Interactions Between Tissues – 3 Germ Layers

by John McLachlan, PhD

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    00:01 However, as we indicated, there are also crucial interactions between tissues.

    00:08 Not everything in the body is specified in advance. This is the explanation for much of the variation between individuals. No two people are exactly the same, and this is important in surgery, for instance, where things like the course of a nerve are predictable but not identical between different individuals. Therefore, surgeons have to take particular care not to cut a nerve or interrupt the blood vessel when they’re carrying out an operation procedure and the reason for this variation is that many of these interactions between tissues are not specified in detail by the genome. Instead, what happens is that tissues are laid down in general positions and then they begin to talk to each other so that they will establish a functional relationship over time. We can actually explore this in tissue culture.

    01:03 So, this is a rather schematic diagram. As you can appreciate, the actual experiment is much more complicated and much more difficult. But here, I’ve imagined placing a piece of muscle from an embryo into a culture medium, and alongside it, I’ve supplied some nerve and some blood vessel. What we find is that under the influence of factors from the muscle, nerves will be attracted towards it. For instance, there are varieties of nerve growth factors, but also blood vessels will be attracted towards it. There are varieties of what’s called angiogenic factors, which can diffuse out from the muscle to interact with tissues in either side. So what will happen is that blood vessels will be attracted towards the muscle, and nerves will be attracted towards the muscle. In fact, if we also had some cartilage present and some developing tendon, what we’d find is that it’s a kind of seek and join rule for tendon and muscle. So the tendon will find the end of the muscle and attach itself to it, and it will also attach itself at the other end to cartilage. So you can see that even in tissue culture environment, it would be possible to build up an almost kind of functional relationship between all of these different tissues. This is particularly important when we come to look at cancer cells. Cancer cells have escaped from the control of normal cell division. They are increasing in number quite rapidly. But normally, as a result, what would happen is that they outrun their local nutrient supply. They will form a little ball of cells, perhaps, hollow in the center because the cells in the middle had not had sufficient nutrients to survive, and they’ll be dying, and perhaps, being replaced by pus.

    02:59 So you see a small ball of cells which was effectively going nowhere. However, if as a result of mutation within the cancer cell, in addition to the mutations which made it divide rapidly, the tumor cells are producing an angiogenic factor, then blood vessels will be attracted towards it. And the tumor angiogenic factors are very similar to the angiogenic factors found in normal embryonic development. Once a blood vessel has reached the tumor cell, then the tumor can begin to grow rapidly. And if cells detach from the tumor and enter the blood system, then they can tumble around the body and begin to invade somewhere else, so the tumor can begin to spread elsewhere in the body as a result of the vascularisation of the supply of blood to the tumor. In some ways, this is one of the most serious steps in cancer development because it both allows cancer to grow and to spread. And you can understand that this is a major field of research interest trying to explore the nature of these factors and how they might be prevented from acting to support tumor growth. So then, let’s look at the summary of what we’ve talked about in this lecture. We looked at the derivatives of the germ layers, the ectoderm, the mesoderm, and the endoderm. We touched on tissue signalling between mesoderm and ectoderm, between ectoderm and mesoderm, and so on. And then we looked at the interactions between tissues, such as attracting nerves and attracting blood vessels towards developing structures. Finally, we saw that this has important implications, and perhaps, even some hope for cancer treatments. Thank you.

    About the Lecture

    The lecture Interactions Between Tissues – 3 Germ Layers by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Interactions Between Tissues – 3 Germ Layers

     John McLachlan, PhD

    John McLachlan, PhD

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