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“Mucosal Block Theory”
Presenter –Seema Bisht
Msc . Medical Biochemistry
Submitted to :- Dr. Aparna
• Normally , the loss of iron from the body of a men is
limited to 1 mg/day.
• Menstruating woman lose iron with menstrual blood .
• Around 10-20 mg of fe is taken in the diet and only
about 10% is absorbed .
• The greatest need of iron is during infancy and
• The only mechanism by which total body stores of iron
is regulated is at the level of absorption .
• Garnick proposed a mucosal block theory for iron
Mucosal block theory :-
• Step 1 :-
• Soluble inorganic salts of iron are easily absorbed from
small intestine .
• HCL present in gastric juice liberates free fe3+ from non-
• Vitamin C and glutathione in diet reduce fe3+ to fe2+ ,
• Which is less polymerizable and more soluble form of
• Vitamin C and amino acid can form iron –ascorbate and
iron – amino acid chelates which are readily absorbed .
• Heam is absorbed as such.
• Gastroferrin , a glycoprotein in gastric juice is
believed to bind iron and facilitates its uptake in
duodenum and jejunum .
• The absorption of iron from intestinal lumen into
mucosal cells takes place as fe2+.
Step 4 :-
• Events in intestinal mucosal cells (
enterocyte /mucosal cell).
• Enterocyte in the proximal duodenum are
responsible for absorption of iron .
• Incoming iron in the fe3+ state is reduced to
fe2+ by an enzyme “ferrireductase” present
on the surface of enterocytes , it is helped
by “vitamin C” present in the foods .
• This protein is not specific for iron as it can
transport a wide rang of divalent cations.
• Once it is inside , it can either be stored as “feritin”
or it can be transferred across the basolateral
membrane into the plasma where it is called
bound to “transferrin” .
• Passage of fe2+ across the basolateral membrane
is carried out by another protein called iron
regulatory protein 1 (IREG1) .
• The transfer of iron (fe2+) from the apical surfaces
of enterocytes into their interiors is performed by a
proton –coupled divalent metal transporter (DMT1)
•Most of fe2+ required to be absorbed is transferred
to plasma by a fe2+ transporter ( FP) .
# Fe2+ in the enterocytes also came from “heam” by
the action of “heam oxidase” enzyme on heam .
# IREG1 may interact with the copper containing
protein called “hephaestin” ,a protein similar to
caeruloplasmin .hephaestin is thought to have a
“ferroxidase” activity which is important in the
release of iron from cell as fe3+, the form in which,
it is transported in the plasma by transferrin.
Overall regulation :-
• Iron absorption is complex and not well
understood mechanistically .
•It is exerted at the level of the enterocyte
where further absorption of iron is blocked if
sufficient amount taken up ,for body need , -
so called dietary regulation exerted by
“mucosal block” (Garnick Hypothesis).
Iron requirements :-
• Varies according to age ,sex, weight , and
state of health.
• Adult male –(10mg/day.)
• Adult female –(20 mg/day.)
• Pregnant woman –(10 mg/day.)
• Lactating woman –(25-30 mg/day).
• Children -10-15 mg/day.
1. Source of iron has marked effect on absorption.
a. Heam iron by animal product ,Hb, myoglobin (absorbs
b. Non heam iron –plant ,heam iron,(absorbs 1-15%).
2. Absorption of non heam iron influenced by:-
• compotion of diet- vit.c, glutathione, meat ,fish
,poultry . Inhibitor –phytates ,tea,oxalate,coffee,
• pH of the intestinal milieu –> “HCL(gastric juice)
librates fe3+from non heam iron-will serve as increase
solubility of dietary non heam iron” ,high alk. pH-
causes precipitation .
• State of health .healthy adult absorbs fe -5-10%( 1-2
mg) , iron deficient –adult absorbs 10-20% ( 3-6 mg ) .
# Diminished absorption of gut due
• Achlorhydria ,
• Achyla gastrica,
• Resection of gut,
• Several Gastrectomitomies,
• Desquamation –less ferritin.
• Parasitic/bacterial/fungal infection,
• Malignancies ,
• RA (rheumatoid arthritis) ,
• PUD (PEPTIC ULCER DISEASES) ,