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Sunday, May 6, 2007

The Tuberculous Granuloma is High Yield for the USMLE

Ahh the Granuloma - a great example of topic that overlaps multiple subjects and any topic that brushes borders with the likes of pathology, immunology and microbiology make for great questions. Here are 5 steps to the granuloma in perfect 3rd grader doodle form:

Step 1:
Inhale the red, ACID FAST rod

M. tuberculosis is only acid fast why?

B/c of the MYCOLIC ACID in the cell wall resists decolorization with acid-alcohol and so it remains red which is the color of the initial stain, carbol fuchsin.

What else stains acid fast? Nocardia which is “partially acid fast”

Step 2: Phagocytosis by alveolar macrophages

Circulating monocytes roll on the vascular endothelium (d/t selectins) and adhere to it (d/t ICAMs) and then transmigrate into the affected area where they are called tissue macrophages.

Macrophages are the main players in the formation of a granuloma

Step 3: Antigen Presentation

Step 4: T Cell Activation

CD4 T Cells are involved

The TH1 subtype

No CD4 T Cells? No Granuloma. AIDS patients who loose their CD4 t-cells well before loosing their CD8 T Cells will make very weak if any granulomas.

Step 5: Macrophage Activation

Did I mention what the main player of a granuloma is? Oh yea, its the macrophage.

The Caseous Granuloma

Note that the caseous necrosis is cottage cheese like and is due to the destruction of the M. TB organism's cell wall's mycolic acids (mycolic acids are lipids).


Anonymous said...

Thank you very much!! your info really works , keep going.

Anonymous said...

This is very clear, thank you.

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USMLE said...

dude standing ovasion to you, thats the best freaking explanation about that I have ever heard inmy life, and the pictures are so suitgeneris that make it unforgetable.

You need to keep doing it with your own drawings, are better and more fun.

at the end you might want to add some real slides, just so people see the real thing.

And one more thing i would like to mention is that why you're not posting new content? plz update your blog so that we can get more knowledge through your blog :)

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