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 From the stomach to the large intestine:  Duodenum ◦ Attached to the stomach via the pyloric sphincter  Jejunum  Ileum ◦ Meets the large intestine at the ileocecal valve © 2015 Pearson Education, Inc.

 Begins in the small intestine via enzymes from: ◦ Intestinal cells ◦ Pancreas  Pancreatic ducts carry enzymes to the duodenum ◦ Bile, formed by the liver, enters the duodenum via the bile duct  The pancreatic and bile ducts come together to form a joint duct that releases into the duodenum – the hepatopancreatic ampulla © 2015 Pearson Education, Inc.

Bile duct and sphincter Accessory pancreatic duct Pancreas Jejunum Main pancreatic duct and sphincter Duodenum Hepatopancreatic ampulla and sphincter Duodenal papilla Gallbladder

 Three structural modifications increase surface area for food absorption: 1.Villi—fingerlike projections formed by the mucosa  House a capillary bed and lacteal 2.Microvilli—tiny projections off of the villi (create a brush border appearance) 3. Circular folds (plicae circulares)—deep folds of mucosa and submucosa © 2015 Pearson Education, Inc.

Blood vessels serving the small intestine Muscle layers Villi Lumen Circular folds (plicae circulares) (a) Small intestine

Absorptive cells Blood capillaries Lymphoid tissue Muscularis mucosae (b)Villi Lymphatic vessel Submucosa Villus

 Protein and some carbohydrate breakdown started in the stomach ◦ Fats begin in the intestine  Enzymes are released by the microvilli ◦ “brush-border enzymes”  Break down larger sugars into simple sugars  finish protein digestion  Protective mucus is secreted  Pancreatic juice and bile

 Pancreatic Juice: pancreatic enzymes are essential and act specifically on organic molecules: ◦ Amylase : starch ◦ A collection of protein enzymes including trypsin ◦ Lipase: fats ◦ Nucleases: nucleic acids ◦ Bicarbonate keeps the pH slightly alkaline  Neutralizes the chyme upon entry to the small int.  Bile: breaks down fats; aids in absorption of fats and fat-soluble vitamins (K, D, E, A)

 Neural and hormonal regulation control: ◦ Pace of digestion ◦ Secretion of enzymes and hormones  The presences of chyme stimulates hormone release by the mucosa ◦ These hormones stimulate the release of bile and pancreatic juice

 Water and most end products (except fats) are absorbed into the blood via active transport ◦ from here they travel to the liver via the hepatic portal vein  Fats are absorbed through diffusion  What remains at the ileum: (the end) ◦ Water ◦ Undigestible foods ◦ Lots of bacteria (which cannot enter the blood)  Peyer’s Patches (clusters of lymph tissue) help prevent this