digestive 1b Flashcards
why is iron needed
for formation of hemoglobin, myoglobin, cytochromes, cytochrome oxidase, peroxidase, catalase, etc
men excrete about ____ mg or iron daily, most via the ____
0.6 mg
feces
women who are between puberty and menopause average ____ mg of iron loss daily.
1.3
excreted iron must be replaced by
ingestion
the body’s handling of iron involves:
____ ____ protein (which when combined with iron is ____ )
____ ____ protein ( ____ )
the regulation of the rate of intestinal iron ____
intracellular storage protein (combined with iron → ferritin)
plasma transport protein (transferrin)
absorption
the regulation of the rate of intestinal iron absorption is accomplished by
the down- or up-regulating of the ferritin gene and by a hormone (hepcidin) that controls the membrane transporter that moves iron out of the SI mucosal epithelial cells
of the approximately ____ grams of iron in the body, about ____ % is in hemoglobin and myoglobin and cytochromes and enzymes; ____ % is in the blood as transferrin; and 15-30% is stored for later use (mostly by the ____ and less so in the ____ ____ as ferritin)
5
70%
0.1%
liver
bone marrow
about 10% of the ingested iron is absorbed into the ____ daily
blood
absorption of iron occurs in various way, including via the protein ____ in the luminal plasma membranes of SI mucosal epithelial cells
DMT 1
after iron absorption into enterocytes, iron exists these cells via the protein ____ , and is then moved into blood capillaries
ferroportin
inside cells (both body cells and intestinal cells), some of the iron is incorporated into ____ , but some of this is released back into the intestinal lumen when cells:
this iron is excreted in ____
ferritin
at the tips of intestinal villi disintegrate
excreted in feces
some of the absorbed iron ions enter the plasma where they combine with a plasma protein (a beta globulin called apotransferrin) to form ____ , which is transported in the plasma
transferrin
excess iron in the blood is deposited
in liver hepatocytes and bone marrow reticuloendothelial cells
small amounts of iron are stored in a very insoluble form called
hemosiderin
when the amount of iron in the plasma falls, some iron in the ____ storage pool is removed and transported in the form of ____ in the plasma to body areas where it is needed (iron is loosely bound in transferrin and can be released to any tissue cell at body locations)
ferritin
transferrin
when worn out RBCs are destroyed in the ____ and ____ , the hemoglobin that is released is ingested by ____ ;
this releases iron that is bound in plasma to transferrin or stored in the ferritin pool to be used as needed for:
liver and spleen
macrophages
the formation in bone marrow of new hemoglobin/RBCs
regulation of iron:
when the body’s amount of iron is sufficient, the increased level of free iron in the blood and in SI epithelial cells leads to
increased transcription of the gene encoding the ferritin protein in the SI epithelial cells
when the body’s amount of iron is sufficient, the increased level of free iron in the blood and in SI epithelial cells leads to increased transcription of the gene encoding the ferritin protein in the SI epithelial cells:
the resulting increased ferritin leads to an increased:
binding of iron in the intestinal epithelial cells and a decrease in the amount of iron released into the blood
when body iron is low, the production of ferritin in intestinal epithelial cells ____ , leading to:
falls
a decrease in the amount of iron bound to ferritin, thus increasing the unbound iron released into the blood
iron regulation also involves ____, a hormone produced by the liver , and ____ a transmembrane protein that transports iron from the insides to the outsides of SI mucosal epithelial cells (and other cells)
hepcidin
ferroportin
when systemic iron stores and concentration are high, ____ release is increased
hepcidin binds to ____ on SI epithelial cells, resulting in the ____ molecule’s being moved to the insde of the cell and degraded
hepcidin thereby prevents iron from being ____ and the iron is sequestered in the SI cells rather than being moved into the blood
hepcidin
ferroportin ferroportin
exported
a lack of iron lead to
anemia
too much iron can cause ____ which can result in:
hemochromatosis
abnormal skin pigmentation, diabetes, liver disease, and heart and reproductive problems
