Human fertilization

Human fertilization is the union of a human egg cell and sperm that occurs in the female reproductive system. This process involves several stages, including ovulation, fertilization, and implantation, resulting in the formation of a zygote, which eventually develops into a fetus.

Ovulation

Ovulation is the process by which a mature egg is released from the ovary. This usually occurs in the middle of the menstrual cycle. The egg then travels down the fallopian tube, where it can be fertilized by sperm.

Fertilization

Fertilization is the fusion of an egg and sperm cell. The sperm must first penetrate the outer layer of the egg, known as the zona pellucida. Once a sperm has penetrated this layer, the egg undergoes a process called cortical reaction which prevents other sperm from fertilizing the same egg. The nuclei of the egg and sperm then fuse, forming a single cell called a zygote.

Implantation

Following fertilization, the zygote begins to divide and grow into a ball of cells known as a blastocyst. The blastocyst travels down the fallopian tube and into the uterus, where it implants into the uterine wall. This process is known as implantation.

Development of the Embryo and Fetus

After implantation, the blastocyst develops into an embryo. The embryo continues to grow and develop, eventually becoming a fetus. The entire process from fertilization to birth takes approximately nine months, or 40 weeks, and is divided into three trimesters.

See Also

• Pregnancy
• Reproductive system
• Embryogenesis
• In vitro fertilization

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  Zygote formation during fertilization

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  Preembryonic development stages

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  Diagram of an ovum