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Questions and Answers
What triggers the activation of the oocyte upon sperm penetration?
What triggers the activation of the oocyte upon sperm penetration?
Which of the following describes the fast block to polyspermy?
Which of the following describes the fast block to polyspermy?
What is the main consequence of polyspermy in fertilization?
What is the main consequence of polyspermy in fertilization?
What happens during cleavage after fertilization?
What happens during cleavage after fertilization?
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What is the morula stage characterized by?
What is the morula stage characterized by?
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Which mechanism acts as the slow block to polyspermy?
Which mechanism acts as the slow block to polyspermy?
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What is the primary outcome of successful fertilization?
What is the primary outcome of successful fertilization?
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What occurs immediately after the zygote formation?
What occurs immediately after the zygote formation?
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Which statement correctly contrasts cleavage and blastocyst formation?
Which statement correctly contrasts cleavage and blastocyst formation?
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What crucial prevention mechanism is reinforced by the slow block to polyspermy?
What crucial prevention mechanism is reinforced by the slow block to polyspermy?
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Study Notes
Fertilization Process
- Sperm migration: Sperm travel through the female reproductive tract, guided by chemical signals from the egg. Only a small percentage reach the oocyte.
- Capacitation: Sperm become capable of penetrating the egg within the female reproductive tract. This involves biochemical changes increasing sperm motility and preparing for acrosomal reaction.
- Sperm-egg binding and penetration:
- Sperm binds to ZP3 receptors on the zona pellucida (a glycoprotein layer around the egg).
- Acrosome reaction: Sperm release enzymes to break down the zona pellucida.
- Sperm fuses with the oocyte's membrane (oolemma), allowing the sperm nucleus to enter the oocyte cytoplasm.
- Activation of the oocyte and prevention of polyspermy:
- Cortical reaction: Cortical granules release enzymes, modifying the zona pellucida, preventing multiple sperm from fertilizing the egg.
- Completion of meiosis II: The activated oocyte completes meiosis II, forming a mature ovum and a polar body.
- Intracellular calcium wave: A sudden increase in intracellular calcium ions (Ca2+) triggered by sperm entry, spreads through the oocyte in a wave-like pattern. This is crucial for oocyte activation.
Mechanisms for Completion of Meiosis II and Polyspermy Prevention
- Completion of Meiosis II: The oocyte is arrested in metaphase II before fertilization. Activation triggers the completion of meiosis II.
- Formation of the Second Polar Body: During meiosis II, a small structure (polar body) containing excess chromosomes is extruded.
- Formation of the Female Pronucleus: The oocyte's genetic material reorganizes into a nucleus (pronucleus), which will later fuse with the male pronucleus.
- Fast block to polyspermy: Membrane depolarization (temporary change in electrical charge) prevents other sperm from fusing with the oocyte membrane.
- Slow block to polyspermy (Cortical reaction): A permanent block, triggered by the calcium wave, as enzymes from cortical granules modify the zona pellucida permanently, making it impermeable to additional sperm.
Formation of the Zygote
- Pronuclei Fusion: The sperm and egg nuclei (pronuclei) fuse, combining their genetic material to form a zygote. The zygote contains a full set of chromosomes.
- Cleavage: Rapid mitotic cell divisions without growth, resulting in a multicellular structure.
- Initial stages of cleavage:
- First cleavage forming two blastomeres within 24-36 hours after fertilization.
- Subsequent divisions: Rapid cell divisions occur, compacting cells.
- Morula stage: 16-32 cells, a solid mass.
- Blastocyst formation: A fluid-filled cavity (blastocoel) forms inside the morula, transforming it into a blastocyst. Blastocyst has two types of cells: inner cell mass (ICM) and trophoblast.
- Zona pellucida disappears: allowing implantation.
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Description
Test your knowledge on the stages of fertilization, including sperm migration, capacitation, and the mechanisms involved in sperm-egg binding and penetration. Explore key concepts such as the acrosome reaction and prevention of polyspermy. This quiz is perfect for biology students learning about human reproduction.
