II. Fundamentals of regulation of GI function: GI secretions, enteric nervous system and GI muscle motility.
A. Four GI secretions important in digestion and absorption of nutrients, host defense & protection of
(C = cholesterol, FSV = fat-soluble vitamins, LCFA = long chain fatty acids, IF = intrinsic factor)
gastric lipase &
all pancreatic enzymes
IF for B12 absorption
bile acids for vitamins ADEK &
50% of LCFA
trefoil peptides, mucin,
duct from ductal cells
via biliary ducts from
1 – 1.5 L/day,
2.5 L/day, isotonic,
0.5 L/day, isotonic,
neutral to alkaline
1.5 L/day, isotonic, pH = 6.8 in
gall bladder, neutral to slightly
alkaline delivered to intestine
protection from acid
B. Intestinal wall and enteric nervous system structure.
A section of small intestine wall is shown below, showing the four major regions (mucosa,
submucosa, muscle layers and serosa) and the important structures in each.
Mucosal epithelial cells bound to their basal lamina absorb nutrients and water.