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Immunology

Here is a problem:

Go to this or other histology links you might find:

http://www.bio.davidson.edu/courses/Immunology/Bio307.html

These all have either cartoons and/or histology sections of all the important primary and secondary lymphoid organs that we talked about. Click through their sections, readings, and animations of primary and secondary lymphoid organs. In particular:

1. Try to identify a central arteriole, the surrounding PALS, and follicle in the spleen. In your post assignment entry, describe in your own words how these 2-D images relate to 3-D structure.

2. Be able to locate the cortico-medullary junction in the thymus. See if you can find different sections so you can visualize the 3-dimensional structure of the organ. List differences you notice about the cortex versus the medulla.

3. Notice how the architecture of lymph nodes differ from spleen, relating this to their differences in how lymphocytes enter and exit.....see your text for details on this. Summarize these different traffic patterns.

Solution Preview

ARCHITECTURAL ANATOMY OF SPLEEN, LYMPH NODES, AND THYMUS

1. Try to identify a central arteriole, the surrounding PALS, and follicle in the spleen. In your post assignment entry, describe in your own words how these 2-D images relate to 3-D structure.

Response: Blood enters the spleen via the splenic artery. It branches into trabecular arteries that spread into the trabeculae and enter the white pulp areas as central arteries. You see, the spleen is covered by a fibrous capsule made up of dense connective tissue. The capsule has internal extensions called trabeculae that divide the spleen into functional units or filtering beds. These are the follicles you mention in the question. They are made up of areas of white pulp and red pulp.

So, what we've got into the spleen is thousands of separate functional units separated by trabeculae extending from the outer capsule all the way to the other surface, the concave surface where the splenic artery and vein enter and exit. Each unit looks like a little three dimensional cone that starts as a "point" at the place where the trabecular vein and central artery exit and enter, and then widens and extends outward as you make your way to the capsule on the outer surface.

The central artery goes through the middle of each follicle, and of course, divides into smaller arterioles as it permeates the red pulp. Around the central artery is the "white pulp." This is sometimes called PALS, which stands for "periarteriolar lymphocyte sheath." That's just a big fancy set of words that means, "lots of lymphocytes that surround the central artery." So, the white pulp is lymphatic tissue made up mostly of ...

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