Tuesday, September 24, 2013
Infectious Disease = Rote Memorization
How do I feel about Infectious Diseases?
I understand this is a common reaction, coming out of the Neurology Domain. I mean, Neuro was awesome; everything was still (relatively) fresh in our minds after taking Neuroanatomy last Spring, and I feel like it's a fairly small minority that came out of Micro the same semester thinking, "Wow, I really learned all of that!"
ID feel very much like the big brother to Micro, but with much less hand-holding. The Sherris textbook has become my best friend, with Goodman & Gilman (Pharmacology) and Robbins (Pathology) rounding out the textbook gang. No matter how much I look up and learn in one day, I have yet to go to bed once during this domain thinking that I made it through enough of the material. Quite the opposite - even after a 12 hour day, I go to bed with a sinking feeling accompanied by the mantra, "Okay, tomorrow I'm really going to have to kick it into gear..."
I used to think I was good at rote memorization - then I came to medical school and learned that what I had thought was rote memorization was actually very logical and well thought-out in comparison. For example, before medical school I thought rote memorization was just memorizing that macrophages swallow big chunks of stuff and digest it. That's not rote memorization, because all of that is in the name - "phage" comes from "phagos" (or phagia or whatever) which means "to swallow," and macro means large (because macrophages are fairly large or because they swallow large things, whatever floats your boat). The meaning is in the name.
What we are memorizing now are things like this: T cells are a kind of lymphocyte. Immature T cells (and B cells, the other main lymphocyte) need the Rag1,2 genes to be able to mature/differentiate into the next stage of development. Immature T cells can go to CD4+ (helper T cells) or CD8+ (cytotoxic T cells) cells. CD4 and CD8 are specific receptors on the surface or T cells. Antigen-presenting cells (APCs) express MHC-I or MHC-II molecules, which help show off bits of pathogens to the lymphocytes. CD4+ T cells interact with MHC-II molecules on APCs and then further differentiate into Th1 or Th2 cells, depending on which signaling molecule gets secreted by the APC and acts on the CD4+ T cell. If it's interleukin (IL) 12, then the CD4+ T cell differentiates into a Th1 cell. If it's IL-4, it differentiates into a Th2 cell. Th1 cells secrete more IL-12 (to help other CD4+ cells differentiate into Th1 cells) and IFN-γ, which activates macrophages and CD8+ T cells. Macrophages then secrete TNF (tumor necrosis factor), which calls in monocytes to help chew up or sequester dead / infected / dysfunctional / foreign cells. Th2 cells secrete more IL-4 (which does double duty in helping CD4+ cells differentiate into more Th2 cells as well as helping naive B cells isotype switch into IgE-producing B cells) and IL-5 (which helps naive B cells isotype switch into IgA-producing B cells). Those immunoglobulins have different functions and act in different areas. For example, IgA is present in serosal and mucosal surfaces and acts to bind epithelium-binding receptors on the surface of bacterial pathogens so that they can't bind to epithelial cells and get in through your nose skin. IgE plays important roles in cross-linking antigens on the surface of mast cells to activate them when an allergen is present, initiating histamine release and the reason why millions of people spray gallons of Nasonex up their noses every year.
So yeah. THAT is rote memorization. There's no way to logic it out what Th1 vs Th2 cells do, or which immunoglobulin (IgA vs IgE vs IgG vs IgM vs IgD) can pass through the placenta and thus go from a pregnant woman to the baby growing inside of her. You just have to memorize that it's IgG.
Sure, we come up with fun mnemonics like Hot T-Bone stEAk for the interleukins, but it's so nonsensical that deep down, it's still rote memorization, just... catchier:
- H for Hot is 1st and is for IL-1, which is a pyrogen and upregulates the COX-1 pathway in the hypothalamus to increase the set body temperature and thus causes FEVER
- T is 2nd and is for IL-2 which activates T cells, specifically Th1 cells and thus CD8+ cells as well
- B is 3rd and is for Bone marrow, which is stimulated by IL-3
- E is 4th and is for IL-4, which stimulates isotype switching in B cells for IgE
- A is 5th and is for IL-5 which stimulates isotype switching in B cells for IgA
THAT is rote memorization at its best.
Aaaand, back to studying ID...
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