Page 274 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

A. Cobalamin (B 12 ) transport B. Absorption of folic acid
Cobalamin
(vitamin B 12 ) B 12 Folic acid
Protein Pte–Glu–Glu–Glu...
In the diet: x In the diet
5–15µg/day 0.6mg/day
(min. 1–5) Pte–Glu 1 (min. 0.05)
HCl
Me–H 4 –Pte–Glu
pH Protein
x
From
B B 12 saliva
12
Stomach
R-protein Vitamin Absorption
Duodenum 1 Intrinsic
factor
B 12
R-protein Jejunum
Pancreas
Plate 10.18
B 12
R-Protein Trypsin
B 12 Pass into blood
IF
B 12
Terminal Pte–Glu 1
ileum
Me–H 4 –Pte–Glu
Glu–Glu...

2 Ca 2+ Pteroyl-
polyglutamate
Specific B 12 hydrolase
binding to pH>5.6
receptors IF Mucosal cell
of ileal
mucosa Lumen (jejunum)
Transcellular
B 12 transport C. Secondary active vitamin absorption
(ca. 1–2µg/day) B 12
TCIII TCII TCI
Na +
3 Na +

Plasma Plasma- Na +
“reserve”
Vitamins
Liver Vit. B 1 ,B 2 ,H: ATP K +
Jejunum
Storage
(3–5mg) Cell metabolism Vit. C:
Ileum
261
Excretion Lumen Mucosal cell Blood
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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