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GASTROINTESTINAL PHYSIOLOGY

Absorption of Essential Elements and Vitamins

Iron

Element	Site of Absorption	Mcchanism
Ca^2*	Duodenum and jejunurn	Active
Fe^2*	Duodenum and jejunum	Facilitated diffusion
Water-Soluble Vitamins
Vitamin C	lleum	Na*-coupled/2° acłive
Thiamin (Bj)	lejunum	Na*-C0upled/2° active
Ribotlavin (B2)	Jejunum	Na~-coupled/2“ active
Biotin	Jejunum	Na*-coupled/2° active
Vitamin B12	lleum	Facilitated diffusion
Pyridoxine (Bb)	Jejunum and ileum	Passive diffusion
Fat-Soluble Vitamins
Vitamin A	Jejunum and ileum	Passive diffusion
Vitamin D	Jejunum and ileum	Passive diffusion
Vitamin E	Jejunum and ileum	Passive diffusion
Vitamin K	Jejunum and ileum	Passive diffusion

Fal-Soluble Vitamins J. Perkins

Figurę 7.38 Absorption of Essential Vitamins and Elements .

The celi mechanisms involved in the absorption of Ca", iron, and several imporiant vitamins are summarized. Vitamin D, (1,25-dihy-droxy-vitamin D,) plays an imporiant role in stimulating inteslinal Ca ‘ absorption. Intrinsic tactor is madę by the stornach (see Figuro 7.12). If insufficient amounts of intrinsic tactor are produced, B,.. deficiency ensues. Failure to property digest fats (see Figurę 7.37) can lead to deficiencies of the fat-solu-ble vitamins. Abbreviations: DMTI, Divalenl metal transporter 1: FR. tuirireductase; H. hephaestin; IF, intrinsic factoi: IREC1, iron-regulated transporter 1; TCII, transcobalamin II; TF, transferom

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