WILTIMS #39: Thymic elegance

Ouch. That test hurt. But the 5-exam week of hell is over! Huzzah!

There is something I wanted to share with you guys that I didn't learn today, but was really impressed with while studying. The thymus is a primary lymphoid tissue, meaning it's a site for blood cell development. Specifically, the thymus is responsible for the maturation of T-lymphocytes. You may remember from your high school biology class (it's ok if you don't) that there are "helper" T-cells and "killer" T-cells. These cells are part of the body's adaptive immune system, which recognizes a threat (from bacteria/viruses/fungi) and both attacks it and remembers it for future reference.

The nifty part is that the discerning thymus essentially weeds out both the lazy and homicidal T-cells before releasing the mature, level-headed ones into the body. It does this in two steps: First, it offers up some practice targets that it would like the T-cells to latch onto. If the cells don't bite, they're killed off. The survivors are then released to the second test area. The thymus again offers up targets, but there's a catch: this time the targets are actually pieces of good structures from within the body. If the T-cells go for these, then they are showing autoimmune capabilities and are also killed. This way only the cells that reliably target antigens are allowed to patrol the body. Elegant huh?

I could not for the life of me find a good diagram of this process, so I whipped this up for you:

TIL: Fascia adherens is found in the intercalated discs of cardiac muscle. This was on my first test today and I had completely forgotten it. Luckily, after looking it up during lunch, I got a different question about it right on test number two.

Study Aid #3

I promise: this is the last long weekend we have until Thanksgiving. From here on out, my posts should be more consistent.

I'm happy to have the time though as we have our second histology test and our first histology practical on Monday. We are one of the few medical schools that still uses microscopes and thus one of the few that still has a practical exam for this field. Whether or not that's a good thing is up for debate...

The diagram to the right is my new version of the concept map I made during my post-bacc year, seen below with the overlapping cellular pathways highlighted. We don't (yet) need to know as much as I needed to know for that old class and the pathways we do need to know have either been described slightly differently or discovered to be in fact different in the intervening years. It's nice to have this foundation to build on!

WILTIMS #31: Dishevelled Cellular Pathways

Click to view the original

The above is a concept map that I made during my post-baccalaureate year while studying for the final in a class called Cell Proliferation, Senescence and Death. It was a fascinating, if overwhelming class but boy am I glad to have taken it because, sure enough, the pathways are part of my histology/cell biology class in med school.

My favorite proteins from that chart are Frizzled and Dishevelled, so named because in the Drosophila fly they coordinate the alignment of hairs.

TI(re-)L: Bad/Bid/Puma inhibit Bcl-2 which down-regulates BAX/BAK which causes Apaf to dimerize in the presence of Cytochrome C, activating Caspase-9, leading to the further activation of Caspase-3 which triggers apoptotic cell death, possibly preventing the development of cancer. Simple!