c is for cookie

in 9th grade, my math teacher wrote on the blackboard one of those cute classroom proverbs that makes teachers seem so wise. this one was a list--maybe 10 items long, i don't remember--of increasingly effective ways of learning. the least effective was reading from a book. the most effective was teaching another person. i grew to despise that math teacher, whom to this day i believe had it out for me and deliberately issued me a poor grade on my final exam, refusing to allow me--or my parents--to see the test. it was my first and last B in high school. needless to say, i'm over it.

but as for her top ten list of best learning methods, i think she was right. it's five days before my end-of-year comprehensive exam, i.e. five days before my first year of medical school is over. i don't necessarily have to pass in order to move on to next year, but i'd like to finish the year on a respectable note. for the past couple days i've sifted through my review books, highlighter in hand, carefully reading every previously-marked page. at this point though, the diminishing marginal utility of every page i read is depressing, and so in these increasingly desperate times i'm looking for a quick, high-yield method of retaining what i'm reading.

enter this shiny new blog. seeing as my primary blog continues to hum along nicely, and as it remains one of the best ways to keep in touch with many of my best friends, i've had trouble justifying this blog's existence. but i think i have a solution (albeit a dry, selfish, nerdy one). every day, starting today, i will post something i have learned in school. it might be a factoid presented to us in class, a summary of a journal article i skimmed in the afternoon, or a difficult concept i can't seem to untangle. whatever it is, i'm fairly sure i'll understand it better just by trying to write it clearly and palatably. and for you, well, maybe you'll find these daily doses of my medical education interesting. if not, i can hardly blame you.

so here's my contribution for the day:

do you remember the sesame street skits with cookie monster and the x-ray machine? cookie monster would step behind the x-ray screen, eat his cookie (100% of which would spray out of his mouth, but that's beside the point), and everyone would watch his cookie bolus make its way down his digestive tract. it was my introduction to gastrointestinal physiology, and i loved it.

so let's say you eat a cookie. after you've chewed it thoroughly and swallowed, the erstwhile cookie slithers down your esophagus, passes through the digestive pearly gates--the lower esophageal sphincter--and settles onto the hot, acid inner surface of your stomach. incidentally, your stomach knew the cookie was coming and made the appropriate preparations to receive it. it's in a relaxed state, thanks to the vasovagal reflex, and therefore ready to be filled. vagal nerve fibers released vasoactive intestinal peptide (VIP) onto myenteric motoneurons to reduce the resting tone of the stomach smooth muscle. also, before you even bit into the cookie, the G cells of your lower stomach (the antrum) released the digestive hormone gastrin into your bloodstream, thereby stimulating the secretion of hydrochloric acid by parietal cells and priming your stomach milieu for the now-famous cookie.

i mentioned the antrum portion of the stomach. the stomach is divided into roughly three sections--the fundus (top), the corpus (middle), and the antrum (bottom). gastric contractions, signaled by gastrin, start in the mid-corpus and increase in force towards the antrum. this asymmetric distribution of motor force results in the characteristic churning motion of the stomach, termed retropulsion. retropulsion pushes antral contents back towards the fundus, where the soupy stomach mixture hits the upper stomach wall and slides down towards the antrum, only to get pushed up again in the next contractile wave. these waves are slow, at roughly 3 per minute, which is why you don't feel your stomach pulsing after you eat. this continues until your cookie resembles putrid orange juice, and this is also where our story ends for today.

p.s. if you spot any mistakes--and there will be plenty i'm sure--please let me know, thanks.