Absorption in the intestine - GI system

Absorption in the intestine

Absorption:

 Simple diffusion
o Water
o Water-soluble small molecules
o Fat and lipid soluble molecules
 Facilitated transport and active transport
o Glucose
o Electrolytes
 Endocytosis
o Larger molecules

Location of absorption:

 Carbohydrate: duodenum -> jejunum -> ileum
 Amino acids: duodenum -> jejunum -> ileum
 Fat: jejunum -> duodenum- > ileum



Enterocyte – a villus epithelial cell


Intracellular hydrolysis – where for example a peptide is transported across the
apical membrane and then hydrolysis inside the cell to amino acids

Luminal hydrolysis followed by intracellular resynthesized – for example where
a triglyceride is broken down into glycerol and fatty acids in the lumen. They are
then transported across the apical membrane where they are combined to
reform a triglyceride, which is subsequently moved into the lacteal.


Carbohydrate digestion:

Carbohydrates: Amylopectin, glycogen, cellulose -> broken down by α-amylase

Oligosaccharides: α- dextrin, di & trisaccharides -> broken down by
oligosaccharidases (brush border) (inc sucrase-isomaltase)

Glucose, galactose and fructose are then absorbed


Sugar absorption: