Day 15: The Respiratory System
An MRI's View
MRI: Front views.
Positions (offset) are indicated:
Today's MRIs are similar to yesterday's,
although the pictures are not as
clear. The chick seems to be more or
less in the same position, head on the
left, in the front view. Perhaps it is
now too cramped in the egg for it to
turn around.
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MRI: Top views.
Here's a top view showing some details of the
heart:
Another feature seems to be the heart, in
frame 107. The bright spots above and
below it are signals from the blood in the
ventricle. These spots are in the wrong
places because they are moving too
rapidly. Notice that each spot has the
same shape. The aorta or vena cava is
visible to the right of the heart, also
with several displaced spots. An
enlargement of the heart area is shown
also.
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MRI: Side views.
Here are some side views. Positions (offset) are
indicated:
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T1 Weighted Image
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T2 Weighted Image
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As noted yesterday, the egg compartments
have changed a lot since last week. However,
today, we were able to compare T1 and T2
images and determine that the smaller
compartment near the small end of the egg
(e.g. CD-56 in frame 112) is probably the
remains of the yolk (the contrast appearance
is similar to the yolk in last week's images.
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In this image you can see a spot between and
below the eyes. This is probably an air passage
- either the mouth or a nasal or sinus
passage. It is dark because there is no longer
any fluid in it - the chick is breathing air
from the air cell!
One noticeable feature is the pair of dark
bars, one on either side of the body (visible in
yesterday's side views). You can see them in
frame 102 (directly above) today. What are
these? We thought they might be the lungs -
collapsed at present since they are not in use -
but it seems that bird lungs are different from
mammals, and may not actually be paired. Or they
might be bones - the equivalent of "shoulder
blades."
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Are these the feet?
Here are two views showing a shadowy
structure that might be the chick's feet. I
think this is a reasonable assignment, since I
was able to follow this through several slices
back toward the body. They are really big!
Notice how they penetrate into the yolk sac
area. Probably what we see is the amniotic fluid
around the feet, rather than the feet
themselves.
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Comments on these images by Carl Gregory.
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