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WILLIAM'S HEMATOLOGY > 43 Iron Metabolism > Flashcards

43 Iron Metabolism Flashcards

1
Q

Iron components in the average Person (mg/ % of total body iron)

Hemoglobin
Storage iron (ferritin , hemosidirin)
Myoglobin
Labile pool
Other tissue iron
Transport iron

A

Iron components in the average Person (mg/ % of total body iron)

Hemoglobin: 2000 (67%)
Storage iron (ferritin , hemosidirin): 1000 (27%)
Myoglobin: 130 (3.5%)
Labile pool: 80 (2.2%)
Other tissue iron: 8 (0.2%)
Transport iron: 3 (0.08%)

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2
Q

Hemoglobin, which is _____% iron by weight, contains approximately____ g of body iron in men and ____ g in women.

A

0.34%
2 g in men
1.5 g in women

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3
Q

One milliliter of packed erythrocytes contains approximately ____ mg of iron.

A

1 mg of iron

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4
Q

Storage forms of iron

A

Ferritin and hemosiderin

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5
Q

Water-soluble or Water-insoluble

Ferritin
Hemosiderin

A

Ferritin: Water-soluble
Hemosiderin: Water-insoluble

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6
Q

Subunit of ferritin that have ferroxidase activity, thereby enabling ferritin to take up or release iron quite rapidly.

Takes up iron more readily but retains it less avidly

A

H (heavy)

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7
Q

Much of the storage iron in the liver and spleen is in ferritin containing mostly______ subunits.

A

L subunits

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8
Q

TRUE OR FALSE

Except under conditions of inflammation, the plasma (serum) ferritin concentration usually correlates with total-body iron stores, making measurement of serum ferritin levels important in the diagnosis of disorders of iron metabolism.

A

TRUE

Except under conditions of inflammation, the plasma (serum) ferritin concentration usually correlates with total-body iron stores, making measurement of serum ferritin levels important in the diagnosis of disorders of iron metabolism.

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9
Q

The cargo protein_____, a ferritin receptor, is increased during iron deficiency and delivers ferritin to lysosomes.

A

NCOA4

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10
Q

Found predominantly in macrophages

Microscopically, in unstained tissue sections or marrow films, it appears as clumps or granules of golden refractile pigment.

A

Hemosiderin

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11
Q

Structurally similar to hemoglobin, but it is monomeric rather than tetrameric

It is present in small amounts in all skeletal and cardiac muscle cells where it may serve as an oxygen reservoir

A

Myoglobin

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12
Q

Size of the labile iron pool

A

80–90 mg of iron

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13
Q

It is now sometimes considered to be equivalent to the chelatable iron pool.

A

Labile iron pool

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14
Q

Includes cytochromes and other iron-containing enzymes

Although a small compartment, it is vital and sensitive to iron deficiency.

A

Tissue iron

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15
Q

Amount of tissue iron

A

6–8 mg

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16
Q

The smallest but the most active of the iron compartments

A

Transport iron

Its iron, almost entirely carried by transferrin, normally turns over at least 10 times each day.

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17
Q

Amount of transport iron

A

3 mg

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18
Q

A dumbbell-shaped glycoprotein with a molecular weight of approximately 80 kDa where each of the two globular domains contains a binding cleft for Fe3+

A

Transferrin

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19
Q

Normally, approximately ______of the transferrin iron-binding sites are occupied by iron.

A

One-third

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20
Q

Apotransferrin (transferrin devoid of iron) is synthesized by

A

Hepatocytes and cells of the monocyte macrophage system

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21
Q

RDA for Iron

Male 19 and above
Female 19 - 50 years
Female 51 years and above
Pregnant
Lactation

A

RDA for Iron

Male 19 and above: 8 mg
Female 19 and above: 18 mg
Female 51 years and above: 8 mg
Pregnant: 27 mg
Lactation: 9 mg

22
Q

Amount of iron excreted in stool

A

~1 mg/day

23
Q

Increase or decrease iron absorption

Oxalates, phytates, and phosphates

Hydroquinone, ascorbate, lactate, pyruvate, succinate, fructose, cysteine, and sorbitol:

A

Oxalates, phytates, and phosphates; red wine: decrease iron absorption

Hydroquinone, ascorbate, lactate, pyruvate, succinate, fructose, cysteine, and sorbitol: increase iron absorption

24
Q

Iron normally enters the body through the gastrointestinal tract, mostly through the

A

Enterocytes of the duodenum

25
Q

The reduction of ferric iron to ferrous iron, in part by duodenal _____________________, ferrous iron is transported into the intestinal villus cell by the _________________.

A

Cytochrome b (Dcytb) reductase

Divalent metal transporter (DMT)-1

26
Q

Basolateral export of ferrous iron is mediated by _________ in association with hephaestin and plasma ceruloplasmin to oxidize iron to the ferric state.

A

Ferroportin

27
Q

Ferric iron is taken up by plasma_______________.

A

Apotransferrin

28
Q

Destruction of aged erythrocytes and hemoglobin degradation occur within

A

Macrophages

29
Q

In humans, the destruction and production of erythrocytes generates most of the iron flux in and out of plasma

A

Monocyte–Macrophage System

(20–25 mg/day recycled in adults vs 1–2 mg/day absorbed)

30
Q

This proceeds at a rate sufficient to release approximately 20% of the hemoglobin iron from the cell to the plasma compartment within a few hours

Approximately _____% of this iron is rapidly reincorporated into hemoglobin.

A

80%

31
Q

Thus, 20% to 70% percent of the hemoglobin iron of nonviable erythrocytes reappears in circulating red cells in _____ days.

A

12 days

32
Q

Regulates plasma iron concentrations by controlling the absorption of iron by the intestinal epithelial enterocytes and its release from iron-recycling macrophages and hepatocytes involved in iron storage.

A

Hepcidin

33
Q

Hepcidin is produced predominantly by

A

Hepatocytes

34
Q

The structural similarity of hepcidin and a class of antimicrobial peptides termed________ suggests that the hormone evolved from the latter to modulate iron homeostasis as a mechanism of body defense against microorganisms.

A

Defensins

35
Q

TRUE OR FALSE

Patients with iron overload and high plasma iron levels are susceptible to such infections, such as with Vibrio vulnificus and Yersinia enterocolitica

A

TRUE

Patients with iron overload and high plasma iron levels are susceptible to such infections, such as with Vibrio vulnificus and Yersinia enterocolitica

36
Q

Hepcidin exerts its iron-regulatory effect by binding to_________, a transmembrane iron-export protein expressed on enterocytes, macrophages, and hepatocytes.

A

Ferroportin

37
Q

Hepcidin production is stimulated by inflammatory cytokines such as interleukin ____, and the overproduction of hepcidin is an important factor in the pathogenesis of the anemia of chronic inflammation

A

(IL)-6

38
Q

Hepcidin transcription is regulated in an iron-dependent manner by the ___________ pathway.

A

BMP pathway

39
Q

Acts as an inhibitor of the interaction of BMP with the receptor

Autosomal recessive mutations cause a very severe form of hereditary hemochromatosis, serves as a coreceptor for the BMPs

A

Hemojuvelin

40
Q

A membrane serine protease that likely acts by proteolysis of hemojuvelin and perhaps also other proteins in the BMP receptor complex

Inhibitory effect of hepcidin transcription

A

Tmprss6 (also called matriptase 2)

41
Q

Humans with mutations of the Tmprss6 ortholog were shown to manifest this condition

IDA that does not improve with oral iron therapy and responds only partially to parenteral iron therapy.

A

Iron-refractory iron-deficiency anemia

42
Q

An erythropoietin-induced erythroblast-secreted glycoprotein that acts on hepatocytes to suppress their hepcidin production and is required for rapid suppression of hepcidin after hemorrhage or erythropoietin administration.

A

Erythroferrone

Erythroferrone binds BMP2/6 secreted by sinusoidal endothelial cells in the space of Disse and thereby inhibits BMP signaling and hepcidin transcription in hepatocytes

43
Q

TRUE OR FALSE

Within hours after the onset of systemic infection, plasma iron concentration increases.

A

FALSE

Within hours after the onset of systemic infection, plasma iron concentration decreases.

44
Q

The main human cytokine responsible for hepcidin induction

A

IL-6

45
Q

Plays a role in the binding and endocytosis of diferric transferrin

A major mechanism for regulation of iron metabolism

A

TfR1

Synthesis of TfR1 is induced by iron deficiency.

46
Q

Also endocytic for holotransferrin, is not thought to be involved in delivering iron to cells but its hepatic expression is necessary for normal hepcidin expression and regulation.

A

TfR2

47
Q

The final steps of heme synthesis take place in____________, where iron is inserted into protoporphyrin by the enzyme__________________.

A

Mitochondria

Ferrochelatase

48
Q

Ringed sideroblast can be stained by

A

Prussian blue

49
Q

TRUE OR FALSE

In iron deficiency and in the anemia that accompanies chronic disorders, sideroblasts almost disappear from the marrow

A

TRUE

In iron deficiency and in the anemia that accompanies chronic disorders, sideroblasts almost disappear from the marrow

50
Q

In normal, iron-replete marrow, much smaller siderotic granules are also demonstrable, scattered in the cytoplasm of about___________of erythroblasts

A

One-third

When heme synthesis is impaired, as in lead poisoning or in the sideroblastic anemias, the mitochondria accumulate excessive amounts of amorphous iron aggregates

Seen by light microscopy as a ring of large blue siderotic granules encircling the erythroblast nucleus (ringed sideroblast)

51
Q

Most iron loss occurs by way of

A

Desquamated intestinal cells in the feces : 1 mg per day

Exfoliation of skin and dermal appendages and perspiration result in much smaller losses.

52
Q

Total daily iron loss

Males:
Menstruating women:

A

Total daily iron loss for

Males: 1 mg
Menstruating women: 2mg

WILLIAM'S HEMATOLOGY (109 decks)

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