General embryology : PART 3 Fertilization

 

Fertilization

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Definition: The process by which male and female gametes fuse to form zygote

Site of fertilization: the ampullary region of the uterine tube

Spermatozoa are not able to fertilize the oocyte immediately uponarrival in the female genital tract but must undergo a) capacitation  b) acrosome reaction to acquire this capability.

Capacitation :is a period of conditioning in the female reproductive tract that in the human lasts approximately 7 hours

The acrosome reaction:which occurs after binding to the zona pellucida, is induced by zona proteins.

The phases of fertilization include

Phase 1: penetration of the corona radiata

Phase 2: penetration of the zona pellucida.

Phase 3: fusion of the oocyte and sperm cell membranes.

The main results of fertilization are as follows

• restoration of the diploid number of chromosomes
• determination of sex
• initiation of cleavage

Egg responses in three ways when the spermatozoon has entered the oocyte

1.      Cortical and zona reactions:

a) The oocyte membrane becomes impenetrable to other spermatozoa.

b) Zona pellucida alters its structure and composition to prevent sperm binding and penetration.

2.      Resumption of the second meiotic division.

3.      Metabolic activation of the egg.

Zygote

This cell formed by the union of an oocyte and a sperm during fertilization

·         Cleavage:itis a series of mitotic divisions that results in an increase in cells, blastomeres, which become smaller with each division.

·        Morula: the 12-16 cell stage of the early embryo at 3 days post conception

• Blastocyst:after the morula enters the uterus from the uterine tube, a fluid filled cavity –  the blastocyst cavity –develops inside it . This change converts the morula into a blastocytes

Q: In which phase of menstrual cycle implantation is occurred?

Ans:implantation is occurred at the secretory phase of menstrual cycle, during this time endometrium is rich in nutrition, secretion present within the glands, stroma cells, also known as decidual cells  are  rich in glycogen and lipid ,