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Questions and Answers
What is the primary result of the meiotic division in oogenesis?
What is the primary result of the meiotic division in oogenesis?
Which phase of fertilization involves the penetration of the zona pellucida?
Which phase of fertilization involves the penetration of the zona pellucida?
What happens immediately after a sperm enters an oocyte during fertilization?
What happens immediately after a sperm enters an oocyte during fertilization?
How many chromosomes do human gametes contain after meiosis?
How many chromosomes do human gametes contain after meiosis?
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What is the first embryonic stage that occurs after fertilization?
What is the first embryonic stage that occurs after fertilization?
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Which layer of the trophoblast is responsible for the invasive properties into the uterine lining?
Which layer of the trophoblast is responsible for the invasive properties into the uterine lining?
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What are the two layers formed by the embryoblast during the bilaminar germ disc stage?
What are the two layers formed by the embryoblast during the bilaminar germ disc stage?
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Which germ layer is established first during gastrulation?
Which germ layer is established first during gastrulation?
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What structure forms from the extraembryonic mesoderm?
What structure forms from the extraembryonic mesoderm?
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The mesoderm layer is primarily responsible for forming which of the following?
The mesoderm layer is primarily responsible for forming which of the following?
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What is the process called when the zygote undergoes rapid mitotic division?
What is the process called when the zygote undergoes rapid mitotic division?
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Which of the following is NOT a cavity formed during the second week of development?
Which of the following is NOT a cavity formed during the second week of development?
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Which of the following structures forms first after fertilization?
Which of the following structures forms first after fertilization?
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Which embryonic structure is indicated as the notochordal process?
Which embryonic structure is indicated as the notochordal process?
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What is the role of the decidua in early pregnancy?
What is the role of the decidua in early pregnancy?
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Which germ layer gives rise to the epithelial lining of the digestive tract?
Which germ layer gives rise to the epithelial lining of the digestive tract?
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What type of cells are formed in the embryoblast during the early blastocyst stage?
What type of cells are formed in the embryoblast during the early blastocyst stage?
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How does the endometrium respond to the implantation of the blastocyst?
How does the endometrium respond to the implantation of the blastocyst?
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Which layer of the bilaminar embryonic disc is located dorsally?
Which layer of the bilaminar embryonic disc is located dorsally?
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Which cavity is formed within the blastocyst?
Which cavity is formed within the blastocyst?
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What axis positions are established by the differentiation of cells in the hypoblast layer?
What axis positions are established by the differentiation of cells in the hypoblast layer?
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Study Notes
Gametogenesis
- During meiosis, diploid cells divide twice to produce four haploid cells (gametes)
- Humans have 46 chromosomes (2n) in a diploid cell, 23 chromosomes (n) in each gamete
- In spermatogenesis, each spermatogonium produces 4 active sperms
- In oogenesis, each primary oocyte produces one active ovum and four polar bodies
Fertilization
- Fertilization is the fusion of genetic material (pronuclei) from sperm and ovum to form a zygote
- Phases of fertilization: penetration of corona radiata, penetration of zona pellucida, fusion of oocyte and sperm cell membranes
- Fertilization typically occurs in the uterine tubes and the resulting zygote takes 4-5 days to implant in the uterine cavity
The Embryonic Period
- The embryonic period spans the first 8 weeks after fertilization
- During the first week, the oocyte finishes its second meiotic division, forming the female pronucleus
- The zona pellucida becomes impenetrable to other sperm
- The sperm’s head separates from the tail, swells, and forms the male pronucleus
- Cleavage begins in the first week, where the zygote undergoes rapid mitotic division
- Blastomeres form, which are progressively smaller cells produced by cleavage
- A morula (solid ball of cells) forms 3-4 days after fertilization, followed by the blastocyst (hollow ball of cells) a day later
- Implantation occurs 7-8 days after fertilization when the blastocyst attaches to the endometrium
- The decidua is the modified portion of the endometrium after implantation
Second Week of Development: Bilaminar Germ Disc
- The embryoblast differentiates into epiblast and hypoblast cells
- Epiblast layer forms dorsally and hypoblast layer forms ventrally, adjacent to the blastocyst cavity (blastocele)
- Anterior cells in the hypoblast layer differentiate into anterior visceral endoderm, defining the embryo's cranial side
- By 4 to 6 days of gestation, both dorso-ventral and cranio-caudal axes are established
- The trophoblast differentiates into two layers: the cytotrophoblast and syncytiotrophoblast
- The embryoblast forms two layers: the epiblast and hypoblast
- The extraembryonic mesoderm splits into two layers: the somatic and splanchnic layers
- Two cavities form: the amniotic and yolk sac cavities
Third Week of Development: Trilaminar Germ Disc
- The developing embryo continues to grow, forming a trilaminar embryonic disc destined to become the fetus
- Four extraembryonic membranes develop: amnion, yolk sac, allantois, and chorion
- Gastrulation occurs, establishing all three germ layers: ectoderm, mesoderm, and endoderm
- Ectoderm forms the superficial layer
- Mesoderm forms the middle layer
- Endoderm forms the inner layer
Trilaminar Germ Disc Development
- Ectoderm differentiates into the nervous system (brain and nerves) and the epidermis of the skin
- Mesoderm is loosely organized connective tissue (mesenchyme) that matures into blood, muscles, bones, etc.
- Endoderm gives rise to the epithelial lining of the digestive and respiratory tracts, as well as other organs. It also forms the endothelial lining of blood vessels.
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Description
Explore the processes of gametogenesis and fertilization in this quiz. Learn how meiosis leads to the formation of haploid gametes and understand the phases of fertilization. You'll also delve into the embryonic period and the early stages of human development.
