Embryology: Introduction

by John McLachlan, PhD

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    00:01 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.

    00:31 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.

    01:13 Without that understanding, the anatomy becomes very hard to understand and very hard to remember.

    01:20 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.

    02:44 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.

    03:45 So let us look at the natural history that actually happens during the early stages of development.

    03:52 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.

    04:10 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.

    04:32 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.

    04:44 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.

    05:21 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.

    About the Lecture

    The lecture Embryology: Introduction by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Embryology: Introduction

     John McLachlan, PhD

    John McLachlan, PhD

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