Acrosomal Reaction
The antifertilizin of sperm interchange with the fertilizin ( ZP3, ZP2 ) of the ovum and undergoes an acrosomal reaction to release the sperm lysins. Main sperm lysins are:-
- Hyaluronidase- It takes action on follicle cells.
- Corona penetrating enzyme- It liquefies corona radiata.
- Zona lysine or acrosin- It helps in the digestion of zona pellucida.
For acrosomal reaction, the best pH, Ca++, and Mg++ ions concentration, and temperature are necessary. In acrosomal reactions, Ca++ contributes at a major level. Fertilization does not take place in absence of Ca++. Through chemical acknowledgment, sticking sperm with the egg of the same species is known as agglutination. Because of acrosomal reaction, the plasma membrane of sperm combines with the plasma membrane of the secondary oocyte, in order that sperm enters the oocyte. This helps in preventing polyspermy (entry of more than one sperm into the oocyte). It makes sure that monospermy (entry of only one sperm enters into the oocyte) takes place. The acrosome contains some zona pellucida digesting enzymes that penetrate further into the ovum layers. When sperm goes deeper the acrosome shrinks.
Process of Fertilization in Human Being
Fertilization is the process in which the union of two haploid gametes i.e. male gamete (sperm) and female gamete (ovum) takes place to form a diploid zygote. The concept of fertilization was given by Leeuwenhoek in 1683. In human beings, inside the ampullary isthmic junction of the oviduct (fallopian tube), fertilization takes place. During mating, the male releases semen into the female’s vagina near the cervix. This is called insemination. While releasing, single semen may have 300 million sperms. At the rate of 1.5 to 3 mm per minute, sperms swim in the fluid medium to reach the site. A million sperms are engulfed by the leucocytes of the vaginal epithelium. The mature Graafian follicle of an ovary eject oocyte. The fallopian funnel received the oocyte and transferred it into the Fallopian tube. After releasing from the ovary within 24 hours secondary oocyte can be fertilized. Already second meiotic division is in progress, so, sperm enters the secondary oocyte. Various changes occur in sperm before fertilization, which prepares it to fertilize the ovum. This is called copulation. It takes nearly 5 to 6 hours for capacitation.