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Questions and Answers
What is the primary role of ovarian follicles in the process of oogenesis?
What is the primary role of ovarian follicles in the process of oogenesis?
- Providing support to the developing oocyte. (correct)
- Facilitating meiosis II in the secondary oocyte.
- Producing the zona pellucida around the oocyte.
- Secreting estrogen to prepare the uterine lining.
How does the number of primary oocytes change from before birth to after puberty in females?
How does the number of primary oocytes change from before birth to after puberty in females?
- Decreases from approximately 7 million to about 4000. (correct)
- Remains constant throughout the individual's life.
- Increases steadily until menopause.
- Increases significantly due to mitotic divisions.
At what stage of oogenesis does the primary oocyte arrest before puberty?
At what stage of oogenesis does the primary oocyte arrest before puberty?
- Prophase I (correct)
- Metaphase II
- Telophase II
- Anaphase I
What triggers the release of GnRH (Gonadotropin-Releasing Hormone) after puberty, initiating the menstrual cycle?
What triggers the release of GnRH (Gonadotropin-Releasing Hormone) after puberty, initiating the menstrual cycle?
Which hormones are directly stimulated by GnRH (Gonadotropin-Releasing Hormone) to regulate the menstrual cycle?
Which hormones are directly stimulated by GnRH (Gonadotropin-Releasing Hormone) to regulate the menstrual cycle?
Approximately how long is the typical human menstrual cycle, which controls oogenesis?
Approximately how long is the typical human menstrual cycle, which controls oogenesis?
What event marks the beginning of the menstrual cycles in females?
What event marks the beginning of the menstrual cycles in females?
In what specific stage of meiosis is the secondary oocyte arrested until fertilization occurs?
In what specific stage of meiosis is the secondary oocyte arrested until fertilization occurs?
What is the main distinction between primary and secondary oocytes regarding meiotic division?
What is the main distinction between primary and secondary oocytes regarding meiotic division?
What is folliculogenesis?
What is folliculogenesis?
What is the direct role of the zona pellucida in oogenesis and fertilization?
What is the direct role of the zona pellucida in oogenesis and fertilization?
How do follicular cells support the growing oocyte in unilaminar primary follicles?
How do follicular cells support the growing oocyte in unilaminar primary follicles?
What structural feature characterizes multilaminar primary follicles?
What structural feature characterizes multilaminar primary follicles?
What is the significance of gap junctions between granulosa cells in a developing follicle?
What is the significance of gap junctions between granulosa cells in a developing follicle?
What initiates the transition from primordial follicles to primary follicles?
What initiates the transition from primordial follicles to primary follicles?
What is the role of liquor folliculi in secondary follicles?
What is the role of liquor folliculi in secondary follicles?
Which structural innovation defines the formation of a secondary follicle during oogenesis?
Which structural innovation defines the formation of a secondary follicle during oogenesis?
What is the main function of the theca interna cells in secondary follicles?
What is the main function of the theca interna cells in secondary follicles?
How does the structure of the theca externa contribute to the function of secondary follicles?
How does the structure of the theca externa contribute to the function of secondary follicles?
Which process is completed in secondary (antral) follicles, leading to the formation of a secondary oocyte and the first polar body?
Which process is completed in secondary (antral) follicles, leading to the formation of a secondary oocyte and the first polar body?
What is the result of the chromosomes dividing equally between two daughter cells during secondary oocyte formation?
What is the result of the chromosomes dividing equally between two daughter cells during secondary oocyte formation?
What is the chromosomal content of the secondary oocyte compared to the primary oocyte?
What is the chromosomal content of the secondary oocyte compared to the primary oocyte?
What characterizes the structure known as the cumulus oophorus?
What characterizes the structure known as the cumulus oophorus?
What is the composition of the fluid found within the antrum of a Graafian follicle?
What is the composition of the fluid found within the antrum of a Graafian follicle?
What is the term of the granulosa cells directly surrounding the zona pellucida in a Graafian follicle?
What is the term of the granulosa cells directly surrounding the zona pellucida in a Graafian follicle?
At what specific stage of development is the oocyte within the Graafian follicle arrested prior to ovulation?
At what specific stage of development is the oocyte within the Graafian follicle arrested prior to ovulation?
Over what approximate time period does a primordial follicle typically develop into a mature follicle?
Over what approximate time period does a primordial follicle typically develop into a mature follicle?
What is the 'stigma' in the context of ovulation?
What is the 'stigma' in the context of ovulation?
Which hormone directly triggers ovulation?
Which hormone directly triggers ovulation?
Following ovulation, where does the secondary oocyte and its corona radiata typically enter?
Following ovulation, where does the secondary oocyte and its corona radiata typically enter?
During each menstrual cycle, what usually happens to the follicles that do not become the dominant follicle?
During each menstrual cycle, what usually happens to the follicles that do not become the dominant follicle?
What crucial role does estrogen play when produced by growing follicles, even if their oocytes are not used?
What crucial role does estrogen play when produced by growing follicles, even if their oocytes are not used?
What is the term for the degenerative process by which most ovarian follicles are eliminated?
What is the term for the degenerative process by which most ovarian follicles are eliminated?
Which cellular event is a key component of follicular atresia?
Which cellular event is a key component of follicular atresia?
What distinguishes atretic follicles from healthy follicles within the ovary?
What distinguishes atretic follicles from healthy follicles within the ovary?
What is the approximate size range of a mature oocyte?
What is the approximate size range of a mature oocyte?
What cellular structures surround and support the oocyte?
What cellular structures surround and support the oocyte?
How is meiosis II completed during fertilization?
How is meiosis II completed during fertilization?
What is the outcome of meiosis II after fertilization occurs?
What is the outcome of meiosis II after fertilization occurs?
How does the process of oogenesis ensure that the resulting oocyte receives adequate cytoplasmic material?
How does the process of oogenesis ensure that the resulting oocyte receives adequate cytoplasmic material?
What is the significance of the fibrous theca externa in the secondary follicle?
What is the significance of the fibrous theca externa in the secondary follicle?
Which of the following represents the correct order of events in folliculogenesis, leading to ovulation?
Which of the following represents the correct order of events in folliculogenesis, leading to ovulation?
In the context of oogenesis, how do granulosa cells support the developing oocyte in a multilaminar primary follicle?
In the context of oogenesis, how do granulosa cells support the developing oocyte in a multilaminar primary follicle?
How does the production of estrogen by growing follicles, even those whose oocytes are not destined for ovulation, contribute to the reproductive process?
How does the production of estrogen by growing follicles, even those whose oocytes are not destined for ovulation, contribute to the reproductive process?
Flashcards
Oogenesis
Oogenesis
The process of producing a mature oocyte from immature germ cells, occurring in the ovaries and continuing in the oviducts.
Prenatal Oogenesis
Prenatal Oogenesis
The stage where the majority of oogenesis steps occur.
Oogonium
Oogonium
A diploid germ cell that divides by mitosis during fetal life.
Prophase I Arrest
Prophase I Arrest
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Postnatal Oogenesis
Postnatal Oogenesis
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Menstrual Cycle
Menstrual Cycle
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Folliculogenesis
Folliculogenesis
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Ovarian Follicles
Ovarian Follicles
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Primordial Follicles
Primordial Follicles
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Unilaminar Primary Follicle
Unilaminar Primary Follicle
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Multilaminar Primary Follicle
Multilaminar Primary Follicle
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Zona Pellucida
Zona Pellucida
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Liquor Folliculi
Liquor Folliculi
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Antrum
Antrum
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Secondary (Antral) Follicles
Secondary (Antral) Follicles
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Theca Interna
Theca Interna
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Theca Externa
Theca Externa
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Secondary Oocytes
Secondary Oocytes
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Follicular Fluid
Follicular Fluid
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Cumulus Oophorus
Cumulus Oophorus
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Graafian Follicle
Graafian Follicle
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Corona Radiata
Corona Radiata
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Ovulation
Ovulation
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Follicular Atresia
Follicular Atresia
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Atretic Follicles
Atretic Follicles
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Oocyte
Oocyte
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Fertilization
Fertilization
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Meiosis II
Meiosis II
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Second Polar Body
Second Polar Body
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Study Notes
- Oogenesis is the process of producing a mature oocyte from immature germ cells.
- It occurs in the ovaries and continues in the oviducts.
- The process starts in early fetal life and continues during puberty.
Prenatal Oogenesis
- Majority of the steps occur prenatally.
- Oogonium divides many times in fetal life through mitosis.
- Oogonia grow before birth to produce primary oocytes.
- Most primary oocytes undergo atresia before birth.
- Females are born with all the primary oocytes they will ever have.
- Primary oocytes do not divide further.
- Primary oocyte starts the first meiosis before birth but stops (arrests) in prophase I until puberty.
Number of Primary Oocytes During Life
- Before birth, there are ~7 million.
- At birth, there are ~2 million.
- Before puberty, there are ~400,000.
- After puberty (during the reproductive phase), there are ~4,000.
Postnatal Oogenesis
- After puberty, GnRH is released from the hypothalamus.
- GnRH causes FSH and LH release
- These hormones control the menstrual cycle, which takes almost 28 days.
- In each cycle, 5-15 primordial follicles start to grow, but only one oocyte gets ready for fertilization.
- Oogenesis is controlled by the menstrual cycle (~28 days).
- After puberty, menstrual cycles begin.
- Oocyte begins meiosis and is arrested in prophase I during fetal life.
- As the menstrual cycle starts, the oocyte completes the first meiotic division.
- It enters the second meiosis and arrests in metaphase II in the menstrual cycle again.
- Meiosis continues if fertilization occurs.
Arrest Points in Oogenesis
- Primary oocyte is arrested in diplotene of prophase I.
- It completes meiosis I and enters into meiosis II.
- Secondary oocyte is arrested in metaphase II until activation or fertilization, which results in a mature egg.
Folliculogenesis
- Oocyte development occurs within follicles.
- Folliculogenesis is the development of follicles.
- Follicles are sac-like structures where oocytes grow.
- Oogenesis and folliculogenesis occur in conjunction with each other.
Ovarian Follicles
- Ovarian follicles' primary role is oocyte support.
- From birth, the ovaries contain numerous immature, primordial follicles.
- These follicles each contain an immature primary oocyte.
- After the first menstruation, a clutch of follicles begins folliculogenesis.
- An ovarian follicle consists of an oocyte surrounded by one or more layers of epithelial cells.
- The follicles formed during fetal life are primordial follicles, consisting of a primary oocyte (2N) arrested in prophase I enveloped by a single layer of flattened follicular cells.
- These follicles are in the ovarian cortex.
- The oocyte in the primordial follicle is ~25 µm in diameter and contains chromosomes in the first meiotic prophase.
- The basal lamina surrounds the follicular cells.
- It forms a clear boundary between the follicle and the vascularized stroma.
- With the release of follicle-stimulating hormone (FSH) from the pituitary, a small group of primordial follicles begins folliculogenesis each month.
- This involves the growth of the oocyte (meiosis continues), proliferation, and changes in the follicular cells and stromal fibroblasts around each follicle.
- An oocyte can grow to a diameter of about 120 µm.
- Follicular cells undergo mitosis and form a simple cuboidal epithelium around the growing oocyte.
- The follicle is called a unilaminar primary follicle.
- Follicular cells continue proliferating, forming a stratified follicular epithelium called the granulosa which communicates through gap junctions.
- Follicular cells are now termed granulosa cells.
- The follicle becomes a multilaminar primary follicle surrounded by a basement membrane.
Zona Pellucida
- Between the oocyte and the first layer of granulosa cells, extracellular material accumulates, called the zona pellucida.
- The zona pellucida contains four glycoproteins secreted by the oocyte.
- It is essential for sperm receptors, binding specific proteins on the sperm surface and inducing acrosomal activation.
- A fluid (liquor folliculi) begins to accumulate in the intercellular spaces between granulosa cells.
- Fluid-filled spaces coalesce to form a single large cavity called an antrum.
- As a result of this, secondary follicles are developed.
- Stromal cells outside each growing primary follicle differentiate to form the follicular theca.
- This differentiates further into two distinct tissues around the follicle.
- A well- vascularized endocrine tissue, the theca interna, with steroid-producing cells secreting androstenedione.
- A more fibrous theca externa with fibroblasts and smooth muscle merges gradually with the surrounding stroma.
- First meiotic division is completed
Secondary Oocytes
- The chromosomes are equally divided between the two daughter cells, but one retains almost all of the cytoplasm.
- The cell is now the secondary oocyte (1N), and the other becomes the first polar body (PB).
- Secondary oocyte contains half the chromosome number (N) of the parent cell.
- The oocyte begins the second meiotic division but arrests again at metaphase until fertilization.
- Follicular fluid contains hyaluronic acid, growth factors, plasminogen, fibrinogen, the anticoagulant heparan sulfate proteoglycan, and high concentrations of steroids (progesterone, androstenedione, and estrogens) with binding proteins.
- As the antrum develops, the granulosa cells around the oocyte form a small hillock, the cumulus oophorus, which protrudes into the antrum
Graafian Follicle
- Granulosa cells surrounding the zona pellucida make up the corona radiata.
- They accompany the oocyte when it leaves the ovary at ovulation.
- The large antrum of a mature or (preovulatory follicle / graafian follicle) accumulates follicular fluid and expands to a diameter of ~2 cm.
- It contains a secondary oocyte (1N) arrested at metaphase II.
- A preovulatory follicle forms a bulge at the ovary surface visible with ultrasound imaging.
- A mature follicle normally develops from a primordial follicle over a period of about 90 days.
Ovulation
- It's the release of oocyte from the ovary.
- Occurs around the 14th day of a cycle.
- Hours before ovulation, the mature dominant follicle bulging against the tunica albuginea develops an ischemic area, the stigma, in which tissue compaction has blocked blood flow.
- Usually only one oocyte is ovulated during each cycle, but sometimes either no oocyte or two or more oocytes may be expelled.
- Ovulation occurs in response to the LH surge.
- The secondary oocyte and its corona radiata cells leave the ruptured follicle at the ovarian surface to enter the fimbriated end of the oviduct.
- During a menstrual cycle, one follicle becomes dominant and develops farther than the others.
- The dominant follicle undergoes ovulation, while the other follicles undergo atresia.
- Large growing follicles produce estrogen before becoming atretic follicles.
- This estrogen stimulates the preparation of the reproductive tract to transport and sustain the embryo if the oocyte from the dominant follicle is fertilized.
Follicular Atresia
- Most ovarian follicles undergo the degenerative process called atresia. Follicular cells and oocytes die and are disposed of by phagocytic cells..
- Follicles at any stage of development including nearly mature follicles may become atretic.
- Atresia involves apoptosis and detachment of the granulosa cells, autolysis of the oocyte, and collapse of the zona pellucida.
- Atretic follicles are follicles (in various stages of maturation) undergoing degeneration.
- After a graafian follicle ovulates, the remaining secondary follicles degenerate.
Oocyte
- A large cell having the potential to feed the zygote during early mitotic divisions.
- The biggest cell of the body at ~120-130μm.
- It is surrounded by zona pellucida and cumulus oophorus cells.
- Feeds and protects the oocyte.
Fertilization
- The process where sperm and oocyte come together to form a new zygote.
- If fertilization occurs, meiosis II is induced to continue when a sperm penetrates the oocyte.
- Meiosis II finishes, and two cells are produced again.
- The chromatids are divided between the two daughter cells, but again, one of these cells is big (oocyte) ,and smaller become the second polar body.
- The second polar body (PB) is extruded.
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