Introduction – Lung Development

by John McLachlan, PhD

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    00:01 Hello, and welcome to this lecture on the lungs and common abnormalities that occur during the course of lung development. So we’re going to look at how the lungs develop, and particularly important, is understanding the maturation of the lungs. Then we’ll look at the major abnormalities and clinical problems of lung development, and then we’ll know how to recognize them. Finally, that will lead us to their clinical significance.

    00:27 So, let’s explore the early stages of lung development. We’ve going to go back to this stage where we’re looking at a cross-transverse section through the embryo, the amniotic cavity up above and the yolk sac down below. We can see that the amniotic cavity is going to sweep around as the embryo begins to fold and rise up into the amniotic cavity. So a little later on, we can see that the foregut and the hindgut are beginning to develop, and it’s from the foregut that the lung is going to develop in its turn. We’ve marked in this one roundabout where the lung will begin to develop, as the yolk sac is beginning to diminish and form a narrow stalk. What we can see is that this is in the ventral part or the lower part of the foregut. At a slightly later stage, the embryo has completed this process of curving into a C-shape. And roundabout where the neck region is where the lung bud is formed in relation to the rest of the foregut. In this view, what we’ve done is to imagine that we’ve taken the foregut and filled it with some solid substance. We’re looking at all the different components of the foregut itself. So coming around from the neck, we can see where the oesophagus is, and then growing off eventually from that, there is the lung bud that’s developing single lung bud, sometimes known as the respiratory diverticulum.

    01:57 At this stage, we’re about 22 days after fertilization. This lung bud is growing ventrally and caudally that is towards the tail. But of course, it’s growing into a mesodermal surrounding tissue.

    02:11 And although the lining of the lung bud is derived from the endoderm, much of the support ground material, and, of course, the blood vessels will come from the mesoderm.

    02:22 This process of bud formation could also be viewed as one of the ridges growing in from the side and pinching off the developing lung bud from the oesophagus. Eventually, they will lie so that this trachea, the developing lung, will lie in front of the oesophagus.

    02:41 Now, let’s focus on the lung bud itself. As we go through the developmental process, what we’ll see is that roundabout 28 days after fertilization it begins to divide into two separate buds. And you can see that one of those buds, the right bud, is lying more towards the tail than the left bud. So this is true from very early stages. As the lung bud continues to grow, so it will continue to divide, probably when it reaches a set size. So by 33 days, a further division is taking place. And what we can see is that on the left-hand side, we have two buds developing, whereas, on the right-hand side, there are three buds developing.

    03:24 This, of course, is so that there will be room for the heart on the left-hand side.

    03:30 This will be true in the adult lung also.

    03:35 The branching process continues all the way through development, gradually coming more and more complex. For the lungs on the left, there will be two lobes, and on the right, there will be three lobes. On the right, these are called the upper, middle, and lower lobes.

    03:50 On the left, they are the upper and lower lobes respectively. Each of these will give rise to a bronchopulmonary segment, a major part of the lung later on in development.

    04:02 And this may be important in cancer where it might be possible to remove just one bronchopulmonary segment if that’s where a tumour should happen to lie. Now, let’s look at the development

    About the Lecture

    The lecture Introduction – Lung Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Introduction – Lung Development

     John McLachlan, PhD

    John McLachlan, PhD

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