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MLSCI 230 > Iron Metabolism > Flashcards

Iron Metabolism Flashcards

1
Q

Ferrous and ferric forms are components of …

A

hemoglobin, myoglobin, and mitochondrial cytochromes

- involved in reduction and oxidation rxns

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2
Q

T or F. Iron has no mechanism for active excretion

A

T; most is bound to protein

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3
Q

Iron Sources

A

10-20 mg/day is ingested from food sources

- only 1-2 mg absorbed (~10%)

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4
Q

Heme iron

A

most bioavailable form Fe 2+; from meat sources

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5
Q

Non-heme iron

A

Fe 3+

  • legumes
  • leafy green vegetables
  • cereals
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6
Q

Absorption of non-heme iron

A
  • enhanced by ascorbic acid and citric acid

- inhibited by polyphenols, phylates, and calcium

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7
Q

How much iron is lost daily through sweat and cell sloughing

A

1-2 mg

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8
Q

How much iron is released through hemolysis of senescent RBCs?

A

20 mg; reused by bone marrow

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9
Q

How much iron is lost through menstruation

A

0.8 mg/day

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10
Q

Iron and pregnancy

A

can require up to 1000 mg of iron

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11
Q

Approximately how much iron is in the body

A

~3500-4000 mg

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12
Q

List the progress of Iron as it is absorbed in the body

A
  • ingested as either Fe 2+ or Fe 3+
  • gastric acid reduces Fe 3+ to 2+
  • absorbed in duodenum and upper jejunum
  • converted back to Fe 3+ to bind to transferrin
  • gets into cells via receptor-mediated endocytosis
  • placed into protoporphyrin IX as 2+
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13
Q

Difference in absorption bw Fe 2+ and 3+

A

2+:
- enters enterocytes through heme transporter (heme oxygenase separates iron from heme)

3+:

  • 3+ reduced to 2+ before enterocytes
  • Ferrireductase: Dcytb
  • now 2+, transported into enterocytes via divalent metal transporter 1 (DMT1)
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14
Q

How does iron get out of enterocytes?

A
  • Ferroportin exports iron to the circulation
  • Hephaestin oxidizes Fe
  • transferrin carries 3+ to tissues
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15
Q

What is hepcidin?

A
  • hormone made by hepatocytes
  • negative regulator of iron absorption
  • binds to ferroportin to prevent iron export
  • limits absorption in gut and prevents release from storage
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16
Q

Hepcidin is an acute phase reactant

A
  • upreg by inflammation and iron overload

- downreg in response to anemia and hypoxia

17
Q

2/3 of the body’s iron is in

A

Hb

18
Q

Storage forms of iron

A
  • ferritin

- hemosiderin

19
Q

Ferritin

A
  • apofer. + Fe 3+ = ferritin
  • globular protein cage w iron inside (M&M’s!)
  • readily accessible!
  • stored in macs, hepatocytes, and developing normoblasts
  • water soluble
  • not visible w light microscopy
20
Q

Hemosiderin

A
  • precipitated aggregates of ferritin
  • fer cage is partially degraded; portion aggregate to form hemosiderin
  • stable but less available
  • not water soluble
    0 visualized w light microscopy using Perls’ Prussian Blue Stain
21
Q

Measures iron in the blood (only transferrin bound)

A

Serum iron

22
Q

Total Iron Binding Capacity (TIBC)

A

indirect measure of the amount of transferrin available to carry iron

23
Q

Transferrin saturation

A

calc of the % of transferrin bound to iron

- serum iron/TIBC x 100

24
Q

Serum Ferritin

A
  • reflects amount of stored iron

- also an acute phase reactant

25
Q

Prussian Blue Stain

A

stains for stored iron (hemosiderin) in bone marrow smears or tissue biopsies

26
Q

Hemochromatosis

A
  • genetic condition that causes increased iron absorption (HFE gene)
  • increased iron and hemosiderin in tissues = organ damage = organ failure
  • treated by regular phlebotomy
27
Q

Hemosiderosis

A
  • iron overload secondary to repeated blood transfusions

- localized hemosiderosis from tissue hemorrhage or increased hemolysis

28
Q

Sideroblastic anemia

A
  • due to inability to produce heme
  • increased or normal iron supply
  • examples: lead poisoning, porphyrias
29
Q

Pappenheimer Bodies

A
  • clusters of blue inclusions in RBCs
  • composed of precipitated hemosiderin, protein, and RNA
  • seen in sideroblastic anemia (and others)
  • not reported in the Edmonton zone
30
Q

decrease in oxygen-carrying capacity of the blood

A

Anemia

31
Q

This arises if there is insufficient Hb or the Hb has impaired function

A

Anemia

  • decreased Hb conctn
  • decreased RBC count
  • decreased hematocrit
32
Q

Causes of anemia

A
  • decreased production
  • increased destruction (immune + non-immune causes of hemolysis, hereditary or acquired RBC defect)
  • increased loss (hemorrhage, etc.)
33
Q

Laboratory diagnosis of anemia

A
  • complete blood cell count
  • RBC indices
  • peripheral blood smear
  • reticulocyte count
  • bone marrow smear and biopsy

MLSCI 230 (36 decks)

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