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Questions and Answers
Which abnormality is characterized by having no sperm in the semen?
Which abnormality is characterized by having no sperm in the semen?
At what stage do primary oocytes begin the first meiotic division?
At what stage do primary oocytes begin the first meiotic division?
What is the primary function of prostaglandins in seminal fluid?
What is the primary function of prostaglandins in seminal fluid?
How many primary oocytes are typically present in the ovaries of newborn females?
How many primary oocytes are typically present in the ovaries of newborn females?
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What happens to the secondary oocyte at ovulation?
What happens to the secondary oocyte at ovulation?
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What is the primary function of meiosis in gametogenesis?
What is the primary function of meiosis in gametogenesis?
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During which phase of oogenesis do oogonia enter meiosis I?
During which phase of oogenesis do oogonia enter meiosis I?
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What is the key difference between meiosis I and meiosis II?
What is the key difference between meiosis I and meiosis II?
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Which of the following statements about spermatogenesis is correct?
Which of the following statements about spermatogenesis is correct?
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What is the significance of crossing over during meiosis?
What is the significance of crossing over during meiosis?
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What is the duration of spermatogenesis?
What is the duration of spermatogenesis?
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Which characteristic of seminal fluid is true?
Which characteristic of seminal fluid is true?
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How many chromosomes do the resulting cells from meiosis I have?
How many chromosomes do the resulting cells from meiosis I have?
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At the end of week 2 of development (day 14), what is the composition of the embryonic disk?
At the end of week 2 of development (day 14), what is the composition of the embryonic disk?
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What is the structure that develops from the inner cell mass?
What is the structure that develops from the inner cell mass?
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The hypoblast contributes to the formation of the ______.
The hypoblast contributes to the formation of the ______.
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What hormone is secreted by the Syncytiotrophoblast to sustain the placenta?
What hormone is secreted by the Syncytiotrophoblast to sustain the placenta?
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What are the two layers of the extra-embryonic mesoderm?
What are the two layers of the extra-embryonic mesoderm?
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At the end of week 2 of development (day 14), what is the composition of the embryonic disk?
At the end of week 2 of development (day 14), what is the composition of the embryonic disk?
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What is the roof of the yolk sac formed from?
What is the roof of the yolk sac formed from?
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What is formed by an extension of the epiblast?
What is formed by an extension of the epiblast?
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What hormone is secreted by the Syncytiotrophoblast?
What hormone is secreted by the Syncytiotrophoblast?
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What is the connecting stalk that connects the two layers of extra-embryonic mesoderm called?
What is the connecting stalk that connects the two layers of extra-embryonic mesoderm called?
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What are the two layers of extra-embryonic mesoderm?
What are the two layers of extra-embryonic mesoderm?
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The inner cell mass or embryoblast develops into the bilaminar embryonic disc.
The inner cell mass or embryoblast develops into the bilaminar embryonic disc.
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Study Notes
Cell Cycle and Gametogenesis
- The cell cycle consists of interphase (growth and DNA replication) and the mitotic phase (cell division).
- Mitosis is somatic cell division, occurring in somatic tissues for growth and repair.
- Meiosis is gametic cell division, taking place in gonads (testes and ovaries) to produce gametes.
Mitosis vs. Meiosis
- Mitosis results in two identical daughter cells, maintaining the diploid chromosome number.
- Meiosis consists of two divisions: meiosis I (reduction division) and meiosis II, resulting in four haploid gametes.
- Meiosis I includes DNA replication and crossing over; no DNA replication occurs in meiosis II.
Importance of Meiosis
- Reduces diploid chromosome number (2n) to haploid (n) for reproductive purposes.
- Facilitates genetic diversity through shuffling of chromosomes and crossing over.
Spermatogenesis
- Transformation of spermatogonia into spermatozoa, occurring in seminiferous tubules of the testes.
- Duration of spermatogenesis is approximately 64 days, starting at puberty and continuing throughout life.
- Comprises spermatocytogenesis (division of spermatogonia into spermatids) and spermiogenesis (maturation of spermatids).
Seminal Fluid Characteristics
- Volume: 3-5 cc; has a characteristic odor and alkaline reaction.
- Contains about 200-600 million sperm per ejaculation; motility exceeding 80%.
- Provides nutrients (fructose) for sperm, prostaglandins for motility, and balances vaginal acidity.
Abnormalities in Seminal Fluid
- Azospermia: absence of sperm in semen.
- Oligospermia: low sperm count.
- Necrospermia: presence of dead sperm.
- Morphological abnormalities: giant or dwarf sperm, abnormal head/tail counts; should not exceed 20%, normally under 10%.
Oogenesis
- Oogenesis is the process of forming mature ova from oogonia in the ovarian cortex.
- Primary oocytes begin meiosis I during fetal life but remain dormant until puberty.
- Monthly during the menstrual cycle, 5-12 primary oocytes complete meiosis I, forming a secondary oocyte and a polar body.
- Secondary oocyte completes meiosis II only upon fertilization, arrested in metaphase prior to this.
Oocyte Statistics
- Total primary oocytes in newborn females: approximately 2 million, decreasing to about 40,000 during adolescence.
- Only around 480 primary oocytes are ovulated throughout a woman’s reproductive life.
Comparison of Gametogenesis
- Male gametogenesis (spermatogenesis) produces multiple sperm continuously, while female gametogenesis (oogenesis) produces limited ova with cyclic release.
- Male gametes are smaller and more numerous; female gametes are larger and fewer.
Case Scenario
- Questions regarding the timing of oocyte maturation emphasize that oogonia enter meiosis I and replicate DNA during fetal life.
Bilaminar Embryonic Disc Formation
- The bilaminar disc forms at the end of the first week of development.
- Composed of two layers: Epiblast (1ry ectoderm) with high columnar cells and Hypoblast (1ry endoderm) with small cubical cells.
- The embryonic plate transitions from a circular to an oval to a pear-shaped structure.
Yolk Sac and Amniotic Cavity
-
Yolk Sac:
- Formed by an extension of the hypoblast.
- Boundaries: Roof from hypoblast; floor and sides from Hauser's membrane.
-
Amniotic Cavity:
- Develops from epiblast extension starting around day 7 or 8.
- Boundaries: Roof and sides by amnioblast; floor by epiblast.
Extraembryonic Mesoderm Formation
- Originates from hypoblast and cytotrophoblast.
- Appears between the trophoblast externally and yolk sac and amniotic cavity internally.
- Extraembryonic Coelom: Isolated spaces in the mesoderm fuse to create a large cavity.
Extraembryonic Mesoderm Layers
- Divided into two layers:
- Somatic Mesoderm: Lines the trophoblast.
- Splanchnic Mesoderm: Covers the primary yolk sac.
- Layers connect at the caudal end, forming the connecting stalk, precursor to the umbilical cord.
- Chorion is formed by the trophoblast and somatic mesoderm.
Trophoblast Changes
- The trophoblast differentiates into two layers:
- Cytotrophoblast: Inner mononucleated cell layer.
- Syncytiotrophoblast: Outer multinucleated mass; creates lacunae filled with maternal blood to form intervillous spaces essential for placenta development.
Clinical Relevance
- Syncytiotrophoblast secretes Human Chorionic Gonadotropin (HCG), promoting progesterone production crucial for sustaining pregnancy.
- HCG becomes detectable in maternal blood and urine by the end of the second week, forming the basis of pregnancy tests.
Quiz Question
- The composition of the embryonic disk at day 14 consists of:
- (B) Epiblast and hypoblast.
Bilaminar Embryonic Disc Formation
- The bilaminar disc forms at the end of the first week of development.
- Composed of two layers: Epiblast (1ry ectoderm) with high columnar cells and Hypoblast (1ry endoderm) with small cubical cells.
- The embryonic plate transitions from a circular to an oval to a pear-shaped structure.
Yolk Sac and Amniotic Cavity
-
Yolk Sac:
- Formed by an extension of the hypoblast.
- Boundaries: Roof from hypoblast; floor and sides from Hauser's membrane.
-
Amniotic Cavity:
- Develops from epiblast extension starting around day 7 or 8.
- Boundaries: Roof and sides by amnioblast; floor by epiblast.
Extraembryonic Mesoderm Formation
- Originates from hypoblast and cytotrophoblast.
- Appears between the trophoblast externally and yolk sac and amniotic cavity internally.
- Extraembryonic Coelom: Isolated spaces in the mesoderm fuse to create a large cavity.
Extraembryonic Mesoderm Layers
- Divided into two layers:
- Somatic Mesoderm: Lines the trophoblast.
- Splanchnic Mesoderm: Covers the primary yolk sac.
- Layers connect at the caudal end, forming the connecting stalk, precursor to the umbilical cord.
- Chorion is formed by the trophoblast and somatic mesoderm.
Trophoblast Changes
- The trophoblast differentiates into two layers:
- Cytotrophoblast: Inner mononucleated cell layer.
- Syncytiotrophoblast: Outer multinucleated mass; creates lacunae filled with maternal blood to form intervillous spaces essential for placenta development.
Clinical Relevance
- Syncytiotrophoblast secretes Human Chorionic Gonadotropin (HCG), promoting progesterone production crucial for sustaining pregnancy.
- HCG becomes detectable in maternal blood and urine by the end of the second week, forming the basis of pregnancy tests.
Quiz Question
- The composition of the embryonic disk at day 14 consists of:
- (B) Epiblast and hypoblast.
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Description
This quiz covers the cell cycle, including the stages of mitosis and meiosis, and the distinction between these two types of cell division. It also delves into the processes of spermatogenesis and oogenesis, particularly focusing on the maturation of female gametes. Test your understanding of these vital biological processes!
