Zoology · Ch 2 — Human Reproduction
Fertilisation and Implantation
Fertilisation and Implantation
Fertilisation is the fusion of a haploid sperm with a haploid ovum to form a single diploid cell, the zygote, and the chapter is careful to point out that it can only happen if sperm and egg are delivered, at the same time, to one specific location — the ampullary-isthmic junction of the fallopian tube. Reaching that point successfully, and then successfully fusing, is itself a multi-step biochemical and physical process, covered in detail in the section that f …
What this figure shows. A sequential four-panel diagram of fertilisation. Panel one shows the sperm migrating through the coat of follicle cells (the corona radiata) surrounding the egg and binding to receptor molecules in the zona pellucida. Panel two shows this binding inducing the acrosomal reaction, in which the sperm releases the enzyme hyaluronidase into the zona pellucida. Panel three shows breakdown of the zona pellucida by these enzymes, allowing the sperm to reach the egg's plasma membrane. Panel four shows the sperm nucleus and other components entering the egg cytoplasm while cortical granules released from the egg cytoplasm form a barrier called the fertilisation membrane around the egg, which now blocks polyspermy — with follicle cells, sperm nucleus, acros …