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Pages 469-470 and 480-484
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 sphincterAccessory pancreatic duct
Pancreas
Jejunum
Main pancreatic duct and sphincter
DuodenumHepatopancreaticampulla and sphincter
Duodenalpapilla
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 vesselsserving the smallintestine
Musclelayers
Villi
Lumen
Circular folds(plicae circulares)
(a) Small intestine
Absorptivecells
Bloodcapillaries
Lymphoidtissue
Muscularismucosae
(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