Question

How does the embryo get nourishment inside the mother’s body?

Answer 1

Hint: The embryo gets nourishment from the mother's body with the help of a specialized membrane unique to mammals. Mammals can be grouped into three categories Prototheria, Metatheria, and Eutheria. The specialized structure is absent in Prototheria and most developed in Eutheria.

Complete answer:
The embryo after implantation in the uterine endometrium undergoes certain changes. The trophoblast layer differentiates and forms finger-like projections known as chorionic villi. The chorionic villi and the surrounding tissue interlink with each other and jointly form a membrane-like structure, the placenta. This placenta acts as the functional and structural unit in between the developing embryo and maternal body. The embryo obtains all its nourishment from the placenta.

The major functions performed by the placenta are:
> Protection of the embryo: Placenta helps to prevent the entry of pathogens from the maternal body, allows antibodies to pass through the membrane, prevents the mixing of maternal blood with fetal blood.
> Exchange of gases: Gases like oxygen diffuse through the placenta to reach the embryo and carbon dioxide is expelled out into the maternal blood from the embryo.
> Supply of Nutrients: Essential amino acids, sugars like glucose, lipids, vitamins, etc pass into the embryo from maternal blood with the help of the placenta.
> Other Functions: Several functions such as thermoregulation, waste excretion by the developing embryo, all are aided by the placenta.

Note: It is important to remember that the placenta does not allow the passage of all antibodies through it. Immunoglobulin G or IgG is the only class of antibody that can pass through the placenta. Also, the placenta can not prevent the passage of HIV from maternal blood to embryonic blood, so if the mother is HIV positive, the child born will also be HIV positive.