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Major Limb Abnormalities – Musculoskeletal System Development

by John McLachlan, PhD
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    00:00 hip structure will begin to adapt itself to the new stress pattern. Now let’s look at some abnormalities. We’ll focus on abnormalities of the limb. This particular condition is one where a child has too many fingers. And this is called polydactyly and of course, it can affect the foot as well. We’ve indicated previously that limb abnormalities are among the most common kinds of abnormalities that humans can show and frequency varies between different groups. So perhaps, one in 3,000 Caucasians; perhaps one in 200 African Americans might show polydactyly. It often runs in families, suggesting that there is somehow a genetic component. What we can now imagine, now that we’ve understood nature of the zona polarizing activity, is that there’s somehow been a disturbance in the ZPA signaling that’s led to this particular condition. Another abnormality is called ectrodactyly and here, fingers are missing in the midline. Fortunately, this condition is rare, although also has a genetic and familial basis. What we can postulate hear, is that there has been damage to the apical ectodermal ridge, which you remember, control the outgrowth of the limb.

    01:14 So perhaps, local damage to the AER stopped the limb buds growing out in the proper manner.

    01:22 Equally, fingers may be fused together in the condition called syndactyly. As we saw, the early limb bud is paddle-shaped, and the individual fingers are separated by local cell death in between the fingers. And if that cell death fails to take place, then the fingers may remain fused or webbing may be developed between the fingers as a consequence.

    01:48 So, in summary then, let’s look back of what we’ve seen so far. We’ve seen the bone develops in particular places, normally, by cartilage models which are subsequently replaced by bone. There’s a complex tissue signaling involved by structures like the zona polarizing activity, and the apical ectodermal ridge. And we can identify from this the kinds of major abnormalities that one might expect to see in humans, and offer an explanation for how these took place. That’s it. Thank you very much.


    About the Lecture

    The lecture Major Limb Abnormalities – Musculoskeletal System Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.


    Author of lecture Major Limb Abnormalities – Musculoskeletal System Development

     John McLachlan, PhD

    John McLachlan, PhD


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