Slideshow: Early Events

Fertilization Begins

#363, Slide 2 of 24

From The Biology of Prenatal Development.

Note:

Fertilization begins when a single spermatozoon penetrates the zona pellucida, which surrounds the oocyte. This event triggers a reaction called the zona reaction, which dramatically alters the outer membrane and prevents the entry of any additional spermatozoa into the oocyte.

Label Key:

1. principal piece of spermatozoon

2. zona pellucida

3. midpiece

4. neck

5. postacromial region

6. acrosomal cap

All ages referenced to fertilization, not last menstrual period.

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