Stages of pregnancy

Pregnancy starts with fertilisation and ends with childbirth. Fertilisation

This is the fusion of a spermatozoon with an ovum.

Spermatozoa

Ovum

Spermatozoa

Ovum

Zona pellucida

Fig 10.2 Fertilisation

The spermatozoon approaches the ovum and penetrates the inner membrane of the ovum called the zona pellucida. This triggers the ovum's meiotic division, following meiosis, and makes the zona pellucida impenetrable to other spermatozoa. After the spermatozoon penetrates the ovum, its nucleus is released into the ovum, its tail degenerates, and its head enlarges amd fuses with the ovum's nucleus. This fusion provides the fertilised ovum, now called a zygote, with 46 chromosomes.

Pregnancy And Childbirth

Pregnancy And Childbirth

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