Question

A young couple visits a fertility clinic and asks the doctor to explain the basic phenomenon
that lead to conception and implantation.
A. Write down the phases of fertilization (3)
B. What is the normal site of implantation and also explain the layer of uterus in which implantation
takes place. (3)
C. Enlist the changes occurring during the third week of development. (4)

Answer 1

A. Fertilization is defined as the fusion of female gamete egg or ovum with the male gamete sperm.
Phases of fertilization includes :

1. Millions of sperm enters the female reproductive tract but only a fee have the capacity tonreach the ovum and fuse with it.
The sperm undergoes capacitative changes inside the female reproductive tract.
The sperm once reaching the egg fuses with the outer membrane of egg known as corona radiata.
2. The acrosome of the sperm than reacts with zona pellucida layer of egg with the help of hyaluronidase enzyme. This helps entry of sperm into the zona pellucida.
3. This is followed by fusion of plasma membrane of oocyte with the sperm.
B. The fertilization takes place in the ampulla of the fallopian tube. This is followed by implantation of the fertilized ovum into the inner most layer of uterus known as endometrium.
The perimetrium is the outermost layer of uterus and myometrium is the middle layer of uterus.
C. During the third week of pregnancy the blastocyte attaches with the endometrium. This results in growing and thickening of the endometrial layerof uterus. The cell of endometrium proliferates and grow to give nutrition to the implanted egg.