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What is a “Diet”?
What are humans supposed to eat?
Are you healthy?
Figure 22.35 Absorption of monosaccharides.
2 As Na+ moves across the
Glucose
Galactose
+
Na -glucose
membrane through a membrane
symport
cotransporter protein (in this
Fructose
transporter
case SGLT), it drives glucose
Na+
against its concentration
Facilitated
gradient into the cells.
diffusion
transporter
Brush border of
intestinal cell
1 The Na+-K+ pump
stores energy that
drives glucose (and
galactose) uptake by
creating a steep
concentration gradient
for Na+ entry into
intestinal cells.
3 Fructose enters the cell by
facilitated diffusion.
Na+
4 All three monosaccharides
exit across the basolateral
membrane via facilitated
diffusion on the GLUT2 sugar
transporter.
Na+
Na+-K+
pump
GLUT2
Na+
K+
Capillary
© 2014 Pearson Education, Inc.
Figure 22.33 Protein digestion and absorption in the small intestine.
Lumen
of intestine
Amino acids of
protein
fragments
Pancreatic
proteases
Brush
border
enzymes
Na+
Na+
Absorptive
epithelial
cell
Amino
acid
carrier
Capillary
© 2014 Pearson Education, Inc.
Apical
membrane
(microvilli)
1 Proteins and protein
fragments are digested
to amino acids by pancreatic
proteases (trypsin,
chymotrypsin,
and carboxy- peptidase), and
by brush border enzymes
(carboxypeptidase,
aminopeptidase,
and dipeptidase)
of mucosal cells.
2 The amino acids are
then absorbed by active
transport into
the absorptive cells, and
move to their opposite
side.
3 The amino acids
leave the villus epithelial
cell by facilitated diffusion
and enter the capillary via
intercellular clefts.
C6H12O6
represents glucose, galactose, fructose