(Transcribed from Dr. Laville’s lecture, 11 Feb 2000 by Brian Buschman)
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This
set of notes was transcribed about two weeks after the original lecture and may
or may not accurately represent the material presented in class by Dr. Laville.
Be sure to study your own class notes.
Iron is found in every cell in the body and has vital properties when it comes to binding of O2 in Hb and Mb. The total amount of iron in our body is about 4-4.5 g. The daily iron loss, and hence the amount of iron that must be taken in, is about 1 mg/day for the average adult male and non-menstruating female. For the menstruating female the amount jumps up to 1.4-3.2 mg/day because of the iron lost with the blood from menstruation. Iron is lost through a number of different methods both physiological and pathological. The physiological losses include:
1) Biliary excretion (because it contains the worn out heme groups to be discarded).
2) Sloughing of intestinal mucosa cells.
3) Blood loss (menstruation or other blood loss).
Pathological losses are usually related to anything that results in blood loss.
Iron is available in many foods but only about 10% is taken into the intestinal mucosa. The presence of vitamin C with the source of iron doubles the amount taken up. Some products antagonize the uptake of iron:
1) Antacids.
2) EDTA (it binds and forms a complex with iron).
3) Caffeine.
4) Phytic acid (which can be found in cereals).
When iron enters the gut it is held by the gastric mucins with will only hold iron in an acidic environment. An effective transport mechanism must be able to both transport iron efficiently and be able to stop the transportation when enough is already in circulation. Iron is taken into the gut cells in the Fe2+ (ferrous) state by transporters called integrins. After the iron is in the mucosal cells it must be oxidized to the Fe3+ (ferric) state to be transported within the body. Ceruloplasmin, or ferroxidase, oxidize the ferrous (Fe2+) into the ferric (Fe3+) form of iron. Mobile ferrin is a protein in the mucosal cells which hold onto the iron and either pass it off to ferritin to hold it in the cell or to transferrin which is located in the blood stream. Mobile ferrin is therefore part of the regulatory process as it decided where to pass the iron based on the amount in the blood.
Transferrin will take iron around the body and pass it to tissues that need it. Most body tissues contain hemosiderin that takes iron from transferrin and holds it until needed. The liver usually has a low amount of hemosiderin unless of an iron overload.
Anemia is a condition with either a low number of circulating reticulocytes or a reduced amount of hemoglobin in the red blood cells (RBCs). There are three types of anemia:
1) Normocytic anemia is where the RBCs are present in the proper concentration but there is a reduced amount of Hb in the RBCs. This is often the result of internal hemorrhage.
2) Macrocytic the RBCs have become huge but the numbers are reduced. It’s often a result of folic acid deficiency. It is characteristic of pernicious anemia.
3) Microcytic anemia has cells that are much smaller therefore being able to carry less Hb and is usually caused by iron deficiency.
Anemia is caused by either inadequate uptake or abnormal losses. Inadequate uptake may be the result of either:
1) A diet that is low in iron.
2) Absorption problems (such as hookworm).
Abnormal losses are usually from:
1) Excessive menstrual flow.
2) GI loss due to excessive mucosal cell sloughing or a GI bleed.
3) Pregnancy.
Hemochromatosis is an abundance of iron in the body, especially in the liver and spleen. Hemochromatosis is associated with many conditions including:
1) Enlarged or shrunken spleen.
2) Skin pigmentation.
3) Diabetes mellitus.
4) Hypogonadism.
5) Joint disease.
6) Heart disease.
Hemochromatosis is caused by:
1) Genetic anomalies leading to excessive uptake.
2) Excessive dietary uptake. This may be a result of having iron and alcohol at the same time. Ethanol inhibits the ability of the intestinal mucosal cells to regulate iron uptake. (When you set up a backyard still don’t use iron pots.)
Tests of Iron Level
There are a number of tests relating to blood iron level. The hematocrit and blood hemoglobin levels are used to measure iron deficiency but are not useful in determining excessive uptake because excessive iron will not be stored as RBCs or in heme (which is what these tests measure).
There is an amount of iron, however small, which circulates freely in the blood. Measuring plasma iron is one way to determine if a patent has either iron deficiency or iron overload. Another other test is to measure serum ferritin as some ferritin leaks out of the mucosal cells into the blood. This amount varies with iron level. The third test is to measure the saturation of transferrin.
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