Transcript The Small and Large Intestines

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
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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
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The pancreatic and bile ducts come together
to form a joint duct that releases into the
duodenum – the hepatopancreatic ampulla
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Bile duct and sphincter
Accessory pancreatic duct
Pancreas
Gallbladder
Jejunum
Duodenal
papilla
Hepatopancreatic
ampulla and sphincter
Main pancreatic duct and sphincter
Duodenum
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Three structural modifications increase
surface area for food absorption:
1. Villi—fingerlike projections formed by the
mucosa
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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
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Blood vessels
serving the small
intestine
Muscle
layers
Villi
(a) Small intestine
Lumen
Circular folds
(plicae circulares)
Absorptive
cells
Villus
Blood
capillaries
Lymphoid
tissue
Muscularis
mucosae
Lymphatic vessel
Submucosa
(b) Villi
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Protein and some carbohydrate breakdown
started in the stomach
◦ Fats begin in the intestine
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Enzymes are released by the microvilli
◦ “brush-border enzymes”
 Break down larger sugars into simple sugars
 finish protein digestion
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Protective mucus is secreted
Pancreatic juice and bile
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Pancreatic Juice: pancreatic enzymes are
essential and act specifically on organic
molecules:
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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
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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
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Fats are absorbed through diffusion
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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