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Questions and Answers
What is the primary role of the acrosome in sperm fertilization?
What is the primary role of the acrosome in sperm fertilization?
Which of the following best describes the process of capacitation in sperm?
Which of the following best describes the process of capacitation in sperm?
What structure in sperm is responsible for motility?
What structure in sperm is responsible for motility?
Why are mitochondria inherited exclusively from the mother?
Why are mitochondria inherited exclusively from the mother?
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Where does fertilization primarily occur within the female reproductive tract?
Where does fertilization primarily occur within the female reproductive tract?
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What is the first phase of fertilization?
What is the first phase of fertilization?
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Which substance is released during the acrosome reaction to help penetrate the zona pellucida?
Which substance is released during the acrosome reaction to help penetrate the zona pellucida?
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At which stage does the morula enter the uterus after fertilization?
At which stage does the morula enter the uterus after fertilization?
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What forms the fetal part of the placenta during blastocyst formation?
What forms the fetal part of the placenta during blastocyst formation?
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What is the primary outcome of fertilization regarding chromosome number?
What is the primary outcome of fertilization regarding chromosome number?
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Study Notes
Fertilization, Cleavage, & Implantation
- Fertilization: The process of mature sperm and ovum meeting and fusing to form a zygote.
- Site: The ampullary region (lateral third) of the uterine tube.
Stages of Fertilization
- Spermatozoa Capacitation: Spermatozoa need conditioning in the female tract (approx. 7 hours in humans) to fertilize an oocyte. This involves removing glycoprotein coats and seminal plasma proteins.
- Acrosome Reaction: Sperm binding to the zona pellucida triggers this reaction. Enzymes (acrosin, trypsin-like substances) are released to penetrate the zona pellucida.
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Phases of Fertilization:
- Phase 1: Penetration of the corona radiata
- Phase 2: Penetration of the zona pellucida
- Phase 3: Fusion of oocyte and sperm head cell membranes
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Results of Fertilization:
- Restoration of the diploid number of chromosomes
- Determination of the sex
- Initiation of cleavage.
Cleavage
- Definition: Mitotic cell divisions that increase cell numbers.
- Site: The uterine tube, medial to the ampulla.
- Morula Stage: The developing embryo of 12-16 blastomeres after fertilization.
- Blastocyst Formation: Fluid from the uterine cavity forms a single cavity (blastocele) as the morula enters the uterine cavity. Blastomeres divide into two groups: the inner cell mass that will form the embryo and the outer cell mass which forms the trophoblast - a key part of the placenta. The zona pellucida disappears prior to implantation.
Implantation
- Definition: Penetration of the blastocyst into the superficial layer of the uterine endometrium.
- Time: Starts around day 6, and completes around day 11 of development.
- Site: The anterior or posterior wall of the uterine body, near the midline.
- Mechanism: The blastocyst attaches to the endometrium by the inner cell mass after the zona pellucida is gone. The trophoblast proliferates forming a cytotrophoblast inner layer and the syncytiotrophoblast outer layer. The latter erodes and burrows maternal uterine tissue, providing nourishment.
Decidua
- Definition: The endometrium after blastocyst implantation.
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Types:
- Decidua basalis: Maternal part of the placenta.
- Decidua capsularis: Covers the blastocyst.
- Decidua parietalis: Remaining uterine lining.
- Decidua marginalis: Junction of capsularis and parietalis.
Clinical Correlates
- Ectopic Pregnancy: Implantation outside the uterus (most commonly in the fallopian tubes). This can lead to potential complications.
- Placenta Previa: Abnormal implantation in the lower uterine segment that can cause complications, potentially interfering with the delivery process.
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Description
This quiz covers key concepts in embryology, focusing on the processes of fertilization, cleavage, and implantation. Explore the stages of fertilization, from sperm capacitation to the fusion of gametes, and understand the importance of each stage in human development.
