GI: Nutrient Absorption

Question 1

Monosaccharides: Glucose, Galactose

Answer 1

Carbohydrates
SGLT 1 (Na+ -dependent Cotransport)

A/w Lactose intolerance
Monosaccharides exit via GLUT 2 transporter (Facilitated)

Question 2

Fructose

Answer 2

Carbohydrate
GLUT 5 (Facilitated Diffusion)

Question 3

Free Fatty Acids (FFA)
Monoglycerides
Cholesterol
Lysolecithin

Answer 3

Lipids

Diffusion (Through micelles formed from Bile salts)

Question 4

Di / Tripeptides

Answer 4

Protein
H+ -dependent Di / Tripeptide Cotransport

Deficient abs. a/w Pancreatic disease

Question 5

Amino Acids

Answer 5

Protein
Na+ -dependent AA Cotransport

Hartnup disease is caused by a lack of the neutral AA cotransporter

Question 6

Fat Soluble Vitamines (A, D, E, K)

Answer 6

Vitamins

In micelles w/ Lipids

Question 7

Water-soluble Vitamins

Answer 7

Vitamins
Na+ -dependent Cotransport

B12 is absorbed by an Independent mechanism involving Intrinsic Factor (IF)

Question 8

Ca2+

Answer 8

Calcium
Calbindin-D28K (Vitamin D-dependent Ca2+ -binding protein)

Needs active Vit. D (1,25-dihydroxycholecalciferol) from Liver and Kidney metabolism; Deficiency of Active Vit. D a/w Rickets (Children) and Osteomalacia (Adults)

Question 9

Iron (Fe2+)

Answer 9

Duodenum

Absorbed as Ferrous Iron (Fe2+,

Question 10

Folate

Answer 10

Proximal Jejunum
Brush border splits polyglutamates into monoglutamates
–> which are absorbed and converted to the transport form
–> 5-methyltetrahydrofolate

Neural tube defects (Congenital effect of Maternal deficiency)
Megablastic anemia

Question 11

Vit. B12 (Cobalamin)

Answer 11

Terminal Ileum
Gastric pepsin releases B12 from food
–> binds to R-protein (salivary secretion) in stomach
–> pancreatic proteases degrade R-protein in Duodenum
–> binds IF (from parietal cells)
–> absorbed in Terminal Ileum

Pernicious anemia (megaloblastic)
Gastrectomy (Loss of Parietal cells)
Deficiency masked by Folate supplementation