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Questions and Answers
What is the duration of the Zygotic Stage of prenatal development?
Where does fertilization occur?
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?
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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?
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What is the purpose of capacitation?
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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?
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What is the outer layer of cells in a morula called?
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How many cells are present in a morula?
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At which stage do cells start to lose totipotency?
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What is the function of the zona pellucida?
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When does implantation of the blastocyst begin?
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How many cells are present after 72 hours of fertilization?
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What happens to the zona pellucida by day 5-6?
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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?
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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?
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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?
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What is the primary function of syncytiotrophoblasts during implantation?
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During which days does the process of implantation take place?
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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?
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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?
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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?
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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?
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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?
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How many cells are present in a morula?
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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.