The small intestine is divided into three regions: the duodenum, jejunum, and ileum. The duodenum secretes bile from the liver, pancreatic juice from the pancreas, and bicarbonate to balance pH. These secretions help to further break down proteins and lipids. Bile emulsifies lipids to aid absorption. Pancreatic juice contains enzymes that metabolize remaining biomolecules. The presence of lipids and proteins triggers the release of cholecystokinin, stimulating the release of bile and pancreatic juice into the small intestine for digestion. Absorption of nutrients occurs in the jejunum and ileum through microvilli in the smooth muscle wall.

1. Unit 3 Notes:
The Small Intestine

3. (1) Regions
• Duodenum: (First Chamber)
–Approximately 10in long
• Jejunum: (Middle Section)
–Approximately 7-8ft long
• Ileum: (Last Section)
–Approximately 12ft long

5. (2) Inside the Duodenum
• Secretes Bile, Pancreatic Juice & Bicarbonate:
–Bile = Yellow-green solution produced by
the liver, stored in the gallbladder.
–Pancreatic Juice = Solution produced by the
pancreas, stored in the pancreas.
–Bicarbonate = pH balancing compound
found in the blood.
• Metabolize all remaining proteins and lipids.

6. (3) About Bile…
• Produced by liver, Stored by Gallbladder.
• Contains:
–Bile Salts
–Waste Pigments (bilirubin)
–Cholesterol & Phospholipids
• Function: Emulsify lipids so that they are
dispersed throughout water, and can be easily
absorbed.

8. (4) About Pancreatic Juice…
• Produced by pancreas.
• Contains:
– Carboxypeptidase (Protein Enzyme)
– Chymotrypsin (Protein Enzyme)
– Amylase (Carbohydrate Enzyme)
– Lipases (Lipid Enzymes)
– Nucleases (Nucleic Acid Enzymes)
• Function: Metabolize all remaining biomolecules.

9. (5) Releasing Bile & Pancreatic Juice
• The presence of Lipids & Proteins 
Release of CCK (cholecystokinin) into
bloodstream.
• CCK stimulates the release of bile + pancreatic
juice out Sphincter of Oddi.

11. (6) About Bicarbonate…
• Used to maintain pH balance within cells
(and water systems).
–Neutralizes acidity of chyme coming
from stomach
• Secreted from Brunner’s Glands along
Duodenum Walls.

12. (7) In The Jejunum & Ileum
• Smooth Muscle with millions of microvilli:
– Microvilli Absorb Nutrients.
– Nutrients directly deposited in blood stream.
– Folds in between are called “Crypts of Lieberkuhn”.
• Crypts of Lieberkuhn:
– Secrete Lysozymes to eliminate any foreign bacterial
cells.
– Secrete Muccin to lubricate and dissolve remaining food
stuff.