🙁 I clearly remember seeing biliary excretion being passive and continuous, but I guess I can take relish in the fact that bile -> feces. Technically, when enterocytes are tossed into the GI, maybe they're taken via portal and then my mechanism?
I also read that PPI's cause B12 anemia since they inhibit paretial cells from secreting H2 and IF...but I can't find that either, all I see is Iron and Ca absorption decreased due to low acid. God this sucks.
Let's give it a tilt-o-whirl!
IRONZ
Iron is ingested in the food you eat. There is one way it gets into the body... through the gut. Iron is absorbed at a rate of about 1mg/day. The maximum absorption of of iron is 3mg/day. It is absorbed into enterocytes, then from enterocytes into the blood stream.
Ferritin and Transferrin are products of how much iron you have. Let's just eliminate those, right now, because they confound the understanding of iron, though you can spend an entire page and a half in a physiology textbook talking about liver synthesis, this up, that down, and why.
Iron in is rate limited (except in people with hemochromatosis who get iron overloaded because there is no "stop absorbing iron" signal). What about iron out? "Out" needs to be clarified. For all intents and purposes, the GI tract is "outside the body" because it has not been absorbed into the blood. So, when you say (correctly) that iron is lost into the stool, what you really are saying is "the iron that was never absorbed is eventually eliminated into the stool, the enterocytes that absorbed it die, slough off, and take the left over 'outside-the-body-iron' with it."
There is
no mechanism in which Iron is taken out of the body, that is, out of the blood, and put back into the environment. This is why people with hemochromatosis get iron overloaded. Too much actually gets into the blood stream, and the body has no means of dealing with it, so it gets deposited in major organs. This is also why people who need regular blood transfusions (Hemophilia B Major), who get 350mg of iron every MONTH (enough iron for the year) with every transfusion need iron chelation with deferoxamine (of the newer oral defisiraox...
spelling).
Bleeding is the only means of removing iron from the body.
The natural question should be
if bleeding is the only way you get rid of iron, and you absorb 1mg/day, won't you be iron overloaded by the time you're 60? Thats a good question. The other way you get rid of iron is to
use it. You use it to make heme. Heme + Globin = Hemoglobin. Hemoglobin goes in red blood cells. Red blood cells last 120 days. When they die, hemoglobin --> un conjugated bilirubin --> liver --> conjugated bilirubin --> bile --> stool. So... heme is eliminated in the form of bilirubin into the stool. Iron is in heme. So... iron is eliminated through the bilirubin into the stool (technically) but it is NOT the processing of iron that does it, it is the processing of hemoglobin that happens to have iron.
So why make the distinction, right? Iron in the stool is iron in the stool. You make the distinction because
hemolysis is NOT a treatment for iron overload. People with chronic hemolysis (sickle cell) need to be supplemented with iron. But people with iron overload cannot get rid of excess iron by increasing biliary excretion. They need medical chelation (multiple transsfusions) or to be blood letted (hemochromatosis).
So while TECHNICALLY "iron is eliminated in the bile" (as hemoglobin), the only REAL way of getting iron out of the body is bleeding. Most of the iron in the stool was never absorbed in the first place, it was the stuff in enterocytes the body never wanted. 
