Oogenesis

Summary

This 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

00:00

👶 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.

05:01

🌟 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.

Keywords

💡Oogenesis

Oogenesis is the process of female gamete formation, central to the video's theme of understanding the biological mechanisms of egg development. It involves meiosis and follicle development, starting in the fetal stage and continuing through puberty and the menstrual cycle. The script describes oogenesis beginning with the primordial germ cell and progressing to the formation of the ovum.

💡Meiosis

Meiosis is a type of cell division that results in four daughter cells, each with half the number of chromosomes of the parent cell. In the context of the video, meiosis is crucial for the production of haploid cells from the primary oocyte, which is halted at prophase one during fetal development and only completed during puberty and ovulation.

💡Follicle Development

Follicle development refers to the growth and maturation of the ovarian follicle, which houses the oocyte. The video script explains how the primary oocyte is surrounded by follicle cells, forming the primary follicle, which later develops into the secondary and then the graafian follicle, culminating in ovulation.

💡Primary Oocyte

A primary oocyte is an immature egg cell that contains the full set of chromosomes. The script details how the primary oocyte undergoes meiosis one but is halted at prophase one, remaining in this state until puberty, when it completes meiosis one to form two haploid cells.

💡Haploid

Haploid refers to cells containing half the number of chromosomes of the species' normal set. In humans, this means having 23 chromosomes. The video explains that after meiosis one, the primary oocyte divides into two haploid cells, one of which is the secondary oocyte.

💡Secondary Oocyte

The secondary oocyte is a cell formed after the completion of meiosis one, containing half the number of chromosomes of the original cell. The script describes how the secondary oocyte is released during ovulation and only completes meiosis two upon fertilization by a sperm.

💡Polar Body

Polar bodies are small cells produced during oogenesis alongside the egg cell. The first polar body is formed after meiosis one and may either degenerate or undergo meiosis two to form second polar bodies. The script explains that all polar bodies eventually degenerate, emphasizing their role in the process but not in reproduction.

💡Ovum

The ovum, or egg, is the female reproductive cell resulting from the completion of meiosis. The script describes the ovum as the final product of oogenesis, formed after the secondary oocyte completes meiosis two, and is capable of being fertilized.

💡Corpus Luteum

The corpus luteum is a temporary endocrine structure in the ovary that produces progesterone. The video script explains that after ovulation, the remaining follicle cells develop into the corpus luteum, which plays a critical role in the menstrual cycle and potential pregnancy.

💡Menstrual Cycle

The menstrual cycle is a recurring physiological process in females involving the changes in the ovaries and the lining of the uterus. The script mentions that the development of secondary and graafian follicles, as well as ovulation, occurs within the context of the menstrual cycle.

💡Fertilization

Fertilization is the process where a sperm cell unites with an egg cell to initiate the development of a new individual. In the script, fertilization is mentioned as the event that triggers the completion of meiosis two in the secondary oocyte, leading to the formation of a zygote.

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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