Developmental biologyLesson 1 of 3 in the course Development and Inheritance

Human Fertilization: Gamete Fusion, Polyspermy, and Early Outcomes

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Fertilization begins with the journey of sperm through the female reproductive tract and the preparation that enables them to fertilize an oocyte. This lesson explains why so many sperm are released, how long sperm and oocytes can survive, and what capacitation does.

During ejaculation, hundreds of millions of sperm, also called spermatozoa, are released into the vagina. Only a small fraction reach the uterine tubes, the usual site where sperm encounter an oocyte. Many sperm are lost along the way: the vagina's acidic environment (approximately pH 3.8) overcomes many, thick cervical mucus blocks others from entering the uterus, and phagocytic uterine leukocytes destroy additional sperm.

All flashcards

What is capacitation?
Changes sperm undergo in the female reproductive tract that improve motility and prepare them to release enzymes needed for fertilization.
How do the fast and slow blocks prevent polyspermy?
The fast block depolarizes the oocyte membrane to prevent additional fusion; the calcium-triggered cortical reaction creates a longer-lasting barrier.
How does fertilization produce a diploid zygote?
The haploid pronuclei derived from the sperm and ovum approach one another, their nuclear envelopes break down, and their genetic material combines.
How do dizygotic and monozygotic twins form?
Dizygotic twins develop from two separately fertilized eggs; monozygotic twins develop when one zygote splits into two.
What is intracytoplasmic sperm injection (ICSI)?
An IVF technique in which one sperm is injected directly into an egg when sperm numbers or function are severely limited.

Quiz questions

  1. What interaction triggers the acrosomal reaction that helps a sperm penetrate the zona pellucida?Answer: The sperm binds to receptors in the zona pellucida.
  2. What change produces the fast block to polyspermy?Answer: A change in sodium-ion permeability depolarizes the oocyte membrane.
  3. Which description identifies dizygotic twins?Answer: Twins formed from two eggs fertilized by separate sperm.
  4. When may intracytoplasmic sperm injection be used during IVF?Answer: When sperm numbers or function severely limit fertilization.
  5. What is the purpose of transferring fewer embryos during IVF?Answer: To reduce the likelihood of multiple-birth pregnancies.

Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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