Human Fertilization | Zygote | Blastocyst | Embryology

#HumanFertilization #Fertilisation #Zygote #embryology

Human Fertilization | Zygote | Blastocyst | Embryology

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▬▬▬▬▬▬▬▬▬▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬

Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally called fertilization. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro.

After the sperm enters the cytoplasm of the oocyte (also called ovocyte), the tail and the outer coating of the sperm disintegrate and the cortical reaction takes place, preventing other sperm from fertilizing the same egg. The oocyte now undergoes its second meiotic division producing the haploid ovum and releasing a polar body. The sperm nucleus then fuses with the ovum, enabling fusion of their genetic material.

When the sperm enters the vitelline space, receptors on the sperm head called Izumo1 bind to Juno on the oocyte membrane. Once it’s bound, 2 blocks to polyspermy then occur. After approximately 40 minutes, the other Juno receptors on the oocyte are lost from the membrane, causing it to no longer be fusogenic. Additionally, the cortical reaction will happen which is caused by ovastacin binding and cleaving ZP2 receptors on the zona pellucida. These two blocks of polyspermy are what prevent the zygote from having too much DNA.
Human Fertilization - Zygote - Blastocyte - Embryology

(0:00-6:58)
Defining Fertilization; Zygote & Embryo.
Fallopian Tube/Uterine Tube anatomy; seat of fertilization.

(7:00-15:12)
Transportation of Ovum & Sperm; in detail.
Role of Luteinizing Hormone(LH) & Follicle Stimulating Hormone(FSH).
Corona Radiata & role of Fimbriae in transport of Ovum into Fallopian Tube.
Differentiating b/w Primary, Secondary & Definitive Ovum; fate of Secondary Ovum in absence of fertilization.

(15:13-24:03)
Slow movement of sperm through vagina; Semen & Ejaculate.
Role of Vesiculase enzyme; vaginal environment & sperm motility.
Energy source for sperm's movement.

(24:05-31:44)
Fast movement of sperm through the cervix & rest of the Fallopian Tube;
Role of Prostaglandins, chemo attractants & cilia of fallopian tube.

(31:46-37:08)
Importance of Capacitation Reaction for the motility & later fertilization of the sperm inside the Fallopian Tube; "Conditioning" of the sperm inside the female reproductive tract.
Only Capacitated sperms are able to cross Corona Radiata.

(37:10-50:20)
Explanation of Acrosomal Reaction; fusion of sperm with oocyte.
Cortical reaction in the ovum leading to Zona reaction; inactivation of specie-specific receptor & impermeability to any remaining sperms.

(50:21-57:52)
Fusion of genetic materials; ovum undergoing 2nd meiotic division; Formation of Definitive Ovum.

(57:54-1:00:06)
Recap:
1-Cortical & Zona reaction.
2-Completion of 2nd meiotic division; formation of definitive ovum.
3-Metabolic activation of Ovum; fate of fertilized & unfertilized ovum.

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