Gastrointestinal Lecture 4 Part 2 Digestion and Absorption of Micronutrients Flashcards

1
Q

digestion of water soluble vitamins

A
  • Vitamin C (ascorbic acid)
  • B complex vitamins (B1 – thiamine, B2 – riboflavin, B3 – niacin, B5 – pantothenic acid, B6 – pyridoxine, B7 – biotin, B9 – folate, B12 – cabalamins)
  • Majority of water-soluble vitamins are absorbed in the first part of the small intestine
  • Absorption coupled to specific sodium co-transporters (except B12 and folate)
    • Folate absorption dependent on a proton-coupled folate transporter
    • B12 absorption occurs in the ileum and requires binding to a protein called Intrinsic factor
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2
Q

Digestion of fat soluble vitamins

A
  • Vitamin A, D, E and K
  • These fat-soluble vitamins are typically consumed bound as esters
    • esters must be hydrolyzed in the gut lumen
    • uptake of free vitamin typically occurs via specific transport proteins
    • Free vitamin typically re-esterified and packaged into chylomicrons
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3
Q

How is iron present?

A

70% of the body’s iron is present in hemoglobin, ~25% as ferritin, and ~3% as myoglobin

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4
Q

How is iron replaced?

A

While the amount of Iron lost from the body is small, the process is unregulated and lost iron must be replaced via the diet

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5
Q

iron absorption

A

Tight regulation of iron absorption means the amount taken up matches what is lost

  • Thus, while the average Iron intake is ~20 mg, only ~5% is absorbed by the body
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6
Q

Most of the iron found in the diet occurs as…?

A

Most of the iron found in the diet occurs as the ferric form (Fe3+), but it is the ferrous form (Fe2+) that is absorbed.

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7
Q

where is Fe3+ reduced to Fe2+?

A

A Ferric reductase in the brush border epithelium reduces Fe3+ to Fe2+

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8
Q

Uptake of Fe2+

A
  • Uptake of Fe2+ into enterocytes is facilitated by DMT1 (divalent metal transporter 1)
  • Once inside enterocytes, some Fe2+ is stored bound to ferritin and the remainder is transported out of the cell and into the circulation.
    • Export of Fe2+ is facilitated by the basolateral transporter ferroportin 1 (FP)
  • Once in the circulation, Fe2+ is converted to Fe3+ , which binds to transferrin
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9
Q

Overall digestion summary

A
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10
Q

What happens if you block fat absorption?

A

Diarrhea >>> steatorrhea

Many pharmacological agents aimed at weight control via controlling fat absorption run into this problem

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