Name: Spermatogenesis
Uploaded: 2019-07-19
Duration: 8 min 2 s
Description: Spermatogenesis is the origin and development of the sperm cells within the male reproductive organs, the testes. Watch this video for more information.

Question

Describe the physico-chemical events that take place during fertilization in humans.

Accepted Answer

Fertilization in sexual reproduction involves the fusion of male and female gametes to form a diploid zygote. It takes place in the ampullary-isthmic junction of the oviduct in humans and involves the following physicochemical events:
1. Capacitation: As sperms reach the female genital tract, they undergo capacitation during which the sperms acquire the capacity to fertilize eggs by the secretions of the female genital tract. These secretions remove coating substances deposited on the surface of the sperms specifically present on the acrosome.
2. Fertilizin and antifertilizin reaction: The agglutination of the spermatozoa by egg and adhesion of the spermatozoa to its egg membranes is known as fertilizin and antifertilizin reaction. Fertilizin is a glycoprotein present on the surface of eggs. Antifertilizin is another chemical substance on the surface layer of the cytoplasm or protoplasm of spermatozoa.
3. Acrosomal reaction: In this reaction, the acrosome releases hydrolytic enzymes called sperm lysins after coming in contact with the surface of the egg covering. The three sperm lysins are:
Hyaluronidase acts on the ground substance of follicle cells.
Corona penetrating enzyme that dissolves the corona radiata cells that are around the female gamete.
Acrosin dissolves the zona pellucida layer that surrounds the oocyte to be unable to reach the ovum.
The binding of the sperm to the egg induces depolarization of the egg plasma membrane that acts as the fast block to polyspermy.
4. Cortical reaction: After fusion of sperm and egg plasma membrane, the egg shows a vertical reaction in which cortical granules beneath the ovum's plasma membrane release enzymes between it and zona pellucida. These enzymes harden zona pellucida, now ensuring the blockage of entry of other sperms.
5. Zygote formation: The egg extends around entering sperm, forming a fertilization core. It takes the entire sperm into the egg.
Sperm contacts with the oocyte and triggers the completion of the second division. The union of the ovum and sperm nucleus, i.e., karyogamy, forms the zygote.

Describe the physico-chemical events that take place during fertilization in humans.

Important Questions on Human Reproduction

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