The journey of life begins with a single cell. But later it is no longer alone. It
divides repeatedly to form a mass of many cells together. And in this video we
are going to learn about this beautiful process that helps us grow to what we
are, from a single cell! Yes! We will be talking about how the EMBRYO develops! Do we have a scientific name for this process
of Embryo development? Absolutely! It is called the process of EMBRYOGENESIS. In simplest words Embryogenesis is the process
that follows fertilization. Where exactly does the fertilization take
place in humans? Yes! It takes place
in the Fallopian tubes of the female reproductive system. However, before
reaching the uterus, the embryo undergoes a series of divisions that help in its
growth and development. Let us focus on one of the fallopian tubes
where the egg cell has got fertilized. Now this fertilized egg cell will divide to
form two cells, followed by four and so on. This results in the formation of a ball like
structure. This ball contains many
cells inside it. Do you know what this ball of cells is referred
to as? When the cell number in it is sixteen then
it is referred to as “MORULA” This further divides to form a structure called
BLASTULA. So will it have double
the number of cells in it? Blastula is just a stage where the cells arrange
themselves such that they form a hollow mass structure. In fact, the cells align themselves to the
ends and leave a cavity within, which gets filled with fluid. Now the next stage of development will be
the BLASTOCYST. It is the stage
where the embryo will have cells that have got differentiated and will even
differentiate further. Now what exactly is this process of DIFFERENTIATION? Let me explain! Have you ever thought that if we all start
our lives with a single cell, then where do all these different types of cells
in our body come from? Yes I know it’s from the single cell that
was present at the beginning. But HOW
is this possible? The answer to this is the Differentiation
process. As the name
suggests, it is the process in which one cell gets differentiated from the other
cells in its vicinity. As a result, we get a whole new variety of
cells from these differentiated ones, after successive divisions. So coming back to the blastocyst stage…
it is now a mass containing differentiated cells. As it grows further, the body of the embryo
begins to develop. But for its proper growth and development,
don’t you think the embryo will require nutrition? Of course yes! And where will it derive the necessary nutrition
from? You may
say the Mother’s body. That’s correct yes, but how will that be
possible when the blastocyst is still moving inside the
reproductive tract? It is not connected
to the point from where it can derive nutrition! Hence the blastocyst needs to
be connected to that particular location. This is where the most important stage of
IMPLANTATION comes into the picture. Can we guess what could it be from the name
itself? Yes! It is the step
where the blastocyst now attaches itself inside the mother’s body at one fixed
position. It implants itself there! And where will this position be? Of course in
the uterus! That is the place where the baby grows right? So the embryo now attaches itself in the uterus. Few of the main reasons for
attachment is deriving nutrition, giving away wastes and exchanging gases. This is served through this barrier that we
can see here. This barrier is an organ
called the PLACENTA! So can we say that the placenta connects the
baby with its mother? Absolutely! Now the embryo is all set to grow into a baby. The stage where the organs of
the baby’s body start developing such that they can be identified, is called as
the FOETAL STAGE. And the embryo can now be called a “Foetus”. The foetus grows in the uterus after taking
the required amount of time and when the growth is completed, the child is
all set to enter this beautiful world! This is how Embryogenesis takes place in most
of the animals. But wait a second…we have seen that a hen
lays eggs, and the chicks emerge out from these eggs. It means they DO NOT grow in the body of their
mother? Yes, development of the embryo takes place
in two different ways. The
parameter to categorise these types is the location of the embryo
development. So how do we categorise the two types? It’s simple. The first type is as we have
seen in the case of humans. The foetus grows inside the mother’s body. It
results in the mother giving rise to the young one directly. Such a type is called
VIVIPARITY. And these organisms will be called as? Yes! They are called as
VIVIPAROUS organisms. On the other hand the case of hen is an example
of OVIPARITY. And the
organisms exhibiting it are called OVIPAROUS organisms. Well this was about the process of Embryogenesis:
the development of Embryos. Do you remember external fertilization? Yes, the fertilization process which
occurs OUTSIDE the female’s body. Fertilization in Frogs is an example of this. However, we still don’t know the process
by which the tiny embryos develop into individual frogs. To understand this interesting process you
need to watch our next video!
