We are starting a series of lectures on embryology. Hello I am Dr. Aizaz from
medicovisual.com. Welcome to this visual lecture. In this lecture we will
discuss that what is embryology and some terms that are related with embryology.
So today we will discuss what is an embryo? What is a zygote and what is a
fetus? These three terms are quite confusing so I want to clear the concept
at the very beginning of this lecture series. Right, then we will discuss that
what is embryology and what is developmental biology? And then some
other terms related with reference. Right, a human consists of about 200 trillion
cells and this multicellular organism that is
made up of that much cells it arises, it originates from only a single cell
and the single cell from which this come, from which the complete organism originates,
it is formed by fusion of male and female gametes. The male gamete sperm and
female gamete ovum. Right, and when they fuse, when they undergo the process of
fertilization and they conjugates the cell that is formed is called zygote.
Zygote literally me to conjugate. So, from zygote complete organism is formed.
Zygote, what is the definition of zygote? Zygote is a cell that is formed by
fusion of male and female gamete. It is a cell that is formed by process of
fertilization and it has potential to form all the cells of an organism, has
potential to form complete organism. It is totipotent, it has potential to form
total cells of an organism. But this is zygote and what is an embryo? As the
zygote grows and differentiates it forms first a ball of cell and then we will
discuss later that then there is cavity is formed and then it starts
implanting into the uterine wall of female, of the mother. Right, after the
process of implantation it is now called embryo. Right, according
to literature before the process of implantation it is also called embryo
but that is pre-implantation embryo. Right, and after the process of
implantation is the actual embryo so zygote is an embryo or not?
Yes it is. Yes zygote is an embryo. Zygote is single-celled embryo.
single-celled pre-implantation embryo. Zygote is a single-cell pre-implantation
embryo. Right,
then embryo, in it what happens during developmental stages of embryo is that
the primordial structures are formed from which different organ system
originates and then primordial of different organs are formed from it.
Right, now at this stage you can see it does not quite resembles the actual
human, the actual human baby but at about ninth week of gestation I mean ninth
week after fertilization, at about ninth week after fertilization it actually
start to resemble the baby of Origin organism to which it belong. In this case
it starts to resemble human baby but it is not just resembling the human but
most of the organ systems have been developed up till now.
Right, above this point they start to differentiate and grow further they have
developed but they differentiate and grow further. So, at this point at ninth
month of sorry nine not month ninth week of gestation the embryo is given a new
name and this new name is called fetus. Why it is give a new name? Because it
starts to resemble the actual organism it start to resemble the baby. Now you
know what is zygote? What's an embryo? And what is a fetus?
Now let's discuss that what is embryology? What do you think what is an
embryology? It's the study of an embryo. Yeah it's study of an embryo most people
think that it is study of embryo as its name indicate that it's the scientific
study of an embryo. But this is not a complete definition. Actually embryology is not
that simple. Embryology is study of developmental stages of an organism
starting from development of gametes, male and female gametes till the birth of
the newborn. So in embryology what we discussed it includes the scientific
study of development of gametes. I mean development of sperm and ovum,
fertilization, study of embryo, study of fetus and the
birth process that is parturition. So study of embryo is just one aspect of embryology,
it is one aspect of embryology but we have to study all these things in
embryology. Fetus, study of fetus is also called Fetology and it is considered
to be a sub-branch of, it is considered to be a branch of embryology.
We can study embryology at two levels general embryology and systemic
embryology. In general embryology we study since the synthesis or
creation of primordia of different organ systems the bi-laminar and
tri-laminar germ disks, will discuss these things later. And in general embryology
we do not focus on development of a particular system we don't study it
system wise but we study it in a chronological order that what happens on
week zero, what happens on week 1, week 2 week 3, month 1, month 2 and so on in this
way we study embryology in general embryology. But in systemic embryology we
study system wise we study the development of different systems the
development of cardiovascular system, the development of GIT, respiratory system
and so on system wise we study them. Right, now you cannot study systemic
embryology directly without understanding the basics the general
embryology, the basic understanding of formation of different primordial
structures so first we will discuss general embryology and then we will
discuss systemic embryology. Right, then embryology can be given a name according
to the organism whose embryology we are studying right for example we are right
now studying human embryology but interestingly the embryology of human it
resembles quite a lot with that of any other mammal, right, and there is medical
embryology or clinical embryology. In medical or clinical embryology we don't
study just these things but we try to apply the basic concept of, the basic
concepts of these things with clinical, with the clinical stuff,
their clinical applications are also studied along with these basic things.
Right, so also we will discuss in clinical and
medical embryology, we will also discuss that how different drugs or
different chemicals lead to different malformations in the baby and this branch
of clinical embryology is called Teratology. Right, so we are discussing
human embryology but we are also discussing medical human embryology or
clinical human embryology. Right, then there is a term called
Developmental biology is it same as embryology? No, it is not same as embryology
start from development of gametes up till the birth of baby.
This development do you think development stops or development ends
when a baby is born? No, no otherwise we all would would have
been a baby up till now we do not remain baby fortunately or
unfortunately we develop into a complete adult human and then we become an
old man or woman and we have to die one day as well. So, embryology is up till
here but developmental biology it also
includes the developmental stages that transforms a newborn into a child and
then child into an adult and then adult into an old man or woman.
Right, so developmental biology it includes all these stages as well but
embryology is a subset, you can say embryology is a subset of developmental
biology. You have a question? Then what is developmental Anatomy? Yeah
there is a term that is called developmental Anatomy it is a field of
study and developmental anatomy is a subset, it is a branch of developmental
biology and in developmental biology we study not just anatomy we also study
the genetics of this this process of development, we study the molecular
biology of these steps. Right, that how different genes work together to
transform an organism from a child to an adult and so on, right,
for example, the genetics of aging process the molecular biology of aging
process and all these things but in developmental Anatomy we all we only
study the structural changes that occurs when men transformation occurs when
these transformation occurs for example fontanelle's are closed and what is the
process of closure of fontanelle's all these things if we discuss in
developmental biology developmental Anatomy similarly you know the xiphisternum
ossifies in old age, all these things are related with developmental Anatomy. It is
a branch of developmental biology but if we discuss that what genes are involved
in let's say aging process that is developmental genetics you can say or
developmental molecular biology rather. Right,
then there are few terms that are related with this embryology, right, let's
suppose if we divide this embryo into front and back part right
anything that, we equally divide it into two parts, so anything that lies towards
the belly on the anterior side is called ventral. Right, vent means belly and
anything that lies behind this plane is called dorsal, dorsal means back. Similarly,
we can divide it into two equal parts upper and lower parts. Right, so cranium
is skull is also called cranium so anything that is superior or above this
part it is called cranial and anything that is below this part towards the
tail end is caudal, caudal mean tail, towards the tail so
caudal is inferior or below this plane. Why we have introduced these terms to
make a subject confusing for you? No, it is not you know in adult anatomy we
call this ventral as anterior and dorsal as posterior and superior and inferior
but why this confusing terminology is used here? Actually,
suppose this is a female legs and you know this is, she is pregnant right now
and in her in her womb you can say that here a babies lies.
Now my question is there this is the actual presentation of baby inside now
here you can see the head of baby the head of baby's cranial or caudal? It should
be called cranial yeah head of the babies cranial but it is superior or
inferior? It is inferior with reference to adult anatomy it is inferior, it is
lying downward so to avoid the confusion with adult anatomy to avoid the
confusion with anatomy of female body we used it this terms ventral, cranial
caudal, right, so that we avoid this confusion so it is not to confuse you
but to avoid the confusion.
Finally I would like to discuss that who this lecture series is for?
This lecture series is mainly for medical and dental students. Embryology
is mostly taught as a beginner course as a primer calls in usually first year of
medical school so during this lecture series I will assume that you don't know
anything about embryology so I will start it with very basic concept at a
very basic level anyone who is interested in studying the developmental
stages of a human is he or she is most welcome to join this lecture whether or
not he is medical or dental student because I think most of you will be able
to understand it with a little background of science. This lecture
series will also be helpful for post-grad students and professionals as
well but you may find it a bit boring so you can use time stamps or you can speed
up the playback speed of this lectures. Thank you so much for watching this
lecture if you like this video please press the thumbs up button and please
subscribe to my channel if you haven't already also please give your comments
regarding this video and please do support me on patreon.