Hello! Welcome to this introductory lecture in which
we look at the question what is embryology
and what is the main meaning for Medicine in
general. And the pattern I am going to follow
is to look first of all, that why embryology
is important in medicine and the important
part of that is looking at how common developmental
defects are and I am going to use Western
Europe as a reference frame because the frequency
of defects varies from area to area.
Next we'll look at the early stages of development
after fertilisation and in particular, very
early stages at which cells begin to become
different from each other because that process
of differentiation is absolutely central to
the process of understanding development in
general and some of these medical implications.
So looking at reasons why embryology is important
very valuable one from medical students is
the anatomy often only really makes sense
in the later development. If you are looking
at how the gut is developed, for instance,
and then that gives you an understanding as
to why it is arranged in particular ways.
Without that understanding, the anatomy becomes
very hard to understand and very hard to remember.
In addition, 2.4 percent of all babies born in
Western Europe have a significant developmental
defect and that means one detectable at birth.
If we're to follow babies forward, we'd find
about the same number again will show signs
of developmental defect that was not obvious
at birth. Deafness sometimes falls into this
category or sometimes heart defects, which
become evident when babies start to walk putting
increasing strain on the heart and showing
up abnormalities that were not detected before-
hand. So that means perhaps as many as 5 percent
of babies in a total have a significant developmental
defect, a number which is much higher than
most people expect. Our next important
aspect for medicine is
reproductive technology. These are In Vitro
Fertilisation and stem cell technology revolutionized
the early stages of assisted reproduction
and look forward to having an even greater
impact in the future. We can imagine for instance,
stem cell is being used to grow in origin
to replace an organ that in some way is not
functioning properly or to repair a spinal
cord that has been damaged or with anything
that we can think of might well be possible,
but is only possible if we understand the
basics of human development.
Then we find many other diseases such as heart
disease, cancer, even possibly schizophrenia,
diabetes - one calling developmental antecedents.
Things have happened during the course of development
that may well have influenced them. For some
of these, we have good reason to believe that
something that happens during the course of
pregnancy perhaps in the fetal period, there
is some influences being exerted on the baby
and this will have consequences decades later
for the adult and if we understood what was
happening here then perhaps we do have a new
tool to address many of these serious kinds
of illness. Of these cancer is probably the
most significant as a killer of other population
in Western Europe. And in many ways cancer
cells are reverting, they are going back to
embryonic behaviour, they're behaving the way the embryonic
cells behaved in their past and we will look
at that in more detail later within this lecture.
So let us look at the natural history that
actually happens during the early stages of development.
And this diagram shows an egg
waiting to be fertilized. It is surrounded
by cells, which are derived from the mother.
These are the corona radiata cells and then
by an impermeable membrane, which does not
contain cells itself. It is called the zona pellucida.
There is a polar body, which came from one
of the myotic divisions and the nucleus is
the only well-marked structure within the
egg itself. And it is about 80 microns in
diameter, which is small as eggs go. You see
in hen's egg or an ostrich's egg. So this is
really rather tiny. These are also large compared
to the normal human cell.
You can see the size of the corona cells nearby that
gives you an idea for a normal human cell
is like in terms of its size. So the egg is
large for a human cell, small for an egg.
It is also relatively featureless. The diagram
does not make this quite clear, but if you
look at photograph of a newly fertilized human
egg, you can see that the cytoplasm does not
contain any obvious structures, it looks fairly
homogeneous. And in the correct environment,
this single, rather small object is capable
of turning into a full human being. So obviously
there are very many important changes that
have taken place along the route and some of
these we will be looking at in this lecture.
And you could call this the central Enigma.
How does something as apparently simple as
an egg turn into something as apparently complex
as a person and you can see from the way I
phrased that question that perhaps the egg
is not as simple as it looks and perhaps unexpectedly
people are not quite as complicated as you
might think. Not everything is specified during
the course of development. There are many examples
where tissues interact with each other, they
talk to each other and come to an agreement
about how they are going to be arranged in
space. So there are three components to the