pages 469-470 and 480-484. from the stomach to the large intestine: duodenum ◦ attached to the...
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Pages 469-470 and 480-484
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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
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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.
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Bile duct and sphincterAccessory pancreatic duct
Pancreas
Jejunum
Main pancreatic duct and sphincter
DuodenumHepatopancreaticampulla and sphincter
Duodenalpapilla
Gallbladder
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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.
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Blood vesselsserving the smallintestine
Musclelayers
Villi
Lumen
Circular folds(plicae circulares)
(a) Small intestine
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Absorptivecells
Bloodcapillaries
Lymphoidtissue
Muscularismucosae
(b)Villi
Lymphatic vessel
Submucosa
Villus
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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
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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)
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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
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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
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