Absorption Of Iron

ABSORPTION OF IRON

Q. 1

Most of the iron in the diet is in the ferric (Fe3+) form. It is actively absorbed in:

 A

Stomach

 B

Duodenum

 C

Large intestine

 D

Ileum

Q. 1

Most of the iron in the diet is in the ferric (Fe3+) form. It is actively absorbed in:

 A

Stomach

 B

Duodenum

 C

Large intestine

 D

Ileum

Ans. B

Explanation:

Gastric secretions dissolve the dietary iron and permit it to form soluble complexes with ascorbic acid and other substances that aid its reduction to the Fe2+ form.

Almost all iron absorption occurs in the duodenum. Transport of Fe2+ into the enterocytes occurs via divalent metal transporter 1 (DMT1).

Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 26. Digestion, Absorption, & Nutritional Principles. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e. 

Q. 2

Iron absorption is increased by the following factor in diet:

 A

Vitamin-C

 B

Phytic acid

 C

Fibre diet

 D

Phosphates

Q. 2

Iron absorption is increased by the following factor in diet:

 A

Vitamin-C

 B

Phytic acid

 C

Fibre diet

 D

Phosphates

Ans. A

Explanation:

In a vegetarian diet, nonheme iron is absorbed very poorly because of the inhibitory action of a variety of dietary components, particularly phosphates, phytates and high fibre content. Ascorbic acid and meat facilitate the absorption of nonheme iron. Ascorbate forms complexes with and/or reduces ferric to ferrous iron. Meat facilitates the absorption of iron by stimulating production of gastric acid; other effects also may be involved. Either of these substances can increase availability several fold.
 
Ref: Kaushansky K., Kipps T.J. (2011). Chapter 37. Hematopoietic Agents: Growth Factors, Minerals, and Vitamins. In B.C. Knollmann (Ed), Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 12e.

 


Q. 3

Transferrin in the blood is saturated with iron normally by:

 A

35%

 B

85%

 C

72%

 D

15%

Q. 3

Transferrin in the blood is saturated with iron normally by:

 A

35%

 B

85%

 C

72%

 D

15%

Ans. A

Explanation:

Transport of Fe2+ into the enterocytes occurs via divalent metal transporter 1 (DMT1). Some is stored in ferritin. A protein called hephaestin (Hp) is associated with ferroportin 1. It is not a transporter itself, but it facilitates basolateral transport. In the plasma, Fe2+ is converted to Fe3+ and bound to the iron transport protein transferrin. This protein has two iron-binding sites. Normally, transferrin is about 35% saturated with iron, and the normal plasma iron level is about 130 microg/dL (23 mumol/L) in men and 110 micro g/dL (19 mumol/L) in women.
 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 26. Digestion, Absorption, & Nutritional Principles. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 4

What is true of iron:

 A

It is stored in ferritin

 B

It is absorbed by Transferrin in the intestine

 C

Spleen in major storage organ

 D

Fe++ is excreted in urine

Q. 4

What is true of iron:

 A

It is stored in ferritin

 B

It is absorbed by Transferrin in the intestine

 C

Spleen in major storage organ

 D

Fe++ is excreted in urine

Ans. A

Explanation:

A i.e. It is stored in ferritin


Q. 5

Iron absorption is decreased by A/E-

 A

Calcium

 B

Tetracycline

 C

Phytate

 D

Ascorbic acid

Q. 5

Iron absorption is decreased by A/E-

 A

Calcium

 B

Tetracycline

 C

Phytate

 D

Ascorbic acid

Ans. D

Explanation:

Ans. is ‘d’ i.e., Ascorbic acid


Q. 6

Iron absorption from intestine is regulated by –

 A

Acid secretion in stomach

 B

Reducing substances in food

 C

Mucosal block in the intestinal cells in according to iron requirement

 D

Alkaline medium in small intestine

Q. 6

Iron absorption from intestine is regulated by –

 A

Acid secretion in stomach

 B

Reducing substances in food

 C

Mucosal block in the intestinal cells in according to iron requirement

 D

Alkaline medium in small intestine

Ans. C

Explanation:

Ans. is ‘c’ i.e., Mucosal block in the intestinal cells according to iron requirement

 “Iron absorption is regulated according to the demand, e.g., when thee is iron deficiency, absorption increases” Robbins 644

  • Various other factors also influence the absorption of iron ‑

Factors affecting iron almrption

A) Decreasing absorption

By complexing (Forming chelate) with iron

  • Phytates                  
  • Milk                     
  • Tetracycline
  • Phosphates        
  • EDTA

o By opposing reduction of ferric form to ferrous form.

  • Pancreatic secretions          
  • Antacids            
  • Alkalies 

B) Increasing absorption

By enhancing reduction of ferric form to ferrous firm.


Q. 7

True about iron absorption are all, except ‑

 A

Major site of absorption is duodenum

 B

Stored as Ferritin

 C

Absorbed in ferrous form

 D

Pancreatic secretions improves the absorption

Q. 7

True about iron absorption are all, except ‑

 A

Major site of absorption is duodenum

 B

Stored as Ferritin

 C

Absorbed in ferrous form

 D

Pancreatic secretions improves the absorption

Ans. D

Explanation:

Ans. is ‘d’ i.e., Pancreatic secretions improves the absorption

Iron absorption

  • Iron is absorbed from upper small intestine mainly duodenum.
  • In diet iron occurs in two forms, haeme iron and inorganic (non-haeme) iron.
  • Haem iron is better absorbed than inorganic iron, but the major fraction of diet is inorganic iron.
  • Inorganic iron is mostly in ferric form; needs to be reduced to ferrous form because iron is absorbed in ferrous form.
  • After absorption ferrous form is once again oxidized to ferric form inside enterocytes.
  • A fraction of absorbed iron is rapidly delivered to plasma transferrin.
  • However, most of the iron is deposited in the enterocytes as ferritin, some to be transferred more slowly to plasma transferrin, and some to be lost when senescent mucosal cells (enterocytes) are sloughed into the intestine.
  • Iron absorption is regulated according to the demand, e.g., when there is iron deficiency, absorption increases.
  • This regulation is mediated by “iron metabolism regulatory hormone”, i.e., hepcidin that inhibit iron absorption.
  • When there is iron deficiency, concentration of hepacidin falls and there is increase iron absorption.
  • Hepacidin also decreases release of iron from storage sites.

Transport and storage of iron

  • Iron is transported is blood in combination with a glycoprotein transferrin.
  • Iron is transported into cells through attachment of transferrin to specific membrane bound receptors.
  • Iron is stored as ferritin (major storage form) or haemosiderin.
  • Ferritin is a complex of iron and apoferritin (iron + apoferritin ferritin).
  • Iron is mainly stored in reticulo-endothelial cells monocytes/macrophages of liver, spleen, bonemarrow.
  • It is also stored in hepatocytes (parenchymal cells of liver) and myocytes of skeletal muscles. Note :
  • Iron is stored in ferritin in ferric form.

Q. 8

Iron absorption takes place in which part of intestine‑

 A

Duodenum

 B

Ileum

 C

Jejunum

 D

Colon

Q. 8

Iron absorption takes place in which part of intestine‑

 A

Duodenum

 B

Ileum

 C

Jejunum

 D

Colon

Ans. A

Explanation:

Ans. is ‘a’ i.e., Duodenum

Almost all iron absorption occurs in the duodenum.


Q. 9

Iron absorption is increased by all except ‑

 A

High vitamin C in diet

 B

High phosphates in diet

 C

Ferrous form

 D

Acidity

Q. 9

Iron absorption is increased by all except ‑

 A

High vitamin C in diet

 B

High phosphates in diet

 C

Ferrous form

 D

Acidity

Ans. B

Explanation:

Ans. is ‘b’ i.e., High phosphates in diet


Q. 10

Iron absorption is inhibited by ‑

 A

Ascorbic acid

 B

Vitamin C

 C

Hepcidin

 D

All of the above

Q. 10

Iron absorption is inhibited by ‑

 A

Ascorbic acid

 B

Vitamin C

 C

Hepcidin

 D

All of the above

Ans. C

Explanation:

Ans. is ‘c’ i.e., Hepcidin


Q. 11

Normal transferrin is saturated with iron ‑

 A

20%

 B

35%

 C

50%

 D

70%

Q. 11

Normal transferrin is saturated with iron ‑

 A

20%

 B

35%

 C

50%

 D

70%

Ans. B

Explanation:

Ans. is ‘b’ i.e., 35%

  • In normal individuals, transferrin is about one third saturated with iron, yielding serum iron levels that average 120 g/dl in men and 100 g/dl in women.

Serum ferritin

  • Most of the ferritin is stored is different organs (liver, spleen, bone marrow).
  • Very small amounts of ferritin normally circulate in the plasma.
  • Since plasma ferritin is derived largely form the storage pool of body iron, its level correlate well with body iron stores. i.e., when there is iron depletion, body store of iron is reduced that inturn leads to decrease in plasma ferritin.

Transferrin saturation and iron binding capacity

  • Iron is transported in the plasma by transferrin.
  • Normally transferrin is 33% saturated (77% free) with iron, yield serum iron levels that average 100-120 g/dl.
  • So, if serum transferrin will be 100% saturated the serum iron will be 300 g/dl. that means the total iron binding capacity of transferrin is 300 to 350 g/dl.
  • When iron store is depleted e.g., in iron dificiency anemia, there is increased synthesis of transferrin that results in increased total iron binding capacity.
  • When iron store is repleted e.g., anemia of chronic disease, there is decreased synthesis of transferrin that results in decreased total iron binding capacity.

Serum transferrin receptors

  • Erythroid precursors have receptors for transferrin by which they recieve iron from transferrin that is utilized for hemoglobin synthesis.
  • When erythroid precursors mature, these receptors are shed into plasma and can be masured as serum transferrin receptors concentration.
  • In iron deficiency state, there is increased erythropoisis in bone marrow→ T concentration of erythroid precursor that results in increased total number of transferrin receptor —> T serum transferrin receptor concentration.


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