Notes from NEET topper
FERTILIZATION
Fertilization in human reproduction is a crucial process that marks the beginning of a new life. It involves the fusion of a male sperm cell with a female egg (ovum) to form a zygote, which then develops into an embryo. Here’s a detailed overview of the process:
- Gamete Formation
In Males: Spermatozoa are produced in the testes through a process called spermatogenesis.
In Females: Ova, or egg cells, are produced in the ovaries through a process called oogenesis.
- Ovulation
The female reproductive cycle involves the release of a mature egg from the ovary, a process known as ovulation. This typically occurs midway through the menstrual cycle.
- Sperm Entry
During sexual intercourse, sperm are ejaculated into the female reproductive tract. Millions of sperm travel through the vagina, into the uterus, and up into the fallopian tubes.
- Fertilization Site
Fertilization usually takes place in the fallopian tubes, specifically the ampulla (the widest section of the tubes).
- Encounter Between Sperm and Egg
Out of millions, only a few sperm reach the vicinity of the egg. The sperm must penetrate the outer layers of the egg, including the corona radiata and the zona pellucida.
- Acrosome Reaction
The acrosome, a cap-like structure on the head of the sperm, releases enzymes that help the sperm to penetrate the egg’s outer layers.
- Fusion of Gametes
Once a single sperm successfully penetrates the zona pellucida, it fuses with the egg’s membrane. This triggers a reaction that prevents other sperm from entering the egg.
- Zygote Formation
The sperm’s nucleus merges with the egg’s nucleus, combining the genetic material from both parents and forming a zygote.
- Genetic Combination
The zygote contains a full set of chromosomes (half from each parent), and it represents the first cell of a new individual.
- Embryonic Development
The zygote undergoes rapid cell division (cleavage) and moves towards the uterus for implantation.
- Implantation
About a week after fertilization, the developing embryo (now called a blastocyst) implants in the lining of the uterus, where it continues to grow and develop into a fetus.
Timing: Fertilization must occur within a specific time frame after ovulation, as the egg’s viability and the sperm’s fertilizing capability are limited (usually 24 hours for the egg and up to 5 days for the sperm). Assisted Reproductive Technology (ART): In cases of infertility, techniques such as In Vitro Fertilization (IVF) may be employed. In IVF, fertilization occurs outside the body, and the embryo is then implanted in the uterus.
