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Questions and Answers
What is the duration of the Zygotic Stage of prenatal development?
What is the duration of the Zygotic Stage of prenatal development?
Where does fertilization occur?
Where does fertilization occur?
What is the term for the event in which a mature oocyte is expelled from the ovary?
What is the term for the event in which a mature oocyte is expelled from the ovary?
What is the function of the acrosome reaction?
What is the function of the acrosome reaction?
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How many stages of prenatal development are there?
How many stages of prenatal development are there?
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What is the term for the process of fusion of the oocyte and sperm cell membranes?
What is the term for the process of fusion of the oocyte and sperm cell membranes?
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What is the purpose of capacitation?
What is the purpose of capacitation?
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At what day of a regular 28-day menstrual cycle does ovulation occur?
At what day of a regular 28-day menstrual cycle does ovulation occur?
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At which stage do cells become arranged in a hollow sphere?
At which stage do cells become arranged in a hollow sphere?
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What is the outer layer of cells in a morula called?
What is the outer layer of cells in a morula called?
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How many cells are present in a morula?
How many cells are present in a morula?
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At which stage do cells start to lose totipotency?
At which stage do cells start to lose totipotency?
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What is the function of the zona pellucida?
What is the function of the zona pellucida?
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When does implantation of the blastocyst begin?
When does implantation of the blastocyst begin?
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How many cells are present after 72 hours of fertilization?
How many cells are present after 72 hours of fertilization?
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What happens to the zona pellucida by day 5-6?
What happens to the zona pellucida by day 5-6?
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What happens to the zona pellucida during blastocyst formation?
What happens to the zona pellucida during blastocyst formation?
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What is the function of the proteolytic enzymes secreted by the syncytiotrophoblast?
What is the function of the proteolytic enzymes secreted by the syncytiotrophoblast?
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During which stage of the menstrual cycle does the uterine endometrium prepare for implantation?
During which stage of the menstrual cycle does the uterine endometrium prepare for implantation?
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What is the main function of the HCG secreted by the syncytiotrophoblast?
What is the main function of the HCG secreted by the syncytiotrophoblast?
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What is the purpose of the lacunar spaces in the syncytiotrophoblast?
What is the purpose of the lacunar spaces in the syncytiotrophoblast?
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How many days after ovulation does the secretory phase of the menstrual cycle begin?
How many days after ovulation does the secretory phase of the menstrual cycle begin?
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What is the primary function of syncytiotrophoblasts during implantation?
What is the primary function of syncytiotrophoblasts during implantation?
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During which days does the process of implantation take place?
During which days does the process of implantation take place?
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What is the most common type of ectopic pregnancy?
What is the most common type of ectopic pregnancy?
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What is the name of the membrane that forms around the exocoelomic cavity?
What is the name of the membrane that forms around the exocoelomic cavity?
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What is the name of the layer of endometrium that the blastocyst burrows into?
What is the name of the layer of endometrium that the blastocyst burrows into?
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What is the structure that forms from the epiblast?
What is the structure that forms from the epiblast?
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What is the main function of the enzymes in the acrosome of a sperm?
What is the main function of the enzymes in the acrosome of a sperm?
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What happens to the oocyte if it is not fertilized within 24 hours of ovulation?
What happens to the oocyte if it is not fertilized within 24 hours of ovulation?
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What is the result of the cortical and zona reactions?
What is the result of the cortical and zona reactions?
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What is the term for the process by which the zygote undergoes a series of mitotic divisions?
What is the term for the process by which the zygote undergoes a series of mitotic divisions?
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What is the term for the cells that result from cleavage?
What is the term for the cells that result from cleavage?
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What is the result of the metabolic activation of the egg?
What is the result of the metabolic activation of the egg?
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How many cells are present in a morula?
How many cells are present in a morula?
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When does the oocyte finish its second meiotic division?
When does the oocyte finish its second meiotic division?
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Study Notes
Prenatal Development
- The three stages of prenatal development from conception to birth are:
- Zygotic (or Germinal) Stage (0-2 weeks)
- Embryonic Stage (2-8 weeks)
- Fetal Stage (9-40 weeks)
Ovulation
- A mature oocyte is expelled from the ovary around the 14th day of a regular 28-day menstrual cycle.
Fertilization
- Fertilization occurs in the ampullary region of the uterine tube.
- The three phases of fertilization are:
- Penetration of the corona radiata
- Penetration of the zona pellucida
- Fusion of the oocyte and sperm cell membranes
- Capacitation is necessary for sperm to penetrate the corona radiata and undergo the acrosome reaction.
- The acrosome reaction releases enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances.
Results of Fertilization
- The main results of fertilization are:
- Restoration of the diploid number of chromosomes
- Determination of the sex of the new individual
- Initiation of cleavage
Cleavage
- Cleavage is a series of mitotic divisions that increase the number of cells, known as blastomeres.
- The cells divide every 12-24 hours, resulting in:
- 2-cell stage (36 hours)
- 4-cell stage (48 hours)
- 8-cell stage (72 hours)
- Morula (12-16 cells) or Blastula
- Until the 8-cell stage, the cells are totipotent.
Blastocyst Formation
- The blastocyst forms around the 5th day.
- Fluid penetrates the zona pellucida into the intercellular spaces of the inner cell mass, forming a single cavity, the blastocele.
- The embryoblast is at one pole, and the outer cell mass, or trophoblast, flattens and forms the epithelial wall of the blastocyst.
Implantation
- Implantation begins around the 6th day.
- The trophoblastic cells over the embryoblast pole penetrate between the epithelial cells of the uterine mucosa.
- Syncytiotrophoblasts secrete proteolytic enzymes to erode the endometrium and human chorionic gonadotropin (hCG) to sustain the corpus luteum.
Uterus at Time of Implantation
- The uterine endometrium passes through three stages during the menstrual cycle:
- Menstrual phase
- Proliferative phase (influenced by estrogen)
- Secretory phase (influenced by progesterone produced by the corpus luteum)
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Description
Learn about the stages of prenatal development from ovulation to implantation, including fertilization, cleavage, and implantation. Understand the normal site of fertilization and results.
