces progesterone.
Q & A
What is oogenesis?
-Oogenesis is the process of formation of the female sex cell, or the female gamete.
What are the two simultaneous events that occur during oogenesis?
-The two events are the meiotic event, which includes meiosis one and two, and the development of the follicle.
At what stage does oogenesis begin?
-Oogenesis begins during the fetal stage.
What is the term for the cell that undergoes mitosis to become the orgonium during the fetal stage?
-The primordial germ cell is the cell that undergoes mitosis to become the orgonium.
How many chromosomes do human beings have, and what does this mean for the cells involved in oogenesis?
-Humans have 46 chromosomes, meaning that cells involved in oogenesis, such as the primordial germ cell, orgonium, and primary oocyte, all contain 46 chromosomes.
What happens to the primary oocyte during fetal development?
-The primary oocyte begins meiosis one but gets stalled at prophase one during fetal development.
How many primary oocytes are produced during fetal development, and what happens to their number after birth?
-About seven million primary oocytes are produced during fetal development, and about six million undergo programmed cell death after birth, leaving one million primary oocytes.
What is the significance of the completion of meiosis one?
-The completion of meiosis one results in the formation of 2 haploid cells, each containing half the number of chromosomes of the organism.
What is the secondary oocyte and what happens to it during meiosis II?
-The secondary oocyte is the larger cell formed after the completion of meiosis one. It begins meiosis II but is stalled at metaphase two until fertilization occurs.
What is the role of the follicle cells in oogenesis?
-The follicle cells surround the primary oocyte and develop into different layers of follicles, eventually forming the corpus luteum if fertilization does not occur.
What is the corpus luteum and what does it produce?
-The corpus luteum is a bundle of cells that develop from the follicle cells after ovulation and is responsible for producing progesterone.
Outlines
👶 Oogenesis and Follicle Development
This paragraph discusses the process of oogenesis, the formation of female gametes, which begins during the fetal stage. It details the meiotic events of meiosis one and two, where the primary oocyte undergoes division to form haploid cells. The paragraph also explains the development of the follicle, from the primordial germ cell to the primary and secondary follicles, and the role of hormones in the process. It highlights the reduction in the number of primary oocytes from seven million at fetal development to one million at birth, and further to about three hundred thousand at puberty. The summary of this paragraph would emphasize the stages of oogenesis, the importance of the menstrual cycle in the maturation of oocytes, and the eventual formation of the ovum upon completion of meiosis two after fertilization.
🌟 Ovulation and Formation of Corpus Luteum
The second paragraph focuses on the final stages of oogenesis and the role of the follicle in ovulation. It describes the transition of the secondary follicle into the graafian follicle, characterized by the presence of an antrum filled with fluid. The paragraph explains that during ovulation, the secondary oocyte is released into the fallopian tubes. If fertilized, it becomes the ovum. The remaining follicle cells then develop into the corpus luteum, which is responsible for progesterone production. The summary would include the process of ovulation, the significance of the corpus luteum in hormone production, and the simultaneous nature of these events with the development of oocytes from the fetal stage through to puberty and the menstrual cycle.
Mindmap
Keywords
💡Oogenesis
💡Meiosis
💡Follicle Development
💡Primary Oocyte
💡Haploid
💡Secondary Oocyte
💡Polar Body
💡Ovum
💡Corpus Luteum
💡Menstrual Cycle
💡Fertilization
Highlights
Oogenesis is the process of female gamete formation, involving meiotic events and follicle development.
Meiosis in oogenesis begins during the fetal stage, with the primordial germ cell undergoing mitosis to become the orgonium.
The orgonium develops into a primary oocyte, which contains 46 chromosomes, the diploid number for humans.
Meiosis I is initiated but stalls at prophase one during fetal development, resulting in about one million primary oocytes remaining after birth.
At puberty, the number of primary oocytes reduces to about three hundred thousand, still at prophase one.
Completion of Meiosis I results in two haploid cells, each with 23 chromosomes.
The secondary oocyte and the first polar body are formed, with the former being much larger and containing more cytoplasm.
Meiosis II begins but is stalled at metaphase two until fertilization occurs.
The secondary oocyte is released during ovulation and completes Meiosis II upon sperm penetration, resulting in the ovum.
The first polar body may degenerate or undergo Meiosis II to form additional polar bodies, which eventually degenerate.
Follicle development begins with the primary oocyte surrounded by follicle cells, forming the primary follicle.
Puberty initiates the menstrual cycle, with follicle-stimulating hormone stimulating the growth of follicle cells.
The secondary follicle forms as the primary oocyte becomes the secondary oocyte, encapsulated by multiple layers of follicle cells.
The antral follicle is characterized by the presence of an antrum, a fluid-filled region, and is ready for ovulation.
Ovulation releases the secondary oocyte, and the remaining follicle cells develop into the corpus luteum, responsible for progesterone production.
The simultaneous occurrence of meiotic events and follicle development is a key aspect of oogenesis.
The number of primary follicles reduces from 7 million at the fetal stage to 1 million at birth, and further to 300,000 at puberty.
The menstrual cycle continues the process of follicle development, leading to the formation of antral follicles and ovulation.
A separate lesson on the menstrual cycle will be provided for further understanding of the process.
Transcripts
oogenesis is the formation of the female
sex cell or the female gamete ogenesis
consists of two events that are
happening at the same time first event
is the meiotic event where meiosis takes
place meiosis one and two and the second
event that occurs at the same time is
the development of the follicle let's
take a look at the meiotic event first o
genesis begins during the fetal stage
itself at the fetal stage the primordial
germ cell will undergo mitosis and
become the orgonium the orgonium then
will develop and grow into primary
oocyte and all this while you can see
the number of cells is 2n this means
that
the cells contain
all the chromosomes of the organism in
human beings we have 46 chromosomes that
means that all these cells the
primordial germ cell the orgonium and
the primary oocyte all contain 46
chromosomes
and then the primary oocyte will begin
meiosis one however meiosis one will be
stalled or will be stuck
at prophase one so the primary oocyte
will stop at prophase one during the
fetal development about seven million
primary oocytes are produced after birth
about six million of these primary
oocytes will undergo programmed cell
death or hypothesis so from the seven
million we now have one million primary
oxides remaining and this primary
oscillates will continue to die until
the female reaches
puberty
at puberty primary oocytes will reduce
to about three hundred thousand and all
are still at prophase one however when
puberty hits
then prophase one will finally continue
on and meiosis 1 will be completed once
myself 1 is completed we have 2 haploid
cells this is the beginning of the
production of haploid cells a haploid
cell contains the haploid number of
chromosomes that is half of the number
of chromosomes of the organism in the
case of human beings we have 46
chromosomes which means haploid cells
will only contain 23 chromosomes one of
each of the homologous chromosome pairs
when we look closely at the two haploid
cells from here
one is much larger than the other one
contains a lot more cytoplasm than the
other and the small cell is known as the
first polar body the larger cell is
known as the secondary oocyte so the
primary oocyte has now formed the
secondary oocyte the secondary oxide
will begin meiosis ii
however once again meiosis ii is not
completed and so what we get is a
secondary oxide that is stalled once
again
at
metaphase two this secondary oocyte is
what is released during ovulation and
now the secondary oxide is going to
remain at the metaphase 2 stage
until a sperm penetrates the secondary
oxide then meiosis 2 is going to be
completed and when myosis 2 is completed
the secondary oocyte will then become
once again you will see cells of two
different sizes one smaller cell and one
larger cell the smaller cell is known as
the second polar body whereas the
largest cell this cell is what we call
the ovum finally the ovum is produced
now what happens to the first polar body
the first polar body may either
degenerate or it could also undergo
myosis two when the first polar body
undergoes meiosis ii
it becomes two further polar bodies
these are cells with very little
cytoplasm at the end of the day all the
polar bodies are going to degenerate now
we go to what's going on with the
follicle development after birth we have
the primary oocyte which was stuck at
prophase one
and then we have a layer of cells
surrounding this primary oocyte known as
the follicle cells when one layer of
follicle cells surrounds the primary
oocyte the combination of these two
things is known as the primary follicle
at puberty when the menstrual cycle
begins follicle stimulating hormone is
released and follicle stimulating
hormone is going to stimulate the growth
of the follicle cells and so from one
layer of follicle cells this is going to
become more and more layers follicle
cells
and
when the primary oocyte becomes the
secondary oocyte as we saw earlier
during the meiotic events
then we have the secondary oocyte
encapsulated by a few layers of follicle
cells this combination is known as the
secondary follicle the follicle cells
are going to continue to grow and
develop until it eventually becomes the
graphene follicle as you can see the
graphene follicle is much larger than
the primary secondary follicle and you
can see we have a region that is filled
with liquid in between this is actually
known as the antrum
so now the graphene follicle is ready to
release the secondary oocyte into the
fallopian tubes from the ovaries this
occurs during ovulation so during
ovulation the secondary oxide is
released now what's left is the follicle
cells and these follicle cells are going
to develop into
what we call the corpus luteum corpus
luteum stands for yellow body it is a
bundle of cells which is going to be
responsible to be producing progesterone
remember that these two events take
place simultaneously so during the fetal
stage
primary follicles are produced and so
you can see primary follicles all around
in the ovary
here here and here they will all be
present
around 7 million but at birth it reduces
to 1 million and at puberty this is when
the process continues and then we have
secondary follicles as you can see we
have the secondary oxide and we have a
few layers of follicle cells surrounding
it this process and the continuing
process from here until the end actually
occurs during the menstrual cycle i will
prepare a separate lesson for that i'll
leave a link in the description below
and so the secondary follicles will then
develop to become
the graphene follicle inside the
graphene follicle we have the secondary
oocyte and this graphite follicle is
then going to release the secondary
oocyte during ovulation secondary oxide
is released
and once it is released the secondary
oxide if fertilized will become the ovum
and finally what's left of the graphene
follicle the follicle cells are going to
become
the corpus luteu if you haven't yet i'll
suggest that you watch spermatogenesis
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