Question

What do you mean by implantation?
(a) Fusion of male gamete with a female gamete
(b) Embedding of an embryo in the thick lining of the uterus
(c) Developing a special tissue between uterus wall and embryo
(d) The period of gestation
(e) None of these

Answer 1

It is one of the stages that occur during the pregnancy where the embryo gets embedded in the endometrium for the supply of oxygen along with the nutrients for developing fetus from the outside of the body.

Complete answer:
Implantation is a mechanism in which a developing embryo makes contact with the uterine wall and stays attached to it until birth, passing through the uterus as a blastocyst.
Zygote cleaves to change into ‘Blastocyst’ which is implanted in the uterus.
Blastulation or Blastocyst formation: Endometrium secretes a nutrient fluid and its mucosal cells become enlarged with stored nutrients. As the morula enters the uterus, it gets a rich supply of nutrients. Outer peripheral cells enlarge and flatten further. They form trophoblast or trophectoderm. Trophoblast cells secrete a fluid into the interior creating a cavity called the blastocoel. As the blastocoel develops, the morula transforms into a blastula known as blastocyst in mammals as of the distinct nature of the surface layer and inner cell mass.
Implantation: It is embedding the blastocyst into the endometrium of the uterus. Blastocyst comes in contact with the endometrium in the region of the embryonal knob or embryonic disc and adheres to it. The surface cells of trophoblast secrete lytic enzymes which cause corrosion of the endometrial lining. They give rise to finger-like outgrowths called villi. Villi not only helps in fixation but also in the absorption of nutrients. Implantation causes nutrient enrichment, enlargement of cells, and formation of the uterine part of the placenta called decidua.
-Progesterone is the hormone which is a steroid hormone produced in the body of females. It helps in the preparation of the endometrium of the uterus which will help in pregnancy. It also helps in the implantation of the embryo to the placenta formed by it.

So, the correct answer is ‘Embedding of an embryo in the thick lining of the uterus’.

Note:
The zygote starts dividing as well as traveling towards the uterus at the same time. It forms morula at about the 4th day. It then forms blastocysts and enters the uterus at about 4 or 5 days after fertilization. Implantation occurs 7 days after fertilization. The formation of the gastrula occurs after implantation.